European Sea Urchin Somatic and Gonadal Responses to Differing Stocking Densities and Seawater Flow Rates: A Case Study for Experimental Design Considerations

Abstract

Sea urchins are often used as model species in anthropogenic studies, and their aquaculture productions have expanded in recent years, yet basic rearing techniques applied in these studies vary and have received little investigation. This study assessed the effect of seawater flow rates and stocking densities on the somatic and physiological characteristics of European sea urchin species Paracentrotus lividus and Psammechinus miliaris. Two experiments were carried out for each species: one using low, medium, and high seawater flow rates (∼0.2, 0.8, and 1.60 L min–1, respectively) and another using low, medium, and high stocking densities [∼38, 76, and 115 ind. m–2 or 0.8, 1.6, and 2.4 kg m–2 (wet mass), respectively]. Within the flow rate experiment, P. lividus showed no significant treatment effects. By contrast, P. miliaris reared in low seawater flow rates had significantly lower relative spine lengths and gonad indices than conspecifics reared under higher flow rates (medium and high). Within the stocking density experiment, P. miliaris reared under low stocking densities demonstrated significantly larger somatic growth (test diameter and whole animal wet mass) relative to those stocked at high densities but were similar to those stocked at medium densities. For both species, gonad indices were largest within low densities compared with those within higher stocking densities (high only for P. lividus, and medium and high for P. miliaris). This study suggests that careful consideration for general holding conditions, and comparison across anthropogenic studies is required, especially across different species. Furthermore, this information could help improve the production effort of European sea urchin species while achieving high marketable attributes.