Are Caribbean coral reefs becoming flatter?

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Coral reefs support rich biodiversity partly because their complex architecture provides shelter and resources for many organisms. Hard coral cover has recently declined rapidly across the Caribbean, but the accompanying changes in reef architecture had not previously been quantified on a large scale.

The researchers conducted what they describe as the first region-wide analysis of changes in reef architectural complexity, using nearly 500 surveys across 200 reefs between 1969 and 2008. Caribbean reef complexity declined nonlinearly, and the most complex reefs nearly disappeared over the last 40 years. Flattening was apparent by the early 1980s, followed by a period of stasis from 1985 to 1998 and then a renewed decline in complexity through the end of the study period.

Loss rates were similar on shallow reefs (<6 m), mid-water reefs (6–20 m), and deep reefs (>20 m), and consistent across all five subregions. The timing of the decline coincided with the loss of structurally complex Acropora corals, mass mortality of the grazing urchin Diadema antillarum, and the 1998 worldwide coral bleaching event induced by the El Niño Southern Oscillation.

Consistently low estimates of current architectural complexity suggest region-wide degradation and homogenization of reef structure. The researchers say the widespread loss of complexity is likely to have serious consequences for reef biodiversity, ecosystem functioning, and associated environmental services.