Here is Dr. Ellen Pikitch's comment: "This study demonstrates that overfishing of one species of fish, such as sardines, can profoundly alter an entire marine ecosystem".
When Sardines are abundant, they eat up phytoplankton in larger quantity than when there are less Sardines in any particular area. If there are phytoplankton uneaten, they sink to the bottom and eventually get decomposed and produce large clouds of Hydrogen Sulfide and Methane gas that surface to the atmosphere above the water line. Why is this important to note? Because "methane is arguably worse, at least for world climate. Pound for pound methane traps 21 times as much heat as carbon dioxide, the most common greenhouse gas."
Next time we open a can of delicious sardine to make our salivating appetitie pacified, perhaps we need to think of the consequences.
Earth's Uncanned Crusaders: Will Sardines Save Our Skin?
By CORNELIA DEAN
Scientists working off the west coast of Africa have identified sardines as an unexpected factor in global warming.
The fish are not acting like cattle or termites, whose gassy emissions (to put it politely) add heat-trapping methane to the atmosphere. Sardines improve the situation, the researchers say. Or they might, if they were not been fished out.
The scientists say that when sardines are plentiful they gobble up ocean phytoplankton, tiny plants that appear in vast numbers when ocean currents produce upwellings of deep water.
But when sardines are scarce, the phytoplankton survive uneaten, only to sink to the bottom, decompose and produce methane and hydrogen sulfide gas that rise to the surface in giant clouds.
Hydrogen sulfide smells like rotten eggs, can poison fish and strips oxygen from water as it moves to the surface, producing anoxic "dead zones."
That's bad enough, but methane is arguably worse, at least for world climate. Pound for pound methane traps 21 times as much heat as carbon dioxide, the most common greenhouse gas.
The researchers, Dr. Andrew Bakun from the University of Miami and Dr. Scarla J. Weeks of the University of Cape Town, devised their plankton-sardine-methane theory while working off Namibia, where once-abundant sardine populations have been devastated since the 1970's by heavy fishing. They described their findings in the current issue of the journal Ecology Letters.
Gaseous eruptions occurred in the area before the heavy fishing began, the researchers said, but they were smaller and less frequent.
They suggest that warming pressures make the nutrient upwellings more frequent and more intense, which, in the absence of sardines, means more and larger eruptions of methane, which in turn contribute to even more warming.
Though some researchers are skeptical about linking sardines to global warming, others think that Dr. Bakun and Dr. Weeks are onto something.
"This study demonstrates that overfishing of one species of fish, such as sardines, can profoundly alter an entire marine ecosystem," said Dr. Ellen Pikitch, who heads the Pew Institute for Ocean Science, which provides financial support for Dr. Bakun.
Other areas where sardines were once abundant, like waters off Northern California, may eventually see similar phenomena if sardines are not restored, Dr. Bakun said, although more research must be done to determine if that is likely.
Unfortunately, sardines are not as commercially important as some other species. "The problem with sardines," he said, "is that the federal government is not that interested in them."