Summary:
Seagrasses and salt marsh species are an ecologically important group of plants that provide critical habitat for ecologically and economically important finfish and shellfish, exceptionally high rates of primary production, filtration of waters running off the land, sequestration of significant amounts of carbon, and sediment stabilization for shallow coastal waters. They thus represent some of the most valuable, and at the same time, owing to their position at the receiving end of riverine systems and their proximity to large population centers, some of the most vulnerable ecosystems on earth.
The direct and indirect effects of the Deepwater Horizon event are likely to have had large impacts on these critical habitats, depending on the amount and type of oil they may have received. Based on data available from NOAA observers, it is clear that there is an east-west gradient in exposure, with greater amounts of oiling in Louisiana and lesser amounts of oiling in northwest Florida.
During the past several years we have gathered quantitative data on seagrass and marsh plant species composition and biomass, as well as their associated mobile macroinvertebrates and juvenile fishes, from a number of locations along the north central Gulf Coast, stretching from Louisiana's Chandeleur Islands to St. Joe Bay, Florida. For a subset of those locations we have also measured rates of carbon and nutrient uptake by the seagrass and marsh beds as well as rates of accrual/erosion of the adjacent shoreline. These data sets provide important baseline information for a Before After Control Impact (BACI) assessment of the effects of oiling.
Using these data sets from more heavily oiled Mississippi, intermediately oiled Alabama and lightly to non-oiled northwest Florida seagrass meadows and salt marshes we propose to test the following hypotheses:
- Abundance of seagrass and marsh plants, as well as macroinvertebrates and juvenile fishes will be significantly reduced by oiling.
- Alternatively, if oil has rafted over seagrass meadows without contacting them, and only salt marshes are oiled, abundance of marsh plants and the associated macroinvertbrates and fishes will be significantly reduced. If this is true, the animals formerly associated with the marsh may move to the subtidal seagrass meadows, where abundance will be significantly increased and species composition significantly altered.
- Recruitment of juvenile snapper, penaeid shrimp, and blue crabs will be significantly reduced this year (2010) due to reduced survival during their early planktonic life stages.
- Growth rates of common young-of-the-year fishes in these habitats will be negatively affected by oiling, and will follow a gradient in growth that is negatively correlated with degree of oil exposure.
- Carbon and nutrient uptake by seagrass and marsh beds will be reduced as plant biomass and productivity are negatively affected by oil exposure
- Accretion rates will be decreased in accruing shorelines and erosion rates will be increased in eroding shorelines as plant biomass and structural complexity (i.e. buffering of wave action) are depressed by oil exposure