Food Web Structure And Energy Source Of The Main Stream Ecosystem In The Middle Reaches Of The Yangtze River Based On The Stable Isotope Analyses

The middle reaches of the Yangtze River has extremely abundant fish resources and is the main habitat for fishes which produce floating eggs. The fishes are main River-lake migratory type (Mylopharyngodon piceus, Ctenopharyngodon idellus, Hypophthalmichthys molitrix, Aristichthys nobilis etc.) and settling type (Cyprinus carpio, Carassius auratus etc.). The ecosystem of the middle reaches of Yangtze River affect by The Three Gorges dam, Gezhouba dam, over fishing, disconnecting lake from Yangtze River and water pollution, study on the food web structure and its energy cycle will be beneficial to understand the fisheries ecosystem status, changes and trend of fishery resources in the middle reach of Yangtze river, will be provide the necessary basic data and technical support for the sustainable utilization of fishery resources and ecosystem protection. This study sampled fishes, particulate organic matter (POM), algae and other organisms in the food web from Yichuang to Hukou sections in the middle reaches of Yangtze River from March, September 2011 and June 2013 to March 2014. Using the stable isotope techniques studied mainly fish trophic level, food web structure, energy source, δ13C and δ15N characteristic of POM and study on validity of the fins instead of white muscle for black carp and silver carps in stable isotope analyses. This paper discusses the potential impact of fishes’ food web and energy flow process due to the Three Gorges dam and Gezhouba dam in the middle reaches of Yangtze River, the main results were as follows:Stable isotope analysis is commonly used to study food web structures and material flows in a wide range of aquatic ecosystems. The trophic level of 44 fish and three aquatic invertebrate species was analyzed by using δ13C and δ15N analysis. Sample collection was executed from Yichuang, Jingzhou, Shishou, Jianli, Chenglingji, Ezhou, Jiujiang and Hukou sections in the middle reaches of Yangtze River from March 2011 to December 2013. In this study, there was significant difference in the δ13C and δ15N values of fishes. The 813C values ranged from -33.83%o (Aristichthys nobilis)～-17.36%o (Silurus meridionalis) and the 815N values ranged from 4.83%o (Misgurnus anguillicaudatus)～15.13%o(Culter alburnus). The δ13C average values ranged from -30.06‰ (Micropercops swinhonis)～-21.24‰ (Paramisgurnus dabryanus) and the 815N average values ranged from 6.91‰ (Mastacembelus armatus) ～14.99‰ (Neosalanx taihuensis). The trophic level of aquatic organisms in the middle reaches of Yangtze River was 2.42～4.88 based on the δ15N values of Bellamya purificata (5.48%o) as the baseline, concentrating primarily on the range of 2.83～3.61, and the average trophic level of fishes were 3.28. Trophic level more than 2.83 accounted for 80.85% of the total organisms. The least trophic levels were Mastacembelus armatus (2.42±0.49) and Parabramis pekinensis (2.56±0.52). The trophic levels more than 4.0 were Neosalanx taihuensis, Coilia brachygnathus, Aristichthys nobilis and Saurogobio dumerili, the values were 4.88±0.01、4.37±0.27、 4.32±0.35 and 4.09±0.78, respectively. The trophic levels values of Micropercops swinhonis, Elopichthys bambusa, Siniperca chuatsi, Culter alburnus, Mylopharyngodon piceus and Silurus meridionalis were 3.99、3.92±0.16、3.89±0.27、 3.87±0.62、3.59±0.69 and 3.59±0.57, respectively. The objectives of this study were to provide basic scientific data for the assessment and utilization of fishery resources, to provide the important reference value for further researches on the dynamic change of fishery resources’ structure and effect of human activity disturbance in the middle reach of t Yangtze River.The food web structure in high water period and drought period of Yichang, Jingzhou, Chenglingji, Ezhou, and Hukou sections in the middle reaches of Yangtze River was analyzed by using δ13C and 815N analysis. This study sampled fishes, particulate organic matter (POM), algae and other organisms in the food web in March and September 2011, July, September and December 2013 and March 2014. Coreius heterokon, Cutter alburnus and Aristichthys nobilis at the top of food web in the high water period, the Siniperca chuatsi and Aristichthys nobilis at the top of food web in the drought period at Yichang section. Neosalanx taihuensis, Coilia brachygnathus, Xenocypris davidi, Channa argus and Siniperca chuatsi at the top of