Connectivity between island Marine Protected Areas and the mainland

In addition to protecting important species or ecosystems, ideally Marine Protected Areas (MPAs) should also act as propagule sources and be located where they can receive larval influxes so as to buffer species against local extinctions and allow genetic mixing. There are many examples of island MPAs across the world because of their advantages compared to mainland sites, and although evidence suggests they effectively protect biodiversity and may have localized fisheries benefits, their contribution to larval export and connectivity to mainland areas remains largely unknown; these are important aspects of MPA sustainability and functioning. Here I examined the genetic differentiation between four island MPAs in northern Europe and their respective mainlands, relative to differentiation of populations along the coast at similar spatial scales for two marine invertebrates (Semibalanus balanoides, planktonic larvae; Nucella lapillus, direct development). These data were used to infer past patterns of larval exchange between populations. Gene flow was restricted at all four locations between the islands and the mainland, compared to gene flow along the coast (for both species) and more distant islands had greater differentiation than those closer to the mainland for S. balanoides, but not for N. lapillus. My results of genetic analysis suggest that island MPAs may not provide as much larval export or receive as much buffering against local extinctions, compared with mainland populations (for a similar sized protected area). My findings are especially relevant to the creation of MPA networks and in understanding the importance of connectivity in achieving the greatest fisheries benefits and in ensuring inter-MPA linkages. Low levels of larval exchange may limit the success of any protected area and may prevent multiple conservation objectives from being achieved.