ARS | Publication request: Historical ecology with real numbers: Past and present extent and biomass of an imperilled estuarine habitat

Submitted to: Proceedings of the Royal Society of London: Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2012
Publication Date: N/A

Interpretive Summary: Due to rapid change since the industrial revolution, it is difficult to understand what many environments looked like historically and thus examine changes over time. This is particularly true for the marine environment where quantitative records of the historic abundance of harvested marine organisms are difficult to discern prior to the 1950's. Fortunately, historical records of reef forming bivalve shellfish in the US are better and we examined records these for oysters in the US from 39 bays for the period 1878-1935 to compare with recent records from 51 bays for 1968-2010. Though oysters had been harvested for thousands of years, extensive harvest in the US began about this time and records were made to document the available resource. We found that there was a cumulative decline of 64% in the amount of area covered by oysters and an 87% decline in the weight or biomass of oysters over this time period. The degree of loss varied by area with almost a complete loss of the small native oyster (Ostrea lurida) on the Pacific coast of the US and also the eastern oyster (Crassostrea virginica) in the northeast Atlantic coast, but some evidence of actual gains in biomass in some bays along the eastern Gulf coast. Still the overall loss in extent and biomass in this area was significant. In addition to being a cultural an economic resource, these oyster reefs have recently been shown to be an important ecological function in estuaries where they remain and this information should assist ecologists and natural resource managers as they strive to maintain and restore coastal ecosystems.

Technical Abstract: Historic baselines are important in developing our understanding of ecosystems and species dynamics in the face of rapid global change. While a number of studies have sought to elucidate the historic abundance of exploited marine populations, there are few that confidently quantify patterns of abundance or extent prior to 1950. Here we present the most accurate assessment to date of the extent and biomass of a marine habitat-forming species over a one hundred year time frame. We examined records of wild native oyster abundance in the United States from a historic, yet already exploited, baseline between 1878-1935 (predominantly 1885-1915) and a current baseline between 1968-2010 (predominantly 2000-2010). We quantified the historic extent of oyster grounds in 39 bays and current extent in 51 bays. Data from 24 bays allowed comparison of historic to present extent and biomass. We found evidence for a 64% decline in the spatial extent of oyster habitat and an 87% decline in oyster biomass between the historic (non-pristine) and modern U.S. baselines. The degree of change varies spatially, with the functional extirpation of Ostrea lurida on the West Coast and Crassostrea virginica in the North East, but evidence of biomass gains in some bays in the eastern Northern Gulf of Mexico. Our data illustrate that while habitat extent is most frequently documented and contrasted over time, it is not necessarily a good predictor of habitat quality, as illustrated by discrepancies between the remaining extent (56%) and remaining biomass (12%) estimated for the Northern Gulf of Mexico.