Sustainment of epiphytic microinvertebrate assemblage in relation with different aquatic plant microhabitats in freshwater wetlands (South Korea)

Aquatic macrophytes determine the physical complexity of aquatic environments and may influence the distribution and feeding habits of fish species. We explored the influence of different microhabitats, including vegetated beds (VB), edges of vegetated beds (EVB), and open water zones (OW), on two exotic fish species (Lepomis macrochirus and Micropterus salmoides) in shallow reservoirs. Lepomis macrochirus was more abundant in VB than in other zones and M. salmoides was mainly distributed in EVB. In VB, L. macrochirus mainly consumed branchiopods and isopods, while M. salmoides in EVB relied on relatively larger food items, such as dipterans, odonatans, and young fish. The consumption of young fish by M. salmoides, including L. macrochirus, showed little difference between winter and summer. Based on these findings, we suggest that young L. macrochirus (~20 cm) utilize VB as a refuge to avoid predation by M. salmoides. Meanwhile, M. salmoides mainly occupied in areas surrounding VB, preying on animals at these edges. As such, the presence of aquatic macrophytes appears to plays a key role in the survival and population growth of L. macrochirus. Proper management of aquatic macrophytes can help reduce populations of exotic fish and support native fish species.

Knowledge and management of aquatic ecosystems (formerly Bulletin Français de la Pèche et de la Pisciculture), an international journal on freshwater ecosystem

Empirical studies suggest that the structural heterogeneity of aquatic ecosystem microhabitat is determined by the diversity and abundance of macrophytes. However, excessive accumulation of free-floating macrophytes on the water surface can reduce the biomass of submerged macrophytes, resulting in a relatively simplified habitat structure. We hypothesized that heavy summer rainfall disrupts the growth of free-floating macrophytes covering much of the Jangcheok Reservoir’s water surface, thereby resulting in a more complex habitat structure by allowing development of a more diverse of macrophytic community. We divided long-term (2008–2017) monitoring data (rainfall, macrophytes, and rotifers) into two groups: Rainy and Dry years, corresponding to years with annual rainfall higher and lower than the total annual average, respectively. We found that summer densities of rotifers fell sharply in Rainy years, but increased continuously in Dry years. This trend resulted in greater autumn densities in Rainy relative to Dry years, which we attributed to changes in habitat related to differential macrophyte development. Moderate disturbance of the water surface caused by high summer rainfall can promote growth of submerged macrophytes by creating large areas of open water and therefore a more complex autumnal microhabitat structure, resulting in seasonal variations in rotifer community structures and populations. Moreover, a highly complex microhabitat structure restricts foraging activity of fish (i.e., Lepomis macrochirus) that prey on rotifers. Based on these findings, we suggest that summer-concentrated rainfall plays an important role in supporting the density and species diversity of rotifers.

Background: This study aimed to identify NO₃⁻-N sources using the stable isotope δ¹⁵N in Chydorus sphaericus (OF Müller), to investigate hydrological characteristics and nutrient states in artificial wetlands near the Nakdong River. Chydorus sphaericus is dominant in wetlands where aquatic plants are abundant, occurring in high density, and is sensitive to wetland water pollution, making it suitable for identification of NO₃⁻-N sources. Results: NO₃⁻-N sources for each wetland were strongly dependent on hydrological characteristics. Wetlands with sewage or rainfall/groundwater as their main sources had high levels of NO₃⁻-N, whereas wetlands with surface water as their main input had comparatively lower levels. Since wetlands with sewage and rainfall/groundwater as their main water sources were mostly detention ponds, their inputs from tributaries or the main river stream were limited and nutrients such as NO₃⁻-N easily become concentrated. Changes in NO₃⁻-N levels at each wetland were closely associated with δ¹⁵N of C. sphaericus. Interestingly, regression analysis also showed positive correlation between δ¹⁵N of C. sphaericus and NO₃⁻-N level. Conclusions: We conclude that the nitrate stable isotope (δ¹⁵N) of C. sphaericus can be used to elucidate the hydrological characteristics of riverine wetlands. This information is important for maintenance and conservation of artificial wetlands at the Nakdong River.

The influence of aquatic macrophytes on distribution and feeding habit of two Asplanchna species (A. priodonta and A. herrickii) in shallow wetlands, South Korea