Keeping the oceans healthy (Image: IA18208 Dave and Fiona Harvey) The high iron content of whale faeces feeds Antarctic krill in the Southern Ocean and elsewhere (Image: J Brokowski) Researcher Nick Gales collects faeces sample from water (Image: Australian Antarctic Division/Sarah Robinson)


Saving endangered baleen whales could boost the carbon storage capacity of the Southern Ocean, suggests a new study of whale faeces. Whale faeces once provided huge quantities of iron to a now anaemic Southern Ocean, boosting the growth of carbon-sequestering phytoplankton.

So says Stephen Nicol of the Australian Antarctic Division, based in Kingston, Tasmania, who has found “huge amounts of iron in whale poo”. He believes that before commercial whaling, baleen whale faeces may have accounted for some 12 per cent of the iron on the surface of the Southern Ocean.

Previous studies have shown that iron is crucial to ocean health because plankton need it to grow. “If you add soluble iron to the ocean, you get instant phytoplankton growth,” says Nicol. The amount of iron in whale faeces means that protecting Antarctic whales could swell populations of phytoplankton, which absorb carbon dioxide.

Antarctic krill (Euphausia superba) feed on the phytoplankton, concentrating the iron in their tissue. And in turn, baleen whales eat the krill.

Iron rations

It had already been suggested that whales recycled iron in the ocean by eating it in krill and making it available to phytoplankton in faeces. But until this study, no one had analysed whale faeces to confirm if it indeed contained significant quantities of iron.

Nicol’s team analysed 27 samples of faeces from four species of baleen whales. He found that on average whale faeces had 10 million times as much iron as Antarctic seawater.

The team confirmed the iron came from krill by analysing the iron content in whole krill and sampling genetic material from the whale faeces for krill DNA. “We confirmed the vast majority of the iron in the poo came from krill,” says Nicol.

Big eaters

Using estimates of the whale population before commercial whaling in the Southern Ocean began early last century, Nicol predicts that baleen whales – now endangered – once consumed about 190 million tonnes of krill every year and produced 7600 tonnes of iron-rich faeces.

Larger populations of whales would have produced more of this “bio-available” iron, leading to bigger phytoplankton and krill populations in turn, says Nicol.

“Allowing the great whales to recover will allow the system to slowly reset itself,” he says. And this will ultimately increase the amount of CO 2 that the Southern Ocean can sequester.

David Raubenheimer, who researches marine nutritional ecology at Massey University in Auckland, New Zealand, says the findings are convincing and important. They highlight a specific ecological role for whales in the oceans “other than their charisma”, he says.

Peter Gill, a whale ecologist at Deakin University in Warrnambool, Victoria, Australia, calls the research “exciting stuff”.

“So many whales were moved from the ocean before we could understand the ocean ecology,” says Gill. “It’s exciting when we can reconstruct the past, and all these bits fall into place.”

Journal reference: Fish and Fisheries, DOI: 10.1111/j.1467-2979.2010.00356.x