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Linking basin-scale connectivity, oceanography and population dynamics for the conservation and management of marine ecosystems

Dubois, M.; Rossi, V.; Ser-Giacomi, E.; Arnaud-Haond, S.; Lopez, C.; Hernandez-Garcia, E.
Global Ecology and Biogeography 25, 503-515 (2016)

Aim: Assessing the spatial structure and dynamics of marine populations is still a major challenge in ecology. The necessity to manage marine resources from ecosystem and large-scale perspectives is recognized but our partial understanding of oceanic connectivity limits the implementation of globally pertinent conservation planning. Based on a biophysical model for the entire Mediterranean Sea, this study takes an ecosystem-approach to connectivity and provides a systematic characterization of broad-scale larval dispersal patterns. It builds on our knowledge of population dynamics and discusses its ecological and management implications. Location: The semi-enclosed Mediterranean Sea and its marine ecosystems are used as a case study to investigate broad-scale connectivity patterns and to relate them to oceanography and population dynamics. Methods: A flow network is constructed by evenly subdividing the basin into subregions which are interconnected through the transport of larvae by ocean currents. It allows for the computation of various connectivity metrics required to evaluate larval retention and exchange. Results: Our basin-scale model predicts that retention processes are weak in the open ocean while they are signficant in the coastal ocean and are favored along certain coastlines due to specific oceanographic functioning. Moreover, we show that wind-driven divergent (convergent, respectively) oceanic regions are systematically characterized by larval sources (sinks, respectively). Finally, although these connectivity metrics were often studied separately in the literature, we demonstrate they are inter-related under particular conditions. Their integrated analyses facilitate the appraisal of population dynamics, informing both genetic and demographic connectivities. Main conclusions: This modelling framework helps ecologists and geneticists to formulate improved hypotheses of population structures and gene flow patterns and to design their sampling strategy accordingly. It is also useful in the implementation and assessment of future protection strategies such as coastal and off-shore marine reserves considering large-scale dispersal patterns, a missing component of current ecosystem management.