The shore area of the island can be divided into three concentric zones influenced by the surrounding saltwater to different degrees.

Crest Vegetation Zone

After a hard summer rain, water percolates through the scant soil of the coastal spruce forest, spilling in tea-colored sheets over the rocks. Where the nutrient-rich liquid collects in rocky hollows, pools form and a short-lived microcosm develops. Almost as if by magic, green algae blooms, turning the water the color and consistency of pea soup. This warm broth teems with backswimmers, blood-red midge larvae, and mosquito wrigglers. These creatures go through a short-lived frenzy of eating, growth, maturation, and mating. Then, in the span of a few days or a few weeks, the pool begins to dry up, the crowded water becomes depleted of oxygen, and the pool that once exploded with life suddenly becomes a dead zone.

Just inches away, the same rock is a granite desert where only a few hardy plants cling, a zone that can be sun-baked in summer and lashed by snow and ice in the winter. Hardy, low growing plants inhabit the Crest Vegetation Zone.

Spray Zone

The spray zone is a transition area between land and sea. Organisms must be able to withstand salt, wind, stormy surf, and summer drying. Few plants can survive in such a harsh environment, but drought-tolerant species like black crowberry, seaside goldenrod, and goosetongue plantain manage to cling to existence in small numbers. The most common organism in the spray zone is a crusty, yellow lichen called Xanthoria. Plants larger than the Xanthoria must vie for precious soil in small cracks in the rock. The black, tar-like Verrucaria lichen sometimes grows inside rock crevices.

Intertidal Zone

As we descend further down the shore, we come to the intertidal zone, the vertical stretch of shore between the levels of high and low tide. On Mount Desert Island, the average tidal range is eight to twelve vertical feet. Within this zone of rapidly fluctuating water levels, temperatures, and oxygen levels, a variety of fascinating organisms make their home. The diversity of life in each tidepool is largely determined by the pool's location within the intertidal zone. In the highest pools, water can alternate between nearly fresh water after a hard rain to hyper-saline after long periods of evaporation. The water in these pools is refreshed only during the highest spring tides. Green algaes such as Cladophora, Chaetomorpha, and Enteromorpha, fish such as sticklebacks, and the occasional periwinkle are about the only organisms that can survive here. Where the water is flushed at each tide, the pools support a greater diversity of life.

Tidepools in the mid-intertidal zone support the greatest diversity of all, since they mix with water from the sea for the longest period of time, and tend to have more stable salinity, temperature, and dissolved oxygen.

The intertidal zone can be divided roughly into six sub-zones defined by prevailing physical conditions and key organisms.

Black Zone: Lying below the limit of the crest vegetation zone and sometimes considered part of the spray zone, the black zone is covered by water only briefly during the highest tides. Calothrix, one of the cyanobacteria (blue-green algae) thrives here. The rough periwinkle, Littorina saxatilis, ventures up out of the tidepools to feed on the nitrogen-rich Calothrix.

Barnacle (High Intertidal) Zone: The acorn barnacle (Balanus balanoides) must be immersed during every tidal cycle. The highest reach of the neap tides defines their upper limit. The lowest reach of the Barnacle Zone depends on the abundance of the barnacle's main predator, the dog whelk (Thais lapillus) and competitors for limited space, such as rockweeds and the blue mussel. Barnacles can survive long periods without immersion by retreating into their calcareous shells. They are masters of survival, able to withstand temperatures from 5 to 111 degrees Fahrenheit. Barnacles survive freezing weather by trapping seawater inside their shells so that ice will form between their bodies and their outer shell, acting as an insulator. In hot weather, barnacles manage to keep cool by evaporating body fluid--a little like sweating. The common periwinkle (Littorina littorea), another creature tolerant of extreme temperature changes, is also found here in abundance.

Rockweed (Wrack) Zone: From the mean low water level up to the Barnacle Zone, brown algaes grow in profusion. Bladder wrack (Fucus vesiculosus) and knotted wrack (Ascophyllum nodosum) are the most common algaes in this zone. Both species attach themselves to the slippery surface of intertidal rocks by sturdy, root-like holdfasts, and use air-filled bladders to hold their blades upright when the tide comes in. Many intertidal creatures take advantage of the cool, moist shelter provided by the rockweeds by burrowing into the collapsed seaweed at low tide.

Mussel (Mid-Intertidal) Zone: Here, where tidepool water is frequently mixed with oxygen and nutrient laden water from the sea, intertidal organisms enjoy greater physical stability than in the upper tidepool regions. Beds of blue mussels (Mytilus edulis) attach themselves to the rocks by byssus, threads made of a substance so strong and pliable that it has been used as a bonding agent in human dentistry. Organisms with a need for higher oxygen levels and more stable temperatures, such as the smooth periwinkle (Littorina obtusata), find a comfortable home here. During high tides, dog whelks glide over the seaweed in search of prey and lower intertidal predators such as the sea star make forays into the mid-zone pools.

Irish Moss (Red, or Low Intertidal) Zone: As the name implies, Irish Moss (Chondrus crispus) and other red algaes dominate the Low Intertidal Zone. Small, moss-like colonies of animals called hydroids as well as several species of sea anemones can be found by gently lifting the curtain of seaweed draped over them at low tide.

