Abstract
Fishing and pollution are chronic stressors that can prolong recovery of coral reefs and contribute to ecosystem decline. While this premise is generally accepted, management interventions are complicated because the contributions from individual stressors are difficult to distinguish. The present study examined the extent to which fishing pressure and pollution predicted progress towards the Micronesia Challenge, an international conservation strategy initiated by the political leaders of 6 nations to conserve at least 30% of marine resources by 2020. The analyses were rooted in a defined measure of coral-reef-ecosystem condition, comprised of biological metrics that described functional processes on coral reefs. We report that only 42% of the major reef habitats exceeded the ecosystem-condition threshold established by the Micronesia Challenge. Fishing pressure acting alone on outer reefs, or in combination with pollution in some lagoons, best predicted both the decline and variance in ecosystem condition. High variances among ecosystem-condition scores reflected the large gaps between the best and worst reefs, and suggested that the current scores were unlikely to remain stable through time because of low redundancy. Accounting for the presence of marine protected area (MPA) networks in statistical models did little to improve the models’ predictive capabilities, suggesting limited efficacy of MPAs when grouped together across the region. Yet, localized benefits of MPAs existed and are expected to increase over time. Sensitivity analyses suggested that (i) grazing by large herbivores, (ii) high functional diversity of herbivores, and (iii) high predator biomass were most sensitive to fishing pressure, and were required for high ecosystem-condition scores. Linking comprehensive fisheries management policies with these sensitive metrics, and targeting the management of pollution, will strengthen the Micronesia Challenge and preserve ecosystem services that coral reefs provide to societies in the face of climate change.
Highlights
Micronesia is comprised of a suite of tropical island nations that together amount to more than 3,000,000 km2 of the north Pacific Ocean, with over 6,000 km2 of coral reefs [1]
No-take marine protected areas (MPAs) varied greatly in their normalized ecosystemcondition scores, ranging from 15 to 100. These results suggested that there are clear differences in MPA effectiveness across Micronesia (Fig 3)
Because the observed fish assemblages were disproportionally weighted by herbivores (57% of the biomass, and 72% of the population densities were herbivores), these findings suggest that grazing rates and herbivore-functional diversity were (i) most sensitive to fishing pressure, and (ii) indicative of fundamental trophic interactions driven by fish assemblages on coral reefs [20,29,44]
Summary
Micronesia is comprised of a suite of tropical island nations that together amount to more than 3,000,000 km of the north Pacific Ocean, with over 6,000 km of coral reefs [1]. This region is home to island societies that have coexisted with marine resources for generations under traditional-tenure systems [2,3]. Growing influences of human-population expansion and cashbased economies have begun to erode the traditional forms of sustainable reef management. These changes have increased pressure upon marine resources [4,5]. The increased frequencies of acute disturbances, and their interaction with chronic stressors from local-pollution sources, have already changed the species composition on many reefs [16,17,18]
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