Effects of stocking density, algal density, and temperature on growth and survival of larvae of the basket cockle, Clinocardium nuttallii

This study determined optimal rearing conditions – stocking density, algal density, and temperature – for hatchery production of the basket cockle, Clinocardium nuttallii, from newly-hatched D-larvae to pediveligers using static rearing systems and discontinuous feeding. The combined effect of initial stocking density (2, 4, and 8 larvae ml− 1) and algal density (10, 25, and 50 × 103 cells ml− 1) on larval growth and survival was examined using a bi-algal diet of Chaetoceros muelleri (CM) and Isochrysis sp. (Tahitian strain, TISO). The effect of algal density (0, 2.5, 5, 10, 20, 40, 60, and 80 × 103 cells ml− 1) as a single factor was assessed using a single-algal diet of TISO and a fixed stocking density (2 larvae ml− 1) held constant throughout the experiment. The effect of temperature (5.9, 10.2, 14.2, 18.2, 21.9, and 26.3 °C) on larval growth and survival was also evaluated. The results showed that, when feeding the bi-algal diet of CM and TISO, an initial stocking density of 2 larvae ml− 1 combined with an algal density of 25 or 50 × 103 cells ml− 1 or an initial stocking density of 4 larvae ml− 1 combined with an algal density of 50 × 103 cells ml− 1 were optimal conditions for larval growth, and survival rate was significantly better in the treatment with 4 larvae ml− 1. When feeding the single-algal diet of TISO, optimal larval growth was observed at algal densities of ≥ 40 × 103 cells ml− 1. These optimal rearing conditions translated into minimum food rations of 18.4 and 20 × 103 algal cells larva− 1 day− 1 using the bi-algal and single-algal diets, respectively, to support maximum larval growth from newly-hatched D-larvae to pediveligers. Within the tested temperature range of 5.9 to 21.9 °C, larval growth was greater with increasing temperature but survival to settlement stage was not affected by temperature. The larvae failed to survive at the highest tested temperature of 26.3 °C.