A Study of the Distribution of Daphnia obtusa and Simocephalus vetulus in Response to Varying Environmental Conditions Using Field and Microcosm Approaches

Abstract

We investigated three shallow wetlands in South Korea to understand the spatial distribution of cladoceran species (Simocephalus vetulus and Daphnia obtusa) associated with different environmental variables, through field sampling, stable isotope analysis, and an experimental approach. The surface and bottom layer of the water was occupied by surface-dwelling and submerged macrophytes, respectively, and the two cladoceran species were distributed correspondingly to the macrophyte distribution pattern. The results of a stable isotope analysis showed cladocerans’ large dependency on the particulate organic matter (POM). The microcosm experimental approach revealed that the life forms of macrophytes determined the vertical distribution of cladoceran species. A greater number of S. vetulus were found on the surface-dwelling macrophytes on the surface, whereas D. obtusa was more abundant in the bottom layer (only in submerged macrophytes) in all treatments. This distribution pattern was largely extended by predation. We identified that the varying distribution pattern would be due to the characteristic habitat utilization of each cladoceran species. Their different habitat use facilitated the coexistence of the two species. Significantly, the macrophytes were supporting the coexistence of the Cladocera species, and may play an important role in enhancing the biodiversity of the wetlands and sustaining its complex food web. The spatial distribution of two cladoceran species, especially those with restricted niches, allow us to understand biodiversity responses of wetland littorals under changing limnological regimes.