How does rising atmospheric CO2 affect marine organisms?

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Coral Reef Resiliency: How Strong or Weak Is It?
Halford, A., Cheal, A.J., Ryan, D. and Williams, D.M.  2004.  Resilience to large-scale disturbance in coral and fish assemblages on the Great Barrier Reef.  Ecology 85: 1892-1905.

What was done
The authors monitored coral and fish assemblages for fourteen years on several fixed sites spread over 80 km of the southern Great Barrier Reef of Australia.  During this period, sometime between November 1987 and October 1989, they report that live coral cover on the shallow northeast flanks of some reefs decreased from more than 80% to less than 10%, "probably as a result of storm damage."  Having documented the nature of the fish and benthic communities of these areas prior to the disturbance (1983-1984), they were able to chart the degree to which the coral ecosystems were able to return to their pre-disturbance characteristics over the following years of their measurement program.

What was learned
Halford et al. report that "hard coral cover increased slowly from 1992 to 1994, then accelerated to be indistinguishable from pre-impact levels by 1998."  They also found that "patterns of species richness of the fish families Acanthuridae, Chaetodontidae, Scaridae, and Pomacentridae mirrored that of hard coral, except the Pomacentridae had not recovered to pre-impact levels by 1998."  More specifically, they say that "of the 26 fish species analyzed for changes in abundance, 88% decreased after the disturbance, then subsequently increased, with all but two recovering to pre-impact levels by 1998."

What it means
Again, in the words of the authors, "both coral and fish assemblages demonstrated resilience to large-scale natural disturbance ? with most taxa approaching the asymptote of abundance and species richness that existed prior to the disturbance."  They note, however, that "this outcome may not necessarily be the case in more isolated systems or those impacted by anthropogenic disturbances," specifically mentioning over-fishing and destructive fishing practices.  Hence, their work gives hope that if the direct deleterious effects of human activities can be mitigated, earth's coral reef ecosystems may yet be saved from the destruction so often decreed for them by environmental extremists.

Reviewed 3 November 2004