Sea-urchin embryo bioassay for in situ evaluation of the biological quality of coastal seawater

The Paracentrotus lividus sea-urchin embryo bioassay, consisting of incubat ion of fertilized eggs in test water and measurement of the percentage of f our-armed plutei larvae developed after the incubation period (2-3 days), h as been adapted for in situ evaluation of seawater quality in coastal areas . Mature sea-urchins are dissected in situ and fertilization is performed i n the field; fertilized eggs are delivered into screw lid 50-ml cylinders w ith 20 mum nylon mesh in both ends filled with sieved local seawater. The c ylinders, tied to 60-cm ropes with weights on one end and buoys in the othe r one, are placed by scuba divers in the test sites at subtidal level and r ecovered after the incubation period. The contents of each cylinder are the n transferred into a vial, fixed with formalin and observed directly under an inverted microscope to record the percentage (N=100) and size (length, N =25) of four-arm pluteus larvae. Our results show that the bioassay can dis criminate between well known polluted and unpolluted sites, but further imp rovement is needed in order to: (1) take into account differences of temper ature between sites; (2) minimize larval mortality due to reasons other tha n pollution. (C) 2001 Academic Press.