ABSTRACT
By using stable isotope techniques, we analyzed the carbon and nitrogen stable isotope ratios of Rhopilema esculentum Kishinouye and its potential feed materials in Liaodong Bay of Bohai Sea, aiming to identify potential food sources and trophic levels of R. esculentum . The results showed that the δ13C and δ15N values for R. esculentum ranged from -20.27 to -23.06 (ave raged at -21.33), and from 6.82 to 10.03 (averaged at 8.25), respectively. The main food sources for R. esculentum included suspended materials, phytoplankton, fish eggs, zooplankton (≤1000 µm), zooplankton (1000-1500 µm), zooplankton (>1500 µm), among which, zooplankton (≤1000 µm) was the most important food source and contributed 71%-88% of the total food sources, followed by zooplankton (>1500 µm) (6%-19%), zooplankton (1000-1500 µm) (0%-22%), suspended materials (0%-10%), phytoplankton(0%-8%) and fish eggs (0%-2%). A Pearson correlation test indicated that there was significant negative relationship between the diameter and δ13C value of R. esculentum (P<0.05), while no significant correlation was found between its diameter and δ15N value (P>0.05). The trophic level of R. esculentum ranged from 2.79 to 3.88 depending on diameter classes,with a mean valu of 3.28 These results indicated that R. esculentum plays a key role in controlling microzooplankton in the Liaodong Bay, which is significant for providing deeper understanding into the tropic structure of biological communities as well as into the material cycles and energy flow of entire ecosystem in the Liaodong Bay.
