COASTAL HABITATS OF NANTUCKET SOUND BY GILBERT NEWTON
One of the reasons that southern Cape Cod is so fascinating to study is because of its rich coastal biological diversity. Nantucket Sound covers an area around twenty-five miles wide and thirty miles long. The shorelines of the Cape and Islands are characterized by a variety of marine habitats including salt marshes, barrier beaches, and estuaries. These systems are both ecologically and economically important. Their special status is the result of the warm southern Gulf Stream mixing with the colder northern Labrador Current.
The waters and coastal habitats of Nantucket Sound harbor many protected and endangered animals, including several species of sea turtles, grey seals, and piping plovers. But these are just the most well-known marine animals. There are many more species in this region, all of which contribute to the area’s remarkable diversity.
Let’s consider some of the significant habitats along these shores. Salt marshes are considered the most productive coastal systems, supporting large numbers of commercial shellfish and finfish populations. Marshes are composed of several conspicuous grass species that provide food and shelter to dozens of different animals. Spartina alterniflora, or cordgrass, is a tall, perennial species that buffers the edge of a marsh, and provides food by direct grazing, or decomposed plant material in the form of detritus. Large mats of cordgrass are transported out to sea at high tide to be consumed by small animals in the water column.
The bulk of the marsh is composed of Spartina patens, or salt marsh hay. This plant grows further from the water’s edge, and also contributes to the productivity of the marsh. Small marsh snails crawl to the tops of the marsh hay blades during high tide. Large populations of fiddler crabs scurry around at low tide. These crustaceans are important ecologically as a food source for birds, and aerate the peat with their burrows, and fertilize the sediments with their wastes.
Salt marshes, and the bays that sometimes surround them, are also homes to commercially important species such as quahogs, oysters, and scallops. Blue crabs, spider crabs, and mud snails can be seen feeding in the creeks. Small schools of mummichogs move into the creeks with the high tide. Occasionally, a horseshoe crab can be seen stranded in one of the numerous pools, or pannes.
Sometimes salt marshes are a part of a larger system known as a barrier beach. A long sand dune community may separate the open sandy beach from an estuary and salt marsh behind it. The estuary is influenced by the ocean and a source of freshwater, either a stream, river, or groundwater.
There are over 200 barrier beaches in Massachusetts, but one of my favorites is a small system in Osterville called Dowses Beach. This is a popular recreational beach in the summer, and is characterized by several “microhabitats” linked and interacting together. The sandy beach is often covered with thousands of slipper snail shells, often tangled with the invasive green alga Codium. At low tide small sanderlings and herring gulls can be seen foraging in the intertidal zone for mole crabs and burrowing worms. Overall, this zone is a relatively hostile environment for living things because of the constant wave action, and rapid changes in temperature, salinity, and oxygen concentration.
The sand dune community has an entirely different assemblage of plants and animals. Beach grass is abundant and helps hold the dune in place with its strong adventitious roots. However, there are other plant species which make up the plant community, including dusty miller, beach pea, wormwood, and seaside goldenrod. The introduced salt spray rose (Rosa rugosa) provides colorful pink and white flowers to the dunes during the summer.
Animal life here represents a transition zone between the marine and terrestrial environments. The protected piping plovers will nest in the open areas, nearly indistinguishable from the sand. Diamondback terrapins make the Cape their northernmost distribution point, and can be found laying their eggs in the dunes. Of course this is also the habitat for the notorious deer tick. The deer tick can inject the bacterium that causes Lyme disease if they bite you.
There are a number of important bays and estuaries which exist along the southern Cape shore including East Bay in Osterville and Waquoit Bay in Falmouth. These ecosystems are major nurseries for fish populations and resting places for migratory birds. Most of these bodies of water are sheltered, and are therefore attractive to species seeking food, habitat, and protection from predators.
Unfortunately, many of these coastal habitats are exhibiting environmental stress from the pressures of increased human populations. One major coastal problem is nitrogen loading which acts as a fertilizer, resulting in harmful algae blooms. The nitrogen is coming from septic systems, road runoff, lawn fertilizers, and the atmosphere, due to the burning of fossil fuels. When the algae die and decompose, the bacteria responsible for decomposition consume oxygen dissolved in the water. Large mats of algae such as Codium can block sunlight to subtidal eel grass beds.
Even recreational uses of sandy beaches can have an adverse effect on these fragile systems if not properly managed. Marine debris can choke and entangle pelagic birds and marine mammals. Nesting sites of endangered bird species such as piping plovers and least terns can be disrupted if not correctly identified and marked. And, as describe earlier, excess nitrogen can seriously damage bays and estuaries.
These critical coastal systems of Nantucket Sound can continue to be enjoyed and sustained for future generations if we remain vigilant in our efforts to understand and protect them. Continued scientific research is the key to maintaining and managing these resources. Fortunately, one of the communities in this region is Woods Hole with its eminent research facilities such as the Marine Biological Laboratory and the Wood Hole Oceanographic Institution. These organizations, along with the many local conservation groups, are perfectly situated to provide data and guidance for this unique and vital region. ecies.