Uncoordinated: Effects of sublethal malathion and carbaryl exposures on juvenile and adult blue crabs (Callinectes sapidus)

Abstract

Blue crabs are an important ecological and economic estuarine species that may be inadvertently exposed to pesticides commonly used for pest and vector control. The lethal and sub-lethal effects of two such pesticides, malathion and carbaryl, on juvenile and adult blue crab survival and muscular functioning were investigated by measuring changes in mortality, righting time (RT)11RT: Righting time, the amount of time required for a crab to return to an upright position after being placed on its dorsal side., and eyestalk reflexes following a single exposure at 3 environmentally occurring concentrations (1 μg/L, 10 μg/L, 100 μg/L). These sublethal responses serve as a proxy for understanding the effects of exposure on behaviors critical to blue crab survival (e.g., predator escape and foraging). Effects on blue crab responses varied with pesticide-type, concentration, life-stage, and exposure-time. In short, all malathion and carbaryl exposures significantly increased juvenile and adult crab RT and abnormal eyestalk responses within 1–12 h of exposure. Significant lethal effects were only observed in adult crabs exposed to 100 μg/L malathion. Thus, a single exposure to low and legally allowable concentrations (i.e., 1–10 μg/L) of either insecticide negatively affected blue crab behaviors. Reduced survival and coordination may harm blue crab populations directly via toxicity or indirectly through decreased foraging or increased predation risk. Blue crabs are important components of estuarine food webs, and changes in their populations or behaviors may have broad ecological consequences. Ultimately, pesticide-stressors may play an important but underestimated role in U.S. blue crab population declines and in coastal ecosystems in which invertebrate predators are important.