Spatial Distribution of Cladocera in a Stratified Palaearctic Lake

Abstract

The spatial distribution of 39 species of Chydoridae, representing seven families, was examined in a stratified Palaearctic lake in Poland (Lake Piaseczno). Thirty-one of the species living in that lake were found to exist exclusively in the littoral zone. No species were found exclusively in the pelagic zone; in this zone, eight species were identified, but all of these were also quite abundant in the littoral zone. Almost all species of Chydoridae and all species of Macrothricidae were found only in littoral, whereas Daphnidae and Sididae families comprised species either restricted to the littoral or occurring in both pelagic and littoral zones. Two Bosminidae species, in turn, displayed quite a consistent distribution in both biotic zones, but differed in their habitat preferences. On the other hand, species of Polyphemidae and Leptodoridae exhibited littoral and littoral-pelagic distributions, respectively. Few species occurred in one habitat only. Most species, despite showing clear preferences for a distinct habitat (or habitats), were also present at lower densities throughout the littoral zone, or the whole lake, in the case of limnetic species. Archetype analysis showed that cladocerans were distributed along the entire gradient of macrophyte characteristics and habitat depth. Among Chydoridae, which displayed the strongest attachment to habitats overgrown by macrophytes, few species showed above 50% similarity to the archetype representing species living among submerged macrophytes with the highest plant per volume infested. Furthermore, many littoral species, including these of the Macrothricidae family, P. pediculus and S. mucronata, avoided staying in habitats with particularly complicated spatial architecture. Regarding their distribution in relation to depth, cladocerans could be grouped into species found in the whole littoral zone, species settling in relatively shallow parts of the littoral zone, species found mainly in habitats 3–6 m deep and species settling throughout the lake. Archetype analysis showed negligible similarity between cladocerans and the archetype representing species living in macrophyte-free habitats in the deepest parts of the lake. The study provides quantitative support showing that cladocerans display a distribution threshold at one time in one lake. Although this group of aquatic invertebrates is widely suspected of being ecologically flexible and tolerant to environmental gradients, individual species showed high spatial segregation according to depth and habitat architecture.