A tiny fish may help hold back massive gas eruptions that turn a stretch of African coastline into a dead zone for marine life. In this month's Ecology Letters, two researchers speculate that hungry schools of sardines may be clearing phytoplankton from the waters off Namibia, reducing the production of toxic gases and potentially helping curb global warming.
For more than a century, people living along Namibia's Atlantic coast have reported noxious, sulfurous gases rising from nearby seas. Often, the eruptions were accompanied by mass die-offs of fish and crustaceans. But it was just in the last few years that researchers began to study carefully the submarine methane and hydrogen sulfide eruptions, which show up on satellite images as swaths of turquoise-colored water as big as New Jersey (ScienceNOW, 11 February). Many scientists believe that the gases are released by decaying phytoplankton--tiny marine organisms--that blanket the sea floor in meters-deep ooze.
Two years ago, researchers Andrew Bakun of the University of Miami, Florida, and Scarla Weeks of the University of Cape Town, South Africa, noticed a brief pause in the nearly constant pace of eruptions. Later, they realized that the dip coincided with a resurgence in local sardine stocks. They speculate that millions of sardines ate the phytoplankton that might otherwise have drifted to the sea floor, reducing gas production.
That link has yet to be proven, Bakun emphasizes. But he says Namibia's experience could serve as a warning to other areas, such as Morocco and California, that have similarly productive offshore waters that could become new dead zones if global climate changes promote phytoplankton blooms. "You might think twice about overfishing sardines," he says, adding that the eruptions themselves add potent greenhouse gases to the atmosphere.
Fisheries biologist Ellen Pikitch of the Pew Institute for Ocean Science in Miami, which funded the study, says the 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."