Cobscook's Rich Diversity of Marine Life
(Published in the Quoddy Tides, March 10, 2000)
A walk along the shoreline of Cobscook Bay during the lowest tides of the month offers a glimpse of the incredible variety and abundance of marine creatures that live here. Green crabs, sandworms, periwinkles, dog whelks, and shrimp-like creatures called amphipods, scurry or slip around or under the rocks and mud. Sea stars and urchins hide beneath thick layers of rockweed while sea anemones are lumped like globs of thick jelly in between the crevices. Some of these creatures, such as soft shell clams and scallops, help support the local economy. Others have no current human use but are no less important to the bay's natural system.
Since the early part of the century, Cobscook has been a popular place for researchers interested in studying diverse forms of marine life. One of those researchers is Robin Hadlock Seeley, a summer resident of Pembroke and a marine ecologist at Cornell University. Seeley grew up on Casco Bay and has been studying the marine life in Cobscook Bay for over 15 years. Her research has focused on periwinkles, and, to some extent, on their interactions with green crabs, a species brought to the United States from Europe during the 19th or early 20th century. Through her explorations, Seeley, like other marine biologists, has developed a keen awareness of the curious characteristics of marine life in the Bay.
For example, she discovered that a particular form of the smooth periwinkle, one of several types of snail found in Cobscook Bay, has been wiped out from other areas of the Maine coast. "Smooth periwinkles are often eaten by the green crab," she explains. "Green crabs, while spreading north along the coast, probably could not establish populations in some parts of Cobscook Bay because of the slightly colder water temperature. As the water temperature increases, we seem to find higher numbers of green crabs in the Bay, which may in turn affect the smooth periwinkles."
Seeley's explorations of rocky shores during the lowest spring tides have turned up a wide variety of marine animals found in subtidal waters in other areas of the Maine coast. Curiously shaped sea squirts, many tentacled anemones, ooze-like sponges, lumpy sea cucumbers, and shell-less snails called nudibranchs, are among the fascinating creatures hidden beneath the seaweed and tucked in nooks and crannies among the slippery rocks. She finds that some species have a wider range of habitat here, in contrast to other areas of the coast.
Many snail species can be found in both the upper and lower areas of the intertidal zone, when they typically are restricted to higher areas of the shore in other places in New England. "There are classic descriptions of where certain species of marine animals live in the intertidal zone - here at Cobscook Bay, you have to throw those classic descriptions out. You cannot make any assumptions - you have to just look and see," she stresses when talking about the bay. She points out that it is not only the physical landscape and tidal range that determines where an animal can thrive, but also species interactions, like predation and competition. She suspects that the abundance of common periwinkles in a particular area influences where the other types of periwinkle are found.
The great diversity of invertebrate animals (without backbones) is also influenced by the variety of habitats found along the shore, from the sandspits stretching south of Lubec, to the cobbled beaches tucked between the ledges of West Quoddy Head, the mudflats found deep in the coves and the rocky outcrops near Reversing Falls. "The physical features of the bay influence the health, size, and location of invertebrate populations," Seeley said.
Most of the bottom dwelling shellfish, marine worms, and other important invertebrates are able to exist together in abundance because of the nutrient rich waters that flow into the bay from the Gulf of Maine. The way the tides flow into the bay allows for a continuous circulating action that keeps the bay from freezing over and may also remove excess nutrients and pollutants. The water is warm enough to allow marine animals that typically live to the south to survive in the bay, but cool enough throughout the summer to permit species that typically live further north to flourish here as well. These factors contribute to the greater variety of marine animals and plants found in Cobscook Bay and elsewhere in the Quoddy region.
In Cobscook Bay, an unusual variety of marine plants and animals are able to thrive together. Understanding the physical and biological conditions that make this possible can help us make use of the bay's resources while not harming the natural balance that created this richness of life. The health and vitality of the Cobscook Bay economy may depend on our understanding of how the many different forms of life are connected to one another.
This column was prepared by Cheryl Daigle and Jim Dow. Cobscook Soundings was a monthly column produced by the Maine Chapter of The Nature Conservancy. Its purpose was to share what is known about the workings of the Cobscook Bay marine environment, so that all who make decisions about the use or care of the bay have the best available information.
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