RESPONSES OF THE SHORE CRAB, CARCINUS MAENAS (DECAPODA, BRACHYURA), TO AN ACUTE DOSE OF CYPERMETHRIN

Abstract

The shore, or green, crab Carcinus maenas (Linnaeus, 1758), is an endemic species of northern Europe. It has become an important species internationally due to its introduction to foreign waters where it has become so successful that it is now considered one of the most serious marine pests in the U.S.A. and Australia (Geller et al., 1997). Carcinus is used in pollution studies, not only because of the widespread and topical nature of the animal, but also because it is easy to maintain in the laboratory, and at high stocking densities. Cypermethrin is a synthetic pyrethroid used as an insecticide and also to treat salmon against the infestation of sea lice (i.e., parasitic Copepoda). It was authorized within Scotland in 1997 for use on salmon farms. Cypermethrin acts on nervous systems by prolonging the opening of Na+ channels leading to trains of spikes in neurons (WHO, 1989). Cypermethrin is especially toxic to Crustacea (cf. Clark et al., 1989), in particular marine decapods (WHO, 1989). This study was designed to investigate the effect of 5 /xg/1 of cypermethrin on the shore crab (the same concentration used to kill sea lice). These findings are reported here in order to share some new ideas for the use of Carcinus as a biomonitoring species. Two 125 litre plastic, static seawater tanks were set up with aeration, each containing 12 Carcinus (70-85 mm carapace width) at 12?C and a light : dark cycle of 12: 12 hours. The crabs were acclimated for 4 days prior to the experiment and were not fed during acclimation or the experiment. The treatment dose of 5 /xg cypermethrin/1 was created in the treatment tank using ethanol as a carrier. The control tank was treated with an equal dose of pure ethanol (0.5 ml). The water in each tank was then mixed to equilibrate the treatments within the tanks. Crabs were observed at various intervals after the start of the experiment to remove mortalities and look for any visually recognizable effects of the cypermethrin. At 96 hours the experiment was stopped and the remaining crabs were externally and