Abstract
Historic baselines are important in developing our understanding of ecosystems in the face of rapid global change. While a number of studies have sought to determine changes in extent of exploited habitats over historic timescales, few have quantified such changes prior to late twentieth century baselines. Here, we present, to our knowledge, the first ever large-scale quantitative assessment of the extent and biomass of marine habitat-forming species over a 100-year time frame. We examined records of wild native oyster abundance in the United States from a historic, yet already exploited, baseline between 1878 and 1935 (predominantly 1885–1915), and a current baseline between 1968 and 2010 (predominantly 2000–2010). We quantified the extent of oyster grounds in 39 estuaries historically and 51 estuaries from recent times. Data from 24 estuaries allowed comparison of historic to present extent and biomass. We found evidence for a 64 per cent decline in the spatial extent of oyster habitat and an 88 per cent decline in oyster biomass over time. The difference between these two numbers illustrates that current areal extent measures may be masking significant loss of habitat through degradation.
Highlights
Humans have been modifying ecosystems and exploiting natural populations for millennia [1]; quantitative data on the impacts of our exploitation over large spatial scales, whether terrestrial or marine, are primarily limited to recent decades [2,3,4]
We summarized the findings into sub-estuarine drainage areas, as listed in National Oceanic and Atmospheric Administration (NOAA)’s coastal assessment framework (CAF) [37]
The Olympia oyster habitat on the west coast was recorded as functionally extinct in all estuaries for which data were available for comparison
Summary
Humans have been modifying ecosystems and exploiting natural populations for millennia [1]; quantitative data on the impacts of our exploitation over large. The vast majority of historical and present-day oyster habitat surveys were conducted for fisheries management purposes and use a relatively consistent approach For these cases, we used the term ‘oyster grounds’ that we define as the wider community complex of which oyster reefs and beds are clearly an important part, but that includes areas of adjacent sediments and shell rubble. For a small number of estuaries, density data were collected at a fine spatial scale but mapping related to larger oyster ground units In these cases, we applied a correction factor to account for the high mean densities reported. (e) Quantitative comparison We found data that allowed direct comparison of historic and present oyster grounds and biomass in 24 estuaries throughout the US and calculated per cent change in extent and biomass over time. All statistical tests were run in R v. 2.13.1 (2011-07-08)
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