Island formation by the earthworm Aporrectodea caliginosa

Extreme soil moisture conditions are expected to occur more often due to climate change. Therefore, it is vital to understand the response of earthworms and their coping mechanism to these conditions. One of the mechanisms used by the endogeic species to avoid anaerobic conditions during flooding is the formation of islands. Such islands created by earthworms have been found in specific landscapes in the Surales in South America. Recently, at a very small scale, island patterns were observed under solar panels in The Netherlands, which seemed to be constructed by the species Aporrectodea caliginosa. A lab experiment was performed with mesocosms with A. caliginosa in mesocosms to determine if they are responsible for the islands. The mesocosms had two different initial conditions (flat or rugged surface) and two different flooding treatments. Earthworm island formation was demonstrated and depended on the initial ruggedness of the soil surface and the rate of flooding. The highest islands were found in treatments with an initial rugged soil surface and the slowest rates of flooding. The earthworm density was higher in the islands than in the surrounding submerged soil.