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. B 268, 2347 (2001).