Twenty years of change in benthic communities across the Belizean Barrier Reef

Abstract

Disease, ocean warming, and pollution have caused catastrophic declines in the cover of living coral on reefs across the Caribbean. Subsequently, reef-building corals have been replaced by invertebrates and macroalgae, leading to changes in ecological functioning. We describe changes in benthic community composition and cover at 15 sites across the Belizean Barrier Reef (BBR) following numerous major disturbances--bleaching, storms, and disease outbreaks--over the 20-year period 1997-2016. We tested the role of potential drivers of change on coral reefs, including local human impacts and ocean temperature. From 1997 to 2016, mean coral cover significantly declined from 26.3% to 10.7%, while macroalgal cover significantly increased from 12.9% to 39.7%. We documented a significant decline over time of the reef-building corals Orbicella spp. and described a major shift in benthic composition between early sampling years (1997-2005) and later years (2009-2016). The covers of hard-coral taxa, including Acropora spp., M. cavernosa, Orbicella spp., and Porites spp., were negatively related to marine heatwave frequency. Only gorgonian cover was related, negatively, to our metric of the magnitude of local impacts (the Human Influence Index). Changes in benthic composition and cover were not associated with local protection or fishing. This result is concordant with studies throughout the Caribbean that have documented living coral decline and shifts in reef-community composition following disturbances, regardless of local fisheries restrictions. Our results suggest that benthic communities along the BBR have experienced disturbances that are beyond the capacity of the current management structure to mitigate. We recommend that managers devote greater resources and capacity to enforce and expand existing marine protected areas and that government, industry, and the public act to reduce global carbon emissions.