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Connectivity is currently emphasized as a key factor in conservation for its role in enhancing biodiversity of an area and giving benefit to the adjacent areas. For most marine species, connectivity is synonomous of larval dispersal. We applied a spatially explicit meta-population model to test the hypothesis that larval dispersal can affect local demographical features, consequently misleading conservation practice in the marine environment. Simulations were carried out in the Gulf of Lions where coastal circulation displays highly variable temporal and spatial submeso-scale structures. Two different benthic invertebrate species were considered: a soft bottom short lived species and a hard bottom long lived one. In the first case, simulations showed that highest densities at equilibrium do not inform on self-persistent populations location. In the second case, simulations showed that connectivity effects may result in out-of-equilibria demographical structure. We emphasized the caveats in the parameterization of demographical models when local demography is controlled by connectivity.

Abstract: Climate‐induced threats are increasingly affecting marine populations worldwide. In the last few decades, several gorgonian species have been affected by mass mortality events in the north‐west Mediterranean, putatively linked to local sea temperature increases during heatwaves. For many benthic sessile species, recovery after disturbances depends upon larval supply shaping the connections among populations. In the Ligurian Sea, genetic analyses showed that some Paramuricea clavata populations recovered after mass mortality events; however, the patterns of connectivity, and the potential role of migration in supporting the recovery of the populations of P. clavata, across its distribution range within the Ligurian Sea are still unknown. In this study, the population genetic structure and migration patterns of P. clavata populations have been analysed across seven sites in the Ligurian Sea, some of which have been affected by mass mortality events. Evidence of a population bottleneck was found in most of the populations studied. Significant genetic differentiation was found among P. clavata populations, reflecting habitat fragmentation at a regional scale, except for two populations found 20 km apart. Continuing gene flow between distant populations was also revealed. Empirical data suggest that gene flow among populations may have contributed to support their recovery from mass mortality events. The study identified populations in the central part of the Ligurian Sea that can be strategic for the regional persistence of the species. These findings highlight that the preservation of key populations could maintain connectivity and gene flow in the metapopulation, and increase the resilience of the species. [ABSTRACT FROM AUTHOR]

Accounting for connectivity is essential in marine spatial planning and the proper design and management of marine protected areas, given that their effectiveness depends on the patterns of dispersal and colonization between protected and non-protected areas. The genetic structure of populations is commonly used to infer connectivity among distant populations. Here, we explore how population genetic structure is affected by pre- and settlement limitations with a spatially explicit coupled metapopulation-gene flow model that simulates the effect of demographic fluctuations on the allele frequencies of a set of populations. We show that in closed populations, regardless of population growth rate, the maintenance of genetic diversity at saturating initial population density increases with species life expectancy as a result of density-dependent recruitment control. Correlatively, at low initial population density, the time at which a population begins to lose its genetic diversity is driven larval and post-settlement mortality (comprised in the recruitment success parameter) —the larger the recruitment success, the stronger the genetic drift. Different spatial structures of connectivity established for soft bottom benthic invertebrates in the Gulf of Lions (NW Mediterranean, France) lead to very different results in the spatial patterns of genetic structuration of the metapopulation, with high genetic drift in sites where the local retention rate was larger than 2%. The effect of recruitment failure and the loss of key source populations on heterozygosity confirm that transient demographic fluctuations help maintain genetic diversity in a metapopulation. This study highlights the role of intraspecific settlement limitations due to lack of space when the effective number of breeders approaches saturating capacity, causing a strong reduction in effective reproduction. The present model allows to: (i) disentangle the relative contribution of local demography and environmental connectivity in shaping seascape genetics, and (ii) perform in silico evaluations of different scenarios for marine spatial planning. [ABSTRACT FROM AUTHOR]