Effect of five benthic diatoms on the survival and development of Paracentrotus lividus post-larvae in the laboratory

The Mediterranean sea urchin Paracentrotus lividus Lamark, 1816 is a resource as food and model organism for scientific research. Increasing market demand, commercial fisheries and destructing harvesting methods produced a dramatic reduction of natural stocks along the Mediterranean coasts. The techniques for in vitro fertilization and growth of larvae and adults are well known but various bottlenecks still hinder the industrial maturity of its aquaculture. In particular, the transition from planktonic larvae to benthic juveniles, as well as their correct development and survival, still represent critical phases, since larval and post-larval experiences are the primary determinant of juvenile fitness. Thus, techniques improving survival and settlement rates in the first two months after fertilization could considerably improve the effectiveness of echinoculture practices. This study was conducted to determine, for the first time, the effect of strictly benthic diatoms on P. lividus post-larval performances, as compared to other micro- and macro-algae. In addition, three larval dietary treatments were applied, to confirm previous findings on the efficacy of algae and formulated diets. In particular, survival and ability to produce competent larvae for settlement were tested in groups subjected to three algal diets (Isochrisis galbana, Rhodomonas baltica and Dunaliella tertiolecta), all integrated with a formulated food. Furthermore, six post-larval feeding regimes, i.e., the benthic diatoms Cocconeis scutellum parva, Diploneis sp., Navicula incerta, Cylindrotheca closterium and Nanofrustulum shiloi, compared with Ulva rigida along with a negative control (absence of food), were tested on larvae deriving from the most effective treatment. Our results confirmed the efficacy of Dunaliella tertiolecta integrated with a formulated food, consistently producing about 60% survival. Furthermore, the most adhesive benthic diatom, Cocconeis scutellum parva, sustained settlement (about 63%) and good survival in the first two months of life of sea urchins.