CORAL bleaching—previously blamed on pollution, El Niño and
global warming—may also be part of a natural cycle, say researchers in
Britain and Mauritius.
Michael Hassell of Imperial College at Silwood Park in Berkshire and his
colleagues studied a reef off Mauritius from 1991 to 1997. The team recorded the
numbers of symbiotic algae in coral tips and found that these varied in a strong
seasonal cycle (Science, vol 283, p 843). The algae give reefs their
colour, but their numbers in summer were sometimes so low that corals appeared
bleached.
