Environmental drivers influencing stonefly assemblages along a longitudinal gradient in karst lotic habitats

Abstract

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.

Peeling the Layers of Caddisfly Diversity on a Longitudinal Gradient in Karst Freshwater Habitats Reveals Community Dynamics and Stability

“…However, the water temperature and the range of its values are a distinguishing property of the specific habitats themselves (and their position in the stream continuum), so there is certainly a strong covariance between the habitat type and temperature in determining caddisfly distribution. This is in concordance with similar research on different macroinvertebrate groups in these habitats [ 21 , 24 , 40 ].…”

“…The karst freshwater ecosystems in the Dinaric western Balkan ecoregion (ER5, [ 20 ]) have been repeatedly shown to be hotspots for freshwater insect diversity, especially when it comes to the habitat-rich ecosystem complex of barrage lake-forming rivers and streams [ 21 , 22 , 23 , 24 ]. As caddisfly communities followed the same trend, exhibiting high biodiversity within these karst ecosystems comprising of springs, different stream types and tufa barriers (e.g., [ 25 , 26 ]), they were chosen as an ideal polygon for the comprehensive testing of different diversity measures.…”

Effects of Environmental Variables and Habitat Integrity on the Structure of the Aquatic Insect Communities of Streams in the Cerrado-Caatinga Ecotone in Northeastern Brazil

“…The pH was an important filter of the structure of the EPT community, and gradients of this variable are known to be an important factor determining the formation of the communities of other groups of aquatic insects (Brasil et al 2018, Ongaratto et al 2018, Ridl et al 2018. Gradients in the pH of the water have been associated with alterations in rainfall patterns, which may change the amount of dissolved solid matter added to the water, which is also dependent on the conditions in the area surrounding the stream (Pérez 2003, Juen et al 2016).…”

A European map of groundwater pH and calcium

“…Ca 2+ > 55 mg L −1 ) values that occur in lowlands visually govern the map, but for ecological differentiation of groundwater-dependent habitats in Europe the differences within the middle part of the gradient, i.e. between pH 5.5 and 7.0, are much more important (Malmer, 1986;Wheeler and Proctor, 2000;Hájek et al, 2006;Rydin et al, 2013).…”

“…Freshwater systems belong to the most endangered habitats (Cantonati et al, 2020a;Tickner et al, 2020), and, among them, groundwater-dependent ecosystems, such as fens and springs, hold primacy (Janssen et al, 2016;Chytrý et al, 2019;Hájek et al, 2020a;Stevens et al, 2020). Species composition and richness of spring systems are generally governed by water pH and calcium concentration (Ca 2+ ), which are highly variable at different spatial scales (Malmer, 1986;Rydin et al, 2013;Peterka et al, 2017;Horsáková et al, 2018;Cantonati et al, 2020a, b). Therefore, understanding the spatial patterns in groundwater pH and Ca 2+ is important not only for general geochemical knowledge and for water resource management but also to the same extent for the conservation of freshwater systems and associated biodiversity.…”