Abstract
The aim of this study was to assess seasonal variation in the food-web structure of fish assemblages in the East (two sites) and the South (one site) Seas of Korea, and to compare the isotopic niche areas between the regions. To do this, we analyzed the community structures and the δ13C and δ15N values for fish assemblages, and their potential food sources collected during May and October 2020. There were spatial differences in the diversity and dominant species of fish assemblages between the two seas. The fish assemblages in the South Sea had relatively wide ranges of δ13C and δ15N (−22.4‰ to −15.3‰ and 7.4‰ to 13.8‰, respectively) compared to those (−22.1‰ to −18.0‰ and 9.8‰ to 13.6‰, respectively) in the East Sea. The δ13C and δ15N values of suspended particulate organic matter, zooplankton, and fish assemblages differed significantly among sites and between seasons (PERMANOVA, p < 0.05, in all cases). Moreover, isotopic niche indices were relatively higher in the South Sea compared to those in the East Sea. Such differences in food-web characteristics among sites are likely due to the specific environmental effects (especially, major currents) on the differences in the species compositions and, therefore, their trophic relationships. Overall, these results allow for a deeper understanding of the changing trophic diversity and community structure of fish assemblages resulting from climate variability.
Highlights
Coastal zones that extend to the margins of continental shelves are complex ecosystems in which biotic and abiotic factors are generally characterized by strong spatial and seasonal heterogeneity, and variability
The alteration of trophic interactions due to changes in community patterns has a significant effect on the structure and functioning of food webs [8,9]
The spatial and seasonal variations in the composition and abundance of fish assemblages may be a feature of fish communities in Korean coastal waters, resulting from environmental changes in physical and trophic conditions affected by regional differences
Summary
Coastal zones that extend to the margins of continental shelves are complex ecosystems in which biotic and abiotic factors are generally characterized by strong spatial and seasonal heterogeneity, and variability. Recent applications to overcome this bias have used stable isotope analysis, based on actual assimilated diets over longer periods, to elucidate the trophic relationships and functioning of animals, and the food-web structure in marine ecosystems [18,19,20] This technique relies on the assumption that the stable carbon and nitrogen isotope compositions of a consumer species reflect those of its diet with the well-known isotopic fractionations (within approximately 1‰ for δ13C and 2–4‰ for δ15N) between them [21,22,23,24]. The δ13C and δ15N values provide information on the origin of assimilated dietary sources for consumers and their trophic positions, respectively [25] This analysis provides an insightful tool for identifying the spatial and temporal variability in the trophic ecology of fish species, and the trophic structure of fish assemblages, through isotopic monitoring in coastal ecosystems [7,9,12].
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