By Rachel Einschlag and Roger Segelken
Disease is increasing among most kinds of marine organisms, according to a long-term study by Jessica Ward of Cornell and Kevin Lafferty of the U.S. Geological Survey.
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| Sea fan corals, like this dead one near the Pacific islands of Palua, were devastated by a 1998 bleaching event, then suffered mass mortality the next year for unknown reasons. Cornell graduate student Jessica Ward, shown conducting the survey for the Global Environment Facility and the World Bank, is part of a team trying to assess worldwide coral disease threats. Drew Harvell/Cornell University |
The study, conducted at the National Center for Ecological Analysis and Synthesis in Santa Barbara, Calif., found that fish are no exception to the troubling trend, despite fewer reports of fish disease over the years. An analysis by Ward and Lafferty of hundreds of previous studies of marine-ecosystem disease was published in April in the journal Public Library of Science Biology (available without charge at http://www.plos.org). The report finds the rate of disease increasing in some taxa, such as in turtles, mammals, mollusks and urchins, but declining in fish.
However, said Ward, a Cornell doctoral student in ecology and evolutionary biology and lead author of the published study, "Disease in fish populations is decreasing only because their numbers are decreasing, due to over-fishing and other factors."
Indeed, she noted, for many populations, there are too few fish left for disease to be observed.
The study was conducted in association with the 15-member Marine Disease Working Group of the National Center for Ecological Analysis and Synthesis, a Santa Barbara, Calif., ecology think tank. Heading the marine disease group is C. Drew Harvell, a Cornell professor of ecology and evolutionary biology. Harvell said: "This is the first quantitative study to provide solid evidence that rates of disease do seem to be increasing in the ocean. It has been hard to tell if disease is increasing because we didn't have proper baselines. It's been much tougher to understand the frequency of marine disease than it is to monitor for SARS, for example, because the ocean is out of sight and out of mind."
Harvell pointed to trends revealed by the study:
Ward and Lafferty developed a literature-based research method to test the increasing-disease hypothesis, a widespread concern among ecologists. The analysts used the number of times diseases were mentioned in the literature as a proxy for actual prevalence of disease over time. Besides making statistical adjustments to account for the increase of scientific publications in recent years, the researchers verified their methodology with raccoon rabies, a widely reported disease of land animals. Because mentions in the literature and the cases of raccoon rabies matched, the researchers concluded the literature citations and the actual cases of marine disease should be consistent as well.
One future application of the study method might be as a management tool for marine ecosystems in need of conservation, or as an aid for trend spotting and finding underwater populations that need to be studied, Ward noted.
"We are seeing so many emerging diseases that it can be overwhelming, and certainly we have to be careful about how dire we make the risk out to be," Ward said. "There are so many things we have yet to understand about the sea. My hope is that the methods developed in our paper can be used to identify those groups most in need of conservation."
The study was supported, in part, by the National Center for Ecological Analysis and Synthesis.
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