Sardines may prevent toxic gas eruptions off the California and African coasts

01/13/05

Milky, turquoise-colored "dead zones," some as large as the U.S. State of New Jersey, that are appearing repeatedly off the coast of southwest Africa, may be a sign of things to come for other areas of the coastlines of the eastern Atlantic and Pacific oceans. Toxic gas eruptions, bubbling up from the ocean floor, kill sea life, annoy human seaside residents, and may even intensify global warming. But the simple sardine may save the day, according to a study from the Pew Institute for Ocean Science.

In an article published in the November issue of Ecology Letters, authors Andrew Bakun and Scarla Weeks compare several areas around the world where strong offshore winds cause an upwelling of nutrients in the ocean and thus a population explosion of phytoplankton, the microscopic plant life that drifts through the ocean. Studying the waters off the coast of Namibia, the scientists found the resulting overproduction of phytoplankton died and sank to the bottom, and the decaying organic matter released copious amounts of methane and poisonous "rotten egg" smelling hydrogen sulfide gas.

As methane is 21 times more effective than carbon dioxide at trapping heat in the atmosphere, the resulting climate change may intensify this upwelling process and the possibility of even larger and more plentiful eruptions.

One key that may keep this situation from worsening, the authors say, is to prevent the overfishing of sardines, which can devour large quantities of phytoplankton.

"The region in question formerly hosted a large population of sardines that have been overfished," says Bakun, a member of the Pew Institute and professor of marine biology and fisheries at the University of Miami Rosenstiel School of Marine and Atmospheric Science. "It is at least encouraging that a minor resurgence of sardine abundance coincided with a noticeable temporary hiatus in eruption frequency off Namibia in 2002."

Bakun and Weeks also warn that the areas around Cape Mendocino, California, and Cape Sim, Morocco, may be dangerously close to the "tipping point," possibly ripe for phytoplankton population explosions followed by their gaseous demise.

"This study demonstrates that overfishing one species of fish, such as sardines, can profoundly alter an entire marine ecosystem in ways that may be difficult or impossible to reverse," says Ellen Pikitch, executive director of the Pew Institute for Ocean Sciences and an expert on fishery science and management.

Pew's Chief Scientist Elizabeth Babcock adds, "The California sardine fishery has recovered somewhat since it peaked in the 1940s and was depleted by the early 1960s. We hope that the fishery can continue to recover to help prevent such a terrible situation from occurring."

The paper evaluates 16 areas around the world, including four along the Pacific coast of North America, for the risk of developing these gaseous eruptions. To learn more, visit the Ecology Letters website at http://www.blackwellpublishing.com/journal.asp?ref=1461-023x.

Bakun's 42 years in marine science includes scientific positions with the International Indian Ocean Expedition, US National Oceanic and Atmospheric Administration's Pacific Fisheries Environmental Laboratory, the United Nations' Food and Agriculture Organization, France's Institut de Recherche pour le Dévelopment (IRD), and Columbia University's International Research Institute for Climate Prediction.

A well-known South African scientist, Weeks has spent the past decade as the principal developer of satellite ocean color information for southern Africa.

Source: Eurekalert & others

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