Synthesis of Local Demography and Regional Connectivity in a Marine Fish Metapopulation

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Most larger marine species, including most bottom-oriented invertebrates and fishes, have a two-stage life history, in which adults spawn larvae that disperse in ocean currents to new locations. Species that live on or near the seafloor are thus distributed in metapopulations, which are groups of spatially isolated adult populations linked by larval dispersal. Insight on the dynamics of marine metapopulations requires knowledge of spatial and temporal patterns of and linkages among: (1) the degree of larval connectivity among local populations, (2) the extent of self-recruitment of larvae back to their natal populations, (3) the physiological condition of recruiting larvae, (4) the relative demographic rates (including recruitment [= birth], growth, reproductive output, and death) of local populations, (5) sources of direct density dependence, whereby the per capita birth rate decreases and/or the death rate increases as population size increases, (6) the level of synchrony of variation in abundance among local populations, and (7) the environments of local populations, including predators, competitors, and habitat structure. This project will investigate these phenomena for the bicolor damselfish, Stegastes partitus, in the Exuma Sound, Bahamas. This system has been the subject of numerous relevant studies. The project spans 3 years (a full generation of the study species), and includes five core study islands separated by up to 200km, and peripheral collection sites separated on the scale of 1000km. Five central questions that focus on both pattern and process relative to metapopulation dynamics will be addressed: (1) What is the spatial boundary of the metapopulation that includes Exuma Sound? (2) What are the levels of self-recruitment within each local population and the patterns of larval connectivity among local populations? (3) How synchronous are population dynamics and demographic rates among local populations? (4) What are the relationships among local populations between larval connectivity and demographic rates, including any patterns of density dependence? (5) How are differences in demographic rates among local populations related to the physiological condition of settling larvae, predator abundance, competitor abundance, and habitat structure? These questions will be addressed using microsatellite-based genetic assignment methods to measure larval connectivity and self-recruitment (assignment tests, clustering methods, and parentage analysis); combined field and laboratory analyses of the condition of new settlers and the demographic consequences of differential condition; demographic monitoring to measure local recruitment, growth, survival, and reproductive output; ecological measures of local resident and transient predator abundance, interference competitor density, and reef structure; and matrix population modeling to link these factors into a coherent and predictive framework to understand the key factors that affect, drive, and regulate population dynamics at both local and metapopulation scales. Intellectual Merit: Understanding the dynamics of metapopulations is important to (1) fisheries biology and management because it provides detailed information regarding spatially explicit dynamics and sustainability of fish stocks, (2) prevent marine extinctions because it provides knowledge of the mechanisms whereby locally extinct populations can be re-established by viable local populations of the same species, and (3) marine conservation in general because it provides information on the ecological mechanisms whereby networks of marine protected areas may be effective.Education and outreach: This project will fund the PhD research of 4 graduate students, and involve at least 12 undergraduates. Participation in this project will promote education in marine ecology and conservation biology directly via the PI's and graduate students' teaching activities, and indirectly via the experiences of undergraduate field assistants.