Fish help to buffer climate change

New research shows that fish play an important role in the fight against climate change.

Research published in the January 16, 2009 issue of Science, co-authored by Villy Christensen, professor at the Fisheries Centre at the University of British Columbia, will change our understanding of the factors that mitigate climate change.

“We had not recognised the role of fishes for climate change before. The fishes serve a role…they perform an ecosystem service,” said Christensen.

The researchers found that fish act as a buffer against carbon dioxide in the world’s oceans because they secrete calcium carbonate, a chalk-like substance that dissolves easily in water and lowers acidity. They also estimated that the number of fish in the world’s oceans is higher than previously thought—almost two billion—which significantly increases their combined buffering power.

“Right now what’s happening is that carbon dioxide is shooting up into the atmosphere, but the oceans are buffering it…what the fishes do has importance as part of this buffering mechanism,” said Christensen.

All fish species secrete calcium carbonate, or limestone. It’s how they metabolise the calcium in the salt water they drink. If they didn’t get ride of excess calcium, they’d develop renal stones, just like humans. It was previously unknown that fish make these ‘gut rocks’ that make up from 15%-45% of the ocean’s calcium carbonate.

Fish are just one part of the carbon cycle, a key factor in our understanding of climate change. It’s been long known that carbon dioxide has had an impact on climate change.

Carbon dioxide in the air can dissolve in water, and by doing so, it makes the water more acidic. As atmospheric carbon dioxide levels rise, more of it will dissolve into the ocean and this process results in the ocean becoming more acidic.

There will reach a point where the buffer provided by fish just won’t be enough to stall the negative effects of ocean acidification, said Christensen.

“Climate models have been saying…that ocean acidification’s going to be a really big problem. It’s something that will affect us within decades.”

The big problem is that coral reefs and plankton, tiny organisms that form the bottom of the marine food chain, are very sensitive to changes in acidity.

The health of a marine ecosystem is intricately tied to, amongst other things, the health of its coral reefs and plankton. The acidification of the oceans would have a devastating effect on both, disrupting the food chain and contributing to climate change in the oceans, says Christensen.

A marine ecosystem will always be affected by the sheer number of fish in the sea. Although two billion sounds like a lot of fish, there’s still a need to responsibly manage fisheries, particularly in provinces like British Columbia. Finding the balance between young and old fish is the key to successful fisheries management, said Christensen.

He adds that for the ocean to maintain its optimal pH, it needs to have lots of healthy, young fish. Old fish, Christensen’s research revealed, are not as good at producing calcium carbonate. They’re less active and drink less water. The ocean needs a constant supply of young fish that produce more calcium carbonate, and sustainable fisheries is one way to go about it.

“Sustainable fisheries is a good thing. You need to keep production high. Just leaving everything to itself is not necessarily going to help us. What we have to avoid in [fisheries management] is what corresponds to forest clear-cutting,” said Christensen.

Now that it’s known that fish play an important role as a buffer against climate change, Christensen added a cautionary note on how humans affect their delicate environment.

“We really have to be careful of how we intervene in the ecosystem. We should be very careful to go out and cut down the forests, fish up all the fish…because we might not understand what role they play [in climate change].”

Photo curtesy of Vilhelm Sjostrom, Flickr Creative Commons