Bellwood et al., 2004:

"Coral reefs, by definition, are three-dimensional shallow-water structures dominated by scleractinian corals. In the absence of severe human impacts, reefs readily reassemble after routine disturbances such as tropical hurricanes¹⁴. However, many contemporary coral reefs increasingly fail to regenerate after natural and human impacts, and instead have undergone a rapid shift to an alternate state^15–18. The most familiar of these transitions is from dominance by corals to dominance by fleshy seaweed, although several other transitions have been documented (Fig. 2). The extent to which alternate states are stable or reversible is poorly understood¹⁹ and represents a major challenge for research and management of reefs.

Until now there has been little success in predicting such regime or phase shifts, because the increased instability of coral reef ecosystems before their collapse has often been unrecognised, even on reefs that are relatively well studied. This cryptic loss of coral reef resilience can be manifested in numerous ways. For example, the collapse of many Caribbean coral reefs was long preceded by dwindling stocks of fishes and increased nutrient and sediment runoff from land^2,16. By the 1950s, when modern studies of reef ecology began, the prevention of macroalgal blooms was increasingly due to a single species of sea urchin, Diadema antillarum. In the 1970s, recorded densities of Diadema on over fished reefs were extraordinarily high, averaging more than ten individuals per square metre in shallow waters^20–23. The magnitude and crowded conditions of Diadema populations²⁴ may have contributed to their eventual demise in 1983-4, when a disease outbreak spread throughout the Caribbean, reducing their numbers by two orders of magnitude²⁵ and precipitating macro-algal blooms that still persist. Today, remnant coral populations are further affected by increasingly prevalent coral disease and climatically induced coral bleaching^6,9.

With the benefit of hindsight, it is clear that long before the widespread loss of coral cover, many Caribbean reefs were on an unrecognised trajectory to collapse. The ecological symptoms included loss of macro-fauna^2,16, reduced fish stocks²⁶, a shift from fish-dominated to echinoid-dominated herbivory as the ecological role of herbivorous fishes was increasingly replaced by a single species of echinoid²², destructive overgrazing and bioerosion by food-limited sea urchins^24,27, and reduced coral recruitment²¹. Yet, although all of these features were exceptionally well documented, nobody put the pieces together in time to forecast their eventual consequence.  We need to do better at recognising and responding to these warnings."

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Citation and/or URL

Bellwood, D.R., Hughes, T.P., Folke, C. & Nyström, M. 2004, Confronting the coral reef crisis. Nature, 429: 827-833 

Spatial Coverage

Caribbean and Great Barrier Reef

Temporal Coverage

1970s to 1990s 

Update Frequency

Not applicable 

Other Information

None