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.