How do whales help mitigate climate change?
This past week, governments from around the world have been discussing how to halt the advancing climate crisis at COP26 in Glasgow.
Experts agree that healthy oceans are key to regulating the climate, as they absorb 25% of carbon from CO2 emissions into the atmosphere and more than 90% of excess heat from the atmosphere.
But climate change poses major challenges for the ocean. Along with acidification, climate change has led to changes in marine ecosystems with severe impacts on species richness and distribution and has also brought unfavorable social and economic consequences for humans.
Whales and other cetacean species are not exempt from this problem, and to date we have seen how climate change can have a wide range of impacts on them. Documented impacts include changes in distribution, changes in the moment and duration of migrations, loss of habitat, and reduced conception and reproductive success rates. These large marine mammals, which are still recovering from the severe impacts of the whaling era, are under extreme pressure from other anthropogenic stresses such as plastic waste, chemical and noise pollution, and collisions, among others.
Due to these factors, multiple cetacean populations may eventually collapse, which could have permanent long-term negative consequences for the functioning of marine ecosystems, as cetaceans play a key and irreplaceable role in marine ecosystems and have been referred to as “ecosystem engineers”.
How do whales and other cetaceans help mitigate climate change?
Large cetaceans play a key role in helping to combat climate change through their key role in the marine ecosystem. These species are considered to act as ecosystem engineers by contributing to the circulation of nutrients within the water column and the transfer of nutrients between waters of different latitudes and sequestering carbon from the atmosphere, both directly and indirectly.
Cetaceans are mobile animals, and many species are migratory, making long journeys across ocean basins, often between cold productive waters to warmer and often oligotrophic waters. These movements, both vertically by diving and surfacing to breathe and defecate, and horizontally with migrations between different latitudes, help the circulation of nutrients throughout the ocean, the fertilization of its waters and are crucial to stimulating fish abundance by improving ecosystem productivity.
On the one hand, movements between the surface and deeper waters cause a vertical transfer of nutrients. Many whale species consume prey at some depth and when they return to the surface to breathe, they also release nutrient-rich fecal plumes. The fecal plumes they release near the surface contain nutrients from the deep ocean that would otherwise be unavailable to surface-dwelling species. Their faeces are particularly rich in iron and nitrogen, both of which are necessary for the development of phytoplankton, which is responsible for generating 50% of the oxygen we breathe, as well as capturing around 37 billion metric tons of CO2, an estimated 40% of all CO2 produced (an amount that according to the IMF – International Monetary Fund – would be equivalent to 1.70 trillion trees or 4 forests like the Amazon).
In addition, these movements in the water column aid the vertical mixing of waters from different layers, contributing to a wider distribution of nutrients and oxygen in the water.
On the other hand, whales that undertake long migrations contribute to the horizontal movement of nutrients by moving between highly productive areas in cold latitudes to breeding areas that are generally found in warmer, less productive waters near tropical latitudes. Nutrient inputs come from their defecations, placentas when giving birth, their carcasses, and the skin they may shed.
Through this mechanism, known as the “whale pump”, whales transport nutrients both vertically, between deep water and the surface, and horizontally, across the oceans, promoting primary production and thus atmospheric carbon fixation.
In addition to aiding the oceanic circulation of nutrients, whales play an important role in carbon sequestration. When they die naturally, whale carcasses sink to the deep ocean, carrying with them enormous amounts of carbon to the seafloor, where they provide habitat and food for many deep-sea organisms. These bodies, which have sequestered carbon throughout their lives, fall to the depths, sequestering the carbon without returning it to the atmosphere. This is known as “whale falls”.
According to a report by the International Monetary Fund (IMF) it is estimated that “each great whale sequesters, on average, 33 tonnes of CO2”.
Researchers estimate that, due to past whaling, during which populations are estimated to have been reduced by about 90%, great whales now store approximately 9 million tonnes less carbon than before.
Through these systems, these large cetaceans help maintain healthy and productive oceans and reduce the impacts of climate change so that their conservation plays a key role in ocean health and climate change mitigation.