RL6 Guide Manual – Handbook of Estuarine Organisms
HANDBOOK OF
ESTUARINE ORGANISMS
Abbreviated version of student book
TABLE OF CONTENTS
Page #
Bacteria ..............................................................................................................
Fungi
Single cell, mushrooms, & bread mold .........................................................
Plankton
Phytoplankton & zooplankton .......................................................................
Marine Macro-algae
Knotted wrack ................................................................................................
Rockweed .......................................................................................................
Sea lettuce ......................................................................................................
Plants
Salt marsh hay ................................................................................................
Smooth cord grass ..........................................................................................
Univalves
Mud snail .......................................................................................................
Slipper shell ...................................................................................................
Bivalves
Oyster .............................................................................................................
Ribbed mussel ................................................................................................
Crustaceans
Barnacle .........................................................................................................
Fiddler crab ....................................................................................................
Green crab ......................................................................................................
Japanese shore crab ........................................................................................
Fish
Killifish ..........................................................................................................
Birds
Great Blue Heron ...........................................................................................
Great Egret and Snowy Egret ........................................................................
Herring Gull ...................................................................................................
Osprey ............................................................................................................
Life cycles ...........................................................................................................
© 2007 Mill River Wetland Committee, Inc.
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RL6 Guide Manual – Handbook of Estuarine Organisms
Bacteria (singular bacterium)
Background Information
Bacteria:
 are simple, microscopic, one-celled organisms.
 can be one of three shapes: round, rod-shaped, or
spiral.
 exist singly, in pairs, in chains, or in groups such as
clumps, mats or films, or filaments.
 (some not all) have a whip-like structure resembling a
tail called a flagellum (plural flagella). The flagellum
helps the bacteria move.
 live in soils, water, organic material, and inside or on
the outside of plants and animals.
 grow to a set size determined by their genetic material
and then reproduce by cell division. Cell division
yields two identical bacteria from the original.
Bacteria in the Estuary
 There are millions of bacteria of various types in the estuary.
 They are one of the most abundant and diverse type of organism found in an
estuary.
 There are so many different types of bacteria that only a small number have
been given names.
 In the estuary, bacteria live:
o in the water mixed in with the plankton;
o in or on plants and animals, dead or alive;
o on or in the mud on the bottom of the estuarine creeks; and
o on or under the mud surface of the estuarine creek shores, mud flats, and
salt marsh.
 Some of the most noticeable bacteria that live in the estuary are the many
types of “Purple Sulfur Bacteria.” These bacteria live just below the mud
surface so that they can receive light to photosynthesize. These bacteria give
the mud its intense purple color.
 Some bacteria such as Pseudomonas natriegens, an estuarine mud
bacterium, can grow and reproduce in less than ten minutes. Bacteria
populations can therefore increase very rapidly but are limited by the amount
of available nutrients.
The Role of Bacteria in an Ecosystem
There are millions of types of bacteria and they live in almost every part of
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
the world, including the estuary. Bacteria are very important for the function of
any ecosystem. They have four important roles in an ecosystem—primary
production, oxygen production, nutrient cycling, and food.
Primary Production
Some bacteria are photosynthetic—they use the energy from the sun, carbon
dioxide, and water to make organic material (their own cell structures). Only
plants, algae, and some bacteria are able to do this. Food webs always start
with a primary producer—plant, algae or bacteria. Our whole world is
dependant on these organisms, which use sunlight to make food (their tissues)
that an animal eats (which may then be eaten by another animal). Animals
(consumers) need to eat something to live and grow—they cannot use energy
from the sun to exist. Bacteria, along with plants and algae, are at the base of
all food chains and webs.
Oxygen Production
In the process of photosynthesis, oxygen gas is given off as a by-product.
What a marvelous by-product! All animals including humans need oxygen to
breathe. Photosynthetic bacteria living in estuaries and the ocean produce much
of the world’s oxygen.
Nutrient cycling
Other kinds of bacteria help cycle nutrients such as carbon and nitrogen in
food webs.
 Carbon cycle
All living organisms are made up of compounds (molecules, cells) that
contain carbon. Scientists refer to living or once-living material from
organisms as organic material. Carbon is essential for living organisms for
many of their bodily functions, especially for energy. Carbohydrates,
compounds containing carbon, are used by organisms for energy.
Only organisms that photosynthesize (plants, algae, and some bacteria) can
make their own carbohydrates through the process of photosynthesis.
(Photosynthesis uses sunlight, carbon dioxide from the air, and water to make
glucose, a carbohydrate.) Plants use the glucose for energy and basic building
material to make the plant parts (leaves, roots, flowers) and for all other
functions within the plant.
Animals can not make carbohydrates and need to eat a plant or another
animal to get the carbohydrates (compounds containing carbon) they need for
their energy, their building blocks for growth, and all their bodily functions.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
There is only a fixed amount of carbon in our world. Once carbon has been
taken in by a plant or animal, it becomes “locked-up” in the organism. Even
after the organism dies, the carbon remains trapped in its organic material.
There must be a way to release the carbon from the organic material so it can be
used again.
Bacteria (and fungi—see Fungi) are the organisms that release the carbon in
organic compounds so it can be reused by photosynthesizing organisms.
Scientists call bacteria and fungi decomposers. They decompose (break down)
the organic material of plants and animals. These decomposers do this by
secreting enzymes that digest (breakdown) the organic material. As a result of
decomposition, carbon dioxide is released back into the air to start the cycle all
over again. If bacteria did not perform this function, dead plants and animals
would build up, and the world would run out of nutrients such as carbon.
In addition to the release of carbon, there is a very important added benefit
when bacteria (and fungi) decompose plants. The full food value of green
plants can not be fully used by all animals because most animals do not have
the enzyme to digest cellulose (the compound that gives plant cells rigidity and
shape). But bacteria and fungi do have enzymes to breakdown the cellulose
into smaller digestible pieces. Bacteria and fungi are especially important in the
estuary because much of the base of the food chain comes from the abundant
estuarine plants.
 Nitrogen cycle
Other types of bacteria are involved in the nitrogen cycle. Plants need
nitrogen (a nutrient) to grow. Air—and air pockets in soil—contains nitrogen
gas, but plants cannot use the gaseous form. Some types of bacteria that live in
the soil near plant roots convert the nitrogen gas into a form that plants can use
to grow. This process is called nitrogen fixation. Nitrogen fixating bacteria are
vital to cycling the nitrogen from the air into the soil for plants.
Food
Bacteria are food for many animals in the estuary. Most consumers of
bacteria in the estuary eat them as part of the general detritus mix found in the
estuarine mud or the estuarine soup (nutrient-rich water in the estuary).
Detritus mixtures (containing bacteria) in the estuarine soup are food for
plankton such as copepods; the larvae of marsh insects such as mosquito larvae;
the larvae of estuarine invertebrates such as crab larvae; adult filter feeders such
as oysters and mussels; and fish, such as mullet or menhaden. Snails scrape
bacteria-filled detritus off creek shore mud with their rough tongues (radulae),
and fiddler crabs remove it from the mud with their bristle- covered mouthparts.
Some animals, such as the mussel Nucula proxima and very tiny nematode
worms, actively select bacteria out of the detritus mixture to eat. Some of the
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
smaller organisms, such as certain tiny protozoans, also pick out specific
bacteria to eat.
Most herbivores in the salt marsh feed on the grasses only after the grass has
been broken down into detritus. Thus, the herbivores eat bacteria along with
the plant detritus.
Summary
Bacteria play vital functions in ecosystems. Without their presence
ecosystems would not function at all.
Bacteria fulfill four important roles:
 Photosynthetic bacteria are the primary producers of many food webs.
 Equally important, photosynthetic bacteria produce oxygen for animals to
breathe.
 Bacteria that decompose organic material recycle nutrients rapidly, ensuring
high estuarine productivity.
 Bacteria are consumed as part of detritus by many organisms in the estuary;
certain organisms actively select specific bacteria to consume.
Bacteria are thus an essential part of food chains and the web of life in the
estuary. They are one of the primary producers for the food web, they provide
oxygen for all animals to breathe, they are the decomposers that recycle
nutrients rapidly that make the estuary so productive, and they are food for
many consumers (animals) in the estuary.
Bacteria sources:
http://en.wikipedia.org/wiki/Bacteria
http://encarta.msn.com/encyclopedia_761574409/Bacteria.html
http://www.ucmp.berkeley.edu/bacteria/bacteria.html
Fungi (singular fungus)
Background Information
There
are
approximately 70,000
fungi that have been
named and described,
but it is estimated that
there are up to 1.5
million types that live
on Earth.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Fungi:
 are a group of organisms (Kingdom) which digest their food outside of
their bodies and then absorb the nutrients into their cells. Examples of
fungi include mushrooms, yeasts, and bread molds.
 are grouped into their own kingdom because they aren’t similar enough to
either plants or animals. They were once considered plants because they
have cell walls made of the same material as plant cell walls. But they are
more similar to animals in that they need to “eat” food to grow (though the
eating is very different from animals).
 are called saprobes because they feed on dead and decaying organic
material. They are also called decomposers because they breakdown the
dead and decaying material into detritus and eventually into useful
nutrients for other organisms to reuse.
 inhabit a wide variety of environments. Each different type of fungus has
different optimum conditions for growth. They live wherever there is
enough moisture, proper temperature and sufficient organic material.
Fungi have the ability to absorb water from damp air, which allows them to
grow in dry environments (unlike bacteria).
 reproduce sexually (male and female reproductive parts) or asexually (cell
division). Some species use both methods at different times while some
reproduce only sexually or some only asexually.
Structure:
 A familiar fungi structure is a mushroom.
 Other fungi are single-celled microorganisms such as yeasts.
 Another common fungal body type is a fungal mat such as a bread mold.
o A fungal mat is a tangled, interwoven mass of tiny, barely visible
thread-like filaments of connected cells called hyphae (HY-fay). The
hyphae secrete digestive enzymes which breakdown the organic
material the fungal mat is growing on into detritus.
o The hyphae then absorb the nutrients released by the digestive enzymes.
o The fungus uses these nutrients to grow.
o Fungi can grow very rapidly because every part of the hyphae can
release enzymes and absorb nutrients.
Fungi in the Estuary
 All types of fungi (mushrooms, yeasts, and molds) are found in estuaries.
 The number of different kinds of fungi in the estuary can be enormous.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
 A few aquatic fungi (fewer than bacteria) are found in the estuarine water,
growing on the particles of detritus.
 Most others are found on the salt marshes, the barrier beaches, and the
upland areas.
 Most estuarine fungi live on and decompose:
o salt marsh grasses and other estuarine plants;
o pieces of driftwood;
o algae; and
o dead animals in the estuary.
 More fungi than bacteria (over one hundred species) are found on aging
and dead plants such as the salt marsh grasses.
 Two species of Ascomycota fungi are the dominant fungi found on dead
Spartina grasses and are responsible for much of the decay of the plant
material.
 Any physical breaking up of plant material into fragments (such as
battering waves or grazing animals tearing off bits of plants) increases
fungal habitat.
 Much of the growth seen on decaying material may be dense populations of
fungal hyphae. But, whereas there are dense populations of bacteria in the
marsh and creek muds and watery soils, fungi are mostly on the surfaces of
these areas, due to their need for oxygen.
