Research published in the journal Ecology Lettersand summarized by Cornelia Dean in the New York Times posits a fascinating link between sardine populations in the ocean and climate change in the atmosphere.
. . . 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 [because of overfishing, for example], 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.
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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.
And later, the Cascadia connection:
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.
Sardine populations, depleted off Northern California, do periodically bloom there still, and sometimes even surge in the Pacific off central Cascadia.
This study is an example of what Barry Commoner long ago labeled, in his classic book The Closing Circle, as the first law of ecology: “everything is related to everything else.” It’s also an example of a corollary of that law: curing one ill afflicting ecosystems (in this case, overfishing) often helps cure other ills, too. One good deed begets another.