Understanding predator–prey interactions is a major challenge in ecological studies. In particular, the accurate identification of prey is a fundamental requirement in elucidating food‐web structure. This study took a molecular approach in determining the species identity of consumed prey items of a freshwater carnivorous fish (largemouth bass,Micropterus salmoides), according to their size class. Thirty randomly selected gut samples were categorized into three size classes, based on the total length of the bass. Using the universal primer for the mtDNAcytochrome oxidase I (COI) region, polymerase chain reaction (PCR) amplification was performed on unidentified gut contents and then sequenced after cloning. Two gut samples were completely empty, andDNAmaterials from 27 of 28 gut samples were successfully amplified byPCR(success rate: 96.4%). Sequence database navigation yielded a total of 308 clones, containingDNAfrom 26 prey items. They comprised four phyla, including seven classes, 12 orders, and 12 families based onBLASTandBOLDdatabase searches. The results indicate that largemouth bass show selective preferences in prey item consumption as they mature. These results corroborate a hypothesis, presence of ontogenetic diet shift, derived through other methodological approaches. Despite the practical limitations inherent inDNAbarcoding analysis, high‐resolution (i.e., species level) identification was possible, and the predation patterns of predators of different sizes were identifiable. The utilization of this method is strongly recommended for determining specific predator–prey relationships in complex freshwater ecosystems.

In this study, the relationship between hydrological characteristics and phytoplankton biomass (chlorophyll a concentration) was explored using long-term hydrological and limnological data (1994–2007) in a flow-regulated river system (the lower Nakdong River, South Korea). This river has four multi-purpose dams and an estuarine barrage, and river flow is extensively controlled. Dynamics of chlorophyll a concentration responded well to changes in hydrology, such as rainfall, dam discharge and river flow. The hydrological characteristics strongly affected the decrease of chlorophyll a concentration in summer to winter but not in spring (p<0.05; n=42). An application of Self-Organizing Map (SOM) model to the database returned three clusters, and strong seasonality in water quality as well as hydrological characteristics was identified. Long-term rainfall data exhibited no statistical tendencies of increase or decrease, with respect to total annual rainfall. In comparison, summer rainfall increased while that of winter (December to the following February) decreased. Summer rainfall affected total dam discharges in all seasons in a positive manner (p<0.05; n=14), corresponding to winter water quality of the lower Nakdong River likely to be dependent largely upon changes in summer rainfall. Therefore, the development of an effective management strategy for summer rainfall and dam discharge control is strongly required.

The objective of our study was to investigate sexual reproduction of Daphnia magna associated with mating behaviors and hatching rates, according to different algal food sources. Since a diatom is known to contain more abundant long‐chain poly unsaturated fatty acids (PUFAs), we hypothesized that the diatom‐consuming D. magna would exhibit more successful reproduction rates. Upon the hypothesis, we designed three experiments using two algal species, a green alga (Chlorella vulgaris) and a diatom (Stephanodiscus hantzschii). From the results, we found that the mating frequency and copulation duration increased in the treatment with S. hantzschii, resulting in a significant increase of hatching rates of resting eggs. In the other two repetitive mating strategies (e.g., one female vs. multiple males, and one male vs. multiple females), we found that the hatching rates of resting eggs were greater in the S. hantzschii treatment. In addition to the mating strategy, male body size significantly increased in the diatom treatment, hence average diameter of penis was also statistically different among the treatments (greater diameter in the S. hantzschii treatment). To examine the effect of algal food quality, we estimated quantity of fatty acids in the two algal species. Our result showed that S. hantzschii had a higher proportion of long‐chain PUFAs than C. vulgaris. Furthermore, a stable isotope analysis revealed that carbon and nitrogen originated from S. hantzschii were more assimilated to D. magna. In summary, our study manifested that diatom consumption of D. magna leads to more successful sexual reproduction. We then discussed how the diatom consumption of zooplankton influences food web dynamics in a freshwater ecosystem.