 Scientists have found evidence of 10,000 reproducing fungal hyphae on
one gram of intertidal mud.
The Role of Fungi in the Estuary
Fungi are vital to the living system of the estuary and the coastal life that the
estuary supports.
Fungi have two main roles in any ecosystem:
decomposition/nutrient cycling (see Bacteria) and food.
Decomposition/nutrient cycling
Fungi greatly increase the nutritional value of Spartina and other plants
growing on the salt marsh (an area less favorable for bacteria). As bacteria do in
other more reliably moist areas, fungi convert the fibrous parts of plants-- whether
cellulose in Spartina leaves, or lignin in old wood--into a rich and nourishing
source of protein (their fungal bodies) for vast numbers of small estuarine
organisms.
As the plant material is slowly decomposed by the fungi, it becomes a more
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
and more consumable and digestible food for other organisms (the consumers).
The consumers eat the fungal spread and excrete what they cannot use as dung
(waste). The dung attracts bacteria and more fungi to the decaying plant. The
bacteria and fungi begin to decompose the previously undigested plant material in
the dung as well as any plant material that hadn’t yet been decomposed.
Consumers eat this new round of bacteria and fungi. They excrete dung. And the
whole cycle continues. In this way the indigestible dead and decaying plant
material is replaced by the mass of enriched fungal bodies—a nutritious food for
the many consumers. During each such nutritional cycle, the carbon content of
the food is released until the organic material is used up.
Without fungi to fill this nutritional role at the base of the estuarine web of
life, the estuarine ecosystem would collapse because so many organisms could
not get enough nutrients to stay alive.
Food
Animal consumers that eat fungi are detritus eaters called detritivores. Fungi
are food for worms, amphipods, oysters, crabs, and snails.
Two amphipods (Orchestia grillus, and O. uhleri) scrape off bits of the fungal
mats that develop on decaying Spartina plants.
A marine snail, Littorina irrorata, both eats AND helps its two preferred
species of fungi. This snail creates a long gash down a Spartina alterniflora leaf
with its radula. The damaged area of the plant attracts the fungi, which the snail
eats. Then the snail deposits its feces in the wound, which attracts more fungi to
grow there, setting up the whole cycle again. This “farming” operation increases
fungal growth—good for the snail but at great expense to the plant!
Summary
Fungi play a vital role in all ecosystems including the estuary. Fungi, along
with bacteria, are the decomposers that recycle nutrients rapidly for other
organisms to reuse. Without the recycling of nutrients, the nutrients would be
depleted and dead plants and animals would build up. Fungi and bacteria help
make the estuary a very productive place—one of the most productive on Earth.
Fungi are also food for many consumers (animals) in the estuary which again
makes the estuary a productive habitat. The productivity of the estuary directly
affects the productivity of the coastal waters.
Fungi sources:
http://cima.uprm.edu/Angel_Nieves.html
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
http://en.wikipedia.org/wiki/Fungus
http://tolweb.org/tree?group=Fungi&contgroup=Eukaryotes
http://www.ucmp.berkeley.edu/fungi/fungi.html
Plankton
Plankton consists of microscopic protists, plants, and animals that drift near the
surface of fresh and salt water and form the base of many food chains. It is a part of
the nutritious “estuarine soup.”
Plankton may be permanent (holoplankton)—organisms that spend their whole
life cycle as part of the plankton community. Examples of permanent plankton in an
estuary are copepods and diatoms. Other plankton may be temporary plankton
(meroplankton)—organisms that are plankton for part of their life cycle, usually when
they are young, such as in the larval stage. Examples of temporary plankton in the
estuary are the larvae of ribbed mussels, crabs, and many of the fish.
Plankton can also be divided into plant-like or animal-like organisms.
Phytoplankton live near the surface of the water because they use the energy
of sunlight to grow (photosynthesis). They are one of the important bases,
producers, in aquatic food chains. Examples of phytoplankton are diatoms,
dinoflagellates, and some photosynthesizing bacteria.
Zooplankton is made up of animals and animal-like organisms. Examples of
zooplankton include copepods and larvae of mussels. Note that zooplankton
includes both permanent and temporary plankton. Zooplankton may eat
phytoplankton only, zooplankton only, or both phyto- and zoo-plankton.
Plankton found in the estuary
Phytoplankton
Diatoms are plant-like (photosynthesizing) singlecelled microscopic organisms that are found
individually or in groups (colonies). Diatoms have a
cell wall made up partially of silica, a compound found
in nature. Diatoms have many different shapes and are
unique in their looks. Some estuarine diatoms are
Skeletonnema and Thalasionema.
Dinoflagellates are single-celled
microscopic
organisms with two long flagella.
Most are plant-like
(photosynthesizing)
organisms.
They have two
flagella that cause the organism to
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
move through the water in a spiral motion. Some estuarine dinoflagellates are
Ceratium and Gymnodinium.
Diatoms and dinoflagellates comprise the bulk of phytoplankton in the estuary.
Zooplankton
Permanent zooplankton includes many species of copepods and comb jellies.
Copepods are microscopic crustaceans that are
abundant in salt and brackish waters. They are a
dominant member of the zooplankton community.
Copepods primarily eat phytoplankton but also do eat
other zooplankton and bacteria. Copepods are usually
tear-drop shaped with long antennae, one eye, and an
exoskeleton similar to a shrimp.
Comb
jellies
are
microscopic
animals
similar to corals and sea
anemones.
They live
only in salt or brackish waters.
Their bodies are a gellike tube-within-a-tube and are
usually colorless. Most
drift with the currents but can
“swim” using hair-like
cilia.
Role of plankton in the estuary
Plankton have three main roles in the estuary: primary production, oxygen
production, and food.
Phytoplankton in the estuary uses the energy from the sun, carbon dioxide, and
water to make organic material (their own cell structures). They are then food for
many of the zooplankton (temporary and permanent).
Phytoplankton also produce oxygen as a by-product of photosynthesis. All
animals require oxygen for respiration.
Zooplankton that eat phytoplankton are food for other organisms in the estuarine
food web. Zooplankton are a very important intermediate link between the
phytoplankton (producers) and the larger animals such as the ribbed mussel,
crustaceans and fish.
Plankton source:
http://en.wikipedia.org/wiki/Plankton
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Marine Macro-algae (Seaweeds)
Knotted wrack: Ascophyllum nodosum
Description: Large algae
Knotted wrack is a large, greenish-brown
seaweed, or large algae. It grows from a
holdfast, which is the disc-shaped anchor that
attaches the algae to a rock or other hard
surface. Usually several branch-like stems
grow from the holdfast of the knotted wrack. In
turn, other limbs branch off randomly from the
stems. Along these branches are two different
kinds of structures. The first are air bladders,
which look like little football-shaped buds
along the stem. They help keep the wrack
floating upright in the water. The other
structures look like tiny leaf buds. When the
wrack is ready to release its reproductive cells,
these buds become much larger. Overall,
knotted wrack can grow up to 10 feet long, but
most are only one or two feet long.
Habitat:
Knotted wrack is found all along the coasts of the North Atlantic Ocean. It
can most often be found in estuaries and along sheltered coastlines with large
enough rocks on which the wrack can anchor itself. Because it attaches itself to
rocks so often, knotted wrack is sometimes also known as rockweed, although
rockweed is technically a different kind of seaweed altogether. In many places,
the rocky area near the low tide mark is often dominated by knotted wrack. It
never grows in deep water because knotted wrack requires sunlight to survive
and must therefore live near the surface of the water. It also doesn’t live on
open ocean shorelines where the rough waters could rip the holdfasts of the
algae from the rocks.
Prey:
Knotted wrack makes its own food by photosynthesis. Because of this, it
needs to anchor itself in shallow water. The knotted wrack’s air bladders exist
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
because of its need for sunlight too. They help keep the wrack floating towards
the surface of the water so it can get as much sunlight as possible.
Predator:
No species eats enough knotted wrack to hurt its growth along our coasts.
Some snails, including periwinkle, do occasionally graze on knotted wrack.
Humans consume more knotted wrack than any other species, although usually
in a processed form. We add the processed knotted wrack to products, such as
gelatin and toothpaste, to make them smoother and thicker.
Life cycle:
Mature knotted wrack “fruit” in the later winter and early spring, but they
don’t actually produce real fruit. Instead, the bud-like structures become much
larger and release reproductive cells into the churning water, much as a flower
spreads its pollen by letting it blow in the wind. Knotted wrack reproduce
sexually, meaning that there are separate male and female organisms. When the
reproductive cells from a male and a female fertilize each other in a rocky,
sheltered area, a new knotted wrack starts to grow. Unlike many types of
seaweed, knotted wrack grows slowly and can live for a long time. It can take
up to 5 years for an individual to mature, and some live for 20 years or more.
Because knotted wrack grows longer each year, the longer the organism is, the
older it is.
Value:
Because knotted wrack grows so abundantly in estuaries and along sheltered
coasts, it provides a great habitat for the smaller animals of these areas. Small
fish, crustaceans, snails, and the small, defenseless juveniles of many larger
species, all find shelter in the thickly-growing beds of knotted wrack. Other
species of microscopic algae grow along the blades of knotted wrack. Some
species of fish and snails graze on the knotted wrack as well.
Knotted wrack sources:
http://omp.gso.uri.edu/doee/biota/algae/phaeo/asco.htm
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin
Company, 1978.
Hillson, C.J. Seaweeds: A Color-Coded, Illustrated Guide to Common Marine Plants of the East
Coast of the United States. University Park, PA: The Pennsylvania State University Press, 1977
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Marine Macro-algae (Seaweeds)
Rockweed: Fucus vesiculosus
Description: Large algae
Rockweed, similar to other seaweeds, is
not a plant. Plants have roots from which
they obtain water and nutrients but seaweeds
do not. Rockweed is a large type of algae
and resembles a plant, but lives its life very
differently. Rockweed looks like a plant
because it anchors itself to a rock or any
hard surface with a root-like structure called
a holdfast. The holdfast does not provide
nutrients to rockweed, however. It only
holds it in place. From the holdfast grows a
single stem-like part. This soon divides out
into several leaf-like branches that are
usually 1 or 2 feet long but can sometimes
grow several feet longer. Along these
stalks, some species of rockweed have a
series of air bladders that help keep the
rockweed upright in the water. Not all
species of rockweed have these bladders,
however. Rockweed is usually a brownish
green and has dark brown or dark green budlike structures at the top of each stalk.
Habitat
Rockweed can be found along the coast far into northern Canada and south
through North Carolina. It is perhaps the most common type of seaweed in
Long Island Sound and its estuaries. It grows in shallow water so it can have
access to sunlight, which it needs to make its own food. Any area that has
rocks or other hard surfaces, such as docks or jetties that are under water during
high tide, is likely to be completely covered with rockweed. Rockweed gets its
name from the rocky shorelines it covers.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Prey:
Rockweed, just as do other seaweed and all other algae and plants, makes its
own food by using photosynthesis. It must grow in shallow water so that it
receives enough sunlight to be able to photosynthesize and survive.
