Determination of the condition of aquatic beetles on the tufa barriers and waterfalls of the Krka NP

Determination of the condition of aquatic beetles on the tufa barriers and waterfalls of the Krka NP
Water beetles belong to the order of beetles (Insecta: Coleoptera). They are found in almost all types of aquatic habitats, except seas and oceans. The most important role in their distribution is occupied by the diversity of microhabitats in a certain biotope, in other words, their preference for a certain type of habitat.

As with other groups of aquatic insects, water beetles are equally affected by the physical-chemical characteristics of the water, primarily the speed of its flow and the concentration of nutrients dissolved in it, which makes them important indicators of the quality of a habitat, i.e. bioindicators. Water beetles react very quickly to changes in their habitat.

Tufa barriers are specific habitats, created by biodynamic processes. In these habitats, the water is enriched with oxygen and often very fast. They contain a community of mosses and waterfall-loving beetles (Insecta: Coleoptera: Elmidae), which is defined as the "carrier of the abiological diversity of karst water systems" and as an indicator of high habitat quality.

Therefore, the main goal of this project was to carry out the first survey of the fauna of aquatic beetles on the waterfalls and tufa barriers along the Krka River, starting from the source and ending with its lower course, which will serve as a basis for future research and provide guidelines for it. Given that no systematic investigation into the fauna of water beetles had yet been carried out in these habitats, the physico-chemical indicators of the water were also measured, with the aim of determining the indicator potential of the mentioned insects. In addition, habitat types were defined according to the type of substrate. The field research was conducted by Ass. Prof. Vlatka Mičetić Stanković, PhD, from the Croatian Museum of Natural History, in the spring and summer of 2023 at a total of nine locations and nineteen sub-locations along the course of the Krka River. Eight families, sixteen genera, and twenty-two species of water beetles were identified. Two families were the most represented: hydraenidae and elmidae, which make up the typical fauna of such habitats, which indicates very high quality water. Two families were the most highly represented: moss beetles (Hydraenidae) and riffle beetles (Elmidae), which compose the typical fauna of such habitats, indicating water of a very high quality.

The diversity and abundance of beetles in the Krka River vary along its course and decrease in the downstream direction. The most important factors that define their abundance and distribution are water temperature, the amount of oxygen dissolved in it, and the type and diversity of microhabitats.

During this research, an entomological box with more than two hundred mounted insects was created, which will be used in education, for familiarisation with investigative methods in entomology and ecology, but also for becoming acquainted with these important inhabitants of tufa barriers.