Rapid spread of Euglena sanguinea Ehrenberg (Phylum Euglenophyta) in South African freshwater bodies: A potential threat

Abstract

Euglena sanguinea is a red-pigmented euglenid species known for producing the ichthyotoxin euglenophycin, which has been associated with fish mortalities in various freshwater systems. First reported in South Africa from the Kruger National Park in 2016, E. sanguinea has since spread rapidly across multiple provinces, forming persistent dense blooms in several freshwater bodies. This study documents its expanding range, with confirmed occurrences in dams, ponds, and wetlands in Limpopo, Mpumalanga, KwaZulu-Natal, and the Western Cape provinces. Microscopic investigations revealed consistently high densities of E. sanguinea dominating algal assemblages at all surveyed sites. Cells varied from green in shaded areas to bright red in full sun and showed typical metabolic shape variability. Water quality data recorded across four sites showed temperatures ranging from 21.6 to 31.1 °C, pH values between 7.23 and 8.0, electrical conductivity from 202 to 541 µS cm⁻¹, and total dissolved solids (TDS) between 102 and 271 mg l⁻¹. The persistent and dense nature of these blooms highlights the potential ecological risk posed by E. sanguinea, especially under changing climatic conditions. The findings emphasise the urgent need for continued monitoring and the development of management strategies to mitigate potential impacts on aquatic ecosystems.