Abstract: To find out the trophic relationships among main biological groups in the offshore food web of Gouqi Island, this study analyzed δ¹³C and δ¹⁵N compositions of the offshore consumers and their potential food sources collected in November 2012 and February 2013. The trophic levels of consumers were calculated based on the stable N isotope ratio. The results showed that the δ¹³C values of potential food sources-the phytoplankton, POM, SOM and macroalgae ranged from -21.7‰ to -14.7‰, and the δ¹³C values of zooplankton, macroinvertebrate and fish ranged from -21.1‰ to -13.7‰. The average C/N ratios of the primary producers and the consumers were 8.5 and 3.7 respectively, with a significant difference between them (P<0.001). Based on the δ¹⁵N values, the consumers could be divided into four trophic levels namely filterfeeding zooplankton, detritivorous/alage small-sized benthic animals, omnivorous animals, and fierce carnivorous fish. The trophic level of Sparus macrocephlus was 4.33, ranking the highest.

Key words: leaf senescence, light quality, endogenous hormone