The importance of behavior on self-recruitment : a modelling approach

All early models of the pelagic phase of coastal organisms made the simplifying assumption that larvae could be treated as passive particles in a flow. This was justified in the early nineties because of both computational limitations and lack of knowledge about the behavioral ecology of marine larvae. However, for more than a decade now, the swimming abilities of coral reef fishes, in particular, as well as their vertical distribution, have been investigated using several methods. All agree on the tremendous swimming speeds and endurance displayed by fish larvae, on their ability to influence their vertical and horizontal distributions and on the potential impact of these factors on connectivity. Yet, no numerical model integrates this kind of behavior more extensively than for the last instants of larval life. We present two numerical models of the whole larval phase which both feature larval behavior. One explicitly integrates larval swimming in a mesoscale environment, around an island, and estimates the impact of swimming on self-recruitment. Because we still know very little about the orientation behavior of larvae in oceanic waters, we deduce their swimming decisions from an optimization method with realistic constraints and a biologically sensible objective (i.e. recruitment). Swimming along these optimal trajectories substantially enhances the possibility of self-recruitment compared to a passive scenario. The other model examines the influence of statistically modeled vertical distributions of larvae in the context of many inter-connected fish populations in the Caribbean. The distribution is shown to markedly modify the connectivity matrix. Overall, both models show that larval behavior has a great influence during the pelagic phase. Many studies show that larvae probably use their swimming abilities to reduce rather than to enhance dispersal, and our findings demonstrate that they can do so very efficiently.