Assessment of recent habitat conditions of Eastern Oyster Crassostrea virginica bars in mesohaline Chesapeake Bay.

Abstract

Eastern oysters Crassostrea virginica in Chesapeake Bay, USA, have been subjected to intense harvest pressure since about 1850 and to disease epizootics since the 1950s. Combined, these processes have degraded the once extensive eastern oyster bottom; the remaining oyster shells, which are required as substrate for successful larval oyster settlement, are thus rendered increasingly susceptible to siltation. Between 1999 and 2001, we used an acoustic seabed classification system and underwater videography to assess oyster habitat conditions throughout Maryland's portion of Chesapeake Bay relative to eastern oyster recruitment and habitat restoration activities. We performed 16 surveys that covered a total of 39 km2 of bottom that were classified in 1911 as supporting productive oyster populations. Over 90% of this area has degraded from productive oyster bottom to mud, sand, or heavily sedimented oyster shell. Seventy percent of the locations we identified as containing unsedimented shell came from within the approximately 90 km2 of oyster bottom that had been subject to the management activity of spreading large volumes of shell at some time between 1960 and 1999. However, video observations of 49 of these locations that had been replenished with shell at various times indicated that any improvements in oyster habitat were short lived, as interstitial spaces in spread shell became highly sedimented after an average period of 5.5 years (n = 49; SE = 1.03). We conclude that the majority of oyster bottom in Maryland is extremely degraded and that no reasonable increase in the scale of present management practices will reverse this habitat decline.