Fish poo affects ocean chemistry

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Scientists from Canada, UK and the USA have demonstrated that the balance of the oceans' acidity may lie in the hands of fish poop.

Publishing their results in a recent issue of the journal Science, Rod Wilson and coauthors calculated the amount of calcium carbonate excreted by fishes and found the amount to be substantially higher than previously thought (to the point where it has a significant affect on the global carbon cycle).

Oceanic production of calcium carbonate (which maintains the alkalinity of the world's oceans) is usually attributed to marine plankton (coccolithophores and foraminifera), but marine fishes are known to continuously excrete carbonate precipitates as a result of their continuous drinking of seawater to maintain salt and water balance.

The authors created two independent mathematical models to calculate the biomass of all the fishes in the oceans (and hence the amount of carbonate precipitates they contribute).

Based on their calculations, fishes produce an estimated 110 million tonnes of calcium carbonate per year, about 3"15% of the estimates for total global new carbonate production in the surface oceans.

The authors predict that the production of carbonate precipitates by fish will accelerate as a result of both increasing seawater temperatures and acidities.

According to Rod Wilson, We have really only just scratched the surface of knowing the chemistry and fate of fish carbonates. Given current concerns about the acidification of our seas through global CO2 emissions, it is more important than ever that we understand how the pH balance of the sea is normally maintained.

Because of the impact of global climate change, fish are likely to have an even bigger influence on the chemistry of our oceans in future. So, it is vitally important that we build on this research to help fully understand these processes and how this will affect some of our most precious marine ecosystems.

For more information, see the paper: Wilson, RW, FJ Millero, JR Taylor, PJ Walsh, V Christensen, S Jennings and M Grosell (2009) Contribution of fish to the marine inorganic carbon cycle. Science 323, pp. 359"362.