Long-Term Chironomid Emergence at a Karst Tufa Barrier in Plitvice Lakes National Park, Croatia.

Chironomids are found in all types of freshwater habitats; they are a ubiquitous and highly diverse group of aquatic insects. Plitvice Lakes National Park is the oldest and largest national park in Croatia and consists of numerous and diverse freshwater habitats, making the area an ideal location for long-term research into the chironomid emergence patterns and phenology. The main objectives of this study were to identify the composition of the chironomid community, determine the phenology of the identified species, and assess the main factors influencing their emergence in Plitvice Lakes. During 14 years of research, more than 13,000 chironomids belonging to more than 80 species were recorded. The most abundant species was found to be Parametriocnemus stylatus. The highest abundance of chironomids was recorded in lotic habitats with faster water current over substrates of moss and algae and pebbles. Water temperature and the availability of organic matter were found to be the main factors that drive chironomid emergence at the tufa barrier studied. In the last years of this study, a prolonged flight period was observed. Although this is not statistically significant (at this stage of the study), it could be due to a higher water temperature in winter.

Defining Patterns and Rates of Natural vs. Drought Driven Aquatic Community Variability Indicates the Ongoing Need for Long Term Ecological Research.

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.

Extreme freshwater discharge events exacerbated by climate change influence the structure and functional response of the chironomid community in a biodiversity hotspot.

Global climate change is expected to exacerbate extreme discharge events in freshwater ecosystems as a consequence of changes in precipitation volume and snow cover duration. Chironomid midges were used as a model organism in this study because of their small size and short life cycles, which enable fast colonization of new habitats and great resilience. This resilience is often expressed in easy recolonization after an extreme event. Chironomid samples together with physico-chemical water measurements were collected for 14 years, between 2007 and 2020, in a karst tufa barrier that is part of the Plitvice Lakes National Park in Croatia. More than 13,000 individuals belonging to >90 taxa were collected. Mean annual water temperature increased by 0.1 °C during this period. Multiple change-point analysis revealed three main periods by discharge patterns: the first one from January 2007 to June 2010, the second from July 2010 to March 2013, characterised by extreme low discharge, and the third from April 2013 to December 2020, characterised by an increase in extreme peak discharge values. Based on multilevel pattern analysis, indicator species of the first and the third discharge period were detected. The ecological preferences of these species indicate an environmental change related to the changes in discharge. Along with species composition, functional composition has changed with the abundance of passive filtrators, shredders and predators increasing over time. Species richness and abundance did not change over the period of observation, thus emphasizing the importance of species-level identification in detecting the earliest community response to change that would otherwise be overlooked.

Checklist of aquatic Diptera (Insecta) of Plitvice Lakes National Park, Croatia, a UNESCO world heritage site.

Studies on aquatic Diptera in the Plitvice Lakes National Park (Croatia) conducted in the last 50 years have produced 157 species and 7 taxa of aquatic Diptera placed in 13 families. Samples were collected at 25 sampling sites representing the four main types of karst aquatic habitats: spring, stream, tufa barriers and lakes. All records of all the aquatic families of Diptera in Plitvice Lakes NP are summarized, including previously unpublished data. Twelve species new for Plitvice Lakes NP are recorded for the first time, belonging to the families: Chironomidae - Labrundinia longipalpis (Goetghebuer, 1921), Nilothauma brayi (Goetghebuer, 1921), Potthastia longimanus Kieffer, 1922, Polypedilum (Polypedilum) nubeculosum (Meigen, 1804), Tanytarsus brundini Lindeberg, 1963; Dixidae - Dixella autumnalis (Meigen, 1838); Scathophagidae - Acanthocnema latipennis Becker, 1894 and Stratiomyidae - Oxycera pardalina Meigen, 1822, Oxycera limbata Loew, 1862, Oxycera turcica Ustuner & Hasbenli, 2004, Nemotelus pantherinus (Linnaeus, 1758), Oplodontha viridula (Fabricius, 1775). The most species-rich family was the Chironomidae with 62 species (and an additional seven taxa), followed by the Empididae with 22 species and Limoniidae with 19 species. The highest number of species was recorded in springs. The relatively low number of species in certain families and the complete absence of some aquatic families shows that further research into the aquatic Diptera in Plitvice Lakes NP is needed.

Is the spatial distribution of lentic water mite assemblages (Acari: Hydrachnidia) governed by prey availability?

Predation is a biotic interaction that links water mites to different taxonomic groups of benthic invertebrates. Diptera larvae (Chironomidae) and microcrustaceans (Cladocera, Copepoda, Ostracoda) are known to be the most commonly preferred prey by water mites. Although these predatory interactions are known from observations and ex situ investigations, the distribution patterns and co-occurrence of water mites and their prey in littoral lentic habitats have been poorly studied. Our goal was to determine whether predation might serve as a significant factor in water mite assemblage composition and distribution. Samples were taken from littoral zones of 21 artificial lakes (reservoirs) in the Dinaric Western Balkan ecoregion of Croatia. At every site, 10 samples were collected with regard to shore slope in depth zones of up to 1 m. In total 490 samples were collected from April 2016 to July 2017. Data analysis showed that the spatial distribution of water mites was partially correlated with the environmental parameters we measured (explaining 45.1% of total water mite variation). A positive correlation between water mite abundance and diversity and depth gradient (favouring more stable conditions in deeper parts of the littoral zone) was also observed. Finally, water mite abundance and species richness variation were found to be best predicted by the abundance of potential prey groups. Predation was statistically determined to be a strong dispersion variable, most probably influencing both spatial distribution and composition of water mite assemblages.