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THE TROPHIC STRUCTURE OF DEMERSAL FISH SPECIES IN SOUTHWESTERN CONTINENTAL SHELF OF NANSHA ISLANDS, SOUTH CHINA SEA
Author(s): 
Pages: 468-475
Year: Issue:  2
Journal: Oceanologia et Limnologia Sinica

Keyword:  southwestern continental shelf of Nansha Islandstrophic structurecarbon and nitrogen stable isotopescommunity-wide metricsdemersal fish;
Abstract: We investigated carbon and nitrogen stable isotope ratios(δ13C and δ15N) of demersal fish species collected in September 2013 in southwestern continental shelf of Nansha Islands, South China Sea by trawling(the net was 92 m long, perimeter 128 m, floating line 49 m, lead line 59 m, mesh size 50 mm, trawling time 1h at 3kn/h) to study the trophic structure of the fish species. Several quantitative metrics based on the δ13C and δ15N ratios were calculated to quantitatively characterize the trophic structure in community-wide aspect. The results show that, the average δ13C and δ15N values of the demersal fish species in the study region were(–19.1±0.8)‰ and(9.7±1.0)‰, in range of –20.4‰— –17.0‰ and 7.9‰— 12.2‰, respectively. The average trophic position was 3.58±0.29 and ranged in 3.06—4.33, indicating that these demersal fish species were mostly carnivorous. δ13C range and δ15N range values based on the quantitative metrics were 3.4 and 4.3 respectively, suggesting a few basal resources in low trophic level of the fish food web in the study area. Total area and mean distance to centroid values were 5.8 and 1.0 respectively, indicating that the overall and average degree of trophic diversity were low. Mean nearest neighbor distance and standard deviation of nearest neighbor distance values were 0.37 and 0.43 respectively, suggesting that the fish food web in this study area has high trophic redundancy, small trophic niche width as well as low degree of trophic niche separation. In addition, fish species Alopias vulpinus and Alopias pelagicus played an important role in trophic structure of fish community of this area. To maintain the integrity of the trophic structure, ensure the sustainable use of fishery resources, and protect marine ecosystem, we recommend forbidding the capture of these two species and moderately fishing some redundant species(Saurida tumbil, Upeneus bensasi, Trichiurus haumela, etc.).
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