Human harvesting impacts on managed areas: ecological effects of socially-compatible shellfish reserves

A common assumption is that ecosystem services respond linearly to changes in habitat size. This assumption leads frequently to an "all or none" choice of either preserving coastal habitats or converting them to human use. However, our survey of wave attenuation data from field studies of mangroves, salt marshes, seagrass beds, nearshore coral reefs, and sand dunes reveals that these relationships are rarely linear. By incorporating nonlinear wave attenuation in estimating coastal protection values of mangroves in Thailand, we show that the optimal land use option may instead be the integration of development and conservation consistent with ecosystem-based management goals. This result suggests that reconciling competing demands on coastal habitats should not always result in stark preservation-versus-conversion choices.

Marine protected areas (MPAs) have been widely adopted as the leading tool for coral-reef conservation, but resource users seldom accept them , and many have failed to produce tangible conservation benefits [3]. Few studies have objectively and simultaneously examined the types of MPAs that are most effective in conserving reef resources and the socioeconomic factors responsible for effective conservation [4-6]. We simultaneously explored measures of reef and socioeconomic conservation success at four national parks, four comanaged reserves, and three traditionally managed areas in Indonesia and Papua New Guinea. Underwater visual censuses of key ecological indicators [7, 8] revealed that the average size and biomass of fishes were higher in all areas under traditional management and at one comanaged reserve when compared to nearby unmanaged areas. Socioeconomic assessments [6, 9, 10] revealed that this "effective conservation" was positively related to compliance, visibility of the reserve, and length of time the management had been in place but negatively related to market integration, wealth, and village population size. We suggest that in cases where the resources for enforcement are lacking, management regimes that are designed to meet community goals can achieve greater compliance and subsequent conservation success than regimes designed primarily for biodiversity conservation.