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) (Online version)
1. Ecosystem-based management of coral reef Ã¯Â¬Âsheries 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 beneÃ¯Â¬Âts to people. If levels of drivers that cause transitions between states are identiÃ¯Â¬Âed, 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 identiÃ¯Â¬Âed between metrics of coral reef processes and structure along a gradient of total Ã¯Â¬Âsh biomass (a proxy for Ã¯Â¬Âshing pressure). Several metrics (macroalgal cover, invertivorous Ã¯Â¬Âshes and Ã¯Â¬Âsh species richness) associated with coral-dominated reefs exhibited thresholds at relatively high Ã¯Â¬Âsh biomass levels (50Ã¢Â€Â“88% of unÃ¯Â¬Âshed biomass).Other metrics (urchin biomass, ratio of macroalgal to coral cover, herbivorous Ã¯Â¬Âshes and coral cover) showed thresholds at lower Ã¯Â¬Âsh biomass levels (28Ã¢Â€Â“37% of unÃ¯Â¬Âshed biomass).3. Ratios of total Ã¯Â¬Âsh biomass in Ã¯Â¬Âshing areas to closed areas (unÃ¯Â¬Âshed biomass) in the Caribbean indicate that reefs may generally be at risk for change at ratios between 0Ã®Â€Â5 (coral dominated) and 0Ã®Â€Â3 (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 Ã¯Â¬Âshing mortality to levels that result in bio-mass ratios near 0Ã®Â€Â5. Fishing down to biomass ratios near 0Ã®Â€Â 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 Ã¯Â¬Âshery management by adaptively limiting Ã¯Â¬Âshing pressure in order to (i)maintain desirable coral reef conditions, (ii) establish a system-speciÃ¯Â¬Âc target for generating pretty good yield and (iii) maintain sustainable multi-species Ã¯Â¬Âshery yields.