[Trophic level of main organisms in coastal water of Lyusi fishing ground based on stable isotope method].

We measured the ratio of δ ¹³ C and δ ¹⁵ N values to estimate the trophic level of main organisms based on a fisheries resource survey in coastal water of Lyusi fishing ground carried out in September 2018. The results showed that δ ¹³ C values of the main organisms ranged from -24.27‰ to -13.24‰, with an average of (-17.15±1.85)‰. The δ ¹⁵ N values ranged from 4.30‰ to 14.61‰, with an average of (11.21±1.90)‰. Results from cluster analysis demonstrated that the main organisms in the coastal water of Lyusi fishery ground could be divided into four trophic groups. The first group was consisted mainly by middle and small fishes, shrimps and other invertebrates. The second group included the small-sized fishes like Konosirus punctatus, Mugil cephalus, etc. and shrimps like Exopalaemon annandalei, Exopalamon carincauda, etc. The phytoplankton belonged to the third group. The fourth group was zooplankton. In the trophic spectrum, the trophic levels of fish, shrimps and crabs, shellfish were 3.2-4.7, 3.2-4.2 and 2.0-4.1, respectively. Most species belonged to the category of middle and high-level consumers. In this survey, the average trophic level of the same species in the coastal waters of Lyusi fishing ground was 0.6, which was higher than that in the East China Sea and Yellow Sea. There was niche overlap of most fish, shrimps and crabs. Those results indicated the growth environment and nutrient structure of most living organisms in this area were generally similar.