Morphology and survivorship of larval Psammechinus miliaris (Gmelin) (Echinodermata: Echinoidea) in response to varying food quantity and quality

Experiments were conducted with the aim of defining the optimal culture conditions for Psammechinus miliaris larvae. Larval response to varying food rations of the microalgae, Pleurocrysis elongata, was assessed by recording the morphological parameters of developing larvae. Larvae on a high ration (4000 cells ml(-1)) showed an extreme reduction in postoral arm length and were unable to maintain their position in the water column. Larvae fed an optimal ration (1500-4000 cells ml(-1) according to developmental stage) displayed a more typical morphology, whereas larvae fed a low ration (500 cells ml(-1))failed to develop to metamorphosis. Survivorship of the larvae to metamorphosis was at best 61%. Larval response to various diet types was measured both in terms of the larval morphology, survivorship during metamorphosis and growth over the post-larval period. The microalgae, Dunaliella tertiolecta, produced more morphologically typical larvae and gave better results in terms of survivorship at metamorphosis (65.8%) than Pl. carterae (48.2%). The resulting juveniles, measured at 10 days post-settlement, were also significantly larger when the larvae had been fed D. tertiolecta. Survivorship over the post-larval period was more consistent when larvae were provided with a substrate coated with a natural biofilm compared with a substrate coated with the microalgae, Tetraselmis suecica. The data suggest that it is possible to produce large numbers of juvenile P. miliaris using these methods. (C) 2000 Elsevier Science B.V. All rights reserved.