Marine Environments
 The total surroundings of a living thing are called the environment .
All environments have living ( biological ) and nonliving ( physical and
chemical ) components.
 The living or biotic
things in an environment are called the
biota . For example, the bacteria, crustaceans, fish , sponges, and
other organisms that live in and around a coral reef are all part of the
coral reef’s
biota . The nonliving or abiotic parts of a coral
reef environment would include the water chemistry, light , salinity,
temperature , and water pressure. Interactions between the
biotic and
abiotic
factors characterize all environments.
 The place or “home” in which an organism is typically found is called
its habitat . A life zone is a region that contains organisms that
interact with one another and with their environment.
Marine Life Zones
Marine life zones include: the intertidal zone, the supratidal zone,
the subtidal zone, the pelagic zone, the neritic zone, the oceanic
zone, and the benthic zone.
 The
intertidal zone
is the area located between high and low
tide. The highest point the high tide reaches on the beach is marked
by a debris line called the
strandline
, which is a line of
seaweed, sticks, and floating material deposited on the beach during
each high tide. The intertidal zone contains a wide variety of marine
invertebrates ( animals without backbones ), including crustaceans ,
worms , and mollusks . Organisms that live in the intertidal zone
are well adapted to living in an environment that has alternating
periods of wet and dry , and the
tides come in and go out
each day.
 The supratidal zone
is the area above the intertidal zone up to
the sand dunes. This area is characterized by salt-tolerant grasses,
shrubs, and then, in the upper
supratidal zone , trees.
The diagram above shows the coastal marine life zones, and some common inhabitants.
 The subtidal zone lies below the low tide line, which means this
marine life zone remains underwater . The subtidal zone includes
an area that is subject to heavy
wave impact , and underwater
turbulence. Because of this, some organisms in this zone have
structures that help them cling to hard substrates to prevent their
being swept away by waves and currents . Examples of organisms
that live in the subtidal zone include: sea stars (incorrectly called
starfish ), marine snails, sea anemones , mussels, barnacles , sand
dollars, flounder , crabs, shrimp, clams, marine algae, and kelp .
Fill in the table below with some subtidal zone organisms and their adaptive clinging structures
Subtidal zone
organism
Sea stars
Marine snails
Sea anemones
Mussels
Barnacles
Flounder
Sand dollars
Kelp
Adaptation to the turbulent subtidal zone
Suction pads on their tube feet
Muscular foot designed for clinging and
movement
Muscular feet designed for clinging (sea
anemones are sessile- they cannot move about)
Secrete byssal threads- tough, fibrous threads
that stick to hard substrates
Secrete an organic glue- allows them to cement
themselves to rocks or other hard substrates
Have flattened bodies and lie on, or bury
themselves in, the sand
Have flattened shells and bury themselves in
the sand, move slowly using tube feet
Anchor themselves to rocky surfaces using a
fibrous pad of tissue called a holdfast
 The pelagic zone is the largest life zone in the ocean. The pelagic
zone covers the entire ocean of water above the sea bottom.
 The neritic zone is part of the pelagic zone , and covers the
region of water that lies above the continental shelf. This zone is
generally less than 200 meters
deep. This is an extremely
productive zone of the ocean, and most of the world’s commercial
fishing takes place in the neritic zone. The neritic zone is so
productive because rivers provide nutrients from the continents to
the ocean in these zones.
 The oceanic zone is the life zone that extends beyond the neritic
zone , and includes most of the open ocean. The upper part of the
ocean zone receives sunlight , whereas the lower part (the vast
majority of the ocean) is in darkness. The part of the ocean that
receives light is called the photic zone (also called the euphotic
zone). Sunlight does not penetrate more than
200 meters deep.
Beyond this is the aphotic zone (meaning “no light”). There is more
life in the photic zone because sunlight allows plants and algae to
live and be an abundant source of food for marine animals.
 The benthic zone
includes the entire ocean floor, from the shallow
intertidal zone , to the deep abyssal plain. Organisms that
inhabit the benthic zone are called benthos .
A cross section of the ocean’s life zones; the pelagic zone includes the neritic and oceanic zones.
Questions:
1) Which life zone is more productive, the neritic or the oceanic?
2) How are some benthic organisms adapted to live in turbulent
waters?
3) What are some adaptations of organisms that live in the aphotic
zone?
1) Why were marine scientists surprised by the biodiversity among the
benthos?
2) What kinds of organisms have been found in the samples that were
collected?
3) How do scientists collect invertebrates that live more than 1km deep?
Estuaries and Coral Reefs:
Habitats of Abundance and Diversity
 Where rivers enter into oceans,
freshwater and salt water mix,
forming an environment known as an
estuary .
 Along the shores of an estuary , there are many inland bays and
creeks. The varied terrain of an estuary, along with its brackish
water (water that is a mixture of fresh and salt water), provides
diverse habitats for marine life. Because they are very nutrient-rich,
and are shielded from turbulent wave action, estuaries are
generally the most biologically productive and diverse environments
found along coasts.
Cross section of an estuary and a barrier beach.
 Sediment, carried to the ocean by rivers, is deposited in
deltas
at river mouths. This sediment is then moved by wave action forming
long ridges of sand called
barrier beaches
. On one side of a
barrier beach is the bay and on the other side is the open
ocean .
