Effects and trends in littleneck clams (protothaca staminea) impacted by the exxon valdez oil spill

Abstract

Littleneck clams, Protothaca staminea, are a common intertidal clam species in Prince William Sound. With several years of results from NOAA/HAZMAT monitoring available, it is possible to infer some trends in clams affected by the Exxon Valdez incident. At oiled and washed sites, Protothaca staminea numbers reflect a different pattern of impact and recovery than other infaunal species, i.e., they do not show a depression in abundance followed by the dramatic population increase observed among many recovering species. Abundance differences between washed sites and unoiled sites may reflect lingering spill impacts. Extrapolation of the current trend suggests population abundance at oiled and washed sites could converge to that at unoiled sites by 2006. Chemistry results showed large declines in tissue aromatic hydrocarbon concentrations between 1990 and 1992. However, statistically significant differences between results for oiled sites and unoiled sited remained until 1997. Littleneck clams bioaccumulate oil to slightly higher concentrations than co-located mussels. Route of exposure has not been identified, but hydrocarbons adsorbed to particulates and food is a likely source. Subtle impacts to Protothaca staminea age structure and other population features may manifest themselves over the longer term. Our goal is to identify and characterize such effects. The overall task of impact and recovery assessment is complicated by factors such as sea otter predation, recovery from other major disruptions like the 1964 earthquake, and El Niña-Southern Oscillation shifts.