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 con ditions for Psammechinus miliaris larvae. Larval response to varying food r ations 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 o ptimal ration (1500-4000 cells ml(-1) according to developmental stage) dis played a more typical morphology, whereas larvae fed a low ration (500 cell s ml(-1))failed to develop to metamorphosis. Survivorship of the larvae to metamorphosis was at best 61%. Larval response to various diet types was me asured both in terms of the larval morphology, survivorship during metamorp hosis and growth over the post-larval period. The microalgae, Dunaliella te rtiolecta, produced more morphologically typical larvae and gave better res ults in terms of survivorship at metamorphosis (65.8%) than Pl. carterae (4 8.2%). The resulting juveniles, measured at 10 days post-settlement, were a lso significantly larger when the larvae had been fed D. tertiolecta. Survi vorship over the post-larval period was more consistent when larvae were pr ovided with a substrate coated with a natural biofilm compared with a subst rate coated with the microalgae, Tetraselmis suecica. The data suggest that it is possible to produce large numbers of juvenile P. miliaris using thes e methods. (C) 2000 Elsevier Science B.V. All rights reserved.