How does rising atmospheric CO2 affect marine organisms?

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Coral Disease in a Warmer World
Yakob, L. and Mumby, P.J. 2011. Climate change induces demographic resistance to disease in novel coral assemblages. Proceedings of the National Academy of Sciences USA 108: 1967-1969.

The authors write that increased disease incidence in corals "has been linked to rising sea temperatures," noting that this link "has inevitably led to projections of increased epizootics in the future," especially in light of the fact that "the overwhelming current trend in ecosystems science emphasizes additive or synergistic deleterious effects of climate change."

What was done
In evaluating this unimodal way of thinking, Yakob and Mumby investigated a number of documented "changes in coral demography, likely borne of climate change," in an attempt to determine the soundness of what we could call this bad-news-only concept. This work, based on what they describe as "the best time series of coral epizootics available" (an outbreak of White Plague type II disease in a population of Dichocoenia stokesi in the Florida Keys) led them to create a simple disease model, wherein coral mortality from an initial disease outbreak reduces the average size of a colony in the post-outbreak population. And because, as they describe it, "smaller colonies have a higher rate of mortality, the average turnover of the post-outbreak population is higher than that before the outbreak," so that "this increase in population turnover makes it more difficult for a second epizootic to occur," with the ultimate result being the fact that "higher demographic rates naturally reduce the ability of the disease to spread within a population consisting of diminutive colonies under high flux."

What was learned
The two researchers conclude -- based on their mathematical analysis and the observations of others -- that "allowing for a more dynamic population turnover in an epizoological model of coral disease not only gives a superior fit to empirical data, but also suggests that emerging coral assemblages could be far less prone to epizootics."

What it means
Yakob and Mumby say their results imply that "projecting the future of a novel ecosystem from trends in the recent past may have misleading results." And since their review of the literature indicates that responses to anthropogenic changes in biotic and abiotic environments generally lead to the creation of novel ecosystems, they conclude that the "high population turnover within novel ecosystems enhances coral resistance to epizootics," and, therefore, that "disease could become a less important driver of change in the future," leading them to "emphasize the need to move away from projections based on historic trends toward predictions that account for novel behavior of ecosystems under climate change."

Reviewed 13 April 2011