| The feeding ecology of Enedrias fangi in Jiaozhou Bay was studied based on the data from four seasonal bottom trawl surveys in Jiaozhou Bay from February to November 2011.Stomach contents method and carbon and nitrogen stable isotope analysis were used to study the food composition, feeding intensity, trophic level of E. fangi in Jiaozhou Bay.Carbon and nitrogen stable isotope analysis were used to study the feeding habits of E. fangi. In recent years, stable isotope analysis has become a powerful tool for studying the feeding habits of fishes. The carbon stable isotope composition of consumers is able to show where the food derive from, while the isotope nitrogen composition can show the position of trophic levels in food web. The method can overcome some of the methodological limitations associated with traditional stomach contents analysis. In this study, carbon and nitrogen stable isotope analysis were employed to explore the feeding habits of E. fangi in Jiaozhou Bay based on the data collected from the bottom trawl survey in May 2011. The results showed thatδ15Nand δ13C values for E. fangi in Jiaozhou Bay ranged from10.14‰ to 15.50%o and from-21.52%o to-18.14%o, respectively, with the average value ofδ15N and δ13C being (12.83±1.10)%o and (-20.42±0.73)%o, respectively.The main food sources of E. fangi in Jiaozhou Bay were Alpheus distinguendus, Trachypenaeus curvirostris, Latreutes anoplonyx, Latreutes planirostris, Nereididae and zooplankton (>900μm). Among them, L. anoplonyx and zooplankton (>900μm) were the most important prey items for E. fangi, accounting for 47%-66% and 35%-40% of food composition, respectively. Pearson correlation test indicated that there was significant positive relationship between the standard length of E. fangi and δ13C values (P<0.05). while no significant correlation was found between standard length and δ15N values (P>0.05).The trophic levels of E. fangi in different size classes ranged from 3.33 to 3.79. with the average trophic level being 3.65±0.14. The trophic levels did not increase with the size classes. Compared with previous studies, the food composition and trophic levels of E. fangi had experienced great changes, and the fluctuation of prey sources and the difference in analysis methods might be the main reason. Furthermore, the variations in trophic levels were also related to the difference in isotope baseline, isotope enrichment, sample size, and standard length of E. fangi.The feeding habits of E. fangi was studied by stomach contents analysis. The results indicated that the prey items ofEnedrias fangi was more than 40 species, with Nereididae, Hiatella orientalis, Gammarus sp. and Euphausia pacifica being the major prey species ofE. fangi. The diet composition of E. fangi varied significantly among seasons,Polychaeta andAmphipoda, Bivalvia and Amphipoda, Polychaeta and Bivalvia were the most important prey items in spring,autumn and winter, respectively, which might relate to reproductive strategy adopt by E. fangi in spawning season. There was significant relationship between standard length and feeding habits, with the increasing of standard length. The trophic level of E. fangi was 3.36, the trophic level of different size group was not significant. The canonical correspondence analysis (CCA) showed that longitude and latitude were the most important variables followed by temperature, NO3andsalinity.Stable isotope analysis has some shortage in terms of food composition contrast with stomach content analysis. Stable isotope analysis can only confirm the main food composition. It is also not very effective in the study of seasonal variation even the diurnal change of feeding habit.The advantage of stable isotope analysis was also obvious. It can identify long-term feeding habit while stomach content analysis can only identify short-term feeding habit. Some items that can be rapidly digested in the stomach, organic detritus and bacterium were hardly identified by the stomach content analysis. The trophic level calculated by stable isotope analysis and stomach content analysis had not significant difference. To sum up, methods can be choosed according to different purposeofresearch. |
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