Ecological Determinants of Larval Connectivity: Linking Genetic Data to Ecological Processes

Population connectivity in the marine environment has different meanings and implications depending on whether the context is primarily ecological or evolutionary. From an ecological perspective the focus is typically on the exchange of individuals among geographically separated subpopulations – encompassing the dispersal phase from reproduction to the completion of the settlement process (including habitat choice and metamorphosis). Such life history events have a strong influence on processes such as population dynamics and recruitment, coupling of ecosystem processes and the nature and rate of response to environmental perturbations. The key in such ecological aspects of connectivity is the importance of within and between generational events across short time-scales on distribution, recruitment and persistence. Genetic estimates that relate in some way to gene flow derive from processes across a fundamentally different time-scale: it is the mean rate of exchange and interbreeding across many generations that drives patterns of population genetic differentiation. Even rare and sporadic gene flow can have a disproportionate impact on genetic differentiation, events that are often difficult to track or detect in real time, especially in the marine environment.  Moreover, our ability to generate ecologically meaningful predictions of population connectivity derived from essentially oceanographic modelling with its inherent local, regional and global stochasticity present a formidable challenge: integrating the ecological and evolutionary perspectives requires careful estimation of the spatial and temporal scale of events at the demographic and genetic levels. Coincident with the requirement to capture processes at different scales is the diversity of tools available for assessing connectivity, including among others, oceanography, genetics and otoliths. Here, we illustrate challenges and insights by exploring briefly the relationship between the methodologies for assessing larval connectivity and the range of spatial and temporal scales pertinent to ecological and evolutionary events, with reference to projected patterns of larval dispersal, retention, recruitment and mortality.