Utility of sea urchin embryo-larval bioassays for assessing the environmental impact of marine fishcage farming
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The environmental impact of two fish farms was assessed by larval toxicity bioassays using the sea urchin Paracetrotus lividus. Larval toxicity bioassays have become important for regulatory and monitoring programs, largely because they are assumed to be good indicators of ecological damage to benthic infaunal communities. The study was conducted in two Mediterranean fish farms which produce gilthead sea bream (Sparus aurata) and tuna (Tunna tuna), respectively. The data obtained from sediment toxicity tests and the physico-chemical characteristics of sediment were examined in two farming production periods to determine the relationships between toxicity and sediment impact. In the gilthead sea bream fish farm, only the sampling stations located at 0 and 35 m were classified as toxic (significant differences from control, p < 0.05) during the winter campaign. A more pronounced toxicity gradient was observed during summer sampling, toxicity being significantly higher in sampling stations 0, 35 and 55 m down current from the fish cages. In the tuna farm, a seasonal toxicity pattern was observed associated to fish farming activity. Most of the stations sampled during the production period showed a highly toxic response (0 m to 125 m from fish cages), while stations further away from the fish farm (175 m to 330 m from fish cages) showed no toxic response. No stations exhibited significant toxicity during the fallow period. Sea urchin larval toxicity was significantly correlated with sulphides and seasonally, with total ammonia nitrogen in both fish farms. The results reported here are promising and indicate that embryo-larval bioassays with the sea urchin P. lividus represent a sensitive tool for describing the environmental impact of fish farming.