Once widely used in industrial processes, polychlorinated biphenyls (PCBs) are now known as one of the most pervasive pollutants in aquatic environments. Despite their ban in 2001, PCBs are still recorded in high levels, especially in marine predators. These high levels are linked to impaired reproduction in these species, and pose risks to public health. This challenges scientists to better understand how PCBs continue to accumulate, predominantly in coastal areas where many chemical plants were located and where communities rely on estuaries for nutrition. We conducted a 6-month experiment in a Georgia (USA) salt marsh where combinations of mussels’ (Geukensia demissa), and other common benthic invertebrates were added to field inclusion cages to assess their effects on PCBs integration into and biomagnification through the coastal food web. We hypothesized that mussels would enhance PCB accumulation in marsh sediments and in fiddler crabs, which graze on algae growing in this sediment, but would have little effect on PCB accumulation in snails and marsh crabs that primarily graze on decaying plant and root material, respectively. We also measured invertebrate stable isotopes to evaluate potential dietary shifts in response to experimental treatments and elucidate mechanisms by which mussels may influence PCB biomagnification pathways.
Results/Conclusions
We discovered that mussels provoked dramatic increases in PCB concentrations in marsh sediments and in the marsh crab, Sesarma reticulatum, relative to control plots without mussels, and that, contrary to our hypothesis, fiddler crabs and snails showed no response to mussel addition. These findings suggest that mussels, through their cascading effects on marsh crabs (a species commonly preyed on by blue crabs, red drum and other predators), and localized effects on contaminant enrichment in the sediment, are playing an important role in driving PCB biomagnification in coastal food webs and distribution in the environment. More broadly, these results demonstrate how benthic invertebrate interactions, such as those between mussels and marsh crabs, can affect PCB integration into food webs and provide critical insight for coastal management by revealing how PCBs are initially incorporated into the estuarine food web prior to making their way to commercially and recreationally important species.