Global change, paleobiology, and conservation of coral reefs

Coral assemblages on Caribbean reefs appear stable on a scale of 10-100 kyr, but they have been ecologically volatile over the past three decades. Two dominant, framework-building corals, Acropora palmata (elkhorn coral) and Ac. cervicornis (staghorn coral), were killed regionally by an outbreak white-band disease (WBD) from the late 1970s though the early 1990s. The question of whether recent excursions from dominance by Acropora have any historical precedent can only be answered by examining Caribbean reefs on an intermediate scale of 0.1–1 kyr. Cores extracted from lagoonal reefs on the Belizean shelf showed that Ac. cervicornis dominated continuously for at least the last 3–4 kyr. Beginning in the late 1980s, WBD virtually eliminated Ac. cervicornis, and Agaricia tenuifolia (lettuce coral) increased opportunistically to become the dominant coral species. At approximately the same time, Ac. cervicornis died from WBD in a lagoonal habitat at Discovery Bay on the north coast of Jamaica. In the Jamaican case, however, the corals were replaced by macroalgae rather than by other coral taxa. Again, the phase shift was unprecedented on a millennial scale. These historically novel turnover events are rooted in the accelerating pace of ecological change at the regional and global levels. Although nutrient loading, overfishing, and other local effects can be important on some reefs, the direct and indirect effects of global warming overshadow local issues. Conserving coral reefs (and other features of the natural world) requires us to confront climate change at the highest levels of government and society.