Good news on fisheries? With rising CO2 levels, 'all bets are off'

Courtesy of the British Antarctic Survey
Krill from the Southern Ocean, along with other forms of zooplankton, may play a key role in stirring the oceans -- a "service" that could be undermined with rising atmospheric CO2 levels and their effect on ocean acidification.

The late Jerry Garcia, of "Grateful Dead" fame, strikes again. The lyrical snippet? "Every silver lining has a touch of gray."

This week's guardedly encouraging study on the state of the world's fisheries, which The Christian Science Monitor covered yesterday, is in many ways a milestone. It acknowledges the problem with overfishing, but also highlights current budding success stories, and the tools fisheries managers used to write them. And it represents a consensus among leading scientists who in the past have been at loggerheads over the health of the world's fisheries.

You can find a summary of the study at the journal Science's website. The full pdf is available by subscription.

But buried deep in comments members of the research team made during a press briefing on the study, University of Washington fisheries scientist Ray Hilborn added a strong caution that had nothing to do with nets, fishing fleets, or no-take zones.

"All bets are off with climate change, particularly ocean acidification," said Dr. Hilborn, one of the study's two lead authors.

That gets a rounding huzzah from Rebecca Goldburg, the Pew Environment Group's lead expert on marine science issues.

"People still haven't really understood the potential impacts of ocean acidification," Dr. Goldburg said during a phone chat.

And therein lies the rub. The progress humanity makes against the against loss of (fill in your favorite ecosystem here) depends at least as much on weaning ourselves from carbon-based fuel sources as it does setting aside linked reserves, controlling chemical pollution and protecting or restoring habitat, or implementing any number of other important measures to protect ecosystems.

Interestingly, the day before Science published its fisheries study, the journal Nature published research suggesting a physical mechanism that could allow tiny plankton to play an important role in ocean circulation -- an under-the-radar ecological service, if the idea holds up to further scrutiny. A full pdf of the study is available by subscription. But you can find a summary here and a Monitor news story here.

In essence the up-and-down migration of these creatures and their larger zooplankton relatives could be responsible for up to half of the contribution marine life makes to vertical mixing in the oceans. And marine life's total contribution may be roughly equal to that of wind and currents.

This vertical mixing is a vital means by which turbulent surface waters are recharged with nutrients from cold, dense, deep waters. And this mixing also affects the ocean's long-term uptake and release of carbon dioxide to and from the atmosphere.

Here, too, the results have implications for the impact of rising atmospheric CO2 levels beyond the considerable changes warming alone is projected to bring.

Many of these tiny creatures are shell-builders. Acidification has been shown to retard or prevent shell-building. Scientists in Australia have looked at the combined one-two punch of natural and human-triggered patterns in acidification in regions of the Southern Ocean and concluded that shell-building plankton there could reach a tipping point and decline dramatically by 2038, far earlier than previous projections.

As Florida State University oceanographer William Dewar put it during a phone chat: "If the biosphere is important to mixing, now you have a tightly coupled problem. Acidification changes the biosphere, that means there's different mixing, which means a different exchange" of CO2 between the ocean and atmosphere, which in turn affects the marine life.

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