November 25, 2004
Protect Sardines To Reduce Atmospheric Methane Greenhouse Gas?

By eating phytoplankton sardines may prevent the process where when phytoplankton die they settle on the bottom of the ocean and then get broken down (presumably by bacteria) to release methane. Over-fishing sardines may increase methane release into the atmosphere.

Milky, turquoise-colored “dead zones,” sometimes as large as New Jersey, of rotting fish and caustic stench floating off the coast of southwest Africa, may be a sign of things to come for other areas along the coastlines of the eastern Atlantic and Pacific oceans. Toxic gas eruptions—bubbling up from the ocean floor to kill sea life, annoy human seaside residents, and may even intensify global warming—cause the dead zones. But the humble sardine may help to 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 report how the resulting overproduction of phytoplankton dies and sinks to the bottom, and how the decaying organic matter releases 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 open the possibility of even larger and more plentiful eruptions.

One action to help keep this situation from worsening, the authors say, is to avoid 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, from the University of Cape Town in South Africa, also warn that areas near 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 population has recovered somewhat since it peaked in the 1940s and was depleted by the early 1960s. We hope that the population can continue to recover as a hedge against development of such a regrettable situation on our own coast.”

Healthy sardine populations for a healthier atmosphere. Who would have thought?

For at least the last 5 years James Hansen of NASA has been arguing that reduction in methane gas emissions is a cheap way to delay global warming while providing more immediate health benefits (see the middle and end parts of that post).

Share |      Randall Parker, 2004 November 25 03:36 PM  Climate Trends

back40 said at November 26, 2004 4:04 PM:

This doesn't seem to consider the whole carbon cycle in oceans. Long term sequestration, rather than just circulation from air to sea to organism and back again, comes from calcium carbonate skeletons of phytoplankton falling to the sea floor.

If the phytoplankton is eaten by a fish it just makes the journey a little more convoluted. It doesn't seem to matter whether the organics end up on the sea floor as carcasses or dung. Fishes can reduce a nutrient pulse by spreading it out, eating here and then swimming there, but it isn't clear that the totals change.

Is this study fooled by concentration, all the methane of decomposition occurring noticeably in one spot rather than spread over a wider area?

Randall Parker said at November 26, 2004 4:50 PM:


Keep in mind that not all breakdown pathways generate methane. Suppose lots of phytoplankton gets eaten by sardines. Well, most of the hydrocarbons in the phytoplankton will be broken down by the glycolysis, the Krebs Cycle and all that. That will not produce methane. Eventually the fish may die and float to the bottom of the ocean and in tbe process of getting broken down by bacteria may produce methane. But the vast bulk of the phytoplankton the fish ate was broken down by intermediary metabolism in the fish long before the fish died.

Someone said at December 9, 2004 3:51 PM:


ron cirotto said at September 17, 2005 9:55 AM:

I would really appreciate if someone could tell me where the data and or the authors of the experiment/study that demonstrates methane gas is 21 more times effective than carbon dioxide as a green house gas?
Is there some sort of a table with naturally, water vapour at the top and all other GHGs compared to it?
ron cirotto P.Eng

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