9416749 Zimmer-Faust The process of recruitment of pelagic larvae into benthic habitats has been given serious attention in biological oceanography because of its role as a "bottleneck" in the population dynamics of marine organisms. In the field of larval ecology, emphasis has been given to : 1) the hydrodynamics of larval delivery to the substratum, 2) the physiological and nutritional condition of larvae, which provides information on survivorship in the field, and 3) chemical cues for larvae that dictate attachment sites in the benthic environment. Dr. Zimmer-Faust has found evidence that larvae of a commercially important species, the American Oyster, respond to a chemical in the water column that is sequestered by adults of the same species. This project will identify the chemical composition of the cue, and perform in situ evaluation of the role of this cue on larval settlement, and will distinguish the role of this water-borne cue versus the larval attraction to chemicals from surface films on substrata, which has been repeatedly documented. This project will contribute to the program's objective of making incremental steps in the understanding of the mechanisms which control the input of larval propagules into adult populations. If the role of water-borne chemical cues is indeed significant, this work could lead to the restructuring of current theory in the recruitment ecology of marine organisms.