Transformation of benthic communities in forest lowland streams colonised by Eurasian beaver Castor fiber (L.)

Abstract

Beavers are an exception among animals in terms of the scale of environmental transformations they achieve. This study investigated primary environmental factors influencing the occurrence of aquatic invertebrates in lowland streams inhabited by the Eurasian beaver. The study was conducted in two forest streams inhabited by beavers, and in an uninhabited stream. In streams inhabited by beavers, the study covered seven ponds. Sections with flowing water were also analysed downstream and upstream of the ponds. Benthos and water samples were collected at each site. Dissolved oxygen (DO) concentration and saturation were the only physicochemical parameters that indicated decreases in water quality in beaver ponds. The benthic communities of different beaver ponds were similar. The taxa that exerted the greatest influence on the similarity of the invertebrate fauna in the ponds were Oligochaeta and Chironomidae. Ostracods were also abundant in the ponds, whereas they were few in the flowing sections. Mayflies (Cloeon) and caddisflies belonging to the family Phryganeidae were also closely associated with the ponds. Caddisflies (Plectrocnemia and Sericostoma), mayflies (Baetis) and stoneflies (Nemourella and Leuctra) exhibited the highest correlation with DO concentrations, which is typical of flowing sections, and avoided stream fragments dammed by beavers. Bivalvia (Pisidium) were also abundant in each of the streams along the flowing sections. The highest number of taxa and greatest taxonomic diversity was observed in sections flowing below the beaver ponds. The engineering activity of beavers transformed the studied lowland streams, resulting in the development of rheophilic and stagnophilic communities of aquatic invertebrates, in free‐flowing and dammed sections, respectively.

Pro-ecological and conservation activities are not always beneficial to nature: a case study of two lowland streams in Central Europe

“…Most cited authors are of the opinion that beavers in flowing waters cause far-reaching changes in hydromorphological, geomorphological, and physicochemical conditions; however, a definite assessment of these changes—whether they are positive or negative—raises certain controversies 33 , 34 , 36 , 58 – 63 . According to the authors of this study, Strumień Kiszewski is an example of lotic habitat degradation.…”

“…Among the positive effects of beaver activity, the most frequently mentioned aspects include increasing habitat diversity thanks to the division of the watercourse into lentic and lotic stretches, an increased density of invertebrates 33 – 36 , as well as reduced sediment content, including that of some biogenic 37 – 39 .…”

How beavers affect riverine aquatic macroinvertebrates: a review

“…More broadly, many studies report increases in regional (gamma) aquatic macroinvertebrate biodiversity with the addition of beaver-created habitats ( Harthun, 1999 ; Kukuła et al, 2008 ; Arndt & Domdei, 2011 ; Law, Mclean & Willby, 2016 ; Czerniawski & Sługocki, 2018 ; Osipov, Bashinskiy & Podshivalina, 2018 ; Law et al, 2019 ; Bush et al, 2019 ; Robinson et al, 2020 ; Washko, Roper & Atwood, 2020 ; Wojton & Kukuła, 2021 ) due to increased habitat heterogeneity ( e.g . adding various lentic areas to lotic systems, increasing woody debris patches, constructing shallow canals) as well as within-patch heterogeneity ( e.g .…”

“…Further, beaver dams can change groundwater hydrology, resulting in colder water temperatures downstream of dams that stimulate mayfly growth and fecundity ( Fuller & Peckarsky, 2011 ). Lastly, the reaches directly downstream of dams can have higher biodiversity ( Wojton & Kukuła, 2021 ), and, as mentioned previously, different FFGs and aquatic macroinvertebrate densities can be found above and below beaver dams due to changing food resources ( Smith et al, 1991 ; Redin & Sjöberg, 2013 ). As the finer mechanics of beaver-altered hydrology, geomorphology, and biogeochemistry become better resolved ( e.g .…”