By Sid Perkins
Most of the variation in the amount of Caribbean coral that turns sickly pale each year is driven by two counteracting forces, a new analysis shows. They are the periodic ocean heating from the climate phenomenon known as El Niño and the occasional cooling action of sunlight-blocking particles high in the atmosphere.
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When ocean temperatures rise even slightly, some species of corals shed the brightly colored algae that live within them, a sometimes-reversible change known as coral bleaching (SN: 8/28/04, p. 142: Available to subscribers at Some corals like it hotter). If bleaching episodes last weeks or months, coral colonies can die, says Jennifer A. Gill, an ecologist at the University of East Anglia in Norwich, England.