Most ecologists have used climate change, as an omnipresent pressure, to support their findings in researching the vulnerability of specific taxa, communities, or ecosystems. However, there is a widespread lack of long-term biological, biocoenological, or community data of periods longer than several years to ascertain patterns as to how climate change affects communities. Since the 1950s, southern Europe has faced an ongoing trend of drying and loss of precipitation. A 13-year research program in the Dinaric karst ecoregion of Croatia aimed to comprehensively track emergence patterns of freshwater insects (true flies: Diptera) in a pristine aquatic environment. Three sites, spring, upper, and lower tufa barriers (calcium carbonate barriers on a barrage lake system that act as natural damns), were sampled monthly over 154 months. This coincided with a severe drought event in 2011/2012. This was the most significant drought (very low precipitation rates for an extended period of time) in the Croatian Dinaric ecoregion since the start of detailed records in the early 20th century. Significant shifts in dipteran taxa occurrence were determined using indicator species analysis. Patterns of seasonal and yearly dynamics were presented as Euclidian distance metrics of similarity in true fly community composition compared at increasing time intervals, to ascertain the degree of temporal variability of similarity within the community of a specific site and to define patterns of similarity change over time. Analyses detected significant shifts in community structure linked to changes in discharge regimes, especially to the drought period.

Freshwater ecosystems, especially springs, are highly sensitive to environmental changes. They are also excellent natural laboratories because of their stable conditions, reducing the number of variables to be considered in field studies. We examined the composition, dynamics and colonisation patterns of macroinvertebrates with respect to canopy coverage and time of day in which available areas are actively colonised. We used artificial substrates that mimicked the natural habitat structure at an isolated karst spring and recovered exposed substrates every 12 h. Physico-chemical parameters of water did not differ significantly regardless of canopy cover. The most numerous representatives and the pioneering champions were larvae of Baetidae (Ephemeroptera) and Chironomidae (Diptera). Simuliidae were also among the most successful pioneering species. Most observed groups more actively colonised substrates in the closed canopy area. Oligochaeta and Gammarus fossarum were more numerous on substrates in the open canopy area. Individuals of all analysed groups showed day-night migration patterns and were more active at night. Coleoptera ( Elmis sp.) were the poorest (re)colonisers among the analysed taxa.

Benthic macroinvertebrates have been thoroughly studied from various points of view, but our knowledge about their colonisation processes and dynamics in karstic springs is still scarce. Karst springs are stable systems that serve as an ideal experimental field site for studying the colonisation processes of benthic macroinvertebrates. Therefore, we conducted a study on the dynamics of their colonisation as a function of environmental characteristics, using artificial substrates that mimic aquatic vegetation. The substrates were placed in both open and closed canopy areas with different motility characteristics. The results showed that more macroinvertebrate individuals, especially Ephemeroptera (Baetidae) and Diptera (Chironomidae), colonised the open canopy area than the closed one. Movable substrates accumulated more particulate organic matter (POM), resulting in higher taxa richness compared to fixed substrates. Flow velocity, canopy cover, and water temperature were the main environmental properties influencing macroinvertebrates colonisation dynamics. The colonisation process began just 12 hours after the substrates were placed in the stream, with the Beatidae and Simuliidae families identified as pioneer taxa. Notably, only Simuliidae showed distinct day-night migration patterns. This study provides a better understanding of macroinvertebrate colonisation patterns in relation to environmental conditions, which is still largely ignored in limnological studies.