Fish At Risk From Ocean Dead Zones
Posted on: Tuesday, 30 September 2008, 08:50 CDT
Scientists said Monday that the number of polluted "dead zones" in the world's oceans are increasing and coastal fish stocks are more at risk than once thought.
Writing in the journal Proceedings of the National Academy of Sciences, researchers said the rise of "dead zones" -- areas of oxygen-starved water -- "are emerging as a major threat to coastal ecosystems globally."
The zones are found from the Gulf of Mexico to the Baltic Sea in areas where algae bloom and use oxygen from the water. They feed on fertilizers washed from fields, sewage, animal wastes and pollutants from the burning of fossil fuels.
"Marine organisms are more vulnerable to low oxygen content than currently recognized, with fish and crustaceans being the most vulnerable," said Raquel Vaquer Suner of the Mediterranean Institute for Advanced Studies in Spain.
Suner’s study showed that the number of "dead zones" had grown to more than 140 in 2004 from almost none until the late 1970s.
Millions of people depend on coastal fisheries for food; crustaceans such as crabs, lobsters and shrimps are less able to escape from low-oxygen waters than fish.
Rising temperatures tied to global warming may make worse the problem of "dead zones," the study says because oxygen dissolves less readily in warmer water.
The first "dead zones" were found in northern latitudes like Chesapeake Bay on the U.S. east coast and Scandinavian fjords.
Others have been appearing off South America, Ghana, China, Japan, Australia, New Zealand, Portugal and Britain.
The study noted many scientists had reasoned oxygen levels could fall to 2 milligrams per liter of sea water before it was considered starved of oxygen.
However, the study found many creatures were far more sensitive; larvae of one type of crab found off eastern Canada and the United States started suffering at oxygen levels of 8.6 mg per liter, slightly below normal levels.
"Currently used thresholds ... are not conservative enough to avoid widespread mortality losses," according to scientists.
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Source: redOrbit Staff & Wire Reports
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