Caddisflies (Trichoptera) of Protected Calcareous Fen Habitats: Assemblages, Environmental Drivers, Indicator Species, and Conservation Issues

Abstract

The caddisflies (Trichoptera) of calcareous fen habitats, in contrast to those of other peatland types, have been poorly researched. We thus conducted a two-year study in south-eastern Poland encompassing four types of such habitats-drained and undrained fens and water bodies (pools and ditches) located within the fens-in order to define trichopteran reference assemblages (PCoA), indicator species (IndVal analysis), and the drivers (both natural and those associated with landscape management, including area protection) responsible for caddisfly species distribution (CCA). The most important environmental driver was habitat persistence. Distance-based RDA analysis revealed a distinct pattern in the distribution of species with or without diapause along the persistence gradient. Environmental drivers associated with plants were also crucial for both fens and water bodies. The key factor influencing the caddisfly assemblages of pools and ditches was the use and management of the surrounding land, whereas in the fens, it was the level of area protection. Physical and chemical water parameters had no statistically significant impact on the assemblages. Some factors can be modified by humans (e.g., water level regulation, vegetation, and landscape management) to maintain healthy ecosystems for aquatic insects.

Keywords: area protection; astatic waters; bioindicators; caddisflies; conservation; drying out; wetlands.

Figure 1

Study area and study sites: A—sites near the village of Urszulin, B—sites near the city of Chełm. UF—undrained fens, DF—drained fens, FD—fen ditches, FP—fen pools. The green lines mark the boundaries of nature reserves. sub-figure (A)—western Polesie region, sub-figure (B)—Wołyń Polesie region.

Figure 2

Trichoptera ((A)—number of specimens, p = 0.7099; (B)—species per sample, p = 0.7836) in four habitats: UF—undrained fens, DF—drained fens, FD—fen ditches, FP—fen pools. Red square—average value, box—standard deviation, whisker—95% confidence interval.

Figure 3

Ordination diagram showing sites vs. caddisfly species with the first two axes of principal coordinates analysis (PCoA): UF—undrained fens, DF—drained fens, FD—fen ditches, FP—fen pools; species are codes as in Table 2; species more sensitive to climate change are underlined, whereas insensitive ones are not.

Figure 4

Relative abundance of species in two functional groups of Trichoptera in each habitat type: UF—undrained fens, DF—drained fens, FD—fen ditches, FP—fen pools. (A)—drought-resistance strategies; (B)—sensitivity to climate change.

Figure 5

Ordination CCA biplots showing the distribution of Trichoptera species in fens (A,C) and fen pools and ditches (B,D) vs. significant (p < 0.05—marked in red, p = 0.051–0.07—marked in orange) environmental factors: Helophytes—density of emergent vegetation, Nymph—density of floating vegetation, Chara—density of underwater meadows, Cover—overall % coverage of a site by vegetation, Trees—density of woody vegetation, Protect—degree of area protection, Fish—pressure from fish, Surr_deg—extent to which an area is utilised or managed. The taxon codes are as described in Table 2.

Figure 6

Distance-based redundancy analysis (db-RDA) plot for the trichopteran assemblages of all fen habitats based on the Bray–Curtis distance (dissimilarity). Persistence vector with p = 0.043. Species with diapause are shown in orange; those without diapause are shown in black. Δ—species.

Figure 7

Two-dimensional non-metric multidimensional scaling (NMDS) plot of study sites representing different protection statuses (red—nature reserves, black—unprotected sites, dot—Natura 2000 areas, square—site not in the Natura 2000 network) based on dissimilarities between trichopteran assemblages (Bray–Curtis distance matrix). Stress value = 0.04.