The influences of river regulations on aquatic biota are insufficiently investigated. We assessed the level of ecological disturbance of the mayfly assemblages through the damming and flow alterations at two highly regulated Mediterranean rivers in Croatia: the Cetina River and its tributary, the Ruda. Contrary to our hypotheses, species richness, abundance and diversity of mayflies increased along the river’s course. At the sites directly influenced by the river regulations, mayfly assemblage changed: it was less diverse and less abundant. However, no obvious influence of the river regulation on the mayfly assemblages was detected for the sites that were indirectly influenced by these alterations. This was most likely due to specific karst hydrology, i.e., the presence of lateral springs along the course of the river. Multidimensional scaling analysis (MDS) revealed grouping of sites according to the similarity in physico-chemical water properties. The pH and water temperature were the most important environmental variables influencing mayfly assemblages. The data on ecology and distribution of mayflies presented in the current study represent a valuable background for further research and conservation practices in the Mediterranean region.

The aim of this study was to determine which environmental factors influence emergence of insects at two contrasting habitats: one with constant and one with variable water temperature. We hypothesized that emergence of holometabolous insects is triggered by water temperature where temperature variations occur, while light is the main stimulus for emergence at site with constant water temperature. We expected that for the emergence of hemimetabolous insects, some additional environmental stimuli might be required. We also expected weather conditions to be more important at sites that lack variations in water temperature. To test our hypotheses we placed six pyramid‐type emergence traps at the two sites. Emergent aquatic insects were collected at 8‐h intervals over a 13‐day period, during peak emergence for most of the target species. Most taxa emerged during the afternoon at both sites. Only Hydropsyche saxonica/instabilis emerged nocturnally. At the site with constant water temperature, emergence of Drusus croaticus was stimulated by length of sunlight period. Emergence of Protonemura auberti was promoted by higher air temperature and humidity of the day before. Brachyptera tristis emerged in higher numbers when humidity and cloudiness were high the preceding day. At site with variable water temperature, an increase in water temperature, with a threshold at 16°C, was a significant factor for the emergence of Hemerodromia unilineata. This study gives new insight into the complexity of relationships between aquatic insect emergence patterns and environmental drivers, and show that light and weather conditions trigger emergence of most insects under constant water temperature conditions, while temperature is a dominant trigger at variable water temperature habitat.

The stonefly fauna of Croatia is poorly known with only 28 species so far officially recorded. This number should be much higher because for some neighbouring countries about 100 stonefly species are known. The aim of this work was to investigate and to compare the diversity and distribution of stoneflies in the continental and the Mediterranean part of the Western Dinaric region in Croatia. The results are based on identification of adult insects and larvae. Adult Plecoptera were collected at the Plitvice Lakes National Park during two years using pyramid-type emergence traps and window traps with 28 stonefly species collected. The research of stonefly fauna of Cetina River was conducted during a one-year period and adults of 15 stonefly species were found. Among 37 stonefly species recorded for both study areas only six species are shared, and 19 species are new for the Croatian fauna as important new findings for the Croatian part of Dinaric region.

Stoneflies are among the most sensitive aquatic insect taxa and therefore arguably the best indicator of the excellent, i.e. pristine, ecological status of surface streams. Karst habitats are one of the most exciting freshwater habitats in terms of biological-geological interplay. They, in turn, support a biodiversity far superior to surrounding freshwater habitats and hence these habitats are designated as biodiversity hotspots. Our study deals with both of these crucial ecological players. We studied stonefly assemblages, their microhabitat preferences and emergence patterns along a karst oligotrophic hydrosystem. The sampling was conducted monthly from March 2007 to December 2008 using pyramid-type emergence traps set in various habitats and associated microhabitats (e.g. springs, rivers, streams, tufa barriers×moss, angiosperm, cobble, sand, silt substrates). Favorable environmental conditions, such as a wide range of karst habitat types with low water temperature and high oxygen concentration, resulted in high stonefly species richness (31 recorded species). Water temperature and pH had the highest influence on stonefly assemblages. Species richness and diversity decreased in a downstream direction. We recorded a longitudinal shift from crenal-epirhithral to epirhithral-metarhithral assemblages with some hyporhithral and potamal elements. Upstream sites were dominated by shredders, while downstream sites had a higher proportion of gatherers-collectors. Several species showed a significant preference for a specific microhabitat type in accordance with their feeding strategies and food availability. The majority of recorded species exhibited univoltine life cycles slow or fast.

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