The number of tracts of the ocean devoid of oxygen, and therefore bereft of complex life, is growing.

In a review piece in this week’s Science Robert Diaz, a researcher at the College of William and Mary in Virginia warns that the dead zones’ number has increased by a third between 1995 and 2007 (paper, press release). Diaz has been studying the things since the 1980s,

He and his co-author Rutger Rosenberg, of the University of Gothenburg, note:

By the end of the 20th century, oxygen depletion of marine systems had become a major worldwide environmental problem, with only a small fraction (4%) of the 400-plus systems that had developed hypoxia exhibiting any signs of improvement. … There is no other variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time as DO [dissolved oxygen].

A lot of these dead zones are caused by civilisation: nutrients from human activities run off into the seas, algae run riot and multiply rapidly, then they sink and die fuelling microbe respiration which takes oxygen out of the water.

“Most of it is agricultural-based, but there is a lot of industrial nitrogen in there, too, if you consider electric generation industrial,” says Diaz (Reuters).

“The overwhelming response of the organisms in our coastal areas is to migrate or to die,” he adds (NY Times). “To adapt to low oxygen water, it has to be a part of your evolutionary history. It’s not something you can develop in a 40- or 50-year time period.”

Jane Lubchenco, former head of the AAAS and a marine biologist at Oregon State University, told the SF Chronicle the report was “a sobering documentation of the growing threat of nutrient pollution in coastal waters around the world”.