The Chickahominy Report

News about Earth, Atmosphere, Water, and Life

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.

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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