Predator:
Because of its tough texture, rockweed is not often eaten by many animals of
the estuary. Humans, however, have been harvesting rockweed for almost 200
years because it is rich in iodine, a nutrient that we need to survive. In fact,
rockweed was the first source of iodine that humans discovered in the early
1800s. We also process rockweed to make products, such as jelly and ice
cream, smoother and thicker.
Life cycle:
Rockweed fruits in the winter. This means that the bud-like structures on
top of each stalk of the rockweed release millions of tiny reproductive cells into
the water. Rockweeds have both male and female parts, so when they fruit,
they release both eggs and sperm. Once the sperm fertilizes the egg, the tiny
algae attach to a rock if the water brings it there. Once attached, it grows over
several years into a mature rockweed. Rockweed can also reproduce asexually.
Sometimes a piece of a rockweed will be ripped off from an individual. This
piece, if the conditions are right, can grow into a separate rockweed.
Value:
While rockweed is not widely eaten, it does provide an important habitat for
smaller algae and microorganisms that live on its stalks. These smaller forms
of life are an extremely important food source for many of the crustaceans and
smaller fish of the estuary. Rockweed also provides shelter from predators for
smaller estuarine animals and the juveniles of larger ones.
Rockweed sources:
http://www.geocities.com/rockweedinfo/Rockweedfx.html
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin
Company, 1978.
Hillson, C.J. Seaweeds: A Color-Coded, Illustrated Guide to Common Marine Plants of the East
Coast of the United States. University Park, PA: The Pennsylvania State University Press, 1977.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Marine Macroalgae (Seaweeds)
Sea lettuce: Ulva lactuca
Description: Large algae
Although sea lettuce somewhat
resembles a head of lettuce—hence its
name—it is not a plant. It is a large
form of algae, or commonly called
seaweed. It has large flat, tissue-thin,
wide blades that are curled at the
edges. These light green blades grow
from a tiny holdfast, a clump of small,
root-like hairs that help the sea lettuce
anchor onto something (usually a
rock). Sea lettuce blades can range in
size from very small up to 20 inches in
length.
Habitat:
Sea lettuce is found all along the Atlantic coast from Canada to the Gulf of
Mexico. It is found both in the open ocean and in the estuaries. One can even
find sea lettuce higher up in the estuary, where the water is less salty, because it
has a higher tolerance for the lower salt levels of brackish water than most
seaweed do. Also, sea lettuce thrives in areas of nutrient rich water. This
makes the estuary, where the water it often very rich in nutrients, a prime spot
to find sea lettuce.
Sea lettuce is usually attached to something. Rocks, shells, docks, jetties, or
even other anchored seaweeds, all make fine anchors for sea lettuce. It can also
sometimes be found floating free, unattached to anything. Sea lettuce is the
most common seaweed found along the Atlantic coastline of the United States.
Prey:
Although sea lettuce is not a true plant because it does not take in water
through a root system, it is similar to a plant in that it makes its own food
through photosynthesis. While sea lettuce grows in a variety of different areas
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
and is very hardy, it can only grow in water shallow enough for some sunlight
to get through. If it does not receive sunlight, it cannot photosynthesize. Also,
sea lettuce thrives in the nutrient rich waters of estuaries.
Predators:
Sea urchins and amphipods, a group of small, shrimp-like creatures, often
graze on sea lettuce. Sea lettuce also provides a habitat for many species of
worms and animal plankton, which are, in turn, eaten by shore birds. Humans
also often eat sea lettuce. It is one of the few seaweeds that people eat in its
whole form. Most other seaweeds are not eaten whole, but instead have certain
substances extracted from them for use in making other kinds of food.
Life cycle:
Sea lettuce reproduces asexually, meaning that there are not male and female
specimens that need to fertilize each other’s cells. Sea lettuce releases
microscopic spores into the water in the spring and summer that are capable of
growing into individuals. While most of these spores do not up grow into fullsized sea lettuces, enough of them grow and take hold to maintain the status of
the sea lettuce as the most abundant seaweed found on Connecticut’s beaches
and in its estuaries.
Value:
Because sea lettuce grows so abundantly, it is an important habitat for many
small species of animals in the estuary. The folds in its blades provide shelter
and protection from predators for not only the small animals of the estuary, but
many of the tiny, larval forms of the larger fish, crustaceans, and other larger
estuarine animals. Also, since sea lettuce thrives in nutrient-rich waters, its
uptake of these nutrients can help limit the amount of some smaller, harmful
forms of algae that might otherwise use the nutrients. Sometimes these harmful
types of algae can be so thick in the water that sunlight can’t get through for
algae and plants to use. An overgrowth of harmful algae can hurt the entire
ecosystem of the estuary.
Sea lettuce sources:
http://www.chesapeakebay.net/baybio.htm
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin
Company, 1978.
Hillson, C.J. Seaweeds: A Color-Coded, Illustrated Guide to Common Marine Plants of the East
Coast of the United States. University Park, PA: The Pennsylvania State University Press, 1977.
Plants
Salt marsh hay (Salt meadow cord grass): Spartina patens
Description: Grass
Salt marsh hay is a slender grass that grows
densely in the higher elevations of the estuary.
When undisturbed it grows straight up, but it is
usually matted down to the ground from the
wind and the extra high tides during the new
moon and the full moon phases. The matted
swirls of grass are said to resemble cowlicks.
The plant is light green in color in spring and
summer. It can grow up to 3 feet tall, although
it is usually about 1 or 2 feet in height. Its
stalks are stiff and hollow, with uprightgrowing leaves that are nearly as long as the
stem. At the top of the stalk are feather-like
seed packets from which the seeds are released.
Habitat:
Salt marsh hay grows in estuaries from Quebec, Canada along the Atlantic
coast to Texas on the Gulf of Mexico. It also grows in some areas on the shores
of the Great Lakes. Salt marsh hay (Spartina patens) grows on the salt marshes
and banks of estuarine channels that are slightly higher in elevation in the
estuary. These higher areas of the estuary are not always covered by brackish
water at every high tide. In contrast, cord grass (Spartina alteriflora) usually
grows in areas that are flooded by the brackish water twice every day.
Prey:
Salt marsh hay makes its own food by photosynthesis, as all plants do. It is
an important primary producer in the estuary. It is adapted to its salty water
habitat and benefits from the nutrient-rich soil and water of the estuary.
Predators:
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Salt marsh hay is usually too large and indigestible for most animals in the
estuary to eat. The food value of salt marsh hay comes as the plant dies and
decays. (See smooth cord grass, bacteria, and fungi.) Its roots are food for a
variety of consumers, such as geese and muskrats. Its seeds are also widely
eaten by birds such as the black duck.
Life cycle:
Salt marsh hay flowers from June to October. The seeds fall from the
panicle—the feather-like seed packet—that grows from the top of the grass’s
stalk. Salt marsh hay reproduces asexually—its seeds do not need to be
fertilized by a plant of the opposite sex. But the primary means of reproduction
is through the rhizome system. A rhizome is a connected, underground,
horizontal stem system (sometimes called a “root stock,” though a rhizome is
not a root). After the rhizome grows slightly away from the original plant, it
will send up a stalk and send down roots. Once the new salt marsh hay plant
has begun to grow up and out of the ground, it also grows the underground
horizontal stems which can form other new stalks of salt marsh hay. Salt marsh
hay plants can grow very close to each other because of the rhizome system of
reproduction. In the winter, the stalks of the grass die, but the rhizomes remain
intact and grow new stalks the next spring.
Value:
Salt marsh hay helps in many ways to make the estuary a productive area. It
provides food—mostly once decomposed into detritus—for many consumers in
the estuary. It provides habitat for small animals such as the salt marsh snail
and amphipods. It provides nesting places for birds such as the clapper rail. It
encourages the development of salt marsh peat soil by trapping sediments (from
the estuarine water) and larger pieces of cord grass and salt meadow hay in its
dense growth. Its dense roots hold the peat soil together, further allowing the
build-up of peat. The thick layer of peat soil absorbs flooding water, protecting
nearby areas from the detrimental effects of flooding. For all these reasons, salt
marsh hay is a very important part of the estuary.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Salt marsh hay sources:
http://life.bio.sunysb.edu/marinebio/spartina.html
http://www.edc.uri.edu/restoration/html/gallery/plants/salt/htm
Tiner, Ralph W. A Field Guide to Coastal Wetland Plants of the Northeastern United States.
Amherst, MA: University of Massachusetts Press, 1987.
Plants
Smooth cord grass: Spartina alterniflora
Description: Plant (grass)
Smooth cord grass is a tall, erect-growing grass that thrives
in the brackish water of the estuary. Depending on the
conditions, cord grass can grow up to 8 feet tall, but it usually
between 3 and 5 feet tall. It is green in color, but it is often
yellowish-brown towards the bottom of its stalk where the water
reaches at high tide in the estuary. The stalk of cord grass is
round and hollow. From the stalk grow long, narrow leaves (up
to one-half meter long by 1 cm wide) that extend straight up
next to the stalk. At the top of stalk is the panicle, a brown,
hairy-looking structure up to 30 centimeters in length that
contains the flowers and, later, seeds.
Habitat:
Cord grass is found along the Atlantic coast of Canada and the United States south to
Florida and along the coast of Texas in the Gulf of Mexico. However, it grows most
abundantly between New Hampshire and Florida, where it is often the dominant plant
species of the salt marsh in the many estuaries. Cord grass grows in the peat soil of the
salt marsh in areas where the estuary’s brackish water reaches twice a day. Any area that
is flooded by brackish water twice daily at high tide, such as the edges of the estuarine
channels, will probably have cord grass growing there. Cord grass does grow higher up in
the estuary, too, in parts where the tide doesn’t always reach, but it does not usually grow
as tall in these areas.
Prey:
Cord grass is a plant, and as all other plants do, it creates its own food by the process
of photosynthesis. Scientists call any organism that photosynthesizes a primary
producer. Cord grass also gets the nutrients it needs from the soil in the estuary. Most
plants cannot tolerate the salt in the water in the estuary, but cord grass is adapted to the
salty water and can take advantage of the nutrient-rich soil and abundance of water. In
fact, cord grass has salt glands that excrete excess salt it has taken in from the brackish
water out onto the surface of its leaves. The salt crystals are often visible on the leaves
when there has not been a recent rainfall to wash the crystals away.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Predators:
The roots of the plant are widely eaten by some ducks and geese. Insects often graze
on the flowering part of the plant and some fish also eat the seeds of the plant that end up
in the water. Cord grass is usually too large and indigestible for most animals in the
estuary to eat. The food value of cord grass comes as the plant dies and decays. Once the
cord grass dies, many processes help to break down the plant parts into nutrients. The
sometimes strong mixing action of the fresh water from the river and the salt water from
the incoming tides physically break the cord grass into smaller pieces. Animals, such as
amphipods, shave off slivers of plant material as they eat their food (algae, bacteria, and
fungi) from the surface of the plant material. But the most important decomposers of the
salt marsh grasses are bacteria and fungi. (See Bacteria and Fungi.) Bacteria and fungi
break down pieces of dead cord grass into smaller and smaller pieces, releasing nutrients
along the way until all the nutrients have been released. The bacteria and fungi and small
plant pieces (detritus) become part of the nutritious estuarine soup and are also mixed in
with the salt marsh soil and estuarine mud. This rich detritus is food for many detritus
eaters in the estuary. The decomposing salt marsh grasses contribute to the high
productivity of the estuary.
