Effects of larval diet and metamorphosis cue on survival and growth of sea urchin post-larvae (Paracentrotus lividus; Lamarck, 1816)

In this study, we present the results of two experiments; in the first one we evaluated the effects of four larval dietary treatments on the survival and growth of the sea urchin Paracentrotus lividus, larvae and post-larvae. In the second experiment we have measured the effects of two different settlement substrates, combined with the presence of conspecifics, on metamorphosis, survival and growth of post-larvae. The microalgae dietary treatments consisted in: Dunaliella tertiolecta (Duna); 50% mixture of Isochrysis galbana and D. tertiolecta (ID); 50% mixture of Chaetoceros gracilis and D. tertiolecta (CD); 33% mixture of I. galbana, C. gracilis and D. tertiolecta (ICD). Although all dietary treatments resulted in a good survival at competence, significant difference in post-larval survival was observed between treatments, and indeed, only larvae fed Duna and CD survived to 180 days post settlement (DPS).  In the second experiment, the settlement substrates consisted in a film of cultured Ulvella lens or a naturally developing biofilm of diatoms, and the employed rearing water was either natural seawater or seawater previously exposed to P. lividus adults. At 10 DPS, larger (p<0.05) post-larvae were observed in the natural biofilm treatment, whilst the presence of conspecifics significantly increased larval settlement in both substrates (p<0.01).  These results indicate that it is important to consider the survival of post-larvae and juveniles to establish the efficiency of the dietary treatment on the hatchery production of P. lividus. Furthermore, it suggests that improved settlement protocols, such as the use of conspecifics, could contribute to increase hatchery outputs. Finally, it confirms the suitability of U. lens as settlement cue but also highlights that further research is required to establish its effectiveness for post-larvae first feedin