The Chickahominy Report

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TNC says shellfish reefs most endangered marine habitats

The eastern oyster formed massive reefs that used to filter the waters of the Chesapeake Bay. (Virginia Department of Environmental Quality)

The eastern oyster formed massive reefs that used to filter the waters of the Chesapeake Bay. (Virginia Department of Environmental Quality)

MECHANICSVILLE, Va. — In a dire assessment of the state of the Earth’s shellfish reefs, The Nature Conservancy announced last week that oyster reefs such as those that were once common in the Chesapeake Bay are the most threatened marine habitats in the world.

The report, Shellfish Reefs at Risk, was unveiled at the International Marine Conservation Congress in Washington, D.C., on Thursday. The report found that that 85 percent of the world’s oyster reefs have been lost, and in some regions the loss of oyster reef habitat approaches 99 percent.

The destruction of the eastern oyster (Crassostrea virginica) population in the Bay has been nothing short of catastrophic. In an often cited study, Roger Newell in 1988 estimated that oyster stocks in the Bay declined from 190 million kilograms (400 million pounds) when intense harvesting began in the late 1800s to 1.9 million kilograms (4 million pounds) in the 1980s. Oyster stocks have decline further since.

The primary cause for these losses include overharvesting, sedimentation, pollution, and the relatively recent arrival of two diseases — Dermo and MSX — that devastated the remaining Chesapeake Bay oyster population.

The destruction of oyster reefs, as well as those formed by other bivalves, such as clams and mussels, have had catastrophic consequences in terms of degradation and loss of ecosystem services that these reef systems provide. Oysters, as filter feeders, can remove a considerable amount of sediment and nutrients from the water column. Prior to 1870, the oysters could filter the entire volume of the Bay in 3 to 6 days. It takes the remaining oysters nearly a year to do the same.

Chesapeake Bay Links:

Chesapeake Bay Program
Chesapeake Bay Foundation
Alliance for the Chesapeake Bay
U.S. Army Corps of Engineers: Chesapeake Bay Oyster Environmental Impact Statement
NOAA Restoration Portal:
Oyster Reefs
Food and Agriculture Organization: Crassostrea virginica Fact Sheet

The increasing concentrations of nutrients fuel the growth of phytoplankton, and that, plus the increased sedimentation from runoff into the Bay, reduces clarity of the water, which in turn reduces the light available for the growth of sea grasses. Sea grass beds are another habitat that plays vital roles in many important Bay organisms. The increased phytoplankton can also consume all the available oxygen in the water column, which creates dead zones — places where animals, such as fish and shellfish, cannot survive.

Oyster reefs form hard substrates necessary for the settling and establishment of young oysters, but other organisms as well, including mussels and barnacles. The structure and potential food availability on an oyster reef attracts economically important species, such as blue crab, croaker, sea trout and striped bass.

Despite recognition of the importance of a healthy Chesapeake to the culture, economy, and environment of the Mid-Atlantic region, policies to turn conditions around have generally been ineffective or inadequate. Nevertheless, The Nature Conservancy report does mention some reasons for hope. Recent research has shown it is possible to restore some of the Bay’s oyster reefs. Given proper protections, the restored oysters can develop resistance to the diseases that nearly wiped out what remained of the Chesapeake’s overstressed oysters the past four decades. Likewise, responsible aquaculture offers economic benefits while simultaneously easing harvest pressure from wild oyster populations and natural reefs.

The Chesapeake may never return to the condition that John Smith witnessed in his 17th century explorations. Nevertheless — while much of the responsibility to save the Bay rests on those who live and work throughout its watershed — restoration of oyster reefs will fix many of the problems we have created.

— David M. Lawrence

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