Optimising microalgae diets in sea urchin Paracentrotus lividus larviculture to promote aquaculture diversification

Abstract The objective of this study was to optimise the rearing of the sea urchin Paracentrotus lividus (Lamarck, 1816) larvae through the choice of an optimal diet. The effects on larvae reared in oyster facilities and using different microalgae species were analysed. Four experimental diets were tested: 1) Isochrysis aff. galbana (Clone T-ISO), 2) Dunaliella tertiolecta , 3) Rhodomonas sp. and 4) a combined diet of these three species (1:1:1). The biometrics of larvae were carried out every two days. Post-larval survival was assessed when competence for settlement was achieved. Induction of settlement was carried out by contact between larvae and oyster shell particles. This method, adapted from oyster farming, was used for the first time in sea urchin culture. After 9 days post-settlement, metamorphosed juveniles were sampled and post-settlement survival was assessed. The biochemical composition (proteins, carbohydrates, lipids) of microalgae and larvae was measured. Age at competence was reached at 15 days post-fertilisation for all diets. Larval survival rate and growth in length and width were higher for larvae fed with Rhodomonas sp. These larvae also had the highest lipid content. Post-settlement survival was higher in larvae fed with the combined diet. Larvae in all treatments demonstrated normal growth and development, but Rhodomonas sp. presented nutritional advantages for sea urchin larvae: a more rapid development and a higher lipid content. The use of Rhodomonas sp., already widely used in oyster aquaculture, as a diet in Paracentrotus lividus culture could be a factor in enabling oyster farmers to diversify towards “echinoculture” and increase their revenue.