Environmental drivers of ichthyofauna community composition of the river ecosystems draining the Lake St. Lucia basin, South Africa

Abstract

Within South Africa, the St. Lucia Basin, comprising the White Mfolozi, Black Mfolozi, Mfolozi Hluhluwe-Mkuze sub-basins, is an ecologically important region. However, the river ecosystems and their inherent biota, especially the ichthyofauna, are inadequately studied. Considering the anthropogenic land-use change currently occurring and the concomitant elevated resource-use, we sought to ascertain the composition of the fish species communities within the basin and the environmental drivers influencing the spatial shifts in these communities to provide baseline information. We collected data from 20 sites in the basin from 2016 to 2018. A total of 4 420 individuals representing 24 fish species, from eight families, were recorded. Using generalised linear modelling, species count data were fitted to sub-catchment factor variables and habitat variables. We observed significant differences in the structure of the ichthyofauna communities between the sub-catchments as well as the environmental drivers to be substrate, mean depth, mean velocity, overhanging vegetation and woody debris. The Hluhluwe sub-catchment was the most diverse, while the White Mfolozi was the least diverse. Continued unsustainable use of the basin's water resources and poor land management practices are likely to shift the ichthyofauna communities into uniform, species-depauperate communities, potentially leading to a loss in ecosystem services and functioning.