Trophic assessment of red seabream (Pagrus major) as a possible bioindicator of human activities in the South Sea of Korea using stable C and N isotopes.

To assess the impact of sand mining on resource utilization by the red seabream (Pagrus major) and the trophic structure of fish assemblages two years after mining activities, we compared stable isotope ratios (δ13C and δ15N) and isotopic niches between aggregated mining and control sites in April and August 2022. Our results showed no spatial differences in the δ13C and δ15N values of red seabream between the sand mining and control sites, suggesting that the mining did not affect their dietary resources. Furthermore, the considerable overlap among fish consumers suggested that the fish food web in mining areas has trophic functions similar to those in natural habitats after mining activities. Overall, our study enhances our understanding of ecosystem conservation and the ecological-based management of coastal areas.

Estuarine dam water discharge enhances summertime primary productivity near the southwestern Korean coast.

The gate opening of estuarine dams discharge a large amount of freshwater into coastal zones during the summer monsoon in northeast Asia. We investigated seasonal and spatial variations in primary productivity (PP) and community structures of phytoplankton on a downstream macrotidal flat and examined the dam discharge effects. Our harmonic analysis of the PP revealed a clear seasonality with a unimodal peak in summer, possibly driven by high ammonium loading through internal recycling. External nitrate supply from the dam-water discharge promoted PP during July-August, generating conspicuous blooms near the discharging site. Phytoplankton community was characterized by a predominance of diatoms all year round and seasonal dominances from dinoflagellates, cryptophytes, and prasinophytes in spring to chlorophytes in summer, reflecting spatiotemporal patterns in ammonium and nitrate supply. Our findings provide new insights into the summer phytoplankton bloom linked to monsoonal rainfall in the shallow coastal seas along the Northeast Asian coast.

Identifying patterns in the multitrophic community and food-web structure of a low-turbidity temperate estuarine bay.

Food web dynamics outline the ecosystem processes that regulate community structure. Challenges in the approaches used to capture topological descriptions of food webs arise due to the difficulties in collecting extensive empirical data with temporal and spatial variations in community structure and predator-prey interactions. Here, we use a Kohonen self-organizing map algorithm (as a measure of community pattern) and stable isotope-mixing models (as a measure of trophic interaction) to identify food web patterns across a low-turbidity water channel of a temperate estuarine-coastal continuum. We find a spatial difference in the patterns of community compositions between the estuarine and deep-bay channels and a seasonal difference in the plankton pattern but less in the macrobenthos and nekton communities. Dietary mixing models of co-occurring dominant taxa reveal site-specific but unchanging food web topologies and the prominent role of phytoplankton in the trophic base of pelagic and prevalent-detrital benthic pathways. Our approach provides realistic frameworks for linking key nodes from producers to predators in trophic networks.