Responses of Signal Crayfish Pacifastacus Leniusculus to Pulse Exposure of Pesticides at Environmentally Relevant Concentrations

Although pesticides are often discharged into surface waters in pulses as opposed to a sustained release, the effect of episodic pollution events on aquatic invertebrates is largely unknown. We monitored change in heart rate and distance moved to assess the immediate response of signal crayfish Pacifastacus leniusculus to short-term exposure to environmentally relevant concentrations of metazachlor (MTZ), terbuthylazine (TER), and thiacloprid (TCL). A significant increase in heart rate and distance moved was detected in four of six crayfish exposed to 20 µg/L MTZ and in two of six exposed to 6 µg/L of TCL and 4 µg/L of TER. A significant correlation between heart rate and distance moved was found in all exposed groups. Increased heart rate was detected at 118±74 s, 189±179 s, and 146±22 s post-exposure to MTZ, TER, and TCL, respectively. These results suggest that exposure to high pesticide concentrations may lead crayfish to attempt to avoid contaminated areas. With lower concentrations, crayfish not exhibiting an escape response may continue to be exposed to lower, but potentially harmful, levels of pollutants. Further study is required to determine whether brief pesticide exposure leads to delayed adverse effects on freshwater crayfish