Dazed, confused, and then hungry: pesticides alter predator-prey interactions of estuarine organisms.

Like predators, contaminant stressors such as pesticides may have large and interacting effects on natural communities by removing species or altering behaviors and species interactions. Yet, few studies in estuarine systems have evaluated the effects of a single, low-dose exposure to pesticides on key predators. Here, we investigated the effects of a common pyrethroid (resmethrin) + synergist (piperonyl butoxide; PBO) mixture used for mosquito abatement on two life stages (adult and juvenile) of an important invertebrate estuarine predator, prey, and fishery species: the blue crab (Callinectes sapidus). The effects of resmethrin with PBO (Res-PBO) were assessed using behavioral and mesocosm experiments to link effects on individuals with changes in predator-prey interactions: (1) In static non-renewal exposures, crabs exposed to 1:3, 10:30, or 100:300 µg l-1 Res-PBO or PBO-alone had increased mortality and reduced locomotor ability within 1-12 h, with higher effects in adults than juveniles. (2) In mesocosms, sublethal exposure to 1:3 µg l-1 Res-PBO altered abult and juvnile foraging ability by  lowering the ability of adult crabs to cannibalize juvenile crabs but increasing juvenile crab foraging rates. Juvenile crabs were also more vulnerable to predation following pesticide exposure. Thus, a single, sublethal exposure to low, environmentally occurring pesticide concentrations reduced blue crab survivorship and locomotor functioning, and altered predator-prey interactions by changing foraging rates and increasing vulnerability to predators. Pesticide stressors may therefore play an important but underestimated role in shaping coastal ecosystems in which invertebrate predators are important and may contribute to U.S. blue crab population declines.