Stable carbon and nitrogen isotopes and fatty acid compositions of Aurelia aurita , Stomolophus meleagris and Cyanea nozakii collected from the Yellow Sea in August 2009, were analysed. δ 13 C and δ 15 N values of the jellyfishes were in the range of −22.0‰ to −17.4‰ and 4.8‰ to 10.6‰, respectively, which indicated that jellyfishes in this study area were mainly dependent on marine-based carbon. The trophic levels of jellyfishes were estimated as between zooplanktons and high level carnivorous fishes. Low C18:1n-7/n-9 ratios and high C20:1 (n-11 and n-9) and C22:1 (n-11 and n-9) concentrations suggested jellyfishes in the Yellow Sea were carnivorous and zooplanktons were an important diet for them. Fatty acid compositions of jellyfishes were characterized by high C20:4n-6 concentration (>10%), with ratios of C20:5n-3/C22:6n-3 >1. Specific fatty acids (C20:1 + C22:1 and C20:4n-6) indicated that both pelagic-derived material and benthic detritus-derived food were diet of jellyfishes. Variations of certain biomarkers (C15:0 + C17:0, C20:1 + C22:1 (n-11 and n-9) and C20:4n-6) in jellyfishes of different body sizes suggested that ontogenetic diet shifts may take place during the growth of jellyfishes. Larger individuals with higher C20:1 + C22:1 (n-11 and n-9) concentration, tended to consume more zooplanktons; while the detritus-derived material made a more significant contribution to the small individuals, as suggested by higher C15:0 + C17:0 and C20:4n-6 concentrations. According to our study, besides the diet, species seemed to influence variations in stable isotopes and fatty acid compositions in jellyfishes.
The nutrient regeneration in the sediment plays an important role in the budget and dynamics of nutrients recycling in the water column. The nutrients in pore waters of sediments were investigated in autumn 1998 and spring 1999 in the Bohai Sea. The diagenesis models were developed for nutrients in sediments, the exchange fluxes of nutrients were calculated from the models. The results demonstrated that nitrification rate, denitrification rate, organic nitrogen content, the dissolved rate of siliceous material, bioturbation, and porosity affect the distribution of nutrients in the pore waters and exchange fluxes of nutrients at the sediment-water interface. Comparison between the exchange fluxes determined from the interstitial water profiles and those from measuring the concentration changes in the overlying water by incubating the intact sediment core in the laboratory on board the research ship shows that the exchange fluxes of nitrate by these two methods were consistent with each other, while the others showed obvious difference. The possible reasons for this are discussed in this work. This study demonstrates that the depth interval has an important effect on the determination of exchange fluxes of nutrients. The depth interval should be as small as possible, so that the benthic fluxes of nutrients are close to the real results.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)