Exploring cumulative effects of aquaculture chemicals in sediment on adult sea urchin behavioral, immunological, and metabolomic endpoints

Salmon aquaculture is a major economic activity in Atlantic Canada. The anti-sea lice therapeutant emamectin benzoate (EMB) and the antibiotic oxytetracycline (OTC) are widely used in aquaculture and are detected in sediments around sites. The green sea urchin Strongylocentrotus droebachiensis is an important benthic species in Canada that may be exposed to these compounds including organic matter near aquaculture sites. A central composite rotatable design was applied to investigate the potential effect of contaminant mixtures on adult green sea urchins during a 140-day exposure to environmentally relevant concentrations of EMB, OTC, and organic matter (OM). Endpoints considered in this study included behavior (righting time) assessed every two weeks, immunology (coelomocyte characteristics and functionality) and gonadosomatic index (GSI) investigated at the end of the exposure. Metabolomic profiling was also carried out in the gonad tissue at the end of the exposure. Two test conditions were found to impact coelomocyte number and cell viability, but immunology fully recovered 80 days post-exposure. No other clear trends in the effect of EMB, OTC, and OM were found on other sea urchin immunological endpoints, nor righting time, GSI or metabolites concentrations. Our results suggest that there is no clear impact of the contaminant mixtures tested on urchins though interactions suggest complex mechanisms that require further testing.