Ubiquitous Rather than Endangered: Current and Predicted Distribution of the Freshwater Red Alga Riverina rivularis in Serbia

The freshwater red alga Riverina rivularis (Liebmann) C.W.Vieira & G.W.Saunders has historically been perceived as a rare or endangered species due to fragmented records and specific ecological requirements. However, the recent literature suggests that its distribution may be far wider than previously assumed, potentially influenced by intensified climate change. In this paper, we evaluated the current distribution of R. rivularis in Serbia, along with the key environmental factors driving its distribution and coverage. Additionally, we assessed the co-occurring benthic algal communities and the key environmental factors responsible for their occurrence. Furthermore, we predicted future species distribution under changing environmental conditions. Our results reveal that R. rivularis is far more ubiquitous in Serbian running waters than previously assumed, showing high tolerance for a wide range of environmental conditions. Hypothetical environmental change scenarios involving increases in water temperature and conductivity, both individually and combined, suggest a potential expansion of suitable habitats for R. rivularis. These findings highlight the importance of systematic monitoring and updated distribution data in freshwater conservation management, suggesting that R. rivularis should be regarded as a widespread component of Serbia’s algoflora rather than a threatened species.