Fishing down a Caribbean food web relaxes trophic cascades

A rapid shift in fish community structure on the Belize Barrier Reef, driven by intense fishing pressure, has relaxed trophic cascades and threatened reef resilience. Over six to seven years (2002-2008/09), large-bodied grouper and carnivorous snapper populations plummeted—grouper encounter probability dropped from 21% to just 2%, while snapper biomass declined sevenfold, primarily in the species Ocyurus chrysurus. Concurrently, parrotfish, particularly the dominant herbivore Sparisoma viride, saw a 41% biomass reduction, with their inclusion in catches rising from 6% to 20%. This fishing pressure led to a dramatic 880% increase in mesopredators like Cephalopholis spp., likely due to reduced predation and foraging constraints imposed by large serranids. Additionally, damselfish densities (Stegastes planifrons and S. partitus) decreased by ~45%, attributed to elevated predation from mesopredators. No such changes were observed in nearby marine reserves. The decline in parrotfish likely contributed to the spread of Halimeda tuna into previously grazed microhabitats, suggesting impaired reef resilience. However, recent Belizean legislation aims to address these issues by improving grouper management and banning the harvesting of most herbivorous fish.

Mumby, P., Steneck, R., Edwards, A., Ferrari, R., Coleman, R., Harborne, A., & Gibson, J. (2012). Fishing down a Caribbean food web relaxes trophic cascades. Marine Ecology Progress Series, 445, 13–24. https://doi.org/10.3354/meps09450