Notes |
Abstract:
The five mass extinction events that the earth
has so far experienced have impacted coral reefs as much
or more than any other major ecosystem. Each has left the
Earth without living reefs for at least four million years,
intervals so great that they are commonly referred to as
‘reef gaps’ (geological intervals where there are no remnants
of what might have been living reefs). The causes
attributed to each mass extinction are reviewed and summarised.
When these causes and the reef gaps that follow
them are examined in the light of the biology of extant
corals and their Pleistocene history, most can be discarded.
Causes are divided into (1) those which are independent of
the carbon cycle: direct physical destruction from bolides,
‘nuclear winters’ induced by dust clouds, sea-level changes,
loss of area during sea-level regressions, loss of
biodiversity, low and high temperatures, salinity, diseases
and toxins and extraterrestrial events and (2) those linked
to the carbon cycle: acid rain, hydrogen sulphide, oxygen
and anoxia, methane, carbon dioxide, changes in ocean
chemistry and pH. By process of elimination, primary
causes of mass extinctions are linked in various ways to the
carbon cycle in general and ocean chemistry in particular
with clear association with atmospheric carbon dioxide
levels. The prospect of ocean acidification is potentially the most serious of all predicted outcomes of anthropogenic
carbon dioxide increase. This study concludes that acidification has the potential to trigger a sixth mass extinction event and to do so independently of anthropogenic
extinctions that are currently taking place. |
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