ASSESSMENT OF CRITICAL THERMAL MAXIMA OF AQUATIC MACROINVERTEBRATES IN THE EERSTE RIVER, EASTERN CAPE, SOUTH AFRICA

The impact of temperature on the physiology, ecology, and evolution of both endothermic and ectothermic organisms is pivotal. Every species possesses a distinct optimum temperature range that is crucial for survivorship. Determining upper thermal limits provides insight into the relative sensitivity of organisms to elevated water temperatures and provides valuable insights when monitoring for environmental thermal alterations. The current study examined the upper (CTmax) thermal limits of ten (10) freshwater macroinvertebrate taxa in the Eerste River, south-western of South Africa. All test insects were acclimated at 17 °C and subsequently exposed to a steady rise in temperature of 0.34 °C per minute using the Critical Thermal Methods (CTM). Generally, we observed a narrow range in thermal tolerance among the test organisms, suggesting that a similar threshold increase in temperature is likely to hamper the population of these organisms. However, significant differences were found in the mean CTmax values among the test insect within the same environment. The most sensitive species were the Aphanicerca species (32.3±1.2) and Chimarra species (33.7.09±2.8). These species may be useful indicators of thermal alteration in their habitats, due to their relatively low tolerance to increasing temperatures and the ease with which behavioral responses can be detected. Consequently, their disappearance from a stream may indicate that thermal or chemical pollution has occurred. We recommend future studies to explore on the adaptation and mitigation measures for climate change to save the biodiversity of Chimarra and Aphanicerca.