How does rising atmospheric CO2 affect marine organisms?

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Emerging Marine Diseases
Harvell, C.D., Kim, K., Burkholder, J.M., Colwell, R.R., Epstein, P.R., Grimes, D.J., Hofmann, E.E., Lipp, E.K., Osterhaus, A.D.M.E., Overstreet, R.M., Porter, J.W., Smith, G.W. and Vasta, G.R.  1999.  Emerging marine diseases - climate links and anthropogenic factors.  Science 285: 1505-1510.

What was done
The authors reviewed the prevalence of diseases of marine taxa, also assessing the contributory roles of human activity and climate.

What was learned
In answering their own question regarding whether or not there has been a recent increase in diseases in the oceans, the authors note that "although the frequencies of such accounts are compelling, whether they are indeed 'new' or are simply artifacts of improved detection requires further evaluation," adding later that the lack of "information for most marine taxa greatly challenges our ability to assess disease novelty."

In regard to serious marine outbreaks of disease of epidemic proportion that have been recently observed, the authors note that "in spite of the impact, little progress has been made in identifying the causative agents for marine diseases or in applying standard epidemiological methods to assess impact or mode of transmission."  Indeed, "of the dozen or so coral diseases currently described for the Caribbean region, the identity of the causative agent is known only for three."

For some marine disease outbreaks in which a causative agent has been identified, the evidence reveals a host shift brought about by changes in climate and/or human activities enhancing pathogen transport, rather than new disease emergence.  For example, a number of diseases common to terrestrial animals have reportedly been transferred to marine life, resulting in severe disease and death for the new marine host.  Such was the case involving a Caribbean coral that was infected by a soil-borne fungus known to cause infections in terrestrial species, which led the authors to suggest that recent bleaching-related mortality events have been accelerated by opportunistic infections.

What it means
It has been postulated that global warming poses a grave threat to the world's coral reefs via coral bleaching.  Yet, as we have pointed out in other reviews (The Distant Past is a Key to the Recent Past, Getting the Baseline Right), corals have successfully survived and thrived throughout prior periods of Earth's history when temperatures were warmer than present.  Why then, do some corals seem suddenly susceptible to warmer sea temperatures?  Part of that answer may rest in the dynamics of host-pathogen interactions that appear to be bringing marine life into contact with diseases to which they are not normally exposed.

Reviewed 15 September 1999