Ecosystem change and establishment of an invasive snail alter gastropod communities in long-lived Lake Malawi

Biotic invasions can have far-reaching effects in isolated, eco-insular systems such as the African Great Lakes, certainly in synergy with other anthropogenic stressors that affect ecosystem stability. Interactions between invasive and indigenous taxa across trophic levels often tend to propagate throughout the ecosystem, but also those at the same trophic level may affect biodiversity. Here, we examine faunal interactions between an invasive Asian morph of the cerithioidean gastropod Melanoides tuberculata and indigenous gastropods in long-lived Lake Malawi. Studying quantitative samples, we document a negative spatial correlation between the established invader and endemic Melanoides species, and positive ones between invasive and native M. tuberculata, and between native Melanoides and schistosome-transmitting Bulinus. Comparison of modern and fossil samples indicates that Melanoides communities have changed since the middle Holocene from consisting predominantly of endemic taxa (95%) toward a dominance by non-endemics (80%). External evidence suggests that ecosystem change, such as increased sedimentation and eutrophication, and interactions between the invasive and endemic Melanoides species are the most likely causes for these changes. More in-depth study of the benthic ecosystem is required to document interaction mechanisms better, but the invasive taxon is playing an important role in reshaping communities and diversity in Lake Malawi.