Development of a reef fish biological condition gradient model with quantitative decision rules for the protection and restoration of coral reef ecosystems.

Coral reef ecosystems are declining due to multiple interacting stressors. A bioassessment framework focused on stressor-response associations was developed to help organize and communicate complex ecological information to support coral reef conservation. This study applied the Biological Condition Gradient (BCG), initially developed for freshwater ecosystems, to fish assemblages of U.S. Caribbean coral reef ecosystems. The reef fish BCG describes how biological conditions changed incrementally along a gradient of increasing anthropogenic stress. Coupled with physical and chemical water quality data, the BGC forms a scientifically defensible basis to prioritize, protect and restore water bodies containing coral reefs. Through an iterative process, scientists from across the U.S. Caribbean used fishery-independent survey data and expert knowledge to develop quantitative decision rules to describe six levels of coral reef ecosystem condition. The resultant reef fish BCG provides an effective tool for identifying healthy and degraded coral reef ecosystems and has potential for global application.

Recovery when you are on your own: Slow population responses in an isolated marine reserve.

Geographic isolation is an important yet underappreciated factor affecting marine reserve performance. Isolation, in combination with other factors, may preclude recruit subsidies, thus slowing recovery when base populations are small and causing a mismatch between performance and stakeholder expectations. Mona Island is a small, oceanic island located within a partial biogeographic barrier-44 km from the Puerto Rico shelf. We investigated if Mona Island's no-take zone (MNTZ), the largest in the U.S. Caribbean, was successful in increasing mean size and density of a suite of snapper and grouper species 14 years after designation. The La Parguera Natural Reserve (LPNR) was chosen for evaluation of temporal trends at a fished location. Despite indications of fishing within the no-take area, a reserve effect at Mona Island was evidenced from increasing mean sizes and densities of some taxa and mean total density 36% greater relative to 2005. However, the largest predatory species remained rare at Mona, preventing meaningful analysis of population trends. In the LPNR, most commercial species (e.g., Lutjanus synagris, Lutjanus apodus, Lutjanus mahogoni) did not change significantly in biomass or abundance, but some (Ocyurus chrysurus, Lachnolaimus maximus), increased in abundance owing to strong recent recruitment. This study documents slow recovery in the MNTZ that is limited to smaller sized species, highlighting both the need for better compliance and the substantial recovery time required by commercially valuable, coral reef fishes in isolated marine reserves.

Effective Dispersal of Caribbean Reef Fish is Smaller than Current Spacing Among Marine Protected Areas.

The oceans are deteriorating at a fast pace. Conservation measures, such as Marine Protected Areas, are being implemented to relieve areas from local stressors and allow populations to restore to natural levels. Successful networks of MPAs operate if the space among MPAs is smaller than the dispersal capacity of the species under protection. We studied connectivity patterns across populations in a series of MPAs in the common yellowhead Jawfish, Opistognathus aurifrons. Using the power of genome-wide variation, we estimated that the maximum effective dispersal is 8.3 km. We found that MPAs exchange migrants likely via intermediate unprotected habitats through stepping stone dispersal. At scales >50 km such connectivity is decreased, particularly across the Mona Passage. The MPA network studied would be unable to maintain connectivity of these small benthic fishes if habitat in between them is extirpated. Our study highlights the power of SNPs to derive effective dispersal distance and the ability of SNPs to make inferences from single individuals. Given that overall reef fish diversity is driven by species with life histories similar to that of the yellowhead jawfish, managers face a challenge to develop strategies that allow connectivity and avoid isolation of populations and their possible extinction.

Recent region-wide declines in Caribbean reef fish abundance.

Profound ecological changes are occurring on coral reefs throughout the tropics, with marked coral cover losses and concomitant algal increases, particularly in the Caribbean region. Historical declines in the abundance of large Caribbean reef fishes likely reflect centuries of overexploitation. However, effects of drastic recent degradation of reef habitats on reef fish assemblages have yet to be established. By using meta-analysis, we analyzed time series of reef fish density obtained from 48 studies that include 318 reefs across the Caribbean and span the time period 1955-2007. Our analyses show that overall reef fish density has been declining significantly for more than a decade, at rates that are consistent across all subregions of the Caribbean basin (2.7% to 6.0% loss per year) and in three of six trophic groups. Changes in fish density over the past half-century are modest relative to concurrent changes in benthic cover on Caribbean reefs. However, the recent significant decline in overall fish abundance and its consistency across several trophic groups and among both fished and nonfished species indicate that Caribbean fishes have begun to respond negatively to habitat degradation.