Physical Disturbance to Eelgrass in Buzzards Bay

Rings of disturbance caused by mooring chains in a mixed eelgrass and
algae covered area near Provincetown.
Photo from MassGIS April 1, 2001 aerial survey.

Dense mooring field in Sippican Harbor, Marion, MA

Channels dredged to docks in a Cape Cod embayment.
Eelgrass was once prevalent here. The loss was due largely
to coastal eutrophication, with sediment resuspension
from boating contributing to the loss.

Physical Disturbance of Eelgrass

by Dr. Joe Costa

Mooring Chains

As the wind changes direction, moorings are pushed in different directions. As they move, their chains are dragged along the bottom. This action can uproot eelgrass and suspend silt into the water colum.

In dense boat mooring fields, like the photograph of Sippican Harbor, Marion, MA to the right, a considerable amount of silt may be suspended in the water column by this process, and may be an important contributor of reduced water transparency in that embayment. More than 2000 moorings are sited in Sippican Harbor.

Sediment resuspension from boats

Boats with inboard and outboard motors, jet skis, and similar activity can cause considerable resuspension of sediments which may worsen water clarity, and cover eelgrass leaves to the extent that the plants are shaded and begin to die off and disappear from portions of embayments. This may have contributed to eelgrass in some areas in Buzzards Bay like Apponagansett Bay in Dartmouth.

In Bourne, hydraulic fishing for shellfish, sometimes referred to as "jet-clamming" is allowed, and was particularly prevalent in the 1980s and 1990s. During the 1980s in Little Buttermilk Bay, plumes of sediments were observed from this activity, and considerable rafts of dislodged eelgrass from this activity. Some residents also asserted that this activity was causing erosion of shorelines in some areas, and filling of channels with fine materials.

Eelgrass Links and References on Disturbance

Chapter 5: Mechanisms of eelgrass (Zostera marina L.) colonization: Patch dynamics and effects of disturbance (820 kb pdf)

PDF fact sheet on Massachusetts DEP eelgrass mapping program, and the Wetland Conservancy Program

Our program was established in 1985 after Congress designated Buzzards Bay an "estuary of national significance." We joined the NEP in 1987. Our mission is to protect and restore water quality and living resources in Buzzards Bay and its surrounding watershed through the implementation of the Buzzards Bay Comprehensive Conservation and Management Plan. Click to read more.

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