How does rising atmospheric CO2 affect marine organisms?

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On Promoting Recovery from Coral Bleaching
Hughes, T.P., Rodrigues, M.J., Bellwood, D.R., Ceccarelli, D., Hoegh-Guldberg, O., McCook, L., Moltschaniwskyj, N., Pratchett, M.S., Steneck, R.S. and Willis, B. 2007. Phase shifts, herbivory, and the resilience of coral reefs to climate change. Current Biology 17: 360-365.

What was done
Working on Australia's Great Barrier Reef within a no-fishing reserve where coral abundances and diversity had been sharply reduced by the serious widespread bleaching event of 1998, the authors "experimentally manipulated the density of large herbivorous fishes to test their influence on the resilience of coral assemblages."

What was learned
Hughes et al. report that "in control areas, where fishes were abundant, algal abundance remained low, whereas coral cover almost doubled (to 20%) over a 3-year period, primarily because of recruitment of species that had been locally extirpated by bleaching." In contrast, they found that "exclusion of large herbivorous fishes caused a dramatic explosion of macroalgae, which suppressed the fecundity, recruitment, and survival of corals."

What it means
Based on their compelling observations, the ten researchers concluded that "management of fish stocks is a key component in preventing phase shifts [such as replacement of corals by macroalgae] and managing reef resilience," which further indicates, in their words, that "local stewardship of fishing effort is a tractable goal for conservation of reefs." In addition, their work clearly demonstrates, as they put it, that "local action can also provide some insurance against larger-scale disturbances such as mass bleaching, which are impractical to manage directly."

We totally agree with these conclusions. The observations on which they are based clearly indicate that with a little help from local residents everywhere, even large-scale bleaching events need not spell the end of earth's rich coral ecosystems, which clearly possess the ability to reconstruct themselves, even after the most serious environmental disasters, if they are not overly challenged by competing lifeforms.

Reviewed 4 July 2007