Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands

The effectiveness of Marine Protected Areas (MPA) to manage natural resources has been undermined in small insular lagoons due to massive mortalities triggered by climatic events that have hit some lagoons but not others. To minimize the future risk of ineffective management efforts, it has previously been argued that management should focus on a multi-island conservation target (regional scale), rather than on individual lagoons (local scale). However, it is unclear how a MPA network designed to meet objectives at a regional scale would impact on the management of resources at the local scale. In particular, it is necessary to understand if a regional plan might incidentally maintain conservation objectives at the local scale, without disproportionately affecting, or relying on particular islands. This study used the population of the giant clam (Tridacna maxima) in a fishery context to explore the distributions of conservation features and socio-economic costs for regional networks (computed within a set of islands), compared to individual islands. Designing a MPA network at regional scale led to unbalanced representation of conservation features among atolls and incidentally missed the targeted level of protection for conservation features at local scale. Moreover, the regional network generated inequitable costs for fishermen between islands, which is likely to lead to poor perceived equity. This study suggests that perceived equity and the representation of local conservation objectives will be major factors to consider, if the French Polynesian authorities follow the path of implementing MPAs in each atoll for a regional-scale resource management plan.