Natural History Project
Alki Beach—Marine Invertebrates
Kira Bendixen
Biology 470/Whitlow
Pink-Tipped Anemone (Anthopleura
elegantissima)—These organisms are
typically found in the intertidal regions
generally attached to rocks or hard
surfaces. When these organisms are
closed you are unable to see the pink
tipped tentacles of the anemone leaving
only an, unattractive light green
organism (www.ptmsc.org).
Taxonomy: Kingdom Animalia 
Phylum Cnidaria  Class Anthozoa  Pink-Tipped Anemone (Anthopleura elegantissima)— Found on
Subclass Zoantharia  Order Actiniatia October 19, 2006 at 12:00pm. The weather was very cold and overcast
 Family Actiniidae  Genus with light intermittent rain.
Anthopleura  Species elegantissima (http://www.ptmsc.org)
Ecological Facts:
 The anemone’s color comes from hosting symbiotic algae in its digestive tract
(http://www.ptmsc.org).
 Due to the anemone’s asexual reproduction, large formations on colony clones are commonly found
on the rocks. Colonies of different clones can be distinguished between just a couple inches between
them; this is suggestive of a battle zone in which the anemones compete for space using their poisonfilled tentacles (www.ptmsc.org).
Field Notes: This specimen was found on October 19, 2006 at 12:00pm. The weather was very cold and
overcast with light intermittent rain. There were many within different individual regions on the surrounding
rocks.
Native Littleneck Clam (Protothaca staminea)—These clams are
typically found higher in the tidal zone in the top 4-6 inches in a
gravel-mud ground. They are characterized by concentric rings along
with ridges which also line the shell. Generally the shells are a grey to
white cream color (http://wdfw.wa.gov).
Taxonomy: Kingdom Animalia  Phylum Mollusca  Class
Bivalvia  Order Veneroida  Family Veneridae  Genus
Protothaca  Species staminea (http://fwie.fw.vt.edu)
Ecological Facts:
 Probably the most important commercial food clam in the
Northwest (http://www.ecy.wa.gov).
 Play an extremely important role in the uptake and recycling of
energy and nutrients. They also filter the water, which allows
them to help maintain a constant flow of energy and nutrients
throughout
their
ecological
environment
(http://www.psat.wa.gov).
Native
Littleneck
Clam
(Protothaca staminea)— Found on
October 19, 2006 at 12:00pm. The
weather was very cold and overcast
with light intermittent rain.
Field Notes: This specimen was found on October 19, 2006 at 12:00pm. The weather was very cold and
overcast with light intermittent rain. There were not very many closed clams laying on the surface of the
ground; they live 4-6 inches beneath the surface. However, many shells were seen.
Horse Clam (Tresus capux)—The horse clam is a close relative to the
geoduck and are generally found in the lower intertidal zones. Sand,
mud, and gravel are where these clams are typically found, amongst the
littlenecks. Their shells are characterized as cream to yellow colored
with patches of brown. They range from four to eight inches across
(http://en.wikipedia.org).
Taxonomy: Kingdom Animalia  Phylum Mollusca  Class Bivalvia
 Order Myoida  Family Hiatellidae  Genus Tresus  Species
capux (http://en.wikipedia.org)
Ecological Facts:
 Horse clams also prefer a habitat where there are eelgrass beds.
However, eelgrass beds also support herring spawning. Due to
increased clam fishing in these areas the eelgrass is being
destroyed and thus having a dramatic negative effect on the
herring populations (http://www.dfo-mpo.gc.ca).
 These horse clams are another organism which plays an
extremely important role in the uptake and recycling of energy
and nutrients by filtering huge quantities of water per day to
help maintain a constant flow of energy and nutrients
throughout
their
ecological
environment
(http://www.psat.wa.gov).
Horse Clam (Tresus capux)—
Found on October 19, 2006 at
12:00pm. The weather was very
cold and overcast with light
intermittent rain.
Field Notes: This specimen was found on October 19, 2006 at 12:00pm. The weather was very cold and
overcast with light intermittent rain. Again there were no closed clams laying on the surface of the ground;
they live about 10 inches or deeper beneath the surface. However, many shells were seen.
Acorn Barnacle (Semibalanus balanoides)—These barnacles are intertidal
organisms, easily taking over anything hard and solid, such as rocks, debris,
clam shells, or even crab shells. Six grey-white plates make up the shell
wall of these adult barnacles. They are typically cone-shaped with an
opening which has moveable plates at the top for feeding
(http://www.arkive.org).
Taxonomy: Kingdom Animalia  Phylum Crustacea Class Maxillopoda
 Subclass Cirripdeia  Order Thoracica  Suborder Balanomorpha 
Family Balanidae  Genus Semibalanus  Species balanoides
(http://www.marlin.ac.uk)
Acorn
Barnacle
(Balanus
Ecological Facts:
crenatus)—Found on October
 Adult barnacles secrete compounds which attract larvae to more 19, 2006 at 12:00pm. The
populated areas. This is desired so that larger populations can weather was very cold and
overcast with light intermittent
accumulate thus increasing their chances for successful fertilization rain.
