Activities vital to all life on Earth take place beneath our feet every single day and some of the most important organisms involved in these processes are often the most overlooked. As our planet undergoes huge changes, animals out of sight should definitely not be kept out of mind! Alex Powell describes how earthworms, small organisms with a very large impact on the health and functioning of our ecosystems, could be affected by the challenges of climate change, and what this could mean for us as humans.
When I told my friends and family that I was going to be doing a summer research project at my university, everyone was excited to find out what I would be investigating. A new disease? Climate change in the arctic? A bizarre, unheard of species from the Amazon rainforest?
However, when I told them it was a project about worms, they switched from enthused to confused. Worms? What have worms got to do with anything?
In actual fact, worms have a lot to do with almost everything, though their importance is scarcely emphasised. In the words of Charles Darwin, ‘it may be doubted if there are any other animals which have played such an important part in the history of the world’ as worms! Earthworms play absolutely vital roles in maintaining the health and quality of our soils, which in turn support life on earth.
Green worm also known as the Allolobophora chlorotica. Image credit: Holger Casselmann on Wikimedia Commons.
They are often referred to as ‘ecosystem engineers’ due to their astounding abilities to alter the properties of soil and influence other organisms within it. By cycling key nutrients and improving soil structure, earthworms are able to increase agricultural productivity: in short, whether there is enough food to feed our growing human population largely depends on these worms doing their job!
However, just like all organisms on our planet, earthworms are being affected by climate change. As extreme weather events such as droughts and flooding are increasing in frequency and severity, these key animals will face novel and unprecedented threats due to soil degradation. Worms rely on the water in soils to keep their body surface moist enough to survive.
A green worm pictured on a log in moist soil. Image credit: Maximilian Paradiz on Wikimedia Commons.
Many fear that soil moisture levels may become too low or even too high for earthworms to function as our climate changes. The degradation of soils involves the decline of soil quality, diminishing its capacity to support life and store carbon, caused by the effects of intensive farming practices and resulting in large environmental consequences such as flooding and mass migration.
My experiment using green worms (Allolobophora chlorotica) aimed to find out how these below-ground beauties might be able to cope with the challenges of our variable environment. I conducted a range of choice chamber trials, which were essentially obstacle courses for worms, aiming to determine a preferred soil moisture range for earthworm function. Worms were placed into soils of a specific moisture level to start and allowed to move through barriers into wetter or drier soils if they so wished. After 24 hours, I would check where each worm had ended up and over the course of 6 weeks, I ran over 50 trials and measured the soil moisture preferences of over 200 green earthworms.
A choice chamber experiment consisting of four soils differing in their moisture contents. Four earthworms were placed into each container and allowed to move throughout it for 24 hours, after which their moisture preferences were inferred. Image credit: Alex Powell.
My results showed that, as expected, the worms really disliked ‘droughted’ soils below 20% moisture by mass. Most chose to occupy soils ranging from 20-35% moisture - despite soils above 30% becoming more sludgy and compact, the worms were not deterred! This suggests that extremely dry, droughted agricultural soils may be a real problem; if such key organisms choose to avoid these soils, their health and capacity to produce crops may deteriorate.
So, what can be done to make sure our earthworms stay where we need them to? Although it might sound like a difficult task, there are some changes that those working in agriculture can make to help achieve this. Some traditional farming practices such as ploughing tend to degrade soils and reduce their capacity to store moisture. By shifting away from these activities in favour of less damaging techniques like the increasingly popular no-till farming, our soils could remain a healthy environment for both earthworms and crops to thrive in.
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