About the Bays

Habitats in the Bays

The MassBays study is large and complex, and its geomorphology supports many habitats that are critical to the health of our estuaries. These include tidal and brackish wetlands, rivers, eelgrass meadows, salt marshes, diadromous fish spawning habitat, tidal flats and rocky intertidal. In many parts MassBays, these habitats are threatened by increasing population and associated infrastructure development, increasing demand for coastal recreational and commercial uses, declining water quality, and more invasive species.

The health and condition of these critical estuarine habitats serve as indicators of environmental conditions in the bays, and we established long-term goals (2050) in our Comprehensive Conservation and Management Plan. Learn more about each of these habitats below.

Eelgrass is a flowering marine plant that typically grows in shallow, protected estuaries, forming underwater “meadows.” Eelgrass meadows protect sea creatures like fish and lobsters when they are young and while they lay eggs and also provide food. With their extensive root systems, eelgrass meadows stabilize the sea bottom and reduce erosion. As a plant, eelgrass generates energy through photosynthesis, producing oxygen and storing carbon. Eelgrass improves water quality as the leaves absorb some pollutants and excess nutrients and cause fine sediment to settle out of the water. In the MassBays study area, eelgrass beds are increasingly threatened by dredging, pollution from stormwater runoff and wastewater, and even boat moorings.

Salt marshes are coastal wetlands that experience regular flooding with the tides. The highly specialized plants that grow in salt marshes can tolerate variable salt concentrations. A healthy marsh serves as a nursery for all types of fish and provide habitat and food to birds and other wildlife. Salt marshes produce oxygen and store carbon, while also improving water quality and serving as protection against coastal erosion from storms.

MassBays’ study area is home to 34,000 acres of salt marsh (as of 2005, the most complete data set), all under threat from sea level rise, invasive species that compete for space and nutrients, ditches and tide gates that alter water flow, development on or near the salt marsh’s edge, and polluted stormwater runoff.

Tidal flats are areas of loose sand and mud that are exposed at low tide and submerged at high tide. These seemingly barren areas in reality support high biodiversity, providing habitat for shellfish like clams and oysters, crustaceans like crabs and shrimp, and invertebrates like worms and sea stars. In more stable areas, algae grows on the sediment and becomes food for grazers like snails, and also produces oxygen to support life in the tidal flats. As tides rise to cover the flats, juvenile fish often swim closer to shore to feed. Crustaceans and shellfish thrive in sheltered tidal flats, providing ready food for migrating and wading shorebirds. The gradual slope of these areas slows the flood waters and lessens the impact of waves on the coast.

MassBays’ study area includes 28,000 acres of tidal flats (according to 20XX maps), and XX of those are open to recreational shellfishing. Wharves and seawalls cause erosion of tidal flats, and sea level rise is predicted to reduce the amount of time existing flats are exposed to air. Pollution from stormwater runoff and oil spills stick to the sand and mud and remain for long periods of time, making shellfish dangerous to eat and damaging the habitat.

Diadromous, or migratory fish, either begin life in freshwater and spend the majority of their life in the ocean, returning to freshwater only to spawn and lay eggs (herring, smelt, shad, brook trout, and sturgeon, for example) or do the opposite – starting their life in the ocean and spending most of their life in freshwater, then returning to the ocean to spawn (for example, American eel). Habitat for Diadromous fish includes the streams they rely on for migration, as well as the areas in which they live and spawn.

Most migratory fish become food for larger fish and other wildlife, playing a key role in the food web both at sea and inshore. Historically, river herring especially were a core component of indigenous peoples’ diet; currently, only state- and federally recognized tribal members are allowed to harvest them, to preserve the remaining population.

MassBays’ study area includes many miles of streams for migration, and ponds known to shelter diadromous fish. Threats to these resources are varied: physical barriers like dams, tide gates and culverts restrict passage and water flow; broken fish ladders also block migration, and some make migrating fish easier targets for predators. Dredging and development close to riverbanks often degrade spawning and nursery areas, while stormwater runoff and wastewater discharges introduce pollution.

About 800 acres of rocky coastline can be found across MassBays’ study area. This is a harsh environment for organisms as the tide covers and uncovers the rocks, exposing the creatures living there to extreme conditions over the course of each day. There is, however, a variety of plants and animals that have adapted to this habitat, including barnacles, mussels, snails, crustaceans, and a variety of invertebrates and seaweeds. These provide birds and mammals with food, and several are commercially important in themselves.

Rocky intertidal zones are especially impacted by sea level rise, changes in water temperature and ocean chemistry, and storms brought about by climate change. Invasive species, over-harvesting, and oil spills are also significant threats to this habitat.

Rocky Intertidal Research in the Boston Harbor Islands National ...

Beaches stretch along more than 100 miles of shoreline in MassBays’ study area, and many are barrier beaches, sandy strips that naturally intercept waves before they reach the shore behind. While beaches are usually thought of as places for people to play or soak up the sun, they are also host to many plants and animals. Birds and mammals hide and feed in beach grasses and shrubs, and others rely on the food and shelter provided by that strip of seaweed, algae, and other aquatic plant life brought onshore by tides and storms, called “wrack.” The tiniest organisms that flourish in the wrack form a central component of the marine food web.

Some beach managers remove wrack to make room for human beachgoers, or to reduce odors and perceived public health concerns, especially where trash has been caught up in the wrack. This not only removes food and shelter for organisms, but also reduces the ability of the beach to resist erosion from waves, contributing to vulnerability of inland structures to storm damage. Other threats to beach habitat are deliberate placement of sand and rocks, wharves and jetties that starve the beach of natural sand movement along the coastline, and pollution from stormwater runoff and wastewater discharges.