Life cycle:
Cord grass flowers during the summer, between July and September. It reproduces
asexually, which means that the seeds do not need to be fertilized by another plant of the
opposite sex. But the primary means of reproduction is through the rhizome system. A
rhizome is a connected, underground, horizontal stem system (sometimes called a “root
stock,” though a rhizome is not a root). After the rhizome grows slightly away from the
original plant, it will send up a stalk and send down roots. Once the new cord grass plant
has begun to grow up and out of the ground, it also grows the underground horizontal
stems which can form other new stalks of cord grass. Cord grass plants can grow very
close to each other because of the rhizome system of reproduction. In the winter, the
stalks of the grass die, but the rhizomes remain intact and grow new stalks the next spring.
Value:
Cord grass is absolutely essential to the survival of the estuary, salt marshes and all the
inhabitants. Because it is perennial—its roots and rhizomes survive year-round—it holds
the moist, spongy soil of the marsh together, even through the highest tides and harshest
storms. The sturdy, upright plants help absorb the energy of the waves and flooding river
and tide water. The dense growth collects silts and other particles to contribute to the
build-up of soil, which encourages more cord grass to grow. Cord grass is food for
animals when it is alive and when dead. When the stalks die, the decomposing plant
material helps fertilize the soil of the marsh and adds detritus to the estuarine soup,
making the entire ecosystem’s food web more productive. Cord grass also provides a
habitat and a protected place for animals of the estuary. The preferred habitat for ribbed
mussels, another ecologically important species, is in the peat soil among the roots of cord
grass plants. During the spring and summer, when the grass has grown tall, many marsh
birds, such as the clapper rail, find shelter and make their nests in stands of cord grass.
Some fish, such as the mummichog, lay their eggs at the base of the cord grass when the
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
tide covers the salt marsh. Without cord grass, no other species, plant or animal, could
survive in the estuary. It is the glue that holds the ecosystem together.
Smooth cord grass sources:
http://life.bio.sunysb.edu/marinebio/spartina.html
Tiner, Ralph W. A Field Guide to Coastal Wetland Plants of the Northeastern United States.
Amherst, MA: University of Massachusetts Press, 1987.
Univalves
Mud snail: Ilynassa obsoletes
Description: Gastropod
The mud snail is a univalve. Univalves live in a shell
with only one piece, as opposed to a bivalve, which has a
two-part shell. The mud snail’s shell is about 1 inch long
and under one-half inch wide and is dark brown or
purplish-black in color. The shell is often covered in mud,
algae, and debris, which help camouflage the snail and
sometimes gives it a fuzzy appearance. The shell is
elongated and spirals into a point at the top. The animal inside the snail is a
gastropod, which means “stomach foot.” This name indicates that the mud snail,
like all snails, moves around by pushing itself with its muscular foot on the
underside of its belly. The mud snail’s soft body is dark gray with faint black
spots. It has a head with a pair of antennae-like tentacles, with two small eyes
below the tentacles. The mud snail has a proboscis, which looks like a tiny
elephant’s trunk. The snail extends the proboscis when it feeds. The snail’s
mouth, with its long, rough tongue, or radula, is at the end of the proboscis. The
mud snail also has a siphon extending from its head, which it uses to draw in
water to its gill to extract oxygen.
Habitat:
The mud snail can be found along the Atlantic coast of North America from
Labrador, Canada, to Florida, as well as much of the Pacific coast. Mud snails are
found in the area between the high and low tide lines, called the intertidal zone.
They like to live near the low tide line of relatively calm beaches and estuaries;
because they rely on their gills to get oxygen from the water, they must be
submerged most of the time. As their name implies, mud snails often congregate
in muddy areas, where their dark color makes them hard to be seen by predators.
If they find themselves exposed at low tide, they will bury themselves in the mud
to retain moisture from which they get oxygen.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Prey:
A mud snail will eat almost anything it can find. It will scrape its radula over
its food, loosening tiny, bite-size bits that it can get into its mouth. At low tide,
mud snails feed on microscopic organisms that coat the mud, such as diatoms,
bacteria, and blue-green algae. Mud snails also eat larger algae, such as sea
lettuce. But mud snails are best known as scavengers. They consume detritus and
feed on dead bodies of animals–such as crabs, clams, mussels, and fish–that have
washed up on shore. A large pile of mud snails can often be found dining on a
single dead organism. Occasionally, a mud snail is able to drill a hole in the shell
of a live bivalve with its radula. Mud snails can tell that food is nearby by
“sampling” the water they bring in through their siphons. The water passes over a
sensory organ in the snail, and the snail can “smell” the food from the water it
takes in.
Predator:
Adult mud snails are eaten by fish, crabs and birds. Rails, gulls, and
sometimes ducks pick mud snails out of the mudflats at low tide. Crabs with
strong claws can crack the hard shell of the mud snail to eat the soft bodied animal
inside. Fish with strong teeth make easy meals of mud snails during high tides.
Sometimes an adventurous fox or raccoon will also dig up a mud snail or two
when the tide is low.
Life cycle:
Mud snails mate during the summer. The female mud snail releases many tiny,
transparent egg capsules, each of which contains several fertilized eggs. The
female will release these egg capsules onto hard surfaces, such as rocks, shells, or
even stiff grasses, in neat rows. Soon after, swimming larvae hatch from the eggs.
These larvae go through several developmental stages; eventually, the larvae stop
swimming, sink to the bottom, and begin to develop their shells. A year or two
later, as adults, they will begin to reproduce. Most mud snails don’t live much
longer than two years, although sometimes they may live up to five years.
Value:
The eggs and larvae of the mud snail are part of the estuarine “soup” that
nourishes so many other organisms.
Because the snails themselves are so numerous, they are an important food
source for many of the larger animals in the estuarine food web. When mud snails
“graze” on the film of diatoms and other micro-organisms on the surface of the
mudflats, they “package” those tiny organisms into a bigger morsel (the snail’s
own body) for a larger carnivore in the next link of the food chain.
Mud snails, despite their small size, may be just as important because of what
they eat. As scavengers they consume detritus and decaying animal carcasses.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Because the process of decay uses oxygen, the mud snail’s “clean-up” habits help
reduce the amount of decay and thus reduce oxygen loss.
Mud snail sources
http://www.omp.gso.uri.edu/discovery/biota/bamudsn.htm
http://www.estuary.uconn.edu/EWP13.html
Barnes, R. D., Invertebrate Zoology. Philadelphia: W.B. Saunders and Holt, Rinehart and Winston,
1980.
Univalves
Slipper shell (Atlantic Slipper Snail): Crepidula fornicata
Description: Mollusk
The Atlantic slipper snail is a single-shelled
mollusk. The oval shell grows to about 4 cm (1 ½
inches) in length. The arched shell is smooth, usually
white with brown, pink, or yellow markings. A shelf
covers half the length of the underside that the softbodied animal can pull itself under. With its muscular
foot, it suctions itself onto any hard surface. They are
commonly found stacked upon each other. These
curved stacks usually have 5-12 snail shells, the
largest snail is on the bottom and the others get
smaller and smaller towards the top of the stack.
Habitat:
Slipper shells live all over the world. The Atlantic slipper snail is native to
protected estuaries and bays along the Atlantic coast from Canada to Florida to
the Gulf of Mexico. It is considered an invasive species in Europe. It can be
the most abundant mollusk in the intertidal area. It attaches itself to hard
surfaces, such as rocks, in muddy bottom areas of estuaries though it can be
found attached to any hard surface, even horseshoe crabs. This snail is so
commonly found on horseshoe crabs that scientists are using the slipper snail to
tell the age of a horseshoe crab! The Atlantic slipper snail tolerates a wide
range of conditions, a reason why it has so easily become invasive in Europe.
Prey:
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Slipper snails are filter-feeders like mussels, oysters, and clams. They have
a mucous covered gill that traps the food particles that are then moved to the
mouth by little hairs (cilia). Slipper snails eat phytoplankton of all sizes. Their
diet also includes detritus and bacteria. Because they are stationary, they
depend on waves and the current to bring their food to them.
Predator:
Slipper snail adults have no significant predators. Most predators cannot
unstick the stacked shells to get to the soft body. Moon snails, with their rasplike radula, can drill a hole in a slipper shell and suck out the fleshy body. The
larvae are food for the many plankton eaters in the estuary.
Life cycle:
A slipper snail starts its life as a male and may change into a female. It is
called a protandrous hermaphrodite. If the young snail settles onto a hard
surface and is not on top of another slipper snail, it will be male. If no other
snail comes on top of it, it will stay male. But if another snail settles on top of
it, the bottom one will change into a female. The individual on top will stay a
male and all others that settle on top will stay male. Therefore, the bottom snail
in a stack will always be female, the others will all be male.
Females spawn two times during May and June. They release 5000-30,000
total eggs per year. The eggs are held in egg capsules of 50 eggs each. After 24 weeks, the eggs develop into planktonic larvae that drift (and “swim”) for
another 4-5 weeks before developing into a young snail capable of attaching
itself to a hard surface.
Value:
Atlantic Slipper Snails, similar to all filter-feeders, play an important role in
cleaning the estuary’s water. When they take in water to eat, they also strain
out pollution, impurities, and other substances that hurt the health of the
estuary. But because they are so abundant in some areas, they are considered a
pest on commercial oyster beds because they compete with the economically
valuable oysters for food and space. Empty slipper snail shells can be homes
for smaller animals in the estuary. Overall, scientists think that the slipper snail
presence in estuaries helps to increase biodiversity which helps to keep the food
web in balance.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Slipper shell sources:
http://academics.smcvt.edu/dfacey/AquaticBiology/Coastal%Pages/slipper%20limpet.html
http://www.issg.org/database/species/ecology.asp?si=600&fr=1&sts=
http://www.ku.lt/nemo/crepidula.html
http://www.njmsc.org/Education/Lesson_Plans/Seashell_Homes.html
Bivalves
Oyster: Crassostrea virginica
Description: Bivalve Mollusk
All bivalves, including oysters, live in a two-part
shell that is hinged on one side and opens on the
opposite side. While there are several species of
oyster, the one that lives in and around Long Island
Sound is called the eastern oyster. Eastern oysters can
grow up to 10 inches long and 4 inches wide, though
most are much smaller (4 to 6 inches). Their shells
are smooth and grayish-white on the inside, and tan or
gray and rough on the outside, with ridges and bumps. The animal that lives inside
the shell is a small, gray, slimy, mushy, jellylike mass. However, it is a more
complex animal than it appears to be. It has a nervous system, a mouth, and a
stomach, just as humans. It also has an organ that we don’t have, namely gills. An
oyster takes oxygen out of the water the same way a fish does. It also has extremely
strong muscles that hold its shells closed to protect its soft body from predators.
Habitat:
The eastern oyster lives in shallow, brackish water for the most part, but can also
be found in salt water as deep as 40 feet. They never live in areas that become
exposed during high tide, though, because, unlike some mollusks, they lack the
ability to survive out of water for very long. Oysters secrete a substance that helps
them stick to rocks or other hard surfaces at the back hinge of their shell. In fact,
many times an oyster will anchor to another oyster. Some oysters can also be found
in muddy or silty-bottomed water as well.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Prey:
Oysters are filter feeders. They have a mouth surrounded by tiny hairs called
cilia. They open their shells and take in gulps of water. The cilia trap algae and
plankton, which the oyster then eats before it spits out the water. Oysters do this all
day, and can gulp in up to 5 liters of water per hour.
