Effects of water temperature over benthic diatom communities: insights from thermal springs

ABSTRACT Background Thermal springs provide extreme ecological conditions for aquatic communities owing to their high water temperature and particular water chemistry. The thermal springs and their connected watercourses provide a thermal laboratory by offering a wide range of temperatures within short spatial distances. To date, the information on how the biodiversity of these springs is related to water temperature or chemistry is limited. Aims We studied the effects of water temperature on diatom community diversity and structure with the objective to supply a baseline for the conservation of thermal springs. Methods We sampled 31 sites of 16 thermal springs across a temperature gradient between 18.5 and 63.0°C in the north-western Iberian Peninsula and related diatom richness and structure to water temperature. Results A total of 124 diatom species were identified in springs with water temperature between 18.5 and 42.4°C. Community diversity decreased with increasing temperature and the highest species richness was found at temperatures ≤ 25°C. Three diatom assemblages were defined, discriminated by temperature ranges (≤25°C, 25–35°C and ≥35°C). Conclusions Water temperature was found to be an important driver of diatom community composition in the thermal systems studied. Temperature affects diatom distribution decreasing diversity with the increase in global water temperature.