Greenwich Bay

Habitat Loss

Greenwich Bay is a composite of interconnected habitats. From the muddy bottom to manmade structures that harbor plants and animals adapted to life on the rocky shore, the bay supports a diversity of life. However, when key features of a habitat—such as critical plant life—decline, the loss affects a number of species that depend on that habitat for survival.

Two such habitats that have been the focus of concern lately in Greenwich Bay are eelgrass beds and salt marshes.

EELGRASS BEDS

Eelgrass ecology

Eelgrass, Zostera marina, is not a seaweed, but a flowering plant whose roots anchor it in the sediments of Narragansett Bay. Eelgrass beds act as a natural filter, slowing down currents so that sediments drop out of the water, keep the water clear and allowing more light to penetrate the water. Eelgrass also serves as a critical habitat for young mussels and scallops, who stick to the grass's blades to avoid being eaten. Young fish, too, use eelgrass as a place to hide from predators. The surfaces of the plant's blades are a good place for small marine algae to grow, and these in turn provide food to a variety of animals. Some ducks and geese graze on the eelgrass itself. Eelgrass may also act as an indicator of water quality. A sensitive plant that requires high levels of light and clear water, eelgrass does not fare well in areas where nutrient levels are high. The presence of eelgrass suggests good water quality, while a decline in eelgrass may be a sign that surrounding waters are becoming degraded.

Decline of eelgrass

Eelgrass beds have all but disappeared from Greenwich Bay, and from most places in Narragansett Bay. The map from 1840 to the present shows historical locations of eelgrass beds. In recent years, aerial surveys found one bed. No single cause of eelgrass decline can be found, although the suspects are a combination of a disease that struck the East Coast in the 1930s, the 1938 hurricane, physical destruction by actitivites such as dredging, and poor water quality.

Salt marshes are tidal wetlands that grow in coastal areas. They are dominated by several species of salt-tolerant grasses. Salt marsh cord grassSpartina alterniflora, is the most salt-tolerant, and grows at the outer edge of the marsh, where it is partially submerged at all times. Salt meadow cordgrass, Spartina patens, grows landward of the alterniflora, and gives the marsh its familiar, grassy look. Farther back from the water, a greater diversity of plants is found. A variety of invertebrates, such as ribbed mussel, fiddler crab, and snails, live in the marsh, while upland animals, such as raccoon, mice, and birds may visit the marsh to feed. Salt marshes also help protect the coastline from erosion, and the quiet waters that surround them provide a haven for juvenile fish. Historically, salt marshes have also been harvested to provide hay for animal feed.

Salt marsh decline

Many of Narragansett Bay's salt marshes have been degraded by filling, road construction, ditching, culvert installation, and runoff pollution. This has severely altered and impaired coastal wetlands in the bay watershed. The fragmentation of saltmarsh systems—caused by construction of roads and railroads, or by the filling in of salt marshes—can interrupt the flow of tidal waters. These changes in the natural water regime can have serious negative impacts on the ecological integrity of an entire saltmarsh ecosystem. An increasing threat to marshes is exotic and invasive plant species.

Although marshes have not suffered such widespread decline as eelgrass beds, their area has been greatly reduced. An exact figure is not known, but between 1955 and 1964, 10 percent of the coastal wetlands in Rhode Island larger than 40 acres in size were filled for property development. This map shows the major remaining salt marshes in the Greenwich Bay area in red.