CORDIO Status Report 2000

Foreword
The temperatures of the world’s oceans are increasing at an accelerating
rate. Recent estimates indicate that the magnitude of these increases
might be as much as several degrees over the next century and undoubtedly,
the impacts of these changes on the Earth’s ecosystems are
likely to become increasingly obvious. Coral reefs have already shown
dramatic responses to the increasing ocean temperatures. Under normal
temperature conditions, reef-building corals, which form the foundation
of coral reefs, are living very near the maximum sea temperatures
that they can tolerate. If they are exposed to even modest increases
in sea temperatures, perhaps only 1° C - 2° C, they become stressed
and often ‘bleach’. This bleaching of corals is a response to stress, and it
occurs when the symbiotic unicellular algae (zooxanthellae) that lives
within the tissues of the coral polyp, are expelled or lost. The coral can
survive for short periods without these zooxanthellae but unless the
stress that caused the bleaching subsides and new zooxanthellae are
incorporated into the tissue of the coral, the coral will die. For several
months in early 1998, the temperature of surface waters (< 10 m) over
much of the world’s tropical oceans increased between 3° C and 5° C.
As a result, corals on reefs throughout the world bleached and, unfortunately,
many died. The mortality of corals was particularly serious in
the central and western Indian Ocean, where as many as 50% to 95% of
all corals died.
The impacts of the 1998 coral mortality are a matter of great concern.
Coral reefs are one of the most diverse, productive and complex
ecosystems on the planet. They are the home of hundreds of thousands
of species, many of which are unknown to science. They are highly
productive, providing food and shelter for most of the fish species caught
in shallow tropical coastal waters. As a consequence, the impacts of such
widespread coral mortality will have a direct bearing on critical marine
and coastal biodiversity and fragile ecosystems that are affected. From
a socio-economic perspective, the impacts of coral mortality are far
reaching, affecting food security as well as local and national economies
that are dependent on reef-based tourism and industry. It is particularly
worrying that models, based on the IPCC Scenario A (dou-
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