The estuary lies on the bay side of a barrier beach.
Estuary communities- Three common types of communities that arise
in estuary environments are:
salt marshes ,
mudflats
,
and
mangroves
. The type of environment that is formed depends
upon several factors including climate, geology, and topography.

Salt marshes (aka wetlands) are typified by marsh grasses such
as cordgrass , a course, tough grass that has special glands that
allow it to secrete salt crystals through its leaves.
Characteristic organisms of a salt marsh community in an estuary.
Question: Create a food chain in this salt marsh community using as
many of the organisms pictured above as you can.
 The calm and nutrient-rich waters of the salt marsh provide an ideal
environment for marine animals to produce offspring . In fact,
these wetlands are often described as the “nurseries” for many species
of ocean fish. One example is the flounder
, which feeds on
killifish, which, in turn, feed on insect larvae.
Question: Why would estuaries be ideal environments for eggs and
newly-hatched fish?

Mud flats are characterized by dark muddy sand and no marsh
grasses. Just as the salt marshes are the nurseries in an estuary, the
mudflats are the
graveyards
, where bacteria
decompose
wastes and turn sand into a dark mud. If you were to dig a hole in the
sand of a mud flat, you would see that under the surface the sand is
black and gives off a
foul odor, like rotting eggs.
Characteristic organisms of a mud flat community in an estuary.
 This smell is caused by the presence of hydrogen sulfide
,a
compound that is the product of decomposition and that accumulates
in sediments that are deficient ( very low
) in oxygen .
 In regions with tropical climates,
mangrove communities , or
mangrove swamps often form along the coastal shores of bays and
inlets. These areas are named for their abundance of red mangrove
trees
. At low tide, the arching roots, which anchor
the
mangrove trees in the muddy sand, are visible. At
high tide , the
water covers the roots, but the tree trunks and leaves remain
above the water
.
 Like salt marshes,
mangrove swamps
are extremely rich in
marine life. Also like salt marshes, mangrove swamps help protect the
shore from erosion. The roots of the mangrove tree hold the
sand
and prevent it from being carried away by
waves and currents .
 During storms,
mangrove swamps act like giant sponges ,
absorbing the water and the impact of storm surges. Federal and local
governments spend hundreds of millions or even billions of dollars
building dikes, levees, and barrier walls to protect against flood
damage from hurricanes along coasts. However,
mangrove
swamps are extremely effective natural barriers that protect areas
farther inland. If these areas were left in a natural state, rather than
removed for development , our coastal areas would be much
better protected from hurricanes.
Organism commonly found in mangrove swamp communities.
Question: What are three benefits mangrove swamps provide for
organisms and the environment?
“Coral reefs are the rainforests of the sea.”
Coral Reef Environments: Coral reefs are tremendously diverse
habitats made up of very hard formations of calcium carbonate ( CaCO3)
built up from the seafloor by living organisms called coral polyps
.
 coral reef formation begins when microscopic
coral larvae settle
on a hard substrate in the sand and develop into coral polyps.
 Coral polyps live in colonies , with each new coral polyp living in its
own limestone home, which it builds. Each new generation of polyps lay
down a new layer of limestone, causing the reef to expand
upward
at a rate of about
2-3 cm
per year.
 Some massive reefs, such as Australia’s Great Barrier Reef
, are
more than 40 meters high and more than 2000 km long. Corals can
grow right up to the ocean surface, but cannot
grow out of the
water .
 Tropical coral reefs are only found in
tropical
and subtropical
regions of the world, between about 30 degrees north and 30
degrees south latitude. Between theses latitudes, the ocean water is
warm
,
clear , and there is plenty of sunlight . These are
the conditions necessary to promote the growth of
symbiotic algae
within the coral polyps that build the reefs.
Characteristic organisms commonly found in coral reef communities.
 The many types and shapes of corals in a coral reef create an irregular
pattern of crevices, depressions, and caves in which organisms can live
and hide
. These solid, stable features provide habitat for a great
abundance
and
biodiversity
of organisms in coral reefs.
Types of Corals
 Corals are classified into two types,
hard corals
and soft
corals . Hard corals include elk horn, staghorn, and
brain
coral, all of which are rigid. Soft corals include sea fan
and
sea
rod
, which are flexible and sway in the currents.
Threats to Corals
 Coral reefs are very
productive
environments, but they are
also very
fragile
. Pieces of coral can be broken off easily; even
touching
coral can damage the thin membrane that protects its
surface. In addition, overfishing
, unrestricted or unregulated
diving , and
development along coasts
(which contributes
large amounts of sediment to coastal waters) all lead to the degradation
of coral reefs.
 Coral reef bleaching is the whitening of coral reefs which results
from the death of
symbiotic zooxantheallae (yellow-green algae
that live within the cells of coral). When these symbiotic organisms
inside the coral die, the coral itself dies.
 Coral reef bleaching is caused by human actions and natural
variations in the reef environment including changes in sea
temperature, and the amount of solar radiation, sedimentation,
pesticides, and fertilizers.
Question: Describe some sources of the impacts listed above, and explain
how they directly effect coral reefs.
 Coral bleaching events have increased significantly worldwide in the
past 20 years. Global climate change may play a role in the increase in
coral bleaching events, and could cause the destruction of major reef
tracts and the extinction of many coral species.