In 1983, the coral reefs of the Caribbean underwent a dramatic ecological change. Populations of a hitherto abundant sea urchin, Diadema antillarum, the most important herbivore in this system, plummeted to less than 3% of their former level. Despite limited recovery in some areas, Diadema numbers have remained low, permitting increased algal growth at the expense of coral, which may hasten the degradation of Caribbean reefs.
Since the mass mortality, there has been controversy as to whether Diadema owed its former abundance to human activities (for example, depletion of the urchin's predators by fishing) or whether it was abundant before humans inhabited the Caribbean. Lessios et al. use mitochondrial DNA sequences to trace the history of Diadema populations, and find that the species has had large population sizes for at least the past 100 millennia, demonstrating that humans probably were not responsible for the pre-crash population levels. This result is relevant to discussions of restoration and management of degraded reefs in the Caribbean.—AMS
Proc. R. Soc. London Ser. B268, 2347 (2001).