Mount Desert Island intertidal zone

• Category: Marine and Oceanic Biomes.
• Geographic Location: North America.
• Summary: This unique and important intertidal biome is important for the variety of habitats it supports.

Mount Desert Island, a large island off the coast of Maine in the far-northeastern United States, is best known for its dramatic confluence of glacially formed mountains, windswept ridges, and rocky coastline in the Gulf of Maine on the North Atlantic Ocean. The island and interdial zone consists of nearly 60,000 acres (24,000 hectares), approximately half of which are included within Acadia National Park, and the remainder held under private ownership. The preservation of this significant resource was an important milestone in the conservation movement in the United States. Mount Desert Island was first protected in 1916 when President Woodrow Wilson established the Sieur de Monts National Monument. It was later re-designated as Lafayette National Park in 1919, making it the first national park east of the Mississippi River. The park was renamed Acadia National Park in 1929.

Geography and Climate

Mount Desert Island is located in a transitional zone along the Maine coast, and is ecologically distinct from inland Maine ecosystems. The characteristics which typify the southwestern portions and the more northerly coastal regions of Maine converge at this area. The overlap between the southerly ecosystems—such as pitch pine woodlands—and the characteristic northern spruce-fir forests, is the result of climate conditions where a variety of ecological systems coexist within a relatively small geographic footprint.

Mount Desert Island experiences more moderate temperatures than inland Maine, thanks to the moderating effect of the surrounding waters. In a ranking of continental US microclimates, the island was found to be second only to the Pacific Northwest regarding its level of annual precipitation. Temperatures vary widely by season here, from below 0 degrees F (-17 degrees C) in the winter to a high of approximately 90 degrees F (32 degrees C) in the summer, with average temperatures around 70 degrees F (21 degrees C).

Geographically, glacial and post-glacial activities have shaped the island into a north-south series of ridges separated by deep U-shaped valleys. The ridges also are separated by crests that rise sharply from the forest cover well below the snowline. These geologic features make for an abundance of streams and rivers that carve out a variety of microhabitats along the rocky shores as they enter the sea.

Somes Sound is also found at Mount Desert Island. The Sound contains some geological features that previously earned it the designation of a true fjord, like those found in Norway. The rugged surface topography extends through the intertidal zone and beneath the waters here and is one of the few fjard-like features on the east coast of the United States and stretches approximately five miles long. However, according to the Maine Geological Survey, The Somes Sound lacked all of the fjord's features, and is instead classified as a "fjard." A "fjord" is a deep, narrow inlet with steep cliffs, typically formed by glacial activity, while a "fjard" is a similar glacial formation but with significantly lower relief, shallower waters, and often more flat, muddy shores, meaning fjords have much more pronounced, steep cliffs compared to fjards; essentially, a fjard is a less dramatic version of a fjord with a flatter profile and less defined features. Nonetheless, the Somes Sound is still an impressive and prominant feature of the Maine coast.

Habitats and Biota

In and above its intertidal zones, Mount Desert Island features many wetland types. Big Heath is a coastal plateau bog ecosystem, notable for its presence this far south. Deer-hair sedge and black crowberry are hallmark flora here. Bass Harbor Marsh, a streamshore ecosystem, has gradients of pure freshwater that transition to brackish tidal marsh and then to reed-rush-forb saltmarsh. Great Meadow contains a red maple and fern swamp, as well as a shrub-reed marsh; Fresh Meadow features tidal creeks amid raised bog areas; while patches of dune grassland are scattered over the largely rocky shorelines.

Robust eelgrass beds are found in the intertidal zones around most points of the island. This habitat is vital as a fish nursery, rich feeding zone for waterfowl, nesting shelter for waders including some of the many migratory species that stop on Mount Desert Island each year, and the most diverse base for the crustaceans and mollusks so important to the food web here.

These habitats provide for both terrestrial and aquatic fauna as diverse as the river otter, horseshoe crab, and bald eagle. Sea birds such as the Atlantic puffin and common eider also are sighted in these waters. The peregrine falcon, harlequin duck, purple sandpiper, and least bittern are among vulnerable species that depend on the Mount Desert Island intertidal zone biome. Approximately forty species of mammals reside on the island; among those most drawn to the intertidal areas are beaver and muskrat.

