Analysis of organic carbon sources in tropical seagrass fish: a case study of the east coast of Hainan Province

Abstract

We analysed the carbon stable isotope (δ13C) of various organic carbon sources, including particulate organic matter (POM), sediment organic matter (SOM), seagrass and its epiphytes, and compared these results with that of 36 fishes, including 27 types of demersal fishes, 6 types of midwater fishes, and 3 types of surface fishes. Our results indicated that there were significant differences in the characteristics of carbon stable isotopes of different organic carbon sources, with δ13C values ranging from −23.35 (POM) to −9.56‰ (seagrass). The range of the δ13C value of the fishes was broad, from –21.84‰ (Dendrophysa russelii) to –10.57‰ (Dasyatis akajei), indicating that fishes had a variety of food sources. For 30 of the 36 fish species, including Plotosus lineatus, Gerres erythrourus, Hypodytes rubripinnis, etc, seagrass and its epiphytes were the main contributors. For 23 of the 36 fish species, including Upeneus tragula, Dasyatis akajei, Cheilodipterus quinquelineatus, their recorded body lengths were less than respective lengths of maturity. These findings indicate that seagrass and its epiphytes are important organic carbon sources for most fishes and play a key role in the energy flow of food web in seagrass ecosystems in this study.