Most Marine Life Worldwide Growing Sicker, Fish Health Slightly Better

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"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.

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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.

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."

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