Predators:
Humans love to eat oysters, but we are not alone. There is a snail called the
oyster drill and a sponge called the boring sponge (because they bore holes into the
oyster’s shell, not because they aren’t interesting!) that have special adaptations to
eat oysters. They both drill holes into the oysters shell to get to the soft-bodied
animal inside, though the sponge doesn’t eat the oyster, but rather uses the shell as a
habitat. Oyster larvae are eaten by many creatures of the estuary, such as fish and
birds. They are also eaten by invertebrates, including jellyfish, sea anemones and
flatworms. Since oyster larvae are tiny and do not have a shell, they are defenseless
against predators.
Adult oysters, however, have hard shells to protect them. Still, many creatures
have found a way to break or open the oyster’s shell. In addition to the oyster drill,
which is the oyster’s most serious predator, a stingray called the cownose ray and
several species of crabs have are able to crack open the oyster’s shell. The ray uses
its hard teeth, while the crabs use their powerful claws. The sea star, another serious
predator, surrounds oysters and other mollusks with its limbs and uses tiny suction
cups on its underside to pry open the oyster’s shell.
Life cycle:
Since oyster larvae are so small and are eaten by so many animals, oysters make
hundreds of millions of eggs in their lifetime to assure that enough survive into
adulthood to keep the species alive. Oysters reproduce sexually, meaning that there
are both male and female oysters, but an oyster will usually change its sex at least
once during its lifetime. Younger oysters are usually male. Once they grow enough
and are big enough to produce eggs, most oysters will change to females. Both
males and females release their sperm and eggs into the water to be fertilized, usually
around June or July. The oyster larvae start growing their shells almost immediately
by secreting calcium and other nutrients around them. After they are about one year
old, young oysters are ready to reproduce. They grow throughout their lives, and
their shell grows with them. It is possible to tell roughly how old an oyster is by
looking at the growth patterns on the outside of its shell—almost like counting the
rings of a tree.
Value:
Most people don’t realize how important oysters are to the environment of the
estuary. Since oysters are filter feeders, they take in gulps of water, including
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
everything in it. This helps clean pollution out of the water. Algae, the main food of
oysters, can also hurt the estuary if its growth is unchecked because algae can lower
the amount of oxygen in the water. Oysters help to limit the amount of algae,
making sure that all the other animals in the water have enough oxygen to breathe.
Oyster shells also make an important habitat for other animals. Special types of
crabs and shrimp live in oyster shells, while barnacles and small sea anemones
anchor themselves to the outside of the shells.
Oyster sources:
http://www.chesapeakebay.net/baybio.htm
http://www.chesapeakebay.net/info/atlanticoysterdrill.cfm
http://aquanic.org/publicat/usda_rac/efs/nrac/nbull18.pdf
Hedeen, Robert A. The Oyster: The Life and Lore of the Celebrated Bivalve. Centreville, MD:
Tidewater Publishers, 1986.
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin Company,
1978.
Bivalves
Ribbed mussel: Geukensia demissa formerly Modiolus demissus
Description: Bivalve mollusk
Ribbed mussels are bivalve mollusks, a large
grouping of mollusks with two-part shells that have
a hinge on one side and can open on the other. Their
shells are about 4 inches long and 1 inch wide, and
are grayish-brown to black in color. The shell’s
shape resembles an oval. The ribbed mussel gets its
name from the ribs and grooves, on the outside of its
shell. The animal that lives inside the shell is a
small, gray, slimy, mushy, jellylike mass, but it is more complex than meets the
eye. A ribbed mussel has gills, a mouth, a stomach, a heart, and a nervous system
just as many more complex animals do. The mussel’s gills are lined with tiny
hairs called cilia that help direct food into the animal’s mouth. The ribbed mussel
also has a strong muscle called a foot, which it extends out of its shell to dig itself
into the mud or sand or to propel itself along the estuary floor.
Habitat:
Ribbed mussels are found all along the east coast of North America, from Nova
Scotia, Canada, to the Gulf of Mexico. They are most often found in the intertidal
zone, the area of the shore or estuary between high and low tides. Some ribbed
mussels submerge themselves under the mud of the estuary by digging with the
foot. Other mussels attach themselves to a rock or other surface with byssal
threads—the tough, strong threads they spin from a gland in their body. Often,
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
groups of muscles will clump together with their threads at the base of tufts of
marsh grass. Mussels can often be seen at low tide, completely out of the water
for hours at a time. They survive this period without being under water by
trapping water in their shells to stay moist and by using the oxygen in the trapped
water.
Prey:
Ribbed mussels, similar to all bivalve mollusks, are filter feeders. They take in
large amounts of water and strain out algae and plankton for nourishment. Ribbed
mussels, which are different from many other bivalves, do not have tubes, called
siphons, for taking in and expelling water. Instead, ribbed mussels open their
shells and use the cilia attached to their gills to propel water and food particles
into their mouths. The mussels take in about a half a gallon of water per hour just
to get enough food to survive.
Predators:
Many animals in the estuary eat ribbed mussels. Many species of crab use
their strong claws to crack or pry open the mussel’s shell. When the mussels are
under water during high tide, they open their shells slightly so they can take in
water. At this time, they are vulnerable to fish. When they are above water
during low tide, animals, such as herons, skunks, raccoons, and muskrats, all find
a way to get into shells of mussels for a meal. Also, larval mussels make up a part
of the plankton population that so many smaller organisms in the estuary eat.
Life cycle:
While many bivalves have both male and female parts, ribbed mussels are
either male or female, never both. From late spring through the summer, they
release their sperm and eggs into the water by the millions. They are stimulated to
begin reproducing by environmental changes they can sense in the water, and all
the mussels in an area usually reproduce at once. The sperm fertilizes the eggs,
and within a day free-swimming larval mussels—which do not resemble adult
mussels—are born. It takes several weeks for the larvae to grow into a juvenile
mussel. Once a juvenile mussel has formed its shell and its thread glands, it may
attach itself to a rock or the base of Spartina alternaflora (cord grass). The ribbed
mussel shell grows larger as the animal grows larger and older. One can tell about
how old the mussel is by counting the ribs on the outside of its shell, much like
counting the rings on the inside of a tree.
Value:
The byssal threads that attach ribbed mussels to the base of cord grass plants
not only help anchor and protect the mussels, but also the plants. The threads
“knit” a mat that holds the marsh soil together and protects it from erosion,
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RL6 Guide Manual – Handbook of Estuarine Organisms
providing a more stable habitat for the grass. Ribbed mussels also improve the
aquatic habitat: they help clean the estuarine waters. When mussels filter water
for nutrients, they also strain out pollution, impurities, and other substances that
hurt the health of the estuary. The action of thousands of mussels and other filterfeeding bivalves, each straining almost a gallon of water an hour, helps cleanse the
water and makes the whole estuarine ecosystem more productive. Ribbed mussels
are also a food source for certain crabs, birds, fish, and mammals. As larvae, the
mussels are part of the plankton population that nourishes so many smaller
organisms in the estuary.
Ribbed mussel sources:
http://academic.brooklyn.cuny.edu/biology/franz/biology25/MUSSELS.HTM
http://www.dnr.sc.gov/cwcs/pdf/Ribbedmussel%20.pdf
http://www.exoticsguide.org/species_pages/g_demissa.html
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin Company,
1978.
Crustaceans
Barnacle: Balanus
Description: Crustacean
While barnacles may resemble small, gray
volcanoes attached to rocks, the animals that live
inside the tiny, cemented structures with which
most of us are familiar are actually arthropods.
Arthropods have hard exoskeletons and complex
bodies. In fact, barnacles are tiny crustaceans, a
large grouping of arthropods, which includes
lobsters, shrimp and other crabs. There are over
1,000 species of barnacle worldwide, but almost all
of them share some common traits. They are as large as 2 inches wide (including
their protective shell) but are usually much smaller. A barnacle lives cemented
head-first to a hard object with its mouth facing outward. It has numerous legs,
which are long compared to the size of its body, that have feather-like hairs on them
that the barnacle uses for trapping food. The barnacle can protect itself from
predators or from the elements by closing a set of hard plates.
Habitat:
Adult barnacles live anywhere between the high tide line and depths of a little
more than 100 feet. They can live as high up on rocks or docks as the high tide line
because they can close their protective plates when they are not covered by water.
They are able to take in enough food during the hours of high tide when they are
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RL6 Guide Manual – Handbook of Estuarine Organisms
covered with water to survive. Barnacles spend their entire adult lives attached to
one place; once they cement themselves somewhere, they cannot change the
location. Barnacles will cement themselves to any fairly hard surface, from clam
shells to rocks to manmade structures such as docks or jetties. Some will attach
themselves to ships or even to whales and dolphins. Wherever there is food to be
found and a hard surface, a barnacle will make its home. A single barnacle is not
usually found attached to a surface. If a hard surface is good enough for one
barnacle, the chances are that many more have settled there as well. However,
barnacles don’t derive any benefit from grouping themselves together.
Prey:
Barnacles eat only plankton. They eat both plant and animal plankton, including
barnacle plankton. When covered by water, a barnacle will open its protective
plates and let its many feathery legs float out into the water. The tiny, hair-like cilia
on the legs help trap plankton, which the barnacle then directs towards its mouth.
Predators:
Barnacles have an obvious defense against predators: their hard shells.
However, their shells are not indestructible, and some animals are able to break
them open to eat barnacles. Certain species of worms, snails, and sea stars have
specialized mouths that enable them to suck barnacles out through the shells. A
few fish (although not many in Long Island Sound) and shorebirds, such as herring
gulls, have strong jaws or beaks that can crack open barnacle shells. Because of
their strong shells, however, no animals in our estuaries rely heavily on adult
barnacles in their diets.
Life cycle:
Adult barnacles are hermaphrodites, meaning they are sometimes males and
sometimes females. They release their sperm and eggs into the open water, where
they mix together and the eggs are fertilized. Some types of barnacles keep their
eggs inside their shells, however, and release the larvae into the water once they are
fertilized. The tiny, microscopic barnacle larvae float in the water with no control
over their direction for about two weeks. After this, they gradually transform into
another stage of larvae that is capable of swimming by using small, hair-like legs on
the underside of their bodies. Once capable of swimming, the larvae will try to find
a suitable place to cement themselves. The larvae choose permanent homes based
on environmental cues they sense in the water. They can even sense if adult
barnacles are nearby, an indication that the area would be suitable for other
barnacles to live. Once the larvae attach themselves, using the cement glands on
their heads, they begin to grow shells around their bodies. Barnacles keep growing
throughout their lives and continue to add to their shells to make room for
increasing body size.
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Value:
Barnacles, as do mussels and clams, eat plankton. This plays a vital role in
maintaining the health and normal activity of the estuary’s food web. If there were
not animals such as barnacles to eat plankton, the estuary’s waters would be choked
with it, making life impossible for the rest of the estuary. Also, because they eat
animal plankton, much of which is the larvae of larger estuarine animals, they help
limit the populations of many animals to levels that are healthy for the estuary.
