Management and conservation of the kelp species Laminaria digitata: using genetic tools to explore the potential exporting role of the MPA Parc naturel marin d'Iroise

Marine protected areas (MPAs) have been depicted as a useful tool for improving fishery management and protecting biodiversity. For example, by acting as source populations, MPAs may provide a spillover of adults/propagules, enhancing recruitment to surrounding, non-protected waters. However, such positive effect will depend on how a MPAs design matches population biology and dispersal abilities of the target species. High levels of intraspecific genetic diversity without pronounced structure have been found in many marine organisms over large spatial scales (from hundreds to thousands kilometres) but do not hold for other ecologically and economically important species such as coral reef fishes, seagrasses and kelps. In particular, the limited potential for dispersal of many macroalgae suggests the occurrence of self-sustaining, closed populations that contrast with the open populations of many fishes and invertebrates. Consequently, the high resilience of fish/invertebrate populations cannot be generalized to the whole marine realm. In the present work, we use genetic tools to explore the role of the MPA Parc naturel marin d'Iroise in the management of the emblematic kelp Laminaria digitata. While kelps have received much more scientific attention than any other seaweed group, there is still critical baseline knowledge which needs to be addressed for their effective management. Our genetic survey of 12 L. digitata populations along the Brittany coast, four of them located within the boundaries of the Parc naturel marin d'Iroise, allowed us to assess the conservation value of these kelp populations. In particular, classical genetic metrics as well as more recent clustering approaches were used to identify and characterize Management Units. Moreover, assignment tests were employed to determine contemporary migration events and source/sink populations. Our results show that populations within this MPA have high conservation value. However, we also identify other populations of conservation interest.