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Global study of world’s most abundant creatures published today in Nature

25 Jul 2019

What is the most abundant animal on the planet? Some may guess mice, or perhaps ants. A simple Google search will give you the answer – it’s nematodes, small worms also called eelworms. There are 440 billion billion (4.4 ± 0.64 × 1020) of them and they exist in all of the Earth’s ecosystems (notably in soil, but also in water and as parasites in animal bodies). Still, because of their microscopic size most of us have never seen, and will never see, one. But they play a critical role in the cycling of carbon and nutrients in ecosystems, and are essential to understanding biological activity in soil. There are nematodes that feed on bacteria, fungi, plants and even on other soil animals, fulfilling several key roles in the soil food web. Indeed, they play a significant role in influencing CO2 emissions from soils, determining whether carbon is locked up in soil organisms or released into the soil and the atmosphere, where it contributes to global warming. Their activity helps create healthy soil conditions for plants to grow and provide crops as well as capture carbon. However, global warming could boost their activity, leading to increased global CO2 emissions from soils, according to an article published today in Nature and coauthored by ASE professor David Wardle.

Because of their importance to ecosystems and vast abundance, researchers want to know more about the distribution of nematodes. The Nature article co-authored by ASE professor David provides the first attempt to map the global distribution of the Earth’s soil nematodes. Interestingly, it shows that, unlike animals living above ground, the abundance of nematodes does not peak in the tropics. Instead, this study provides conclusive evidence that the majority of the world’s nematodes live in high latitudes, with 38.7% found in boreal forests and tundra, (North America, Scandinavia and Russia); 24.5% in temperate regions; and only 20.5% in the tropics and sub-tropics.

The article also provides a new improved calculation of the world’s population of soil nematodes, far greater than the previous. There are about 57 billion soil nematodes for every human, and their total biomass is around 300 million tonnes – approximately 80% of the combined weight of Earth’s human population of 7.7 billion people.

Nematodes are generally more active at higher temperatures, so the large nematode populations in the arctic and sub-arctic make these regions very sensitive to warming. These regions compose a major reservoir of soil carbon stocks, and may release much more carbon as a result of increased soil animal activity and a prolongation of the plant-growing season due to human-induced climate change.


Link to the paper:

Van den Hoogen, J., Giesen, S., Routh, D., Ferris, H., Traunspurger, W., Wardle, D. A., de Goede, R. G. M., et al. 2019. Soil nematode abundance and functional group composition at a global scale. Nature