Fish are crucial in oceanic carbon cycle

Roberta Kwok in Nature News: Fish may play a more important role in the marine carbon cycle than previously thought, a new study shows. Researchers have found that fish excrete prodigious amounts of a mineral, calcium carbonate, that had been thought to come almost exclusively from marine plankton such as shelled algae.

Biologists knew that bony fish — a group that includes most fish apart from cartilaginous ones such as sharks and rays — produced calcium carbonate in their guts to rid themselves of excess calcium ingested from seawater. But this process hadn't been factored into models of ocean chemistry. "This is the first study that has even tried to link carbonate production by fish to global carbon cycles," says Rod Wilson, a fish physiologist at the University of Exeter, UK.

…The models suggested that there are between 0.8 billion tonnes and 2 billion tonnes of fish biomass in the oceans. And this indicates that bony fish produce 40 million–110 million tonnes of calcium carbonate per year, the study says. The range accounts for 3%–15% of the estimated total.

The lab results can be extrapolated to global fish populations, says Wilson, because the predictions are based on well-studied relationships between fish metabolism, mass, activity level and temperature. The estimate is conservative and could be as high as 45% of total calcium-carbonate production under more liberal assumptions, he says. The study appears in Science…

Tuna illustration from NOAA