WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Journal of Food, Agriculture & Environment Vol.9 (3&4): 649-654. 2011 www.world-food.net Helsinki, Finland e-mail: [email protected] Study on the feeding habits of fishery organisms in the Yangtze River estuary and the 13 southern Yellow Sea in spring with δ C method Zhongyi Li, Zhimeng Zhuang, Fangqun Dai and Xianshi Jin* Key Laboratory for Sustainable Utilization of Marine Fisheries Resource, Ministry of Agriculture, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Science, 106 Nanjing Road, Qingdao 266071, China. *e-mail: [email protected] Received 18 June 2011, accepted 10 October 2011. Abstract The Yangtze River estuary and the southern Yellow Sea are the natural habitats for numerous marine organisms. These systems are influenced both by oceanic water and the runoff. The main objectives of this study were to compare the feeding habits of organisms from these two areas using stable isotopes to calculate the percent reliance on benthic prey and to compare the results of stomach content analysis from the previous researches the carbon stable isotope technique. The ratios of carbon stable isotopes (δ13C) of 19 fish species and 12 invertebrates in the Yangtze River estuary, and 14 fish species and 10 invertebrates in the southern Yellow Sea in spring, 2005, were examined. The results showed that there were 10 fishery species that had the same feeding habits in the Yangtze River estuary and the southern Yellow Sea. The percent reliance on benthic prey of organisms in the southern Yellow Sea was mostly higher than those of organisms in the Yangtze River estuary. If the feeding habits types of the two methods were identified using only pelagic feeding, benthic feeding and mixed feeding habit three categories, there were 20 out of 23 organism species that had the same feeding habits. The study showed that the feeding habits of fishery organisms had spatial variations, and the carbon stable isotope technology can be used to calculate the feeding habits of organism practically. Key words: Feeding habit, fishery organism, China, Shanghai, Yangtze River estuary, the southern Yellow Sea, spring, δ13C. Introduction Aquatic organism feeding behaviour is a complicated course, isotope ratios of organisms can also reflect the coupling of the affected by many biological and abiotic factors, such as organism’s benthic and pelagic environment, the organisms living in the middle habitat, nutritional condition, seasonal change, geographic area water layer having the ratios between those of benthic and pelagic and alternative foods. Aquatic organisms mainly feed some certain organisms. Therefore, the different carbon stable isotope ratios species, sometimes alter their feeding strategies for adapting to of organisms in different water layers can be helpful in studying their new habitats. The study of feeding habits of marine organisms their feeding habits. A few researchers have used stable isotopes could provide useful information on the trophic class of fishery to distinguish the feeding habit of similar species or the feeding organism in food web and management strategy options in multi habit of different developmental stages of the same species, and species fishery 1. to study the influences of feeding habits of species on environment A few methods have been developed to evaluate the feeding and other species. However, most of these researchers mainly habits of organisms, such as stomach content analysis, fatty acid focus on continent species 8-10, only a few studied marine species, analysis and stable isotope analysis. Stable isotopes are for example, Vander Zanden and Vadeboncoeur 11 and Sherwood increasingly used as natural indicators, particularly in aquatic and Rose 12 have calculated the feeding habits of marine organisms organism studies. An organism’s δ13C and nitrogen isotope δ15N using δ13C signature. ratios are integration of the isotopic signatures of prey items that In this study, the feeding habits of fishery organisms in the have been assimilated, and the ratios vary with food and living Yangtze River estuary and the southern Yellow Sea were compared conditions. The rate at which an organism will realize isotopic using stable isotope techniques following Vander Zanden and equilibrium within its diet depends on growth and tissue Vadeboncoeur 11 and Sherwood and Rose 12. The feeding habits conversion rates 2, 3. of fishery organisms were analyzed by calculating the proportion In aquatic ecosystem, δ13C of organisms varies with their of planktonic and benthic invertebrates in diet. These results were environment. Davenport and Bax 4 found that the carbon stable compared with the previous results obtained by using stomach isotope ratios of plankton were lighter (more negative delta) than content analysis method. The Yangtze River estuary and the those of benthos. Pinnegar and Polunin 5 also