engleski

Paterns of distribution and abundance of alien and native peracarid crustaceans in Croatian large rivers

Peracarid crustaceans (orders Amphipoda, Isopoda and Mysida) represent one of the most important group of invaders in European freshwaters that largely contribute to the homogenization of macroinvertebrate fauna. The aims of this study were to investigate distribution, density and assemblages of native and alien Peracarida in Croatian large rivers, their relationship with physico-chemical parameters and their proportion in total density of benthic macroinvertebrates as preliminary assessment of their impact. Hand net sampling (25×25 cm, mesh size 500 μm) was conducted twice (in 2015 and in 2016 or 2017), at 48 locations on four major large rivers (Danube-4 sites, Sava-21, Drava-20, Mura-3). Quantitative samples (20×0.0625 m2) were collected at each site in a shallow bank area of rivers (44 sites) or two reservoirs on Drava (2 sites), while deeper parts of the same reservoirs were sampled using Ekman grab (3×0.0225 m2 at 2 sites). In a total, 16 species were recorded, five native (Amphipoda- 4, Isopoda-1) and 11 alien species (Amphipoda- 8, Isopoda-1, Mysida-2). The highest number (10 spp., all alien species) were found in the Danube River, while subsets of alien species were found in the Sava (5) and Drava Rivers (6). The Mura River and the most upstream reaches of the Drava and Sava Rivers in Croatia have not yet been colonized by invasive peracarids and native species still thrive there. The most widespread alien species, present in the Danube, Sava and Drava Rivers, were isopod Jaera istri (29 sites) and amphipods Dikerogammarus villosus (24) and Chelicorophium curvispinum (22). The most upstream distributed species were amphipod D. haemobaphes in the Sava (631 rkm) and D. villosus in Drava River (270 rkm). Characteristic species for Sava were D. haemobaphes and C. sowinskyi, for Drava and Danube D. villosus and C. curvispinum, and additionally C. robustum for Danube. Significant differences were found in peracarid assemblages between all four rivers. Interestingly, extremely cold winter in January 2017 caused decrease of invasive amphipod D. villosus and enabled native species G. fossarum and S. ambulans to become more abundant than D. villosus at two sites in Drava. Proximity to the Danube River, as source of all invaders, and colonization history together with physico- chemical parameters, explained observed variation in peracarid assemblage between studied rivers. Proportions of alien Peracarida in total density of benthic macroinvertebrate was very spatially variable with the highest average and maximum values in the Drava River and lowest in the Sava River. Long-term monitoring of the distribution and abundance of invasive peracarid species is essential prerequisite for better understanding of the changes in macroinvertebrate assemblages in Croatian large rivers.

peracarid ; invasive species ; distribution ; rivers ; Croatia

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