(http://www.mbayaq.org).
 These barnacles are found everywhere and are heavily populated wherever they are found. Because
they are in such high abundance and are filter feeders they have a major impact on the recycling of
nutrients in the water of their surrounding environment (http://pick5.pick.uga.edu).
Field Notes: This specimen was found on October 19, 2006 at 12:00pm. The weather was very cold and
overcast with light intermittent rain. Barnacles were in incredibly high abundance attached to anything hard,
rocks, shells, debris, etc.
Purple Sea Star (Pisaster ochraceus)—This is the most
abundant sea star and is seen in the higher tidal zones
attached to rocks hovering over clams and mussels for food.
They have five regenerative arms and their colors can range
from orange to purple. The spines covering their backs are
hard and blunt to the touch (http://www.7thfloormedia.com).
Taxonomy: Kingdom Animalia  Phylum Echinodermata
Class Asteroidea Order Forcipulatida  Suborder
Asteriadina  Family Asteriidae  Genus Pisaster 
Species ochraceus (http://www.racerocks.com).
Purple Sea Star (Balanus crenatus)—Found on
October 10, 2006 at 3:30pm. The weather was
Ecological Facts:
very cold with mild wind and few gusts. The
 These organisms have extremely unique eating habits. water was rough with many waves.
The tube feet on the underside of the five arms are
used to pull apart bivalves to expose their flesh. The sea star will then insert its own stomach into the
cavity of the flesh and secrete digestive enzymes which then break down and digest the prey
(http://www.7thfloormedia.com).
 As a keystone species, purple sea stars, have a major impact on their surrounding environment. In
areas where these species have been removed, the ecological diversity has seen a dramatic decrease
(http://www.racerocks.com).
Field Notes: This specimen was found on October 10, 2006 at 3:30pm. The weather was very cold and
overcast with mild wind and few gusts. The water was rough with many waves. The sea stars found their
way to the protected regions of the rocks. There were a group of sea stars all found together, while in other
areas there were none present at all.
Shield Limpet (Lottia pelta)—These limpets are found
attached to rocks and other smooth surfaces throughout the
higher and lower tidal zones. The diameter of their oval
shells is about 4cm and the apex stands only at about 1.5cm
tall. The coloring patterns seen on these limpets can vary
greatly with irregular striping patterns to many colors such
as
green,
brown,
creamy
white,
etc
(http://www.nwmarinelife.com).
Taxonomy: Kingdom Animalia  Phylum Mollusca
Class Gastropoda  Subclass Prosobranchia  Order
Archaeogastropodia  Family Acmaeidae  Genus Lottia
 Species pelta (http://www.nwmarinelife.com ).
Shield Limpet (Lottia pelta)—Found on October
10, 2006 at 3:30pm. The weather was very cold
with mild wind and few gusts. The water was
rough with many waves.
Ecological Facts:
 Overtime limpets can actually form depressions in the rocks they are living on, which allow them to
maintain firm holds to that rock upon attack or rough waters (http://www.nwmarinelife.com).
 There is little competition for food between the varying limpet species; this is most likely due to the
high variability of nutrient diets and digestive enzymes for each species of limpet
(http://www.rosario.wwc.edu).
Field Notes: This specimen was found on October 10, 2006 at 3:30pm. The weather was very cold and
overcast with mild wind and few gusts. The water was rough with many waves. After a long time of
searching, this was the only limpet that was seen in the entire region. It was interesting and unexpected that
there was not a higher volume of limpets present.
Purple Shore Crab (Hemigrapsus nudus)—These crabs are found under
rocks within the intertidal or shallow subtidal zone. The open rocky areas
are where these organisms prefer to be. Crabs have two pinches and four
smaller legs used for movement. The shell color of these crabs ranged
from dark green to a deep red with a white underside. Typically these
crabs will only grow to be a maximum of two inches in length
(http://www.seasky.org).
Taxonomy: Kingdom Animalia  Phylum Anthropoda  Subphylum
Crustacea  Class Malacostraca  Subclass Eumalacostraca  Order
Decapoda  Suborder Pleocymata  Infraorder Brachyura  Family
Grapsidae

Genus
Hemigrapsus

Species
nudus
(http://www.nwmarinelife.com).
Green
Shore
Crab
(Hemigrapsus nudus)—Found on
October 10, 2006 at 3:30pm. The
weather was very cold with mild
wind and few gusts. The water
was rough with many waves.
Ecological Facts:
 Shore crabs offer a huge contribution to keeping the beaches
cleaner with their scavenging instincts. Although they do eat a
variety of algae, they also feed upon dead animals.
 These shore crabs are also highly competitive when it comes to food and habitat space. Recently
they have been creating a negative impact on their ecological environments due to their high
abundance. Because there are so many it seems as though they are out-competing some of the other
native species.
