The Rocky Shore

On a rocky shore, waves can be powerful enough to erode the rock, yet colonies of small marine animals can withstand these forces by withdrawing into narrow crevices or attaching themselves permanently to the rocks. These creatures survive not only the pounding surf at high tide but also the harsh conditions of life out of water, including 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, and in mid-winter the water within their bodies can turn to ice before thawing as temperatures rise and allowing these shellfish to become active again. Animals in this intertidal area are alternately exposed to land and marine predators, with birds feeding along the shore at low tide and carnivorous fish arriving from the sea at high tide. Common periwinkles feed by scraping algae from moist rocks, then retreat inside their shells and remain inactive when the shore is dry. At low tide, herring gulls feed on snails and mussels, carrying mussels into the air and dropping them onto rocks and pavement to crack open the shells, while gulls can break periwinkle shells with their beaks. Lobsters live farther offshore, where constant water cover protects them from winter cold, summer heat, and the drying summer sun. Blue mussels are held fast by flexible threads adhered to rock with a strong adhesive, which prevents them from being washed away at high tide, and they feed by pulling plankton-rich water into their bodies and straining out the plankton. Barnacles, once just a few weeks old, cement themselves to rocks and feed by opening their hinged shells and using their hooked legs as nets to strain plants and animals called plankton from the water.

Newport, Rhode Island · United States