Kelp (Brown Algae, or Subtidal) Zone: Just below the low tide level is a zone of startling diversity. Beds of waving kelp hide several species each of sponges, scale worms, brittle stars, sea stars, sea cucumbers, sea urchins, snails, nudibranchs (sea slugs), and fish. Young lobster take shelter here, as well. An interesting development in recent years is the apparent increase in lobster survival: as the urchin harvest increases each year, kelp beds flourish and so, theoretically, do lobster. Sea urchins eat the holdfasts (roots) of kelp, setting the whole algae adrift and killing it in the process. When urchin populations diminish, the kelp beds regenerate and create superior cover for young lobsters.

Bays

From lobsters to marine mammals, the sheltered waters of Blue Hill Bay and Frenchman Bay provide food, protection, and suitable breeding grounds for numerous species of marine life.

The waters around Mount Desert Island are studded with smaller islands and rocky ledges. Bald eagles and ospreys nest on many of the bay islands, which are too small to support populations of large land predators, yet provide ready access to the water and abundant supplies of fish to feed growing chicks. On cliffs and rocky ledges, eider ducks, several species of gulls, black guillemots (distant relatives of the puffin), and other bird species breed and raise their young.

The bays around Mount Desert Island are also one of the best places in the state of Maine to observe harbor seals. These plump, 5-6 foot seals are often seen swimming in the waters of Blue Hill Bay, Frenchman Bay, and the Great Harbor to the south of Mount Desert Island, or hauling out on rocks at mid to low tide. Unlike whales, seals cannot give birth or nurse their young in the water. They must spend a significant time with their young exposed on the rocks of the intertidal zone. Birthing (pupping) and nursing, then, are times of extraordinary peril for young seals. To minimize their vulnerability to predators--which include bald eagles, domestic dogs, and humans, despite a ban on seal killing since the Marine Mammal Protection Act of 1972--seals prefer to pup on remote ledges or on the rocks and beaches of small islands. Areas with the right conditions for pupping are fairly rare in the eastern United States: on this coast, there are no harbor seal pupping ledges south of Maine.

Seals also need to haul out periodically to rest and dry off. Most seals have a favorite ledge that they may return to every day. Some individuals even return to a particular favorite spot on the ledge. Around Mount Desert Island, some of the favorite seal haul outs are the protected ledges of Indian Point in Blue Hill Bay, East Bunkers Ledge in the Great Harbor, Egg Rock in Frenchman Bay, and several small ledges in the upper reaches of Frenchman Bay.

During the summer and early fall, solitary gray seals are often sighted. Although they do not breed in the bays around Mount Desert Island, they hunt and haul out in some of the same areas that harbor seals prefer. They can be distinguished from harbor seals by their larger size (7-8 feet long and 600-800 pounds) and their prominent, curved nose. The gray seal's scientific name, Halichoerus grypus, literally means "hook-nosed pig of the sea".

Several species of cetaceans (sea mammals) also call the waters of Mount Desert home. Minkes--small baleen whales about 15-30 feet long--are often seen from cruise ships, ferries, and tour boats. Occasionally, finbacks and humpbacks make their way into the bays.

Far more common is the 6 foot, 120 pound harbor porpoise. Although harbor porpoise somewhat resemble their distant cousins the dolphins, these little cetaceans are usually all work and no play. Unlike the bottlenose dolphins found in warmer waters on the East Coast, harbor porpoise dart through the water in pursuit of schooling fish such as mackerel or herring but do not usually leap out of the water. They usually ignore boats and are rarely, if ever seen playing in the bow waves or wakes of ships.

White-sided dolphins also swim into Mount Desert Island waters, but probably stay off shore most of the time. When they do venture closer to land, they are often misidentified as harbor porpoise.

Conservation Easements

Every year, millions of people come to Mount Desert Island to visit Acadia National Park and to experience the wildlife of Frenchman and Blue Hill Bays. As tourism increases, so does development of shoreline and island areas. Along with development come the unavoidable dangers of pollution and disturbance of bay habitats. This is the dilemma: how do we protect these precious bay and island habitats without buying up the land, making it into a preserve, taking land off town tax rolls, and banning people from the area? Acadia National Park has offered a solution to unchecked development in the form of conservation easements.

In 1986, the boundaries of Acadia National Park were fixed and the park can no longer add land outside those boundaries. However, it can acquire a property owner's right to develop his or her land through something called a conservation easement. The lands under easement remain in the hands of the private property owner and they stay on the tax rolls--very important to the towns of Mount Desert Island, which feared that the federal government would buy up all the open land in the area--but are protected from damaging development.

Conservation easements on Mount Desert Island and smaller islands in the surrounding bays protect critical nesting areas for bald eagles and other birds. They also ensure that shoreline habitat and that pristine watershed areas critical to wildlife and commercial fish and shellfish species will remain undeveloped. As of 1997, Acadia National Park had protected 6,000 acres through 150 easements. Fifty of those easements protect islands in the bays surrounding Mount Desert Island . . . and the tally of critical areas protected through conservation easements grows every year.