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.

The consistent supply of fresh fish to commercial markets may mask growing fishing footprints and localized depletions, as fishing expands to deeper/further reefs, smaller fish, and more resilient species. To test this hypothesis, species-based records and fisher interviews were gathered over one year within a large, demand-driven coral-reef fishery in Chuuk, Micronesia. We first assessed catch statistics with respect to high windspeeds and moon phases that are known to constrain both catch and effort. While lower daily catch success was predicted by higher windspeeds and greater lunar illumination, total daily landings fluctuated less than fishing success across environmental gradients. Instead, daily landings were mainly driven by the number of flights from Chuuk to Guam (i.e., international demand). Given that demand masked local drivers of overall catch volume, we further evaluated species-based indicators of fisheries exploitation. Most target species (75%) had either a positively skewed size distribution or proportional contributions that were dependent upon favorable conditions (i.e. season and moon phases). Skewed size distributions indicated truncated growth associated with fishing mortality, and in turn, suggested that size-based management policies may be most effective for these species. In contrast, environmentally-constrained catch success indicated species that may be more susceptible to growing fishing footprints and may respond better to gear/quota/area policies compared to size policies. Species-based responses offered a simplified means to combine species into fisheries management units. Finally, a comparison of commercial and subsistence landings showed higher vulnerability to fishing among species preferentially targeted by commercial fisheries, offering new insights into how commercial harvesting can disproportionately impact resources, despite having lower annual catch volumes.

Escalating climate impacts on coral reefs are increasingly expanding management goals beyond preserving biodiversity to also maintaining ecosystem functions. Morphological and ecological species traits can help assess changes within reef communities beyond taxonomic identities alone. However, our limited understanding of trait interactions between habitat-building corals and associated reef fishes and whether they are captured by current monitoring practices hampers management. Here, we apply co-inertia analyses to test whether trait assemblages in corals and fishes co-vary across different habitats and test whether different components of the reef fish community (fisheries vs. non-target species) display distinct relationships. We find that spatial co-variation across habitat types between coral and fish traits is strengthened by the addition of non-target fishes. Additionally, even in fisheries with diverse targets, non-target species make unique contributions to the overall trait structure and highlight the importance of considering monitoring protocols when drawing conclusions about traits and ecosystems.

Article impact statement: Groups of species that share similar traits respond differentially to fishing pressure, which can be used to structure management actions.