Field Notes: This specimen was found on October 10, 2006 at 3:30pm. The weather was very cold and
overcast with mild wind and few gusts. The water was rough with many waves. Every rock that was turned
over displayed a high abundance of these shore crabs. They were very quick to find coverage after they had
been exposed.
Periwinkle (Littorina planaxis)—Periwinkles are found on rocky shores
in the splash zone, which is the highest zone in the upper intertidal zone.
These organisms are characterized by three whorls in their white to grey
colored shell. Generally the shell will be rough or uneven due to the
constant splashing by waves and rocks (http://www.pelicannetwork.net).
Taxonomy: Kingdom Animalia  Phylum Mollusca Class Gastropoda
 Order Mesogastropoda  Family Littorinidae  Genus Lottorina 
Species planaxis (http://www.clarku.edu).
Periwinkle (Littorina planaxis)—
Found on October 10, 2006 at
3:30pm. The weather was very cold
with mild wind and few gusts. The
water was rough with many waves.
Ecological Facts:
 Periwinkles are capable of adapting to extreme environments through behavioral and structural
changes. They have a negative geotaxis reflex, which allows them to detect gravitation of the earth to
move up rocks. Also, they have a phototaxis movement, which allows them to move toward light.
Structurally they secrete a mucous lining when exposed to air to prevent desiccation
(http://www.pelicannetwork.net).
 These organisms are the dominant herbivores in the intertidal region. They continue to dominate due
to their mode of reproduction. With dispersal of eggs with the tides, the eggs are carried to new
locations immediately (http://www.clarku.edu).
Field Notes: This specimen was found on October 10, 2006 at 3:30pm. The weather was very cold and
overcast with mild wind and few gusts. The water was rough with many waves. In many crevasses between
rocks in the intertidal many periwinkles were found; they were either attached to the rocks themselves or had
been knocked off and were floating in the water near the rocks.
Blue Mussels (Mytilus edulis)—These mussels are found living amongst
barnacles on rocks and other hard surfaces throughout the intertidal zone
and the shallow, subtidal zone. The shell is a bluish-black color and is
elongated to the shape of a kidney bean, usually about one to four inches
long.
The inside of these shells are a pearly white color
(http://www.ocean.udel.edu).
Taxonomy: Kingdom Animalia  Phylum Mollusca Class Bivalvia 
Subclass Heterodonta  Order Mytiloida  Family Mytilidae 
Subfamily Mytilinae  Genus Mytilus  Species edulis
(http://en.wikipedia.org).
Ecological Facts:
 When compared to other shellfish, mussels are the most efficient
feeders. They will consume most everything that is in that water,
thus making the water cleaner (http://www.ocean.udel.edu).
 Mussel beds are extremely important for maintaining diversity of
benthic invertebrates such as marine worms and crustaceans
(http://www.maine.gov).
Blue
Mussels
(Littorina
planaxis)—Found on October 10,
2006 at 3:30pm. The weather
was very cold with mild wind and
few gusts. The water was rough
with many waves.
Field Notes: This specimen was found on October 10, 2006 at 3:30pm. The weather was very cold and
overcast with mild wind and few gusts. The water was rough with many waves. All the blue mussels that
were found were amongst barnacles. Some seemed to be embedded into the rock itself. No mussel beds
were observed.
Thatched Barnacles (Semibalanus cariosus)—The thatched barnacles
are commonly found in the middle and low intertidal zones; they are
attached to rocks, which are exposed to high volumes of crashing waves.
These barnacles are characterized by only four wall plates, with a shell
that is more of a white in juveniles and then a more reddish color in adults
(http://www.marine.gov).
Taxonomy: Kingdom Animalia  Phylum Arthropoda  Subphylum
Crustacea  Class Maxillopoda  Subclass Thecostraca  Infraclass
Cirripedia  Superorder Thoracica  Order Sessilia  Suborder
Balanomorpha  Superfamily Balanoidea  Family Archaeobalanidae
 Genus Semibalanus  Species cariosus (http://www.itis.usda.gov).
Thatched Barnacles (Semibalanus
cariosus)—Found on October 10,
2006 at 3:30pm. The weather was
very cold with mild wind and few
gusts. The water was rough with
many waves.
Ecological Facts:
 Thatched barnacles are effective competitors and are thus capable
of altering the distribution of other species which may need rock
space, such as mussels and other barnacle species
(http://www.marine.gov).
 Sometimes these barnacles can grow so large that they will no longer be prey for sea stars and
gastropods. This can also alter the organism dynamic within the surrounding ecological environment
(http://www.marine.gov).
Field Notes: This specimen was found on October 10, 2006 at 3:30pm. The weather was very cold and
overcast with mild wind and few gusts. The water was rough with many waves. These barnacles looked
substantially different than the acorn barnacles. They seemed to be larger overall and were in varying
regions.