Abstract
Future global climatic and environmental change is emerging as one of the
major research priorities of coral reef scientists and the managers and
policymakers they inform. On coral reefs, most predictions of the effects
of global climate change have been confined to temperature-induced coral
bleaching, rising sea level and changing ocean chemistry. Recent reports
have also identified the poleward expansion of reef corals in response to
climatic warming.
The Ugly
Bleaching which is the loss of algal symbionts – the plant cells that live
in the coral animal - is a response to a number of potential stresses.
These stresses vary regionally and seasonally, and they may act singly or
together to cause corals to bleach. The most obvious of these is
temperature-induced stress. Corals are typically exposed during local
summertime to temperatures near the upper limits of their survival.
Accordingly, coral reefs are often considered to be the ecosystem most
threatened by global warming.
Field and laboratory studies have shown that sustained, anomalously high
summertime water temperatures are associated with coral reef bleaching and,
if temperatures are elevated for a prolonged period, many species die.
Coral bleaching in response to anomalously high summer-season temperatures
has become more frequent since the early 1980s with the earliest known
bleaching event in Florida having occurred in 1973. At least seven
bleaching episodes along the Florida reef tract have been documented since
then. The increased and widespread nature of these coral bleaching events
over the past two decades is convincingly correlated with increases in
maximum sea surface temperature (SST). During the warm El Niño event of
1997-98, about 16% of the world’s reef area was destroyed. In Belize,
Central America there was a complete collapse of lagoonal coral populations
in response to the 1998 event.