Factors affecting colonisation success of the anecic earthworm Lumbricus terrestris (L.) in mesocosms on temperate pasture

Background & aims: Changing precipitation patterns require climate adaptive measures to improve water regulation. Deep vertical earthworm burrows dug by the anecic species Lumbricus terrestris contribute to water infiltration rate and capacity, and deeper plant root growth. L. terrestris is considered a native species to western Europe, reaching its highest abundances in pastures. In pastures where the species is currently absent, water regulation could improve after inoculation with these earthworms. We conducted a field experiment to test the feasibility of introducing L. terrestris. Methods: Mesocosms were installed at two Dutch dairy farms. One farm had a resident L. terrestris population, the other did not. Subsequently, L. terrestris was introduced: half of the mesocosms received locally collected earthworms (NL), and the other half received commercially imported inoculum from Canada (CA). Twelve months later, the mesocosms were harvested and all earthworms were counted. Results: The field experiment proved that L. terrestris can survive and produce offspring after introduction. At the location with a resident population, 15% of the L. terrestris introduced (tagged with Visible Implant Elastomer-tags) had survived, and at the L. terrestris-free site this was 26%. A hypothesised interspecific competitive relationship with Lumbricus rubellus (Hoffmeister) was not confirmed. Locally collected inoculum performed equal to or better than the commercial inoculum. Conclusions: Earthworm origin seems to influence chances of mesocosm colonisation success. VIE-tagging possibly interfered with survival. Future research could involve the role of pathogens and colonisation success in a non-enclosed set-up for a longer period of time.