Acadia National Park - Life Along the Coast

Much of Acadia's marine life resides on the rocky coast in the area between high and low tides. Twice each day the sea rises and falls 9 to 14 feet, alternately flooding and exposing the shore. To survive here, plants and animals must be able to withstand not only continuously changing conditions (the amount of water, its temperature and salinity, and the sun's intensity are forever in flux) but also the effects of waves, storms, and winter frost. That any living thing can tolerate such extremes is remarkable indeed: that thousands of creatures thrive in this rigorous world is truly a marvel.

Like a high-rise building, the intertidal area is divided into horizontal bands, or floors. On the top floor, within reach of ocean spray but beyond the high-tide line, algae cover rocks with a blackish smudge. Representative of the oldest life-form on earth, these algae are covered with a slippery, gelatinlike covering that protects them from drying out. Periwinkles, snails with corkscrew-shaped shells, sometimes crawl up here from lower levels to graze on the algae. Only half an inch long, the periwinkle boasts a tonguelike structure called a radula that bristles with thousands of teeth.

Water is the music of Acadia, played by ocean waves as they rhythmically crash against the rocky, cliff-lined coast and then retreat, setting the tempo for shoreline life. When the tide recedes, sea stars find refuge in tide pools. Rock crabs and whelks, in contrast, must survive exposure to the air and escape detection by such winged predators as gulls, and so they hide under rocks and seaweed to await the sea's return. Harbor seals do just the opposite: at low tide they scramble atop rocks and loll lazily in the sun. After the waves roll back in, the seals jump into the water, frolicking and surface diving.

Inland, the melody is carried by running streams, where muskrats and playful river otters dig waterside dens and use their tails as rudders when they swim. Above the water, the green heron perches on a woody snag, occasionally sounding a harsh squawk. Loudest of all is the male bullfrog as he sings his deep-voiced solo, the notes reverberating through the forest like the music of a string bass.

The snail uses it as a sharp, serrated scraper to remove algae from the rocks. When the front end becomes dull, the creature simply pushes forward a freshly grown tooth-studded section of radula.

The stretch of rock below the periwinkles, exposed to the air for several hours twice each day and pounded in between by crashing waves, is perhaps the most difficult place in which to live, unless you are a barnacle. Barnacles are hardy creatures. With a superstrong glue, they cement themselves to rocks; with their volcano-shaped shells, they can withstand the force of waves exerting a ton and a half of pressure per square foot. Airtight plates at the top of the shells clamp shut at low tide, preserving moisture inside, and open at high tide, letting three pairs of feathery arms come out to net tiny bits of food in the water.

The stationary barnacles are an easy target for dog whelks, sea snails that force barnacles open and devour the animals inside. The color of the whelk's shell varies with its food. Those that feed mainly on barnacles are white; a diet of mussels may produce black, brown, or purplish shells. If a dog whelk alternates mussels and barnacles, its shell may develop stripes.

Whelks abound one zone down from the barnacles, where rockweed, a brown, rubbery seaweed, floats on the high tide, its stem branching out like antlers, and air bladders making it buoyant. Though this location is more hospitable than places higher on the shore, rockweed is still beaten about by the waves, and it must attach itself securely to rocks by means of a holdfast, a mass of strong rootlike structures. When the tide goes out, the plant becomes draped over the rocks, its slippery fronds affording protection to mussels, periwinkles, whelks, crabs, and other small life.

Irish moss, a slippery red seaweed, occupies the level below. Sea urchins and crabs can usually be found at this level, but at low tide they retreat to the lowest zone, which remains underwater nearly all the time. Here the long, leathery strands of kelp, another seaweed that uses a holdfast as an anchor, bend with the waves. Starfish, or sea stars, creep about in the kelp. They have miraculous powers of regeneration: an injury to one arm, most species have five, may result in two or more growing back to replace it.

Out beyond the tidal zone, lobsters scavenge in shallow waters, bewhiskered harbor seals lounge on surf-splashed rocks, and harbor porpoises cruise below the surface, frequently rising for air. Porpoises, members of the whale group, have a remarkable sensing ability: they can find prey by bouncing sounds off it. So accurate is this sonarlike system that it enables the porpoises to identify a creature by its echo and thus to pursue their favorite foods. Other whales, such as finbacks and humpbacks, also ply these waters, surfacing from time to time to blow misty sprays high into the air. Overhead, herring gulls swoop and soar on 4 1/2-foot wingspans, adding their raucous calls to the sounds of the restless sea.