Ecosystem services are lost when facilitation between two ecosystem engineers is compromised by oil

Nearshore marine ecosystems are among the most productive areas in the world. Unfortunately, these areas also receive pollutants released into oceanic and riverine waters. Six years following the Deepwater Horizon oil spill, the largest in US history, the complexity of ecological injuries in this system is just now being elucidated. Here, we describe a novel pathway of injury from oil spills by documenting how the loss of oysters near marsh edge as a direct result of shoreline oiling and clean-up activities can double rates of coastal erosion. As part of the natural resource damage assessment, we examined the impact of shoreline oiling on eastern oysters Crassostrea virginica near the marsh edge at 187 sites in Louisiana and Mississippi Sound in 2013. For marshes that experienced heavy oiling, oyster habitat was 77% less abundant than in areas where no oil was observed. Areas near marshes characterized by more moderate levels of oiling had 33% less oyster habitat than areas where no oil was observed. Similarly, the number of sites without any oyster habitat was higher in heavily and persistently oiled areas compared to areas where no oil was observed (56 vs. 24%). The consequences of this loss are substantial and include loss of essential fish habitat, reduced nutrient cycling, and decreased erosion buffering. For a subset of the sites where erosion rate was also measured between 2010 and 2013 (n = 79), shoreline loss was more than twice as high (2.1 vs. 0.9 m yr(-1)) in areas lacking oyster cover. Our findings provide evidence that loss of nearshore oyster habitat can disrupt the strong facilitation between oysters and marsh vegetation.