The Micronesia Challenge: Assessing the Relative Contribution of Stressors on Coral Reefs to Facilitate Science-to-Management Feedback

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.

Local Stressors, Resilience, and Shifting Baselines on Coral Reefs

“…The environmental factors used in this analysis are well-documented drivers of fish and coral assemblage structure across Micronesia [35], including wave energy, watershed size, fishing access, and pollution. Wave energy values were generated for each site using a 10-year record of wind-speed, fetch distance, and angle of wind exposure (Quicksat wind data sets from 1999 to 2009; https://winds.jpl.nasa.gov), [35].…”

“…Wave energy values were generated for each site using a 10-year record of wind-speed, fetch distance, and angle of wind exposure (Quicksat wind data sets from 1999 to 2009; https://winds.jpl.nasa.gov), [35]. Watershed sizes (km 2 ) were measured in ArcGIS using United States Geological Survey topographic maps.…”

“…Latent variables accounted for multiple factors that together determine resilience, and were less sensitive to small localized disturbances. For instance, Micronesia reefs with high coral cover often have low diversity, while those with lower cover, following disturbances, generally have higher diversity, and both components are important indicators of resilience [35] Ecological attributes used to generate fish latent variables were fish assemblage biomass, predator biomass, biomass ratios of large-to-small bodied herbivores, Shannon-Weaver diversity, and species richness. Large herbivore species were defined as those with estimated asymptotic lengths over 40 cm, while small herbivore species were defined as those with asymptotic lengths under 40 cm.…”

“…Large herbivore species were defined as those with estimated asymptotic lengths over 40 cm, while small herbivore species were defined as those with asymptotic lengths under 40 cm. These attributes were chosen by a regional working group of scientists to represent key ecological functions [35]. The individual attributes were standardized and averaged together to generate latent variables.…”

“…As a result, scientists generally agree that reefs are in decline, but disagree on the magnitude of individual drivers of decline and how to prevent them [11,27,28]. Three prominent drivers of reef decline can be synthesized from existing literature, which many not be mutually exclusive: 1) increased disturbance frequencies from climate change [29–31], 2) pollution [32–34], and 3) fishing [15,35,36]. Identifying the relative magnitude of these potentially synergistic drivers of decline is important because previous studies have concluded that our ability to mitigate global change is negligible compared to our ability to manage local stressors [37,38].…”