The Emergence of the Family Scirtidae (Insecta: Coleoptera) in Lotic Karst Habitats: A Case Study over 15 Years.

Simple Summary: This study is a case study on the diversity patterns, population aspects, emergence and ecological drivers of the so-far poorly studied water beetle family Scirtidae. Although they can be very abundant in karstic lotic freshwater habitats, there are still insufficient data on their biology and ecology. The family was studied over a period of 15 years in specific lotic habitats of springs and tufa barriers in the karst freshwater ecosystem of Plitvice Lakes NP, Croatia. Scirtidae showed a longitudinal gradient, as the genus Elodes was recorded only in the spring area, while the genus Hydrocyphon was found only in downstream sites with tufa barriers. Their emergence showed a seasonal character, with males dominating earlier in the season and females appearing later. The type of substrate determined their distribution, with a preference for bryophytes. Their abundance and emergence were primarily determined according to the parameters that showed the greatest fluctuations over the 15-year period: water discharge, water temperature and oxygen saturation. Compared to previous results from similar studies on other insect groups, our results clearly show the high potential of the family Scirtidae as indicators of habitat quality. Due to ongoing changes and a decline in biodiversity, science today should rely on long-term species-based ecological studies. We have conducted a long-term ecological dynamics study on the water beetle family Scirtidae, which, although it is very abundant in benthic communities, is still poorly studied. The main objective of this study was to investigate the population aspects (composition, diversity, sex ratio) and ecological aspects (emergence patterns, seasonal dynamics and preferences for environmental factors) of the family Scirtidae over 15 years in Plitvice Lakes NP, Croatia. The study was conducted at three sites and in five different substrate types. A total of three taxa with different distributions were recorded in the study area: Hydrocyphon novaki and H. deflexicollis on the tufa barriers and the Elodes sp. in the spring area. The sex ratio was in favour of males in spring and early summer, while it shifted in favour of females towards the end of autumn. The abundance and emergence of the family were primarily determined by the environmental parameters which showed the greatest fluctuations over a period of 15 years: water temperature, water discharge and oxygen saturation. Our results clearly show that Scirtidae can be used as indicators of stream zonation and habitat quality. Based on the methodology and the results of this study, we conclude that Scirtidae should be used in future monitoring and protection measures in karst freshwater habitats in southeastern Europe. [ABSTRACT FROM AUTHOR]