Karr, Kendra; Fujita, Rod M.; Halpern, Benjamin S.; Kappel, Carrie V.; Crowder, Larry B.; Selkoe, Kimberly A.; Alcolado, Pedro M.; Rader, Douglas N. 2015. Thresholds in Caribbean coral reefs: implications for ecosystem-based fishery management. Journal of Applied Ecology. Vol: 52. Pages 402-412. (Abstract)
1. Ecosystem-based management of coral reef ï¬sheries aims to sustainably deliver a diverse portfolio of ecosystem services. This goal can be undermined if the ecosystem shifts into a different state, with altered ecosystem functions and beneï¬ts to people. If levels of drivers that cause transitions between states are identiï¬ed, management measures could be aimed at maintaining drivers below these levels to avoid ecosystem shifts. 2. Analysing data from a large number of Caribbean coral reefs (N = 2001), suites of non-linear thresholds were identiï¬ed between metrics of coral reef processes and structure along a gradient of total ï¬sh biomass (a proxy for ï¬shing pressure). Several metrics (macroalgal cover, invertivorous ï¬shes and ï¬sh species richness) associated with coral-dominated reefs exhibited thresholds at relatively high ï¬sh biomass levels (50â€“88% of unï¬shed biomass).Other metrics (urchin biomass, ratio of macroalgal to coral cover, herbivorous ï¬shes and coral cover) showed thresholds at lower ï¬sh biomass levels (28â€“37% of unï¬shed biomass).3. Ratios of total ï¬sh biomass in ï¬shing areas to closed areas (unï¬shed biomass) in the Caribbean indicate that reefs may generally be at risk for change at ratios between 0î€5 (coral dominated) and 0î€3 (macroalgal dominated). Similar relationships were found for coral reefs in the Indian Ocean. While these results illustrate thresholds at the scale of the entire Carib-bean, assessing local reefs is advisable because biomass levels vary within the region, and reef trajectories depend on past, present and future local conditions.4. Synthesis and applications. If the thresholds in this study are generalizable to scales relevant to management, it may be possible to produce sustainable yield while simultaneously maintaining coral-dominated reefs by restricting ï¬shing mortality to levels that result in bio-mass ratios near 0î€5. Fishing down to biomass ratios near 0î€ 3 may increase the risk of overfishing (resulting in lower long-term yields) and transition to macroalgal-dominated reefs.Thresholds offer a simple and powerful way for managers to operationalize precautionary ecosystem-based ï¬shery management by adaptively limiting ï¬shing pressure in order to (i)maintain desirable coral reef conditions, (ii) establish a system-speciï¬c target for generating pretty good yield and (iii) maintain sustainable multi-species ï¬shery yields.