AR-News: Cornell U: fish no exception to disease trend

[Mary Finelli]

FISH NO EXCEPTION TO TREND IN MARINE-ORGANISM DISEASE
Cornell University, April 13, 2004
http://www.newswise.com/articles/view/504150/


Disease is increasing among most kinds of marine organisms, according to a 
long-term study by Cornell University and the National Center for Ecological 
Analysis and Synthesis in Santa Barbara, Calif. And fish are no exception to 
the troubling trend, despite fewer reports of fish disease over the years.

The analysis of hundreds of previous studies of marine-ecosystem disease is 
published this month 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, says Jessica 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." Says Ward, "Undoubtedly there are 
fewer and fewer cases of pneumonia among veterans of World War I , but that 
doesn't mean the veterans are becoming healthier. They are becoming fewer in 
number, and so are populations of wild fish." indeed, she notes, for many 
populations, there are too few fish left for disease to be observed.

The study was conducted by 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. She 
comments: "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 points to trends revealed by the study: Sea turtles are suffering 
from large tumors caused by a herpes virus that has spread over the last two 
decades. Marine mammals have a variety of viral and bacterial ailments, some 
of which also seem linked to human activities. Mollusks, such as 
commercially farmed oysters, could be experiencing increasing stresses from 
both climate and aquaculture practices. Corals had an increase in bleaching, 
although not in actual disease. Only sea grasses and sharks display no 
apparent increases in disease levels; both groups have disease, but it does 
not appear to be increasing.

Ward worked with collaborators to develop 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 notes. "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 says. "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."

Kevin Lafferty of the U.S. Geological Survey's Western Ecological Research 
Center co-authored the report. The study was supported, in part, the 
National Center for Ecological Analysis and Synthesis.

Related World Wide Web sites: The following sites provide additional 
information on this news release. Some might not be part of the Cornell 
University community, and Cornell has no control over their content or 
availability.

Ecology and Evolutionary Biology at Cornell: http://www.eeb.cornell.edu/

This story was reported and written by Rachel Einschlag, a student 
science-writing intern in the Cornell News Service.

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