A meta-analysis to compare the sensitivities of earthworms and enchytraeids to different stressors

Earthworms and enchytraeids are soil organisms involved in key soil functions, such as organic matter turnover and soil structure, at different scales. In natural soils, these organisms are exposed and sensitive to different abiotic factors (e.g., climate, land use and management) and are often used as bioindicators of human disturbances, particularly chemical stress. However, the sensitivity of these two groups of Oligochaeta (Annelida) to different stressors has never been compared. Using data from 49 publications and 330 observations, we performed a meta-analysis to compare the sensitivities of earthworms and enchytraeids to all kinds of stressors under similar test conditions. Earthworms and enchytraeids were found to be equally sensitive to chemical stressors (mean effect size −0.61 [-2.53; 1.30]) regardless of the studied endpoint (mortality or reproduction). Most of the observations dealt with the effects of pesticides (42 %) and heavy metals (40 %) on both organisms. No difference in sensitivity was revealed when these two stressors were considered separately. Regarding the two most studied species of enchytraeids and earthworms, the mean effect sizes of all the possible combinations of Eisenia fetida (41 % of the studies) or Eisenia andrei (48 %) or Enchytraeus crypticus (73 % of the studies) or Enchytraeus albidus (27 %) did not reveal any differences in sensitivity. This study also highlights the lack of studies on environmentally relevant (i.e., representative of natural soils) enchytraeid and earthworm species. We also revealed that mostly ecotoxicologists have compared the sensitivities of these two key soil organisms when they are exposed to and threatened by other important factors, such as agricultural practices and climate change.