Threats

Despite National Park status, threats continue to call into question the long-term vitality of the island and its ecosystem. Human impacts on Mount Desert Island, most notably within Acadia National Park, include significant effects from tourism, pollution, invasive species, land use changes, and climate change. These threats can lead to altered ecosystems with impacts on flora and fauna, rising temperatures, longer growing seasons, increased storm intensity, and changes in precipitation patterns

Most severe are those impacts associated with the recreational over-use of Mount Desert Island. With over 3 million visitors annually, Acadia National Park is one of the most heavily used national parks. In 2023, Acadia National Park had 3.87 million visitors, which was 30 percent higher than the average annual visitation from 2010 to 2019. This was the third-highest visitation ever for the park. Mitigating ecosystem degradation is an ongoing challenge for park managers and residents alike. Effects from tourism include increased traffic and congestion on roads and trails, erosion from foot traffic on sensitive coastal areas, pollution from vehicle emissions, and potential disturbance of wildlife due to human presence. Development pressures on the remaining privately owned land also remain a constant; such land is valuable and sought after. To help mitigate these effects, the local Bar Harbor community created a plan for implementing responsible tourism practices to minimize environmental impact as part of their overall climate action plan.

Other threats common to the Atlantic seaboard include algae bloom, or red tides, and periodic invasions of non-native species. Non-native species threaten native flora and fauna by competing for essential resources like food, water, and sunlight. In Acadia National Park, nearly one-third of the plant species are non-native, with twelve of these categorized as high management concerns by the National Park Service. To address this, park officials use an integrated pest management strategy that emphasizes understanding invasive species' biology and employs minimally toxic treatments.

The potential impacts of sea-level rise associated with global warming also presents the challenges of protecting against saltwater intrusion, and beach and bank erosion. Rising temperatures causing shifts in plant and animal life, increased frequency and intensity of storms, changes in precipitation patterns, and potential decline of cold-adapted species like red spruce. Mount Desert Island faces multiple climate change impacts. Rising sea levels lead to saltwater intrusion, contaminating freshwater aquifers, and accelerating beach and bank erosion that threatens habitats and infrastructure. Shifting temperatures alter the distribution of plant and animal species, with some declining while others thrive. Increased storm intensity worsens erosion and other climate effects, while changes in precipitation patterns influence vegetation and freshwater availability.

Bibliography

Collier, Sargent F., and G. W. Helfrich. Mt. Desert Island and Acadia National Park: An Informal History. Down East Books, 1978.

Dubuc, Leslie J., et al. “Predicting Occurrence of River Otters by Habitat on Mount Desert Island, Maine.” Journal of Wildlife Management, vol. 54, no. 4, 1990, pp. 594-99.

"Ecology at Acadia National Park." Geology and Ecology of National Parks, www.usgs.gov/geology-and-ecology-of-national-parks/ecology-acadia-national-park#:~:text=Non%2Dnative%20species%20pose%20a,the%20effects%20of%20recent%20fire.&text=A%20lake%20in%20Acadia%20National%20Park. Accessed 2 Jan. 2025.

"Founding Acadia." National Parks Service, www.nps.gov/acad/learn/historyculture/founding.htm#:~:text=In%201919%2C%20President%20Wilson%20signed,Acadia%20National%20Park%2C%20was%20adopted. Accessed 2 Jan. 2025.

Kelley, John T. "Somes Sound, Mount Desert Island, Maine." Maine Geological Survey, Nov. 1998, digitalmaine.com/cgi/viewcontent.cgi?article=1312&context=mgs‗publications#:~:text=Thus%2C%20on%20the%20basis%20of,applies%20better%20to%20the%20sound. Accessed 2 Jan. 2025.

“Maine Natural Areas Program.” Maine Department of Inland Fisheries and Wildlife, . Accessed 2 Jan. 2025.

May, Rachel. "Here's Why Scientists Are Studying Maine's Coastline." National Geographic, 26 Oct. 2021, www.nationalgeographic.com/travel/article/rockweed-protects-maines-vibrant-coastline-heres-why-scientists-are-studying-it. Accessed 2 Jan. 2025.

Morison, Samuel E. The Story of Mount Desert Island. Little, Brown, and Co., 1960.

Starr, Johnathan, et al. "Acadia National Park Climate Change Scenario Planning Workshop Summary." 6 Oct. 2015, www.nps.gov/subjects/climatechange/upload/Scenario-Workshop-ACAD-508compliant.pdf. Accessed 2 Jan. 2025.

"Town of Bar Harbor Climate Action Plan: Goals and Strategies 2021-2026." Town of Bar Harbor Climate Emergency Task Force, Nov. 2021, www.barharbormaine.gov/DocumentCenter/View/5373/Climate-Action-Plan-November-2021#:~:text=Greenhouse%20gas%20emissions:%20The%20release,the%20natural%20global%20carbon%20cycle. Accessed 2 Jan. 2025.