Ocean fertilisers

Picture: NOAA.With the International Whaling Commission’s scientific committee due to consider approval for Japan’s re-modelled scientific whaling program in late November, results of several studies undertaken in the US and Australia all serve to demonstrate the important role whales play in maintaining healthy oceans, ensuring sustainable, productive fisheries, and mitigating the impacts of climate change .

In May, a research paper published by Flinders University PhD graduate Trish Lavery found that nutrient-rich whale faeces were crucial in ensuring the mammals’ feeding grounds remained healthy, due to the rich food source faeces provide that sustain and promote the growth of other fish and plant species.

“Previous models have assumed that all prey eaten by whales is lost to marine ecosystems, and thus harvesting whales would allow the prey that would have been consumed by that whale to become available for harvest by fisheries. We modelled the effect of blue whales on marine productivity by examining both the amount of prey consumed and the amount of prey stimulated as a result of the whales defacating large amounts of nutrient-rich faeces in the surface waters of the ocean. We found that blue whales essentially fertilise their own feeding grounds with the nutrients needed to sustain the growth of their krill prey,” Lavery said.

Her findings endorse several years of ongoing whale research led by Joe Roman, a whale biologist at the University of Vermont’s Rubenstein School of Environment and Natural Resources, and Harvard University’s Professor of Biological Oceanography James McCarthy. Results of their latest study, published in July’s issue of journal Frontiers in Ecology and the Environment, confirms the importance of whales in the maintainance of healthy marine ecosystems, and suggests that areas of ocean were more productive where whales were once more numerous.

“With high metabolic demands and large populations whales probably had a strong influence on marine ecosystems before the advent of industrial whaling: as consumers of fish and invertebrates; as prey to other large-bodied predators; as reservoirs and vertical and horizontal vectors for nutrients; and as detrital sources of energy and habitat in the deep sea,” the report states.

Whales travel vast distances throughout the oceans so the nutrients produced in their faeces are released and spread widely in a fountainous ‘liquidy, flocculent plume’. Roman said this ‘whale pump’, helped to promote the growth of the phytoplankton that are the base of the marine food chain.

While the nutrient-rich faeces produced by whale species living in northern hemisphere oceans assist in replenishing scant supplies of nitrogen, research undertaken by the University of Tasmania’s PhD candidate Lavenia Ratnarajah has found whale populations that call the Southern Ocean home, are crucial in ensuring the iron content in these waters is maintained. Although there are other sources of iron in the region, from atmospheric dust, shelf sediments, underwater volcanoes and icebergs, the reduction in whale numbers is causing a greater decline in the phytoplankton that supports all marine life.

“Their poo contains over ten million times higher iron concentrations than sea water and the population has diminished over the last century or so, that’s a massive decline in iron that’s going into the water naturally,” Ratnarajah said.

Fewer whales also holds implications for climate change. The UTas study found that defacation by the 12,000-strong sperm whale populations in the Southern Ocean removes approximately 200,000 tonnes of carbon each year from the atmosphere. This suggests whale faeces not only ensure healthy and productive ecosystems, the poo also serves to reduce the impacts of climate change through its capacity to remove carbon dioxide.

Anne Layton-Bennett
References: “Whales as ecosystems engineers” by Joe Roman et al
“Whales sustain fisheries: Blue whales stimulate primary production in the Southern Ocean by Trish J. Lavery et al
“Bottoms up: Importance of whale poo on world’s oceans” by Lavenia Ratnarajah et al

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