How does rising atmospheric CO2 affect marine organisms?

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Zooxanthellae Diversity and Coral Bleaching
Reference
Fagoonee, I., Wilson, H.B., Hassell, M.P. and Turner, J.R.  1999.  The dynamics of zooxanthellae populations: A long-term study in the field.  Science 283: 843-845.

What was done
The authors analyzed zooxanthellae population density within the coral Acropora formosa on a weekly basis in a lagoon in Mauritius from August 1991 through March 1997.  The data were statistically tested to see if zooxanthellae were influenced by various environmental parameters, including time of year, temperature, dissolved oxygen concentration, and nitrate and phosphate concentrations.

What was learned
The data revealed considerable variation in zooxanthellae density with fluctuations over three orders of magnitude occurring during the period of study.  Fall and winter densities generally were three times greater than spring and summer densities.  Statistical analyses suggested that "temperature and solar radiation may be important" in explaining the observed variation in zooxanthellae density, although the authors state that "there may be other factors also related to season that are significant."

What it means
Coral bleaching results when zooxanthellae leave their host coral, presumably as a result of environmental or anthropogenic stress.  This study suggests that, given the natural seasonal variability in zooxanthellae density, such bleaching events in corals within lagoons "may be frequent and part of the expected cycle of variability."


Reviewed 1 March 1999