Barnacle sources:
http://www.mesa.edu.au/friends/seashores/barnacles.html
http://www.museum.vic.gov.au/crust/barnbiol.html
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin Company,
1978.
Crustaceans
Fiddler crab: Uca pugnax
Description: Crustacean
There is no mistaking a male fiddler crab for any other
animal. One of the male’s front claws is many times larger
than its other front claw, and makes up about half of the
animal’s body weight. While there are almost 100 species of
fiddler crabs throughout the world, the Atlantic marsh fiddler
crab is the species found in Long Island Sound estuaries. It
grows between 1 and 2 inches in width and its large front claw
will often be as long as its body. They are grayish brown in
color. The male’s larger claw can be on either side of its body, unlike hermit crabs,
which always have their larger claws on the right. If the larger claw is ripped off of the
fiddler crab, the smaller one will start to grow into the larger claw, while the ripped-off
claw will grow into the smaller one. Females and juveniles have equal-sized front claws.
Habitat:
Fiddler crabs can be found in estuaries all over the world, but it is the Atlantic marsh
fiddler crab that is found from Canada to Florida. It is most prevalent between Long
Island Sound and the Chesapeake Bay in Maryland. Fiddler crabs spend most of their
lives walking on land rather than under water. In fact, although they have gills, fiddler
crabs get their oxygen from the air, rather than the water. Their gills only need to be
kept moist to for the fiddler to breathe. When high tide arrives, fiddler crabs retreat into
their burrows and plug their burrows with mud which creates an air pocket in the burrow
from which they breathe until low tide comes again. When the tide recedes, fiddlers dig
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
out their burrows and come out onto the marsh to feed. Next to each hole will be large
balls (10 cm) of excavated mud indicating a fiddler dug itself out after high tide. Any
smaller mud balls are products of the eating process. Fiddlers sometimes go into their
burrows during low tide for protection against predators and to stay cool on a hot day.
Prey:
Despite their ferocious-looking claws, fiddler crabs do not attack smaller animals for
food. The big claws are used for defense and for attracting mates. Fiddlers do not stray
far from their burrows for food. Fiddler crabs ingest the marsh soil which contains their
food: fungi, bacteria, plankton, algae, and decaying matter. They strain these food
particles from the mud with mouth hairs. The remaining mud is deposited onto the
marsh surface as little balls. The large claws of the male often get in the way when the
fiddler is trying to scrape little bits of food off of a rock or a mudflat, which it does with
its smaller claw. Females, who do not have the large claw of the males, have much less
trouble eating. Because of this, they use less energy searching for food and need to eat
less than the males.
Predators:
Fiddler crabs are an abundant and reliable food source for some of the estuary’s
larger birds. Because fiddlers move around on the exposed mud of the estuary during
low tide, and because there are usually so many of them around, they provide a quick
and easy meal for herring gulls and sometimes herons. Even hawks and ospreys will eat
fiddlers if there is not a plentiful supply of other food available. Mammals such as foxes
and raccoons also eat fiddler crabs if they find themselves near an estuary at low tide.
All they need to do is walk out onto the mud. Other crabs, including blue crabs, will dig
into the fiddlers’ burrows to eat them when they are buried during high tide.
Life cycle:
The fiddler crab has an interesting mating ritual. During the summer, the male enters
his burrow, but leaves his large claw exposed. He waves the large claw back and forth
(as if playing a fiddle, hence the name) to try to attract a mate. If a female stops to watch
him, the male will come out of his burrow, show himself to the female, and then quickly
return to wave his claw around some more. If the female is interested, she will crawl
into the burrow with the male. The male will then plug the hole at the top of the burrow
and the pair will mate. The female crab will carry around her batch of fertilized eggs on
her underside for about two weeks, after which she releases them into the water. Soon
after, the eggs will hatch into tiny, baby crabs. Those that survive to adults will molt, or
shed their hard outer shell, several times as they grow bigger and bigger. Fiddler crabs
are estimated to live up to 2 years.
Value:
Fiddler crabs are extremely important to the health of the estuarine ecosystem.
Because they survive largely on decaying matter, called detritus, they help keep nutrients
moving through the ecosystem. In the process of digesting their food, fiddlers convert
that food into basic nutrients, such as nitrogen, which will be deposited back onto the
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
marsh surface as fecal matter. This nutrient-rich material “fertilizes” the marsh soil,
which helps other estuarine organisms such as cord grass, to grow. The constant digging
and re-digging of the marsh soil brings up trapped nutrients in the detritus to the surface
to be added to the estuarine soup. Digging also adds oxygen to the soil, which plants
need for respiration. Digging also loosens the marsh soil, making it easier for plant roots
to grow. Fiddler crabs are also an important and reliable source of food for the birds and
other animals that eat them. Any healthy estuary will have lots of fiddler crabs scurrying
about at low tide, showing that there is plenty of food for the animals at the top of the
estuary’s food web.
Fiddler crab sources:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Uca_pugnax.html
http://camel2.conncoll.edu/ccrec/greennet/arbo/publications/34/CHP38.HTM
http://rivercenter.uga.edu/education/summit/k12/k12fiddlercrab.htm
http://www.chesapeakebay.net/baybio.htm
http://www.dnr.sc.gov/marine/mrri/acechar/specgal/fiddler.htm
http://www.vims.edu/~jeff/fiddler.htm
Crustaceans
Green crab: Carcinus maenas
Description: Crustacean
Green crabs are crustaceans, a large grouping of
arthropods, which includes lobsters, shrimp and other
crabs. Crustaceans have hard exoskeletons and
segmented bodies and many legs. Green crabs have
five pairs of legs, the front of which have “toothed”
claws. Green crabs vary in color from dark brown to
green to orange but they get their name because the
murky waters of the estuaries in which they are often
found causes many of them to appear light green in
color. The body of the green crab is fan shaped and grows up to about 3 inches
wide. Each side of its carapace has 5 points. The top front edge of the body
has prickly points. Its eyes are on stalks coming from the top edge of the front
of the body, and its mouth is on the underside of the body between the eyes. Its
legs are about as long as its body is wide.
Habitat:
Green crabs are an extremely flexible species. Unfortunately, this means
that they often wind up in places where they are unwelcome and hurtful to the
ecosystem. They are native from northern Africa to northern Europe, but they
have been an invasive species present from Nova Scotia to the Carolinas since
the early 1800s. They have also made homes off South America, southern
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Africa, the west coast of the United States and Canada, and southern Australia.
They have been so successful in different parts of the world because they can
tolerate muddy, rocky, or sandy bottomed waters, a great range of water
temperatures, and an even greater range of water salinity. They are predicted to
spread into other geographic areas in the future as well. In Long Island Sound,
they primarily live on the muddy bottoms of our estuaries.
Prey:
Another reason why green crabs are so tolerant is that they will eat almost
anything. Bivalves such as mussels and clams are the favorite food of green
crabs because they are tough to eat for many animals but are easy for the crab’s
powerful claws to break or pry open. They will also eat fish, worms, shrimp,
other crabs, and plants as well. Green crabs are an unwelcome and harmful
invasive species because they are particularly fond of commercially important
bivalve mollusks. In the estuaries of Long Island Sound and its nearby waters,
green crabs have done serious damage to the populations of ecologically
important clams, oysters, and mussels.
Predators:
A prime predator of the green crab is the larger and fiercer blue crab. In
areas with strong blue crab populations, green crabs have not been a problem
because the blue crabs have kept their population in check. For example, there
are few green crabs in Chesapeake Bay where blue crabs are very prominent.
Larger fish and birds will also eat green crabs, but the blue crab remains the
only animal that can truly keep the green crab’s population in check.
Life cycle:
The female will lay and then hold thousands of eggs on her underside for
several days. The eggs can only be fertilized by a male right after the female
has molted, or shed her hard outer shell. Once she has molted, a male fertilizes
the eggs. The female will then migrate to an area with saltier water, near the
edge of the estuary or even farther out into the open ocean, to release the eggs.
Eggs hatch into microscopic larval crabs which then undergo a series of
transformations and gradually grow larger and larger. After several weeks, they
finally resemble a small crab. These juvenile crabs will then migrate back
towards a sheltered area in the estuary where they can hide in beds of marsh
grasses for protection until their hard shells form. Green crabs molt many times
throughout their lives as they grow bigger.
Value:
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
In their native Europe, green crabs play an important role in the food web of
the European seas and estuaries. However, in Long Island Sound, green crabs
are an unwanted invasive species. They eat a large number of oysters and
clams, which play an important role in filtering the estuary’s water and keeping
it clean, as well as mussels, which help keep the soil structure of the estuary
intact. Unfortunately, humans don’t like to eat green crabs, so harvesting has
not helped to limit their population here.
Green crab sources:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Carcinus_maenas.html
http://aquanic.org/publicat/usda_rac/efs/nrac/nbull18.pdf
http://seagrant.gso.uri.edu?daytrip/coastlines/salt_marsh.html
http://www.tiltedworld.com/memcc/carcinus/eastus.html
Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin
Company, 1978.
Crustaceans
Japanese shore crab (Asian shore crab, Pacific crab) Hemigrapsus sanguineus
Description: Crustacean
Japanese Shore crabs are crustaceans, a large
grouping of arthropods, which includes lobsters,
shrimp, and other crabs. Crustaceans have hard
exoskeletons and segmented bodies and many legs.
Japanese shore crabs have 5 pairs of legs with
alternating light and dark bands of color (usually
shades of brown). Japanese shore crabs vary in
color from blotchy green to purple to orange-brown
to red. The carapace of the Japanese shore crab is square-shaped and has 3
spines on each side. It is a fairly small crab; adults are usually about 1.5 inches
wide. Adult males have a hard bulge between the pincers on their front claws.
Other crabs do not have this structure and its presence can be used to identify
the crab.
Habitat:
Japanese shore crabs are an invasive species that are native to the western
coast of the North Pacific Ocean (southern Russia). They were first spotted in
New Jersey in 1988; it is assumed that they were brought over in ships’ ballast
water. They have spread rapidly up and down the coast and are found on the
Atlantic intertidal coastline from Maine to North Carolina. They are now the
most common crab in the intertidal area in Long Island Sound. Japanese shore
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RL6 Guide Manual – Handbook of Estuarine Organisms
crabs are a very flexible species. They tolerate a wide range of salinity and
temperature. They live in any shallow intertidal rocky region. Because they
tolerate a wide range of habitat conditions, they are expected to continue to
spread.
Prey:
Japanese crabs are called “opportunistic omnivores”. They will eat
anything—living or dead that they find in their habitat. They will eat
macroalgae such as sea lettuce, salt marsh grasses, larval and young fish, and all
invertebrates from amphipods to snails to mussels to barnacles to worms. Their
extremely flexible diet is another reason why they have become the dominant
species of crab in the intertidal rocky zones of the Atlantic coasts.
Predators:
Fish such as the rockfish eat Japanese shore crabs. Seagulls are an important
predator of the Japanese shore crab. In its native habitat in the North Pacific
Ocean, there are parasites that infect these crabs and help control the population
numbers. Because those parasites are not present in the Atlantic so the crab
population here has no natural control and can increase to unhealthful numbers.
