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.

Effect of the Human Utilization of Northern Snakehead (Channa argus Cantor, 1842) on the Settlement of Exotic Fish and Cladoceran Community Structure

“…Although the results of empirical studies suggested that aquatic macrophytes are utilized as refuge by various animals to avoid predatory fish, including crustaceans [67][68][69], the results of this study show that vegetated areas with a high density of L. macrochirus do not provide efficient habitats for cladocerans. We observed a low density of pelagic cladocerans in wetlands in the mid-lower reaches of the Nakdong River in which L. macrochirus is dominant.…”

Changes in Antibiotic-Resistance Genes Induced by the Grazing Effect in Three Cladoceran Species

“…However, previous studies have suggested that the negative effects of ARGs mediated by D. obtusa in freshwater ecosystems are difficult to predict. Choi and Kim [44] pointed out that frequent movements of pelagic cladocerans, including D. obtusa, make them easy prey for predators searching for food. As long as there is no refuge, such as aquatic macrophytes in freshwater ecosystems, D. obtusa numbers can be very low or absent due to the continuous foraging activity of fish on cladocerans [19,45].…”

The Use of Winter Water Temperature and Food Composition by the Copepod Cyclops vicinus (Uljanin, 1875) to Provide a Temporal Refuge from Fish Predation

“…The consumption of zooplankton as a main food source for invertebrates (e.g., dragonfly larvae, mosquito larvae, and fly larvae) and fish is sufficient to stimulate the development of defense strategies to avoid predators [ 15 , 16 ]. For example, in shallow wetlands, zooplankton communities are mainly abundant in areas with a high aquatic macrophyte cover, because prey location by fish is hindered by their leaves and stems [ 17 , 18 , 19 ]. In particular, wetlands can support higher densities and species diversity of cladoceran communities than other freshwater ecosystems (e.g., rivers or reservoirs) due to the active use of aquatic macrophytes by cladocerans that are vulnerable to fish predation [ 20 ].…”