Niche separation by littoral-benthic Chydoridae (Cladocera, Crustacea) in a deep lake - potential drivers of their distribution and role in littoral-pelagic coupling

Niche separation of 22 species of benthic Chydoridae was examined in a depth gradient in the littoral zone of a deep Lake Piaseczno (eastern Poland), by using a trap sampler. Individual species showed high segregation across the littoral zone according to depth, macrophyte biomass, total organic carbon (TOC), conductivity and pH, of which the depth turned out to be the most important. The species Acroperus harpae, Alona affinis, Alonella nana, Leydigia acanthocercoides, Pseudochydorus globosus, Pleuroxus trigonellus and Pleuroxus aduncus were found in the whole littoral zone, but the remaining Chydoridae species displayed clear spatial distribution, e.g. Coronatella rectangula, Acroperus elongatus, Alona guttata, Alonella excisa, Alonella exigua, Rhychotalona falcata, Monospilus dispar and Pleuroxus truncatus settled the shallower parts of the littoral, whereas Eurycercus lamellatus, Camptocercus rectirostris, Pleuroxus laevis, Graptoleberis testudinaria, Alona costata, Pleuroxus uncinatus and Alona intermedia were found mainly in areas located 3-6 m deep. To find out the role of Chydoridae in littoral-pelagic food web coupling, the contribution of chydorids to total number of Cladocera in the guts of fish was estimated showing that they are an important intervening link in nutrient movement from the littoral to the pelagic zone, as their contribution to the total cladoceran number found in guts of fish caught in the pelagic zone was even as high as 98%. This study provides more insight into the nature of constraints associated with littoral-benthic cladocerans' habitat preferences and their importance in littoral-pelagic coupling.