Most of this information is from the WSU / Island County Beach Watchers site.
Photosynthetic, multicellular algae. Color is not a very useful in distinguishing algae. Bull kelp is an annual growing to 24m (80ft) in one season. Rockweed growing on ... rocks have floating bladders. These are its sexual reproductive organs. There are over 500 species of "seaweeds" in BC.
- Green and red seaweeds
Also called sea slugs, nudibranchs are mollusks. Creatures of the intertidal or subtidal zones, there are many species ranging from 3cm to 20cm (1 to 8 inches). These often colorful creatures sport a variety of projections or appendages. Eats sponges, anemones, worms, barnacles.
Very simple colonial animals that are often overlooked. Species in this area encrust rock or shells and range in color from bright red, orange, purple, yellow-green to tan. Sponges filter food from the water coursing through their internal cavities.
Anemones are usually found attached to rocks that have some accumulation of sand or shell bits. The most common anemone found in Island County is the pink-tipped anemone, with a green column & pink tentacles. The green coloring is due mainly to the green algae they eat.
Sea stars are found in inter- & sub-tidal zones. Sea stars usually have 5 arms which are regenerative & will grow back if one is severed. Each arm has hundreds of tube feet used for locomotion & gas exchange. Sea stars are predators & feed on barnacles, mussels & clams. They feed by hunching over prey, forcing the shells apart, & inserting their extrudable belly to dissolve & eat inner parts.
Related to urchins, these animals live in the lower intertidal and subtidal. Soft bodied, ranging up to 25 cm (10 inches) sea cucumbers are bright red, orange or white and covered with numerous tube-feet projections. Filter feeders.
Urchins, found in the low tide zone, have sharp spines. A device in the mouth known as Aristotle's Lantern includes strong teeth that allow the urchin to scrape algae off rocks. Urchins are usually immobile but can move rapidly when approached by enemies such as sea stars, birds, cod or otters. They were called "sea eggs" by Native Americans who collected them for their yellow gonads.Sand dollars are echinoderms, flat relatives of sea urchins. They use their short spines to burrow into the sand. The "petal patterns" on the sand dollar house tube feet which are used for respiration. Sand dollars live only on sandy beaches, where they burrow for food & protection. Food particles are filtered through the dense spines by mucous-coated cilia & tube feet. Sand dollars are a favored food of flounder, cod & haddock
Limpets, with a low conical shell, adhere tightly to rocks with their strong foot. Most limpets have a definite place of their own on the same rock, and roam up to 3 feet at night to scrape algae off rocks with their rasping tongue, then return to the same spot.
Mussels and oysters
Mussels have strong shells, and feed on detritus and plankton filtered from the sea. Each mussel filters 2 to 3 quarts of water an hour. Mussels attach themselves to rocks & objects by fibers called byssal threads. When the tide leaves them high & dry, they breathe by passing air over their moist gills. Mussels are eaten by sea stars, whelks, & humans. They are raised commercially on rafts in Penn Cove & Holmes Harbor.
Clams have shells made of two halves which are hinged together with 1 or 2 large muscles to keep the shell pulled shut. Clams have a foot for burrowing. Clams have 2 siphons - 1 brings in water, which flows over the gills extracting oxygen & trapping food particles, which are sent to the mouth. The water is then expelled through the other siphon.
Snails (Periwinkles and whelks)
Periwinkles live in the spray zone, out of the water most of the time, covered only during the highest of tides. Few marine plants & animals can survive in this zone. Periwinkles use their long radula (toothed tonguelike structure) to scrape algae off rocks for food. When the water recedes, periwinkles seal themselves to rocks with a mucus produced by their foot. Periwinkles are thought to be ancestors of land snails.
Chitons are mollusks, with shells made of 8 overlapping plates. Chitons clamp themselves to rocks using their foot and their "girdle" (the part of the shell that encircles the chiton & 8 plates) to withstand weather & wave action. Chitons are active at night, moving slowly to scrape algae off rocks with their radula. When handled, chitons curl like an armadillo.
Barnacles live in the high tide zone. They tolerate long periods of exposure by closing very tightly & trapping a small amount of water inside their shell. Barnacles feed by opening up & sweeping the water with their feathery legs to collect plankton. Barnacles attach themselves to objects by secreting a brown glue which anchors them to the substrate.
Isopods and amphipods
Crustaceans these animals feed on plant debris. Found in a variety of colors, most are small less than 3cm. They have antenna, but have way too many legs to be confused with insects. People do sometimes call them "beach fleas" but are not related and are useful beach cleaners.
The abdomen of a crab folds tightly beneath its body. By turning a crab over, its sex can be determined: abdomens of female crabs are wide, while males' are narrow. Females hold eggs between their body & abdomen. Empty crab shells found on the beach may be the old homes of crabs who have "molted" or crawled out of their old shell to grow a new, larger shell. Crabs are active scavengers, eating both dead & live food, & are often found hiding under rocks.