World's marine life is getting sicker

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> World's marine life is getting sicker

> http://www.newscientist.com/news/news.jsp? id=ns99994897

>

> 16:55 19 April 04

>

> NewScientist. com news service

>

> For years, apparent increases in illness among marine creatures, from

whales

> to coral, have left marine scientists with the uneasy suspicion that the

> seas are increasingly plagued by disease. Now, US researchers have

uncovered

> the first good evidence that they are right.

>

> In 1998, a dozen of the world's top experts on diseases of marine animals

> warned that sea creatures seemed to be getting sick more often, with more

> diseases.

>

> New viruses had appeared in whales and seals, while corals were dying of

> fungal and algal infections. Pilchards succumbed to viruses and an

> aggressive parasite expanded its range to attack commercial oysters,

> scallops and clams. In the Caribbean, some unknown bacteria wiped out what

> had been the dominant sea urchin.

>

> But there was no way to tell if the apparent increase was simply due to

more

> scientists paying more attention to marine disease. There was no baseline,

> as no one had ever measured disease incidence in any of these species

> decades ago.

>

> Now, Jessica Ward, at Cornell University in Ithaca, New York, has shed

> important new light on the problem by looking at how the number of reports

> of marine diseases in nine different groups of marine creatures has

changed

> in the scientific literature since 1970.

>

> " We wanted to find out if something was actually happening, " Ward told New

> Scientist. " For most groups of organisms, we found that yes, there is

> something going on out there. Now we hope more people will try and figure

> out where it is coming from. "

>

> True incidence

>

> Ward, with Kevin Lafferty, of the University of California in Santa

Barbara,

> first tested whether changing numbers of scientific reports of rabies in

US

> raccoons matched the true incidence of the disease, which is known

> independently. They matched, suggesting more scientific reports really do

> mean more disease.

>

> The pair further tested the relationship by removing the most prolific

> laboratory from the publications they collected for each group of marine

> creatures - just in case increased reporting reflected only one

scientist's

> funding success. This did not change any apparent disease trends. Neither

> did taking out multiple papers on one well-reported disease event, such as

> the Caribbean urchin die-off.

>

> So using scientific reports as a measure, Ward and Lafferty found that

> disease has increased in turtles, corals, marine mammals, urchins, and

> molluscs such as oysters.

>

> Illness seems to have remained steady in the shark and shrimp families,

and

> in seagrasses. Surprisingly, disease reports have diminished for fish.

>

> Easy prey

>

> There are numerous possible reasons for rising disease. One, Ward

suggests,

> is increasing sea surface temperatures due to global warming. This can

cause

> corals to bleach, making them easier prey for infections.

>

> Warming has also led to the northward spread of the oyster parasite

> Perkinsus. And warming is thought to accelerate the growth of tumours in

> turtles caused by a herpes virus.

>

> Another possible factor is that human over-fishing has destabilised marine

> ecosystems. For example, when the urchins in the Caribbean died, corals

were

> overwhelmed by the algae the urchins used to eat. " Normally fish would

have

> eaten the algae instead, but they weren't there, " says Ward.

>

> Other suggested causes include:

>

> . new pathogens from domestic animals, such as dog distemper virus and the

> parasite Toxoplasma

>

> . bioaccumulation of toxins weakening marine mammals' immunity

>

> . new species carried across oceans in ships' ballast tanks introducing

new

> diseases

>

> In the face of all this, the apparent health of fish is intriguing. Ward

> says this could be because the fish are simply fewer in number. Many

> pathogens die out among animals that are not packed densely enough to pass

> the infection on. But it is also possible, she says, that the frequency of

> disease is just as bad or worse - but fewer fish mean fewer observations,

> and fewer reports.

>

> Journal reference: PLoS Biology (vol 2, p 542)

>

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>

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>

> For more related stories search the print edition Archive

>

> Weblinks

>

> Ward and Lafferty paper

>

> Harvell et al paper

>

> Ecology and evolutionary biology, Cornell University

>

> Kevin Lafferty, of the University of California in Santa Barbara

>