Sea urchin recruitment: Effect of diatom based biofilms on Paracentrotus lividus competent larvae

Abstract

Eight different experimental substrates were tested on Paracentrotus lividus competent larvae in order to evaluate their potential for inducing metamorphosis and enhance survival after recruitment. Two benthic diatoms species, Nitzschia laevis (NL) and Halamphora coffeaeformis (HC), were selected according to their capacity to adhere and to form strong biofilms. They were tested in monocultures and in a mixed biofilm (MIX) that was also tried in combination with Gamma-Aminobutyric Acid, involved in triggering some invertebrate metamorphosis (MIX + GABA). Histamine (HIS) was also used as a treatment according to the high metamorphosis rates that have been recorded for this compound on other sea urchin species. Finally, a natural microphytobenthic biofilm (NATURAL) and oyster shells particles colonized by epiphytic diatoms (SHELL) were sampled from the mud of a refining oyster pond. Batches of 21 days-old larvae were placed on each experimental substrate and their effect was compared to a negative control of filtered sea water (without any treatment; FSW). Metamorphosis rate was daily recorded in each treatment. The sea urchin larvae on substrates NL, NATURAL, GABA + MIX and SHELL showed significantly higher metamorphosis rates than larvae on the other treatments (P < 0.001), reaching more than 90% in 72 h. Survival rate was assessed at 10 days post-metamorphosis in these four treatments. No difference was observed between them in terms of metamorphosis rate or survival rate (more than 60% for the four experimental substrates). Results demonstrate that the transition from planktonic larvae to benthic juvenile could be promoted through diatom-based biofilms. These substrates represent efficient metamorphosis inducers for P. lividus larviculture but we suggest to use preferably N. laevis biofilms in order to promote practical and safe solutions for farmers.