Methodological basis for the optimization of a marine sea-urchin embryo test (SET) for the ecological assessment of coastal water quality

The sea-urchin embryo test (SET) has been frequently used as a rapid, sensitive, and cost-effective biological tool for marine monitoring worldwide, but the selection of a sensitive, objective, and automatically readable endpoint, a stricter quality control to guarantee optimum handling and biological material, and the identification of confounding factors that interfere with the response have hampered its widespread routine use. Size increase in a minimum of n=30 individuals per replicate, either normal larvae or earlier developmental stages, was preferred to observer-dependent, discontinuous responses as test endpoint. Control size increase after 48 h incubation at 20 °C must meet an acceptability criterion of 218 μm. In order to avoid false positives minimums of 32‰ salinity, 7 pH and 2 mg/L oxygen, and a maximum of 40 μg/L NH3 (NOEC) are required in the incubation media. For in situ testing size increase rates must be corrected on a degree-day basis using 12 °C as the developmental threshold.