Research On Trophic Structure Of The Major Fishery Species From The Yangtze Estuary Based On Stable Isotope Technology

Four trawl surveys respectively in November 2014, February, May and August 2015 were conducted in the 14 sites in the Yangtze River estuary(31°00.000′~31°46.000′N,121°03.000′~122°11.000′E). 35 fishes were collected, including 14 benthonic invertebrate. Phytoplankton, zooplanktons of 4 particle sizes(<300um, 300~500um, 500~900um,>900um), particulate organic matter(POM) and sediment organic matter(SOM) were collected respectively in these sites. Stable isotope analysis of all samples was implemented in the Analysis and Determination Center of Shanghai Jiao Tong University. The analysis results show that the ratios of stable carbon and nitrogen isotopes of fishes have a large span: squalidus argentatus has the smallest δ13C value(-29.78 ±0.11‰), while tuenioides rubicundus has the largest δ13C value(-14.25 ±0.07‰), which has a span of-15.53‰ and average value of-20.64 ±3.71‰. Hypophthalmichthys molitrix has the smallest δ15N value(9.26 ±0.06‰), and acipenser sinensis has the largest δ15N value(15.39 ±0.30‰), the span of which, nearly 7.13‰, is smaller than δ13C, and the average value of which is 11.90 ±1.71‰. The δ13C value of invertebrate has a small span: from-22.22 ±0.13‰(of eriocheir sinensis) to-14.84 ±0.07‰(of charybdis japonica); the value of span is 7.38‰ and the average value is-18.86±2.28‰. Scapharca subcrenata has the smallest δ15N value(7.73 ±0.09‰), and eriocheir sinensis has the largest δ15N value(13.53 ±0.07‰); the value of the span is 5.80‰ and the average value is 10.47 ±1.75‰. Among plankton, zooplankton of 500~900 μm has the smallest δ13C value(- 21.76±0.15‰), while zooplankton(>900 μm) has the largest δ13C value(- 20.87±0.04‰), and the average value is-21.32±0.48‰; zooplankton(>900 μm) has the largest δ15N value(6.72±0.10‰), and zooplankton 100~300 μm has the smallest δ15N value(5.26±0.19‰), and the average value is 6.05±0.66‰. The δ15N value of phytoplankton is 4.84‰.According to the results of the stable nitrogen isotope test, the trophic level of the main fishery biologies in Yangtze River estuary was calculated in the trophic level formula: TL=(?15Nconsumer- ?15Nbaseline)/△ ?15N+2. The trophic level of biologies ranges from 1.02(phytoplankton) to 4.6(acipenser sinensis), and the length of trophic level is level 4. The trophic level of fishes spans from 2.52(hypophthalmichthys molitrix) to 4.60(acipenser sinensis), and fishes of level 2 account 28% of the totality of fishes, those of level 3 account 53%, and those of level 4 accounts 19%. The trophic level of invertebrate is from 2.00(Scapharca subcrenata) to 3.96(Eriocheir sinensis). Among plankton, phytoplankton has the lowest trophic level(1.02), and zooplankton has the trophic level ranging from 1.16 to 1.66. Based on the calculated result of trophic level, continuous nutritional spectrum of main fishery creatures in the Yangtze River estuary was constructed.The food sources of main fishes in the Yangtze River estuary were analyzed by using stable carbon isotope, and the research shows that sedimentary matter is the main food sources of the majority of fishes, the secondary source is particulate organic matter, and phytoplankton is also an important source of nutrients. According to the analysis result of Iso Source Software, fishes in the Yangtze River Estuary can be classified into 3 groups: the first group mainly takes POM as food sources, including fishes such as Pseudobrama simony, Parabramis pekinensis, Leiocassis longirostris; the second group mainly takes phytoplankton as food sources and representative fishes include Pelteobaggrus nitidus, Collichthys lucidus and Miichthys miiuy; and the third group of fishes including Acanthogobius ommaturus, Chaeturichthys stigmatias and Mugil cephalus mainly takes sedimentary matter as food sources.