Sea urchin recovery from mass mortality: new hope for Caribbean coral reefs?

Abstract

Coral reefs are often referred to as the rainforests of the sea, although, as Davidson (1) points out, one could equally well call rainforests the coral reefs of the land. Regardless, these two ecosystems do indeed share several important attributes, most notably high diversity and severe declines worldwide over the last several decades. There are many differences, however, between reefs and rainforests, including the nature of the threats that they face. Whereas the trees that underpin rainforest ecosystems are largely lost by the direct activities of people (harvesting or land clearing), corals are declining through a far more diverse and less well understood concatenation of events and processes. Studies of the reefs of the north coast of Jamaica have provided scientists with some of the clearest examples of reef fragility and apparent collapse (2, 3), and consequently they have become a textbook case of environmental doom and gloom. In a paper by Edmunds and Carpenter (4) in this issue of PNAS, Jamaican reefs again play a central role, but for the first time in recent memory, reef recovery rather than continued decline seems at least possible. Their findings confirm the central importance of herbivory for the maintenance of healthy coral reefs, and provide surprising but encouraging evidence that formerly abundant organisms can linger at extremely low densities for nearly two decades, and then rebound.