Summary1. Ecosystem-based management of coral reef fisheries 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 benefits to people. If levels of drivers that cause transitions between states are identified, 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 nonlinear thresholds were identified between metrics of coral reef processes and structure along a gradient of total fish biomass (a proxy for fishing pressure). Several metrics (macroalgal cover, invertivorous fishes and fish species richness) associated with coral-dominated reefs exhibited thresholds at relatively high fish biomass levels (50-88% of unfished biomass). Other metrics (urchin biomass, ratio of macroalgal to coral cover, herbivorous fishes and coral cover) showed thresholds at lower fish biomass levels (28-37% of unfished biomass). 3. Ratios of total fish biomass in fishing areas to closed areas (unfished biomass) in the Caribbean indicate that reefs may generally be at risk for change at ratios between 0Á5 (coral dominated) and 0Á3 (macroalgal dominated). Similar relationships were found for coral reefs in the Indian Ocean. While these results illustrate thresholds at the scale of the entire Caribbean, 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 fishing mortality to levels that result in biomass ratios near 0Á5. Fishing down to biomass ratios near 0Á3 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 fishery management by adaptively limiting fishing pressure in order to (i) maintain desirable coral reef conditions, (ii) establish a system-specific target for generating pretty good yield and (iii) maintain sustainable multi-species fishery yields.

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En octubre del 2002 se estudiaron las comunidades de esponjas en cuatro localidades del arrecife de la costa este de Bahía de Cochinos, Cuba. En cada localidad se establecieron sitios de muestreo de esponjas en las zonas ecológicas de cabezos coralinos (3 m), terraza somera (6-10 m) y terraza profunda (15 m). Se utilizó el método de transecto lineal de 10 m como unidad de muestreo para medir el cubrimiento del fondo y el marco cuadrado de 1 m para estimar la densidad de la comunidad. Los índices de heterogeneidad y de riqueza de especies mostraron variabilidad entre sitios y cierta tendencia a incrementarse con la profundidad. Se encontraron 30 especies pertenecientes a 19 familias y 21 géneros. Las especies más comunes fueron Mycale laevis, Aplysina cauliformis, Cliona aprica, Aplysina fistularis y Ectyoplasia ferox, las cuales conformaron el 48% del total de individuos identificados. La densidad fue moderada (2-8 ejemplares/m2) y se encontró variación entre sitios. La estación más cercana a mar abierto mostró un valor inferior, posiblemente por ser la más dañada tras el paso del huracán en el 2001. El estado general de la comunidad fue bueno, según los valores de diversidad alcanzados y las especies predominantes, aunque se muestran evidencias de afectaciones recientes producto de un huracán.The sponge communities at four locations on the east coast of Bahía de Cochinos were surveyed in October 2002. At each location, sampling sites were established in the ecological zones of patch reef (3 m), shallow terrace (6-10 m), and deep terrace (15 m). The line-transect method with a 10 m line as sampling unit was used to measure sponge bottom coverage, and a 1 m square grid was used to quantify sponge community density. Species heterogeneity and species richness indices showed variability among sites and tended to increase with depth. Thirty species belonging to 19 families and 21 genera were found. The most common species were Mycale laevis, Aplysina cauliformis, Cliona aprica, Aplysina fistularis, and Ectyoplasia ferox, which comprised 48% of the total individuals identified. Sponge density was moderate (2-8 specimens/m2) and showed variation among sites. The nearest station to open sea showed a lower density value, possibly due to disturbance from the passage of a hurricane in 2001. The general condition of the community was good, based on the diversity values reached and the predominant species, although evidence of impacts from recent hurricane were observed.

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