9529730 MORSE The goal of the research is to determine whether molecular signals and mechanisms similar to those that control larval settlement, metamorphosis and recruitment of the Agariciid corals also regulate these centrally important processes in Acropora palmata, one of the most ecologically important, abundant and rapidly growing major reef-building corals of the Caribbean. This question is of major ecological significance because A. palmata is representative of the most specious genus of corals on Earth, and is representative of the ecologically dominant corals that reproduce by synchronous mass spawning to yield larvae that lack endosymbiotic algae (zooxanthellae). The corals in which signal-dependent induction of larval settlement and recruitment previously had been demonstrated (the Agariciid corals) reproduce by brooding and release of mature larvae that already contain endosymbiotic zooxanthellae, and these corals often play relatively minor ecological roles in the natural environment. Following up on recent research leads, the specific objectives of the proposed renewal are to test the following specific hypotheses: (1) That specific crustose coralline algae are required to induce larval settlement and metamorphosis of the mass-spawning A. palmata; (2) That chemosensory recognition mediates larval responsiveness to any such required substratum; (3) That the molecular inducer of settlement and metamorphosis recognized by A. palmata larvae is an algal (or microbial) cell- wall compound identical or closely similar to that which controls larval settlement, metamorphosis and recruitment of the sympatric Agariciids; (4) That larval recognition of this inducer molecule (purified and immobilized on a "larval flypaper") can be shown to be responsible, in part, for substratum-specific settlement, metamorphosis and recruitment of A. palmata in the natural environment; and (5) That species-specific differences in larval orientation at settlement reduce the potential for competition between Acropora palmata and Agaricia humilis. ***
