This rocky outcrop is sometimes eroded by waves powerful enough to tear a hole in them. Colonies of small marine animals living on the shore, however, can withstand these forces. Some withdraw into narrow crevices, others attach themselves permanently to the rocks.
These creatures can survive not only the pounding surf at high tide, but also the harsh conditions of life out of water. The retreating tide exposes them to the drying summer sun and the freezing temperatures of winter. On hot summer days, the shells of periwinkles, barnacles, and mussels prevent their body moisture from evaporating. In mid-winter, the water within their bodies can turn to ice, however, as the temperature rises, the ice thaws and these shellfish again become active. The animals living in this intertidal area are alternately exposed to land and marine predators. At low tide, they are vulnerable to birds feeding along the shore. High tide brings carnivorous fish from the sea.
Common periwinkles feed by scraping algae from moist rocks. When the shore is dry, they retreat inside their shells and remain inactive.
At low tide, herring gulls feed on snails and mussels. They carry mussels into the air and drop them onto rocks and pavement to crack open the shells. Gulls are able to break periwinkle shells with their beaks.
Lobsters live farther offshore. Always covered by water, they are protected from winter cold, summer heat, and the drying summer sun.
Flexible threads, adhered to a rock by a strong adhesive prevents the blue mussel from being washed away at high tide. The mussel pulls plankton-rich water into its body straining out and eating the plankton.
When just a few weeks old, barnacles cement themselves to rocks. By opening their hinged shells and using their hooked legs as nets, they strain plants and animals called plankton from the water.