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Copyright © 1998
Nova Scotia Museum

Creatures of the Rocky Shore

Starfish aren't fish. They are boneless creatures with spiny skins called echinoderms. Turn a starfish over to see the hundreds of suction cup "tube feet" that pull it along. The hole in the middle is a mouth, and sometimes you catch the pale-brown stomach ballooning out through the mouth to digest food outside the animal. Look also for a red eye spot at the tip of each arm. The eyespots detect only light and dark. Starfish eat mussels and snails.

Sea Urchins are spiny-skinned invertebrates. Urchins chew seaweed with a complex "jaw" contraption called Aristotle's Lantern. This jaw is about the size of a grape, but all you can see of it are the five "teeth" in the urchin's tiny mouth. Turn an urchin upside down in the seawater and watch it right itself, to see the long tube-feet and spines in action. Pieces of urchins you might find high up on the shore were probaby left by gulls, which drop urchins on rocks to smash them open for food.

Crabs roam the middle and lower shores. Lift up rocks to find them at low tide. The orange ones (Rock Crab) give a very painful pinch; the green ones (Green Crab) give a lightly less painful pinch and seem more inclined to run than fight. Crabs are scavengers, the clean-up crew of the seashore. Count the legs - there should be four pairs plus the claws, but crabs often lose legs and can regenerate them. To hold a crab safely put your thumb and forefinger on either side of the top shell. Tell the sex of a crab by looking underneath, where its little abdomen folds under and lies against the bottom shell: males have a narrow, tapering abdomen, while females have a broad abdomen which unfolds to carry the eggs. Also, keep an eye out for fast-moving periwinkle shells—they may be home to a hermit crab. Their beautiful blue eyes on stalks are worth a close look.

Mussels live attached to rocks by strong threads near the pointy end of the shell. Mussels strain small edibles out of the seawater, and the Blue Mussel is itself edible. Horse Mussels—large, with a purple outer shell—often contain small odd-shaped pearls. Are you as strong as a starfish? Try to pull apart the two shells of a live mussel, as the starfish does.

Periwinkles are plant-eating snails. Rough Periwinkles, on the upper shore, have tall pointy shells and brood their young inside the mother's shell - the upper shore is too dry for a jelly mass of eggs. Smoooth Periwinkles live lower on the shore and lay eggs in a jelly mass, while the large Common (edible) Periwinkles release egg capsules into the sea. Periwinkles walk many metres each tide cycle on their one fleshy "foot". Look for the brown or black operculum, attached to the foot. It seals the shell shut, like a submarine hatch, when the tide is out. Periwinkles graze on seaweeds, big and microscopic. Watch for places where a narrow band either side of a crevice is cleared of seaweeds - there may be periwinkles living in the crevice and creeping out at high tide to graze.

Dogwhelks are meat-eating snails. They are nearly white, with pointy shells and a distinctive notch in the bottom of the big shell opening. Dogwhelks eat mussels and barnacles by drilling holes in their shells with a rasp-like ribbon of teeth in their mouth. Then the dogwhelk injects a little poison and crawls around to rasp off bits of the prey animal's flesh. Keep an eye out for mussel or snail shells with perfect little round holes in them—the calling card of the dogwhelk.

Barnacles are related to crabs - they have jointed legs. Their cone-shaped shell is a permanent home. Inside, the soft barnacle stands on its head and waves its feathery feet out the door to catch tiny floating edibles. To watch this feeding action, find a portable barnacle rock and place it in the water. Try splashing some water to simulate the rising tide. The very young barnacles are free-floating creatures—the sea disperses them. But did you ever wonder how immobile creatures like barnacles mate?

Amphipods are the little many-legged animals you find thrashing under rocks, or hopping in piles of decaying seaweed. Watch them swim to see how they got the name "side-swimmers". Some people call them sand fleas, but they don't bite. Amphipods are an important food source for bigger animals. They are crustaceans, like crabs and shrimp.