Life cycle:
Japanese shore crabs reproduce in large numbers. They breed from May to
September twice as long as native crabs. The female lays up to 50,000 eggs at a
time and can lay this amount 3-4 times during the breeding season. The larvae
drift in the water for one month and then begin to develop into crabs through
several stages. The larvae can be transported over great distances as they drift
with the currents. Japanese shore crabs have an average life span of 3 years.
Value:
In their native region, Japanese shore crabs play an important role in that
food web. However, in Long Island Sound, this invasive species poses a threat
to the food web. This crab competes with the native species of crab for food
and habitat space and has caused the decline of other crab species along the
Atlantic coast. Studies have shown that it is the predominant species of crab
found in the intertidal zone in Long Island Sound. Many regions are reporting
that it is the only intertidal crab found now. Populations of other species such
as fish and shellfish are adversely affected by the presence of so many of these
crabs. Scientists are actively monitoring where and how many of these crabs
are found. They are also monitoring the other estuarine and marine species.
They are also conducting experiments to learn more about the crab itself. The
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
total impact of the introduction of this crab into habitats along the Atlantic coast
is not yet known.
Japanese shore crab
http://cars.er.usgs.gov/Nonindigenous_Species/Asian_shore_crab/asian_shore_crab.html
http://www.iisgcp.org/EXOTICSP/Japanese_Shore_Crab.htm
http://www.sgnis.org/publicat/2mb_16.htm
NONINDENGOUS SPECIES INFORMATION BULLETIN: Asian shore crab, Japanese shore
crab, Pacific crab
The Ecology of the Japanese Shore Crab and its Niche Relationship to the Green Crab along the
Coast of Connecticut, USA
Fish
Killifish
Description: Fish
There are several species of
killifish that live in estuaries near
Long Island Sound: the mummichog
(Fundulus heteroclitus), the banded
killifish (Fundulus diaphanous), the
rainwater killifish (Lucania parva),
the spotfin killifish (Fundulus luciae), and the striped killifish (Fundulus
majalis) are some. One feature that all the killifish have in common is that they
are small. The largest of these species of killifish is the striped killifish, which
rarely grows longer than 6 inches. Most of these species are about 3 or 4 inches
long as adults. All killifish have one dorsal fin and a flat, non-forked tail fin.
Most of these killifish are green or brown on top with a silvery bottom. We are
able to identify the different species because each species has different
markings, such as stripes, spots, and bands.
Habitat:
Killifish usually live in brackish water, but can also be found in fresh water
and salt water. They are most often found in shallow water near the shore,
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
where their food is abundant. They can withstand conditions of low oxygen
levels and extreme variations in salinity. The different species of killifish have
ranges that differ from each other, but as a group the killifish found in
Connecticut live as far north as Canada and as far south as Florida. Because
they are so small, killifish usually travel in large schools to try to avoid being
eaten. The spotfin killifish can be found in the salt marsh among the Spartina
grasses at high tide in waters that average 2 or 3 cm deep. At low tide spotfins
can be found in shallow muddy tide pools, or at the bases of clumps of
Spartina.
Prey:
Killifish eat plankton (phytoplankton and zooplankton) and animals.
Killifish live in shallow water where a lot of sunlight gets through. Because the
water is shallow, algae (phytoplankton) are in the water that the killifish live in.
Killifish also eat insect larvae such as the larvae of mosquitoes, tiny
crustaceans, mollusks, worms, and small fish.
Predators:
Killifish are an important food source for larger fish. Many species of
killifish make excellent bait because they are a favorite food of popular sport
fish, including bass and bluefish. Birds, such as egrets and herons which feed
mostly on small fish, eat killifish.
Life Cycle:
Killifish spawn in the summer. The females lay their eggs in large clumps
that sink to the bottom and stick to vegetation or to the muddy bottom where the
males fertilize them. The eggs are only one or two millimeters wide. Most of
the hatched eggs will not survive to adulthood. Of those that do make it, in
most species of killifish it takes one year before the young fish are ready to
spawn themselves. Most killifish only live two or three years.
Value:
Killifish are a big part of the diet of many larger fish and birds. Without
them the food web of the estuary would not survive. Killifish also eat algae. If
there were too much algae in the shallow water in which the killifish live, there
would not be enough oxygen in the water to support marine life. What’s more,
we should all thank the little killifish when summer comes around. If they were
not around to eat mosquito larvae, we would all be getting bitten more often!
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Killifish sources:
http://fish.dnr.cornell.edu/nyfish/Cyprinodontidae/bandedkillifish.html
http://fish.dnr.cornell.edu/nyfish/Cyprinodontidae/mummichog.html
Thomson, Keith Stewart; Weed, W.H. III; Taruski, Algis G.; and Simanek, Dan E. Saltwater
Fishes of Connecticut. Hartford, CT: State Geological and Natural History Survey of
Connecticut, Department of Environmental Protection, 1978.
Birds
Great Blue Heron: Ardea herodias
Description: Bird
The Great Blue Heron is a tall, slender bird. It
can grow up to 4 feet tall, with a wingspan of
almost 6 feet. The Great Blue Heron has a long,
skinny neck that is shaped like the letter S. It
straightens its neck out very quickly, however,
when it is striking at its food with its long, pointy,
yellow bill. The heron’s neck is sometimes almost
half the length of its entire body when stretched
out straight. The Great Blue Heron is so called
because its back feathers are a grayish-blue in
color. Its face and belly are white, and it has a
long, black plume of feathers sweeping back from
the front of its head.
Habitat:
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Great Blue Herons can be found all over North and South America. They
are found wherever there is marshland, composed of either fresh or brackish
water. The only places they are not found are in high mountains, in deserts and
in the extremely cold northern parts of Canada. The Great Blue Herons that
live near Long Island Sound migrate south during the winter, but herons in
warmer climates tend to stay there year-round. Herons are particularly fond of
marshy areas with trees nearby because they choose to build their nests high up
in trees where their eggs cannot be eaten by predators. The nest is a bulky
structure of sticks and branches lined with grass. Herons usually build their
nests in colonies, called rookeries, with other heron nests in a tree canopy near
water. If the nest survives the winter, the heron that made it will likely use it
again the next year.
Prey:
Great Blues are one of the top predators of the estuary. They eat fish,
worms, crabs, crayfish, frogs, shellfish, and even small rodents and snakes.
They are able to move their necks very quickly, striking at their prey with their
long, sharp bills. A heron will spend long stretches of time wading through the
water until it spots something it wants to eat. Then, it will stay completely still
until its prey is within striking distance. It will uncoil its neck and stab at its
prey, grabbing it before the prey even knows what has hit it.
Predators:
Great Blue Herons are large birds with no natural predators of the adult bird.
Their population is limited only by how much food is available in the
ecosystem’s food web. Great Blue eggs, however, are sometimes eaten by birds
and the occasional raccoon, skunk, or fox, if the nest has been built too close to
the ground.
Life cycle:
Herons begin to mate in the spring. Males and females court each other, and
once they have paired up, they will build a nest together. Females usually lay
three to five eggs, which both the male and female will sit on and watch for
about a month before they hatch. While they lay many eggs, most heron
couples can only raise two chicks at a time. They feed the strongest and biggest
chicks of their litter, while the others are not fed and soon die. After about two
months the young herons leave the nest and are on their own.
Value:
Great Blue Herons are one of the estuary’s top predators. They will eat
almost anything that can fit down their throats, so if any smaller animal in the
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
estuary has become overpopulated and is negatively affecting the balance of the
food web, the heron is there to help by eating that animal. One can tell if an
estuary’s food web is healthy by seeing how many Great Blue Herons there are
around. If there are healthy herons wading in the water, the rest of the
ecosystem is probably healthy, too.
Great Blue Heron sources:
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Great_Blue_Heron_dtl.html
http://www.chesapeakebay.net/baybio.htm
http://www.mbr-pwrc.usgs.gov/id/framlst/i1940id.html
Sibley, David The Sibley Guide to Bird Life and Behavior. New York: Alfred A. Knopf, 2001.
Birds
Great Egret and Snowy Egret: Ardea alba and Egretta thula
Description: Birds
The Great Egret and the Snowy Egret look very
much alike, but they are easy to tell apart. Both
birds have all-white feathers, and a patch of yellow
skin in front of each eye. They both have long,
skinny legs, long necks and bills, and tufts of
feathers on top of their heads. The Snowy Egret is
smaller, has a black bill, black legs, and yellow
feet. The Great Egret is larger and has a yellow bill
and all-black legs. The Snowy Egret grows up to
two feet long, but its wingspan reaches over three
feet. The Great Egret can grow to be about 40
Snowy Egret
inches long with a wingspan of well over four feet.
Egret feathers are slick and oily so that water does
not stay on them when they get wet as they are
© 2007 Mill River Wetland Committee, Inc.
Great Egret
RL6 Guide Manual – Handbook of Estuarine Organisms
searching for food. Both the Great Egret and the Snowy Egret are considered
“wading birds” because they have adaptations for wading in shallow waters to
hunt fish, frogs and other prey. Their long legs and necks allow them to forage
in the estuaries, and their bills are adapted for spearing and grasping prey.
Habitat:
Great Egrets are found in many places around the world, from southern
Canada to Argentina and in Europe, Africa, Asia, and Australia. Snowy Egrets
are found along the Atlantic coast from southern Maine southward and inland
across the western United States. They are also found as far south as the
Caribbean and South America. Both Great Egrets and Snowy Egrets can be
found near lakes and rivers as well as the estuary, as long as there is marshland
nearby from which they can feed. Egrets build their nests anywhere from high
up in a tree to right on the ground near the shoreline if there are not many
predators around. The Great Egret builds its nest a bit higher in trees than the
Snowy Egret. The nests are small and made of sticks, then lined with grass and
leaves. Both kinds of egrets will often build their nests in colonies near herons
and other egrets. The nests are built near water because that is where the
egret’s food lives.
Prey:
Egrets use their long legs, big feet, and long bills to catch food in shallow
water. They eat mainly fish but eat all types of other aquatic animals. They use
their feet to stir up animals such as crustaceans, frogs and other amphibians, and
small fish from the bottom of the water, and then either spear them or scoop them
up with their long bills. On land, both species of egret will eat insects and
sometimes small snakes and lizards as well.
Predators:
In Connecticut, adult egrets have few natural predators. Egret eggs and babies
are more vulnerable, however. Owls, raccoons, and even crows will make a meal
out of egret eggs if the nest is not well guarded. Human development of the
egret’s habitat is a far greater threat to the egret’s survival because development
destroys good nesting and foraging areas.
Life cycle:
As many birds do, egrets pair for life. Egrets attract mates by growing long
plumes of feathers on their head and back that they shed after they mate. In the
late 1800s and early 1900s egrets were hunted for their plumes which were used to
decorate women’s hats. This plume hunting reduced the populations of Great
Egrets and Snowy Egrets by more than 95 percent. The populations recovered
after the egrets were protected by law. Male egrets reach the breeding colony
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
before the females and begin nest-building to attract a female. Once paired, both
continue to build the nest and defend it from other birds. If the pair has mated
before, they will often return to the same nesting site they used the previous year.
