Larval Growth and Metamorphosis of South Eastern Mediterranean Sea Urchin Paracentrotus lividus (Echinodermata: Echinoidea) Fed Different Microalgal Diets

摘要

Objective: The current study was carried out to investigate the effects of four algal diets on the growth and metamorphosis of the larvae of the common sea urchin Paracentrotus lividus . Methodology: Sea urchin brood s tock was collected from the South Eastern Mediterranean (SEM) off Alexandria Coast, Egypt. Three individuals were induced to spawn by injecting them with 0.5 M KCl. The produced echinopluteus larvae were fed on four microalgal diets consisting of Chaetoceros calcitrans (D1), Nannochloropsis oculata (D2), Tetraselmis suecica (D3) and a mixture of the three algal species at equal ratio (D4). The study lasted for 28 days, while algal diets were provided only until day 21 when no planktonic larvae were observed in the water column. The groups fed on D1 and D4 showed normal larval structure during perimetamorphic period. The D1 started to show abnormalities at day 16, while D4 had seldom abnormalities until the end of the study. The D1 and D4 also showed an early competency of about six days and early release of immature rudiment on day 12 and 13, respectively. Results: The D1 resulted in higher survival rate in perimetamorphic period, while D4 showed higher survival by the end of the experiment, compared to other diets. On the contrary, larvae fed D2 and D3 managed to delay metamorphosis by 9 days and delay in the release of the juvenile bud until day 21, with a larger test diameter than D1 and D4. The D2 and D3 resulted also in abnormalities in the preimetamorphic larval structure and higher mortality rates near the end of the experiment. Conclusion: The present study suggests that C. calcitrans , N. oculata and T. suecica , whether used as uni-diet or tri-algal diet, succeeded to support P. lividus larval development to competence and subsequent metamorphosis. However, they failed to increase larval plasticity and to produce an adequate sized juvenile rudiment.