Anthropogenic influences on benthic food web dynamics by interrupted freshwater discharge in a closed Geum River estuary, Korea

• Published in: Environment international 2019-10, Vol.131, p.104981, Article 104981
• Main Authors: Noh, Junsung, Yoon, Seo Joon, Kim, Hosang, Lee, Changkeun, Kwon, Bong-Oh, Lee, Yeonjung, Hong, Seongjin, Kim, Jaeseong, Ryu, Jongseong, Khim, Jong Seong
• Format: Article
• Language: English
• Subjects: Animals; Biota; Carbon - analysis; Dam; Estuaries; Food Chain; Fresh Water; Marine invertebrates; Nitrogen - analysis; Republic of Korea; Rivers; Sea dike; Stable isotopes; Tidal flats; Yellow Sea
• ISSN: 0160-4120; 1873-6750
• DOI: 10.1016/j.envint.2019.104981

Stable isotope analysis was used to investigate the benthic food web dynamics in the Geum River estuary where continuous river flow has been blocked by a sea dike over the past 25 years. In order to address the dike effect(s) on distribution of food sources (i.e., organic matters and microphytobenthos) and their utilization by marine predators, a three years monitoring survey (total of 30 surveys) was seasonally conducted at four fixed locations at both inside of dike and outer tidal flats. All the collected biota (total of 19 species; >1100 individuals and microphytobenthos) and abiotic (n = 118) samples were analyzed for carbon (δ13C) and nitrogen (δ15N) stable isotopes. In particular, two dominant marine bivalves inhabiting outer reach of tidal flats, Mactra veneriformis and Cyclina sinensis, were targeted to identify their feeding strategies that being related to a year-round population growth. In general, the stable isotopic signatures of samples indicated dissimilarity in distribution of organic matters between inside and outside of dike, supporting geographical and/or trophic isolation. The taxa-dependent trophic levels are also evidenced in consistent manner, with two to three levels being positioned over the years. Meantime, their dietary contributions varied in time, i.e., seasonal chances in compositions of major food sources (microphytobenthos and particulate organic matters) were observed for two target bivalves. Such temporal variations could be further linked to selective feedings that evidenced by age(size)-dependent and/or tissue specific distributions. Altogether, the present study suggested seasonality, diet preference, and growth dependent food web dynamics in the Geum River estuary. Overall, the present study suggested that the stable isotopic technique could be a powerful tool for characterizing the long-term anthropogenic influences of a sea dike on marine food-web dynamics. [Display omitted] •Isotopic compositions of marine organisms and food sources identified in a closed estuary•Terrestrial organic matters in discharged water lesser contributed to benthic food web.•Microphytobenthos contributed as key diet for macrobenthos in growth dependent manner.•Benthic bivalves showed organ-specific allocation of organic matter for nutrient storage.•A closed estuary preventing a natural river flow altered typical marine trophic pathways.