All organisms use chemicals to assess their environment and to communicate with others. Chemical cues for defense, mating, habitat selection, and food tracking are crucial, widespread, and structurally and functionally diverse. Yet our knowledge of chemical signaling is patchy, especially in marine environments. In our research we ask, "How do marine organisms use chemicals to solve critical problems of competition, disease, predation, and reproduction?" Our group uses an integrated approach to understand how chemical cues function in ecological interactions, working from molecular to community levels. We also use ecological insights to guide discovery of novel pharmaceuticals and molecular probes. In collaboration with other scientists, our most significant scientific achievements to date are: 1) characterizing the unusual molecular structures of antimicrobial defenses that protect algae from pathogens and which show promise to treat human disease; 2) understanding that competition among single-celled algae (phytoplankton) is mediated by a complex interplay of chemical cues that affect harmful algal bloom dynamics; 3) unraveling the molecular modes of action of antimalarial natural products towards developing new treatments for drug-resistant infectious disease; 4) discovering that progesterone signaling and quorum sensing are key pathways in the alternating sexual and asexual reproductive strategy of microscopic invertebrate rotifers - animals whose evolutionary history was previously thought to preclude either cooperative behavior (quorum sensing) typically associated with bacteria and hormonal regulation via progesterone typically seen in vertebrates; 5) identifying a novel aversivechemoreception pathway in predatory fish thatresults inrapid recognition and rejectionofchemically defended foods, thereby protecting these foods (prey) from predators. Ongoing projects include: 1) Waterborne chemical cues in the marine plankton: a systems biology approach (including metabolomics); 2) Exploration, conservation, and development of marine biodiversity in Fiji and the Solomon Islands (including drug discovery, mechanisms of action, and chemical ecology); 3) The role of sensory environment and predator chemical signal properties in determining non-consumptive effect strength in cascading interactions on oyster reefs; 4) Regulation of red tide toxicity by chemical cues from marine zooplankton; 5) Chemoreception of prey chemical defenses on tropical coral reefs.