Diverse patterns of larval coral reef fish vertical distribution and consequences for dispersal and connectivity

Many populations rely on dispersal as a critical life history event, from seed dispersal in plants to migration behaviors in birds, insects, and fishes. Species traits alter dispersal propensity and distance, and these in turn influence fitness. Vertical distribution behaviors, as have been observed in many taxa of fish larvae, are assumed to influence planktonic transport. Particular attention has been paid to the potential adaptive benefit of increased retention near the parental population due to ontogenetic vertical migration (OVM), in which larvae move deeper with age. By combining a large observational dataset with individual-based modeling, we investigated the prevalence of OVM compared to other behaviors, and the effects of different vertical behaviors on dispersal and connectivity. We analyzed two years of monthly field observations of larval vertical distribution behaviors for 23 taxa of coral reef fish, with resolution across larval ontogeny. We found a diversity of behaviors both within and among coral reef fish families, with three prevalent patterns: surface dwelling, ontogenetic vertical migration (OVM), and wide vertical spread. Using generalized versions of these three behaviors, we modeled larval dispersal throughout the Caribbean Sea over 5 years, for two pelagic larval durations (PLDs) that are typical of coral reef fishes. Models of surface-dwelling behavior generally led to more long-distance dispersal, lower local retention, and higher population connectivity than the uniformly-distributed and OVM behaviors. These latter two behaviors with deeper distributions during all or part of the larval stage had similar outcomes for dispersal, connectivity, and local retention. Similar impacts of behavior on dispersal, connectivity, and retention were observed under both short and long PLD. We also found that the effects of vertical behavior on larval dispersal were stronger than the effects of seasonal or interannual variation in currents. Our results suggest that there are other advantages beyond higher local retention that contribute to the selection of a complex behavior such as OVM—these may include predator avoidance, temperature-driven metabolic changes, and directional swimming.