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PM19 Field-Based Effects Measures
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(PM291) An estuarine sediment-overlying water in situ toxicity assay with crabs (Carcinus maenas) based on postexposure feeding.

Moreira, S1, 2, Moreira-Santos, M3, Guilhermino, L1, 2, Ribeiro, R3, 1 CIIMAR - Centro Interdisciplinar de Investigação Marinha e Ambiental, Porto, Portugal2 ICBAS - Instituto de Ciências Biomédicas de Abel Salazar, Porto, Portugal3 IAV - Instituto do Ambiente e Vida, Coimbra, Portugal

ABSTRACT- This study developed and evaluated the suitability of a short-term sublethal in situ toxicity assay for estuarine sediment-overlying waters, with the Decapoda Carcinus maenas, based on postexposure feeding. It consisted of a 48-h in situ exposure period followed by a short postexposure feeding period (30-min), essential for preventing organism physiological recovery from toxicant exposure. A precise method for quantifying postexposure feeding rates of C. maenas using the Polychaeta Hediste diversicolor as food source was first developed and optimized under laboratory conditions. Secondly, the sensitivity of the postexposure feeding response was investigated by exposing organisms to sublethal and lethal concentrations of cadmium. Thirdly, the influence of several environmental conditions (salinity, temperature, substrate, food availability, and light) on postexposure feeding was investigated, to identify factors other than toxicity that may influence the assay response. After a 48-h exposure to cadmium, postexposure feeding depression was found to occur below lethality, the feeding IC50 and the LC50 being 4.33 and 27.92 mg/L of copper, respectively, indicating that postexposure feeding is a sensitive response and has potential as an assay endpoint. Only temperature and salinity were found to significantly influence postexposure feeding rates. The effectiveness of the proposed in situ assay was then investigated by deploying organisms at two reference and five contaminated Portuguese estuaries. Recovery rates between 90 and 100% were obtained at all sites. No significant differences in postexposure feeding rates, adjusted for site differences in salinity and temperature, were observed among reference sites. Furthermore, a significant postexposure feeding depression (16.3-72.7%) was observed at all contaminated sites relatively to pooled references, demonstrating that postexposure feeding was a general and responsive sublethal endpoint. Therefore, the in situ assay with C. maenas was shown to be a suitable tool to perform short-term sublethal in situ assessments of sediment-overlying water toxicity in estuarine ecosystems.

Key words: sediment-overlying water, in situ assay, postexposure feeding, Carcinus maenas


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