科研之友
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摘要
Coastal upwelling zone hosts most fishing grounds worldwide and nitrogen dynamics in those systems mainly have been addressed through the nutrients replenished the ecosystem. Compared with coastal and upper-layer ecosystems, relatively limited knowledge has been explored by nitrogen isotope imprints through the food webs of mesopelagic fishes and their links to upwelling characteristics. Here, we collected several species of mesopelagic fishes in the mid-west region of the South China Sea (SCS) and analyzed them by biochemical methods (fatty acids, 813C, 815N, and 813C of fatty acids). Due to the occurrence of upwelling, we want to evaluate the variation of nitrogen isotope compositions among these mesopelagic species and their links to the upwelling nitrogen supply. The 815N of mesopelagic fishes in the non-upwelling area was depleted by 2 & PTSTHOUSND; when compared with those in upwelling area, which indicated different nitrogen sources impacting for fishes in the two areas. A combination of multi-biochemical proxies was used to divide mesopelagic fishes into six groups and indicated that the feeding behaviors and upwelling were the main factors to affect the biological composition of mesopelagic fishes, even in such small regions. The differences in 815N values between the upwelling and nonupwelling areas allowed us to estimate that N2 fixation supported about 37% of the N-demand of food sources in the non-upwelling area, which was larger than the 10% in the upwelling area. These results illustrate that nutrients from the deep layers in upwelling systems might be the main factors that cause differences in 815N in mesopelagic fishes between upwelling and non-upwelling areas. Thus, more studies of N dynamics in mesopelagic fishes should be conducted in the upwelling systems to illustrate the impact of climate changes on fish biomass in the future.
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