An assessment of the acute impact of the sea lice treatment ivermectin on a benthic community

Ivermectin has been proposed as a feed additive treatment for infestations of sea lice on caged salmonids. This paper presents an assessment of the acute effects of this chemical on a typical intertidal benthic community. Significant differences were observed in both the abundance and biomass of the benthic community with contamination by ivermectin. As the concentration of ivermectin increased, the changes to the benthic community occurred more rapidly. Hediste diversicolor was the most sensitive of the species present, with 100% mortality occurring within 14 days at an ivermectin concentration of 8.0 mg m(-2). Corophium volutator was also found to be sensitive, with 100% mortality occurring with 14 days at a concentration of 80.0 mg m(-2) ivermectin. At lower concentrations, however, size-related differences were observed in the impact of ivermectin on this latter species. Impacts on Oligochaeta are also presented. The potential toxic effects of this chemical on the benthic communities is discussed in relation to its proposed use in fish fanning and its persistence in the marine environment. Crown Copyright (C) 1998 Published by Elsevier Science B.V. All rights reserved.