What whale falls can teach us about biodiversity and climate change

Anaëlle Durfort quantifies carbon sequestered in marine fauna for her PhD in ecology at the University of Montpellier, France, to highlight the links between biodiversity and climate change.

Why are you investigating carbon sequestration in animals?

The way in which carbon moves into the ocean through whales demonstrates the complex links between biodiversity and climate. Climate change affects living organisms, which themselves affect greenhouse-gas emissions.

One striking example comes from my master’s degree, also at Montpellier, which focused on quantifying the carbon sequestered in the Southern Hemisphere since 1890 by the carcasses of five species of whale. Because they’re so huge, whales hold a lot of carbon in their tissues and, after dying, they trap that carbon on the ocean floor for more than a century. But the effectiveness of these animals as a carbon ‘pump’, moving carbon from the atmosphere, and eventually to the bottom of the ocean, varies according to the size of cetacean populations.

Before they were exploited on an industrial scale, whales were abundant in the Antarctic, and a team that I worked with during my master’s estimated that they sequestered a total of 400,000 tonnes of carbon per year¹. We calculated that this figure had dropped to 60,000 tonnes by 1972, because of the impact of centuries of commercial whaling. Since whaling was banned temporarily through an international agreement in 1986, populations have been slowly recovering.

But the projected restoration of whale populations depends on the extent of climate change (as well as on factors such as the incidence of collisions between whales and ships). Looking at two scenarios, we estimated what the biomass of whale carcasses on the sea floor would be by 2100. Under the worst-case scenario proposed by the Intergovernmental Panel on Climate Change (in which global warming ranges from 3.3 °C to 5.4 °C by 2100), the sequestration would reach 170,000 tonnes per year. Without climate change, recovered whale populations would be able to sequester nearly twice as much carbon.

Whales won’t save the climate — global carbon emissions reached 10 gigatonnes (10 × 10⁹ tonnes) in 2021 (ref. 2) — but my work shows how human activities are affecting the carbon sink that these animals provide, and might stop its recovery.

Your research now focuses on krill. Why?

Yes, I’ve moved down the food chain. My research focuses on assessing the biomass of Antarctic krill (Euphausia superba), small crustaceans that are essential to the Antarctic food web — and especially to whale diets.

Looking at carbon sequestration mediated by exploited species such as whales and krill, the team I work with highlights the links between biodiversity, human activities and climate. Krill catching on an industrial scale, often for pet food or aquaculture supplements, has an impact on the entire marine food chain, as well as on biogeochemical cycles.

More generally, the practice raises questions about using krill as a resource: are the benefits worth the environmental and climate damages? All of us should consider our activities with these questions in mind.

What do you think of putting a carbon price on whales?

Looking at how much carbon whales can lock in, some economists and non-governmental organizations put a carbon price on the animals, betting that having this in place will encourage carbon offsetting and protect the animals. The idea is that companies, by paying the price in funding whale protection, can claim carbon credits for every whale they save.

But this commodification of nature in the name of conservation seems problematic to me. These solutions are part of the same economic and societal framework that put us in the ecological and social crisis we are facing. This is not in line with the transformative changes that we need. What needs to change is our relationship with nature.

You attended COP15, the United Nations biodiversity conference held in Montreal, Canada, in December 2022. What was it like?

I was part of the Global Youth Biodiversity Network (GYBN), with more than 100 young representatives from all continents. This was a great experience for me, both as a scientist and as an environmental activist.

The conference was also an opportunity to get to know more about international biodiversity-conservation policies, to see the underlying mechanisms. What struck me most was the complexity of the negotiations — groups of all sorts were attending, including states and observers, such as non-profit entities, businesses, Indigenous people — and the technical nature of the debates. A lot is going on apart from the main negotiations between states’ representatives, with many interests represented at networking sessions and lobbying during the side events.

At the GYBN, we had some victories, including Target 22 of the new Global Biodiversity Framework, which guarantees the participation of Indigenous peoples and local communities in decision-making on biodiversity-conservation policies.

Have you ever seen a whale

Unfortunately, no. My work is in front of a computer, making models to look at how carbon-sequestration dynamics evolve under global warming and in response to commercial fishing. This work requires a lot of scientific collaboration, to access models of ocean change and population dynamics. I do a lot of cooperation, but no fieldwork.

Source: Ecology - nature.com