Inducing substance for abalone larval metamorphosis from the crustose coralline alga Hydrolithon samoense

Abstract

Abalone larvae swim for several days before they metamorphose into a miniature adult organism.Crustose coralline algae (CCA) induce substratumspecific metamorphosis of abalone larvae.The metamorphosis is triggered by chemical substances, such as g -aminobutyric acid (GABA) 1 and thyroid hormones, 2 but these substances have not been found as free compounds in CCA.Morse and Morse studied settlement-inducing substances from CCA and suggested that settlement was controlled by precursors or metabolites of phycoerythrin structurally related to GABA. 3 However, the active substances in the algae remained unspecified. 4Seki et al .reported that abalone larval metamorphosis was induced by dibromomethane produced from algal surfaces. 5The chemical structure of CH 2 Br 2 is quite different from that of GABA.The present study on inducing substances in CCA focused on low-molecular weight compounds, and resulted in the isolation of d -aminovaleric acid (5-AVA) as an inducer.Larvae of two species of abalone Haliotis discus discus and Haliotis discus hannai were supplied by Shizuoka Prefectural Sea Farming Center, Shizuoka Prefectural Thermal Effluent Utilization Research Center, and Yamagata Prefectural Sea Farming Center.Three or 4 days after fertilization at 18-20 C, the veliger larvae were transported to the University of Shizuoka.Assays were performed by slight modifications of the procedure described