Local Stressors, Resilience, and Shifting Baselines on Coral Reefs

Abstract

Understanding how and why coral reefs have changed over the last twenty to thirty years is crucial for sustaining coral-reef resilience. We used a historical baseline from Kosrae, a typical small island in Micronesia, to examine changes in fish and coral assemblages since 1986. We found that natural gradients in the spatial distribution of fish and coral assemblages have become amplified, as island geography is now a stronger determinant of species abundance patterns, and habitat forming Acropora corals and large-bodied fishes that were once common on the leeward side of the island have become scarce. A proxy for fishing access best predicted the relative change in fish assemblage condition over time, and in turn, declining fish condition was the only factor correlated with declining coral condition, suggesting overfishing may have reduced ecosystem resilience. Additionally, a proxy for watershed pollution predicted modern coral assemblage condition, suggesting pollution is also reducing resilience in densely populated areas. Altogether, it appears that unsustainable fishing reduced ecosystem resilience, as fish composition has shifted to smaller species in lower trophic levels, driven by losses of large predators and herbivores. While prior literature and anecdotal reports indicate that major disturbance events have been rare in Kosrae, small localized disturbances coupled with reduced resilience may have slowly degraded reef condition through time. Improving coral-reef resilience in the face of climate change will therefore require improved understanding and management of growing artisanal fishing pressure and watershed pollution.

An applied framework to assess exploitation and guide management of coral‐reef fisheries

“…The present findings corresponded with a complimentary, fisheries‐independent study that reported predator (primarily) and large invertivore and herbivore (secondarily) losses were key drivers of shifting baselines in ecosystem condition between 1986 and 2015 in Kosrae, with declines most pronounced where access to fishing grounds was highest (McLean et al. ). Both studies suggested that similar functional components of the fishery and ecosystem were compromised, helping to identify species that contribute most toward ecosystem‐based management targets.…”

Human and environmental gradients predict catch, effort, and species composition in a large Micronesian coral-reef fishery

“…We therefore hypothesize the replacement of large-bodied species with smaller-bodied counterparts in accordance with trophic position may be more a consequence of fishing pressure and less a consequence of natural factors. In support, this same trend has been observed elsewhere in Kosrae, Micronesia [ 30 , 52 ], and on Guam [ 53 ]. In all these instances, mid-sized species that dominated landings of snappers and groupers had skewed size distributions indicating compensatory density dependence responses.…”

Seascape models reveal places to focus coastal fisheries management

“…High waves may provide a refuge from fishing pressure (Branch and Odendaal , McLean et al. ) and flush reefs and mitigate land based source pollution, thus improving habitat quality (Fabricius , ). Highly wave exposed areas also have less small‐scale structure such as from branching corals and support fewer small species, while large fishes are stronger swimmers and thus able to subsist in areas with high wave energy (Friedlander and Parrish , Friedlander et al.…”