Toxic effects of Ostreopsis ovata on larvae and juveniles of Paracentrotus lividus.

Recently, in the Mediterranean Sea and in other temperate regions, mass mortalities of marine organisms and human diseases have been caused by blooms of the dinoflagellate genus Ostreopsis, palytoxin (PLTX) producing species. Such blooms are cause of health, economical and environmental concern, particularly when affecting edible species of commercial relevance that, additionally, play key ecological roles, with cascading effects through the whole ecosystem. The present research aims at the evaluation of the effects produced by Ostreopsis ovata blooms on the early stages of Paracentrotus lividus (Lamarck, 1816). This sea urchin species is considered one of the key controllers of the structure and dynamics of Mediterranean algal communities. Further, P. lividus is an edible species and its gonads (roe) are considered a culinary delicacy: in many areas the harvesting of this species has lead to overexploitation. Through three eco-toxicological assays we tested mortality effects produced by four O. ovata concentrations (4, 40, 400 and 4000 cell ml1) on P. lividus competent larvae, using O. ovata cultured at 20 8C and 25 8C, and on juveniles, using O. ovata cultured at 20 8C. Both O. ovata culture and growth medium devoid of algal cells were tested. Juveniles turned out to be more sensitive than larvae to O. ovata presence, the latter showing significant mortality only at extremely high O. ovata concentrations. Furthermore, temperature at which the algal cultures were grown played an additional role. The results of the present research are particularly relevant given the commercial and ecological relevance of P. lividus.