Benthic life in karst spring-The life cycle and secondary production of benthic macroinvertebrates under the effects of constant water temperature

Because of the thermal stability and the persistence over geological time scales of their aquifers, the permanent karst springs may act as a glacial refuge, as well as serve as in vivo laboratories for the testing of various ecological hypotheses. For these reasons, our main hypotheses were: i) to the constant water temperature benthic species will response by specific voltinism and life-cycle length will be different from those that the species usually have in non-spring habitats; ii) under the constant water temperature the particular species and whole community will have higher biomass turnover like in similar non-spring habitats. Investigation was performed in large cave karst spring Vyvieranie in the Western Carpathians. In total, 40 species of benthic macroinvertebrates were identified in the studied karst spring. The trajectory of the annual change of the benthic community structure clearly showed a returnable pattern at the species density and biomass level. The constant water temperature throughout the year was reflected by specific life-history trajectories in certain benthic species. While some species had fixed voltinism (e.g. Ephemerella mucronata, Isoperla sudetica), others indicated having a flexible life-cycle pattern. In the species with a flexible life cycle, the trajectory of larval development occurred in two different ways. In the first case, a constant water temperature extended larval development (e.g. Protonemura auberti, Leuctra albida). In the second case, the addition of a winter cohort was recorded (e.g. Gammarus fossarum, Rhyacophila tristis, Protonemura austriaca). The productivity of this benthic community was considerably higher than that previously found in other submountain limestone streams in the Western Carpathians.