Egrets lay three to five eggs once per year. Both the mother and father will sit on
the eggs to keep them warm. The eggs hatch after three or four weeks. By the
fall, the young egrets can feed themselves and are ready to fly south for the winter.
Value:
Egrets are an important predator of many of the smaller organisms of estuaries.
The abundant crustaceans and small fish would be overpopulated if there were no
egrets to feed on them. Since egrets eat many young fish as well as smaller
species of fish, they also help to thin out the populations of the larger species of
fish.
Great Egret & Snowy Egret sources:
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Snowy_Egret_dtl.html
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Great_Egret_dtl.html
http://www.mbr-pwrc.usgs.gov/id/framlst/i1960id.html
http://www.mbr-pwrc.usgs.gov/id/framlst/i1970id.html
Sibley, David The Sibley Guide to Bird Life and Behavior. New York: Alfred A. Knopf, 2001.
Birds
Herring gull: Larus argentatus
Description: Bird
While there are many species of gulls
throughout the world and even in the
Northeast, the most recognizable and
abundant species of gull in Connecticut is the
Herring Gull. Herring Gulls are fairly large
birds, measuring up to almost 2 feet long with
a wingspan of almost 5 feet. They have white
heads, necks, and bellies, light gray backs and
wings, and black or dark brown tail feathers.
They have yellow eyes and yellow beaks with
a distinctive red spot towards the front of their
lower beak. Their beaks are long and point slightly downwards. The legs of
Herrring Gulls are long, slender, and pink colored. Each leg has three forwardfacing webbed toes, which help the gull swim on top of the water, and a tiny
fourth toe behind its ankle that helps it walk on land. Gulls take several years to
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
mature. For the first three or four years of the gull’s life its plumage has
varying shades of brown and gray with brown spots.
Habitat:
Gulls can be found all over the world, usually wherever there are large
bodies of water nearby. Herring Gulls are found all along the Atlantic coast of
North America, as well as along the Great Lakes. While some gulls are
permanent residents, most fly north during the summer to breed and south
during the winter to avoid the cold. In addition to living near estuaries, oceans,
and large lakes, gulls will live wherever there is food, including in major cities
and near garbage dumps.
Prey:
Gulls will eat almost any food they can find, including fish, crustaceans,
mollusks, insects, small birds, eggs, floating dead animals, decaying plant
matter, and garbage. They eat clams and oysters by digging them up and
dropping them on a hard surface from high in the air in order to break the shell.
Similar to raccoons, gulls have thrived as human development has increased in
their natural habitat. Human garbage and waste provides food for far more
gulls than the natural ecosystem could support.
Predators:
Adult gulls have few predators, but their eggs and chicks are vulnerable to
many predators. Because gulls build their nests on the ground, the young are
particularly vulnerable. Other birds, including other gulls, and mammals such
as raccoons and skunks will often try to make a meal out of young gulls or gull
eggs.
Life cycle:
Gulls build their nests on the ground. The nests are made of sticks and grass
and are often located in the estuary among some of the taller grasses, but are
usually built on higher ground such as hilltops or cliffs near beaches. Gulls
usually mate for life. They breed in the spring and summer, laying three or four
eggs that hatch within a month. Both the male and female gulls care for the
chicks. For the first three or four years of the gull’s life, it grows larger and can
be identified by specific plumage patterns at specific ages in the young bird’s
life. The white and gray plumage recognized as belonging to Herring Gulls is
that of the mature adults, usually at least four years old.
Value:
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Because gulls will eat almost anything, they can help control the population
of any small marine species that may have become overpopulated at any given
time. More importantly, because they scavenge on decaying plant and animal
matter, they help clean up the soil and water of the estuary.
Herring Gull sources:
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Herring_Gull_dtl.html#food
http://www.mbr-pwrc.usgs.gov/id/framlst/i0510id.html
Sibley, David The Sibley Guide to Bird Life and Behavior. New York: Alfred A. Knopf, 2001.
Birds
Osprey: Pandion haliaetus
Description: Bird
The Osprey is a relatively large
raptor, or bird of prey. Adults are
usually just less than 2 feet long in their
bodies, but their wingspans are much
larger (up to almost 6 feet). They have
brown backs and wings and white
bellies and legs. They have white
crowns and foreheads with brown
stripes leading from their eyes to their backs. The undersides of their wings are
white with brown bands. They have large yellow eyes with keen sight that let
them spot fish in the water from high in the air. They have sharp talons for
catching fish and a sharp, down-turned beak that helps them rip the fish apart to
eat them.
Habitat:
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Ospreys live all over the world, from cooler climates in Connecticut to
warmer, tropical climates. Ospreys do not like the cold, however, and will
migrate to warmer areas during the winter. The Ospreys we see here in
Connecticut fly to South America during our winter because it is summertime
in South America when it is winter here. Ospreys live near shorelines,
estuaries, rivers, and lakes: wherever there are fish to eat. They tend to stay
close to shore, where the water is shallower, so they have a better chance of
seeing fish swimming near the surface. Ospreys build their nests here in North
America because that is where they breed and raise their young (rather than in
South America). Their nests are made of large sticks and branches and are
usually built at the top of tall, dead trees. Any tall structure with a flat top
makes a good site for an Osprey nest, however, so they often make their
summer homes on telephone poles and other manmade structures, such as duck
blinds, channel markers, and nest platforms designed especially for Ospreys.
Prey:
Ospreys eat almost exclusively live fish. In Connecticut, Ospreys eat mostly
flounder, which lie on the water’s bottom in shallow water and can easily be
scooped up, and herring and menhaden, which swim in schools close to the
surface, where they are easily seen and caught. The only fish Osprey won’t eat
are the ones that are too heavy for them to fly with. Occasionally an Osprey
drowns because its talons get stuck in a fish too large for it to lift. When an
Osprey sees a fish it can catch, it swoops down feet first to catch it in its talons.
Fortunately, the Osprey has adaptations including thick, oily, waterproofed
feathers and closeable nostrils that enable it to be submerged briefly in the
water. The Osprey will then fly with the fish in its talons back to its nest or a
perch in a tall tree, where it rips the fish apart and eats it.
Predators:
Adult Ospreys have few, if any, real predators. Large owls sometimes eat
adult Ospreys, but not enough to affect the Osprey’s population in any way.
Osprey eggs and babies, however, are more vulnerable, and are sometimes
eaten by owls, other birds of prey, and raccoons that climb up into the Osprey’s
nest. Humans have had the greatest effect on Osprey populations. From the
1950s until the early 1970s the populations declined drastically because of the
use of the pesticide DDT. After DDT was banned, Osprey populations
increased rapidly.
Life cycle:
Ospreys here in Connecticut arrive from the south as soon as the waters have
thawed, usually in late March. Ospreys mate for life, and the pair will usually
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
return to the same nesting site it used the summer before. The birds will try to
breed as soon as their nest is ready, so that when their chicks are born they will
have enough time to mature and be able to fly south in the fall. Once the young
birds are three years old, they will start looking for mates of their own. Males
will fly in circles with fish or nesting materials in their talons in hopes of
wooing a female.
Value:
Ospreys are at the top of the food chain. Few Ospreys are eaten by other
animals. The Osprey’s role in the estuary’s ecosystem is to eat as many fish as
possible. If not for the Osprey, certain fish species would be overpopulated and
overeat eat smaller fish species, disrupting the ecosystem’s food web.
Osprey sources:
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Osprey_dtl.html
http://www.chesapeakebay.net/baybio.htm
http://www.mbr-pwrc.usgs.gov/id/framlst/i3640id.html
Poole, Alan Forsyth Ospreys: A Natural and Unnatural History. New York: Cambridge
University Press, 1989
Sibley, David The Sibley Guide to Bird Life and Behavior. New York: Alfred A. Knopf, 2001.
Life cycle of a barnacle
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Life cycle of a bivalve
Life cycle of a crab
Bibliography
Books
Arms, Karen and Camp, Pamela S. Biology, Holt, Rinehart & Winston, NY 1979.
Barnes, R. D., Invertebrate Zoology. Philadelphia: W.B. Saunders and Holt, Rinehart and Winston,
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Daiber, Franklin C. Animals of the Tidal Marsh, Van Nostrand-Reinhold, NY, 1982.
Day, John W., et al Estuarine Ecology, John Wiley & Sons, Inc., NY 1989.
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Gosner, Kenneth L. A Field Guide to the Atlantic Seashore. Boston. Houghton Mifflin Company,
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Green, J. The Biology of Estuarine Animals, University of Washington, London, 1968
© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
Hedeen, Robert A. The Oyster: The Life and Lore of the Celebrated Bivalve. Centreville, MD:
Tidewater Publishers, 1986.
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Tiner, Ralph W. A Field Guide to Coastal Wetland Plants of the Northeastern United States. Amherst,
MA: University of Massachusetts Press, 1987.
Wallace, Robert L. and Taylor, Walter K. Invertebrate Zoology, A Laboratory Manual, 6th Ed.,
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Whitaker, John O. Jr. and Hamilton, William J. Jr. Mammals of the Eastern United States. Ithaca,
NY: Cornell University Press.
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© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Red-tailed_Hawk_dtl.html
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© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
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© 2007 Mill River Wetland Committee, Inc.
RL6 Guide Manual – Handbook of Estuarine Organisms
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Reports and Papers
“A Fungus Disease in Bivalve Larvae,” H.C. Davis & V.L. Loosanoff. U.S. Fish & Wildlife
Svc. Milford, CT.
“Fungal farming in a snail,” Silliman, Brian R., & Newell, Steven Y., Dept. of Ecology and
Evolutionary Biology, Brown University, Providence, RI, 02912 and University of
Georgia, Sapelo Island, GA, 31327 (Ed. by Robt. T. Paine, Univ. of WA, Seattle, apprvd.
10/21/03, rec’d 8/14/03 - Nat’l Acad. of Sciences 12/23/03 - Vol. 100, No.26.
“Plants and Animals of Long Island Sound,” Weiss, Howard M., et al, Project Oceanology,
Groton, CT, 1995.
Consultants
Bull, Milan B. Director, Connecticut Audubon Society, Burr St., Fairfield, CT
Cuomo, Carmela, Ph.D, Assistant Professor and Coordinator, Marine Biology, University of
New Haven, West Haven, CT
Pitchford, Stephen, Microbiologist, Biological Laboratory, National Marine Fisheries
Service, Milford, CT
Wagner, David, PhD, Ecology and Evolutionary Biology, University of Connecticut, Storrs,
CT
Illustrations & Drawings
Illustrations pp. 53, 55, 57, 59, 61 by permission from A Beachcomers Botany by Loren C.
Petry and Marcia G. Norman
Illustrations pp. 63, 69, 71, 73, 75, 79 by permission from Tidal Marsh Invertebrates of CT
Bulletin 20, CT Arboretum
Illustrations pp. 51, 83, 85 taken from http://en.wikipedia.org
Line drawings, pp. 77, 89 by Ellie Carrera
Line drawings, pp. 43, 65 by Richard Rossiter
Line drawings, pp. 52, 81, 87 by Jocelyn T. Shaw
Line drawings, pp. 47, 52 by Sarah Weinrod
Line drawings, p. 67 by Judy S. Wilkinson
© 2007 Mill River Wetland Committee, Inc.