food web in the high water period, the Coilia brachygnathus and Aristichthys nobilis at the top of food web in the drought period at Jingzhou section. Siniperca chuatsi, Coilia brachygnathus, Silurus meridionalis and Elopichthys bambusa at the top of food web in the high water period, the Coilia brachygnathus, Silurus meridionalis and Elopichthys bambusa at the top of food web in the drought period at Chenglingji section. Culter alburnus, Silurus meridionalis, Elopichthys bambusa, Mylopharyngodon piceus and Siniperca chuatsi at the top of food web in the high water period, the Silurus meridionalis, Elopichthys bambusa, Mylopharyngodon piceus and Siniperca chuatsi at the top of food web in the drought period at Ezhou section. Coilia brachygnathus, Culter alburnus, Saurogobio dumerili, Silurus meridionalis, Siniperca chuatsi and Mylopharyngodon piceus at the top of food web in the high water period, the Culter alburnus, Hemibarbus maculatus and Hemibarbus labeo at the top of food web in the drought period at Hukou section. On the river flow gradient in the middle reach of Yangtze River, the δ13C value of fishes has downward trend along with the river flow, and the δ15N value has very little changes.Stability using isotope technology and combining the isotopic mixture Model (IsoSource Model), it studies the energy source and the potential impact of nine fishes (Ctenopharyngodon idellus, Carassius auratus, Cyprinus carpio, Hypophthalmichthys molitrix, Parabramis pekinensis, Siniperca chuatsi, Silurus meridionalis, Culter alburnus and Pelteobagrus fulvidraco) in the middle reach of Yangtze River after the impoundment of the Three Gorges dam. Their 813C and δ15N value range from-29.25±3.22 to -24.26±2.8,8.42±1.9 to 11.67±0.9, respectively. The C/N ratio range from 3.26±0.12 to 4.23±0.9, the C/N ratios of 7 fish are more closely to besides C. auratus and P. fulvidraco. The IsoSources model is adopted to calculate frequency energy contribution of four potential carbon source (POM, fixation of algae, C3 and C4 plants) for 9 fish, the results found that the main energy source of 9 fish was the POM and C3 plants.To understand the temporal and spatial variation and source of suspended particulate organic matter (POM) after the impoundment of the Three Gorges Reservoir, we sampled POM at Yichang, Shishou, Chenglingji, Ezhou and Hukou section in the middle reaches of Yangtze River from July 2013 to March 2014. The results show that the δ13CPOM value changes between 25.21%～19.12%, the δ15NPOM value changes between 2.58%o～2.58%o, C/N average value changes between 6.99～ 15.5, the δ13CPOM was highest in July, and is low in March and December, this may cause by a large number of foreign material inflows in flood season in July. Through the analysis of variance found δ13CPOM has no significant difference between March and December, there were significant differences between the rests of the month (p< 0.001), and there is no significant difference between each sample section.δ15NPOM has significant difference between July and September (p<0.001), there is no significant difference between the rest of the month, the Chenglingji and Jiujiang section has significant differences (p<0.001), no significant difference between the rest. Using the binary mixture model calculation, the POM consisting mainly terrigenous organic matter, the average contribution rate was 72.8% and there is obvious seasonal variation, proportion of terrigenous organic matter is high (81%～92%) in July (flood season), and is low (20%～53%) in March and December (low water season), with closely relation to the runoff of the Yangtze River.Stable isotope analyses of carbon and nitrogen are now widely used in trophic relations and energy flow study. Stable isotope analysis of fishes is often performed using muscle that requires sacrificing animals. Nonlethal sampling provides an alternative way for evaluating isotopic composition for species of concern or individuals of exceptional value. In this research we compared stable carbon and nitrogen isotope values of white muscle with those from fins (nonlethal) in Mylopharyngodon piceus and Hypophthalmichthys molitrix in the middle reaches of Yangtze River. Averaged fin δ13C value was 0.22%o higher than muscle, while fin δ15N value was 0.66%o higher than muscle. Both fish showed strong linear correlation inδ13C and 815 N value between their nonlethal sampled fin and their muscle tissue, support the use of nonlethal sampled tissues for stable isotope analyses of fish (R2>0.9,p<0.001).