Coral reefs have tremendous environmental, economic, and cultural value but are in dramatic global decline. Over the last 4 decades, coral cover on Caribbean reefs has declined by ~80% and on Pacific reefs by more than 50%. Declines are being driven by a host of anthropogenic stresses including global change, overfishing, pollution, and disease spread, but all of these stresses generally result in losses of corals, increases in seaweeds, and then a loss of reef resilience as seaweeds dominate and suppress corals. In recent years, it has become increasingly clear that seaweed impacts on coral microbiomes may play a large role in coral declines and lack of recovery. Although these unseen microbes may be critical players on coral reefs, too little is known of their dynamics and ecological function. This results in part from the difficulty of studying complex microbial communities (coral microbiomes) in ecologically meaningful field settings. This project involves an interdisciplinary investigation that may overcome several of these limitations and allow an ecologically realistic assessment of the dynamics, chemical interactions, and ecological function of coral microbiomes in a natural reef community. The proposed work integrates techniques and theory from the fields of community ecology, chemical ecology, and molecular microbiology and genomics, and involves a collaboration between the labs of Mark Hay and Frank Stewart.