discovered that Southern Yellow Sea are the natural habitats for numerous marine organisms with enriched δ13C values were usually related to the organisms. These systems are influenced both by oceanic water benthic food web, and organisms with depleted carbon stable and the runoff. It is helpful in studying the difference of the isotope ratios were usually influenced by the pelagic food web. ecosystem structure of the two areas and protecting them by Hobson et al. 6 and Chandra et al. 7 found that the carbon stable comparing the feeding habits of fishery organisms from them. Journal of Food, Agriculture & Environment, Vol.9 (3&4), July-October 2011 649 Materials and Methods Stable isotope analysis: All samples were thawed and rinsed with Study sites: The feeding habits of the organisms in the Yangtze distilled water. The tissues of different fishery organisms were River estuary and the adjacent southern Yellow Sea were studied. selected as follows: white back muscle for fish, abdominal muscles The boundary between the southern Yellow Sea and the Yangtze for shrimp, and leg muscle for crab. Zooplankton were acidified River estuary was marked according to Xu et al. 13. The two adjacent with 1 M HCl to remove carbonates, and rinsed in distilled water areas have different physical, chemical and biological to neutral. All samples were freeze-dried at -80°C 19, 20, then all characteristics, and are impacted by the runoff of the Yangtze freeze-dried samples were ground into powder using quartz mortars, River. The Yangtze River is the longest (6300 km) river in Asia and and the powder of the same species were mixed together. the fifth largest river in the world. On average, 9.24×1011 m3 fresh Isotopic analysis was completed in the Stable Isotope water is transported into the sea annually, including 8.9×105 tons Laboratory, College of Resources and Environmental Sciences, 4 6 14 TIN, 1.4×10 tons PO4-P and 2.0×10 tons SiO3-Si . The Yangtze China Agricultural University. A Delta XL, continuous flow-isotope River estuary is known as feeding and spawning grounds for ratio mass spectrometer was connected to a Carlo Erba Elemental many important commercial species, such as largehead hairtail Analyzer. In order to ensure the accuracy of the results, a standard (Trichiurus haumela), Japanese anchovy (Engraulis japonicus) sample was analyzed 2 or 3 times after each group of five samples, and crabs 15. The adjacent Yellow Sea is a semi-enclosed sea, to keep equipment in good working order. The carbon stable surrounded by the west coast of the Korean peninsula and the isotopic composition of a sample was quantified relative to an east coast of China. It is shallow, with depth ranging from 90 m in international standard reference material (Pee Dee Belemnite the central trough to less than 20 m within 50 km off the coast. The limestone). The ratio of 13C/12C (δ13C) is expressed as the relative deepest water is confined to the north-south trough which runs per mil differences between the sample and conventional gas from the northern boundary of the Yellow Sea to the continental standards 21. shelf break southwest of Cheju Island. Another feature of the R bottom topography is the east-west asymmetry of the bathymetric 13 ª R sample s tan dard º 3 G C= « R » u10 gradients. Generally, the bathymetric gradients are relatively smaller ¬ s tan dard ¼ on the Chinese side than those on the Korean side 16. where, R = 13C/12C, the accuracy of δ13C is ± 0.5 × 10-3. Sample collection and pretreatment: Samples were collected from the Yangtze River estuary and the adjacent southern Yellow Sea Feeding habit analysis: Pelagic, mixed and benthic feeding types (30.5° to 33.5° N, 122° to 125° E) onboard R/V “Beidou” in April were defined based on the percent reliance on benthic prey, as and May, 2005. Twenty-seven stations in total were sampled, indicated by carbon stable isotope measurements. The feeding including 10 stations in the southern Yellow Sea and 17 stations habit was calculated as: in the Yangtze River estuary, respectively (Fig. 1). Samples were randomly collected (all specimens were collected when their Percent reliance on benthic prey (Bp)= 13 13 13 13 G CC G C P G CBˉG CP u100 number was less than 5, at least 5 specimens were collected for δ13 δ13 δ13 δ13 the other species). Zooplankton size larger than 900 µm and where, Cc, Cp and CB is the mean C of a consumer, pelagic benthic crustacean invertebrates were selected as pelagic and invertebrate, and benthic invertebrate, respectively 8-10. Note that benthic food web base prey. They were collected with a standard the mixing model assumes 0.6‰ trophic fractionation for δ13C, the medium- and large-sized zooplankton net from bottom to surface value originated from the research of Cai et al. 22, based on the in each station. The zooplankton were transferred to the filtrated results of indoor feeding experiment of Japanese anchovy.