Assessment of Pontoscolex corethrurus, an exotic earthworm, in contrasting protected subtropical forest habitats in North-East India

Earthworm as ecosystem engineer greatly affects soil properties in various ecosystems, and are widely known for their role in enhancing soil fertility. However, invasive species cause environmental harm and have negative impact on native species. Considering the negative impacts of invasive species, it is imperative to study the diversity and population density of exotic species in Manipur, under Indo-Burma biodiversity hotspot. Samples (earthworm and soil) were collected during January to December 2018 from two subtropical forest ecosystems by simple digging and hand-sorting methods. The study sites are relatively undisturbed forest ecosystems under subtropical climatic conditions. Soil temperature and moisture ranged from 15.05 ± 0.16 °C to 24.26 ± 0.60 °C and from 21.24 ± 0.01% to 41.11 ± 0.03% in Site-I, and from 15.72 ± 0.41 °C to 24.46 ± 0.38 °C and 17.12 ± 0.06% to 39.71 ± 0.03% in Site-II, respectively. Species richness was higher in Study Site-I than in Site-II, with 7 and 5 species recorded respectively. These species belonged to 6 genera and 4 families, of which 4 were exotic. The majority of recorded species belonged to the family Megascolecidae. P. corethrurus was found to be the highest in density with 62.37% in study site-I and in study site-II, P. corethrurus represented 38.65% next to Drawida species with 45.89%. Its population density was highest in the community dominated by exotic species. Shannon diversity index values of 1.29 at Site I and 1.17 at Site II were observed, indicating higher species diversity at Site I. Species were positively correlated (p < 0.05) with soil moisture and temperature in the study sites. From the present study, it can be concluded that the invasion by P. corethrurus is proceeding even in undisturbed areas which may impact the native species and soil physico-chemical properties. Further in-depth research is encouraged for finding out the possible remedies to check the population density of exotic species.