Influence of microalgal species and dietary rations on larval development and survival of the purple sea urchin, Strongylocentrotus purpuratus (Stimpson, 1857)

This study evaluated the effect of diet and ration on the growth and survival of larvae of the purple sea urchin, Strongylocentrotus purpuratus. Larval total length, mid-line body length, body width, post-oral arm length, time to reach metamorphic competency, and survival rate were assessed during the experimental period (28 days). In the first experiment, seven algal diets [i.e. Dunaliella tertiolecta, Chaetoceros muelleri, Isochrysis sp. (Tahitian strain) and all possible binary and tertiary combinations] were assessed, along with a control treatment of no food. Larvae reared on the bi-algal diet of D. tertiolecta/Isochrysis sp. and the uni-algal diet of D. tertiolecta provided significantly better growth than all other treatments. Larvae were successfully raised to metamorphic competency with both the binary combination of D. tertiolecta/Isochrysis sp. and the single species D. tertiolecta within 28 days of culture, whereas larvae in all other dietary treatments failed to reach competence within 28 days. In the second experiment, a bi-algal diet (D. tertiolecta and Isochrysis sp. at equal biovolumes) was evaluated using five rations: (1) low ration: 1.25 × 103 cells ml− 1; (2) normal ration: 2.5 × 103 cells ml− 1; (3) standardized ration: 2.5 × 103 to 10.0 × 103 cells ml− 1, with increasing ration according to developmental stage; (4) medium ration: 5.0 × 103 cells ml− 1; and (5) high ration: 10.0 × 103 cells ml− 1. Typical echinoid larval development in all body dimensions was only achieved for larvae offered the standardized ration. Larvae reared on this ration attained metamorphic competency within 28 days, whereas larvae fed the fixed rations (lower or higher concentrations) failed to attain competency by the end of the experiment. In general, in comparison to larvae fed the standardized ration, larvae on the low ration showed longer post-oral arm length and narrower body width whereas larvae on the high ration showed shorter post-oral arm length and body width in relation to their total length. Overall survival (from prism stage to metamorphic competency) for the best treatments in both experiments was 44.4 ± 2.9 and 53.3 ± 1.9% (mean ± SE) for the binary diet of D. tertiolecta/Isochrysis sp. and standardized ration treatments, respectively. Based on these results, larvae fed a binary combination of D. tertiolecta and Isochrysis sp. or D. tertiolecta alone with a ration increasing with developmental stage is recommended for hatchery production of S. purpuratus.

► We identified the best microalgal diet and ration for larvae of the purple sea urchin.
► The best diet was Dunaliella tertiolecta, either alone or with Isochrysis sp.
► The best ration was one that increased over time with larval developmental stage.