Sublethal effects of azamethiphos on shelter use by juvenile lobsters (Homarus americanus)

The use of pesticides to treat sea lice infestations in aquaculture may have negative impacts on non-target organisms such as the American lobster (Homarus americanus). Juvenile lobsters spend most of their time in shelter to avoid predation. This study examined: (1) whether the organophosphate pesticide azamethiphos affected shelter use by juvenile lobsters; (2) whether leaving shelter was a form of azamethiphos avoidance; and (3) whether azamethiphos affected shelter re-entry. The experiments were performed on juvenile lobsters (6.5-8 mm carapace length) in individual aquaria with an artificial shelter placed on a sand substrate. Azamethiphos concentrations of 0, 100, 500 and 1000 mu g l(-1) were used. Ten-minute short-term pulsed exposures to azamethiphos mimicking field conditions resulted in no shelter exits or lobster deaths. Under continuous exposure to azamethiphos, all lobsters left their shelters and the time to shelter exit and death decreased with increasing azamethiphos concentration. Survival of lobsters placed in fresh seawater following shelter exit was 100% for the 100 mu g l(-1) treatment, 50% for the 500 mu g l(-1) treatment and 33% for the 1000 mu g l(-1) treatment. Time to re-enter the shelter following exposure to azamethiphos was significantly shorter than the control for lobsters exposed to 100 mu g l(-1) and significantly longer than the control for lobsters exposed to 1000 mu g l(-1). Shelter exit appears to be a form of avoidance behavior to high concentrations of azamethiphos. At concentrations used by the aquaculture industry (100 mu g l(-1) and short exposure times), azamethiphos would not affect lobster shelter use. However, if the concentration or exposure time increased, mortality could occur directly due to this pesticide or indirectly as a consequence of leaving shelter. (C) 2000 Elsevier Science B.V. All rights reserved.