A Study On Trophic Structure Of Nektonic Organisms In The Min Estuary

To understand the fisheries community composition and trophic structure,seasonal bottom trawl surveys were conducted in the Min Estuary(119°40?-119°55?E,25°50??26°14?N)containing 11 sampling sites in 2015(Jan,May,Aug and Nov).The samplings were identified,and the values of stable isotope ?13C?815N of muscle samplings were determined.Based on the data,the continuous nutrition spectrums were drawn to analyze the trophic structure of fisheries community in the Min Estuary.The results showed:In the Min Estuary,a total of 149 species of the nektonic organisms were sampled,among which 105 species were from fish,36 species from crustacean and 8 species from cephalopod.In winter,63 species were sampled,including 41 species of fish,20 species of crustacean and 2 species of cephalopod.In spring,75 species including 54 fishes,17 crustacean and 4 cephalopod were sampled.In summer,91 species including 64 fishes,21 crustacean and 6 cephalopod were sampled.In autumn,71 species were sampled,including 47 species of fish,19 species of crustacean and 5 species of cephalopod.In the nektonic organisms of the Min Estuary,in winter the value of ?13C ranged from-20.29‰to-14.43‰ with a span of 5.86‰,and the value of ?15N ranged from 7.63‰ to 14.01‰ with a span of 6.38‰;in spring the value of ?13C ranged from-24.57‰ to-18.35‰ and the value of ?15N ranged from 7.87‰ to 14.12‰,with a span of 6.22‰ and 6.25‰ respectively;in summer the values of 813C and ?15N varied from-23.11‰ to-18.17‰ and 8.13‰-14.02‰ respectively,and in autumn the value of ?13C and815N varied form-22.39‰ to-16.92‰ and 8.30‰-15.29‰respectively.The seasonal change of value 813C could be attributed to the species wintering migration,plankton and algae fading,and photosynthesis intensity.In the Min Estuary,the trophic level of the fish community varied from 1.7 to 3.6,with an average value of 2.6 and a span of 1.9.According to the trophic level,about 24%of the total fish species were in 2.0-2.5,and 51%of the fishes in 2.5-3.0,23 species accoumting for 21%of the fishes in 3.0-3.5;and 3 species above 3.5.Seasonally,the trophic level ranged in 1.7-3.6 in winter,and 1.8-3.6 in spring,-2.0-3.6 in summer,1.9-3.8 in autumn.No significant differences were founded in the trophic level variations and the average values in the four seasons.The number of fish species in percent with the trophic level in 2-3 was 72,higher 63 in winter,61 in summer and 68 in autumn 68%.Species with trophic level above 3 were accounting for 37%of the total fish sampling in summer,higher than the other seasons.All the difference could be explained by the seasonal species turnover.The fisheries community in the Min Estuary could be divided into 5 trophic groups and constructed 2 food chains as:high trophic level benthic carnivorous group--middle trophic level benthic omnivorous group,and high trophic level carnivorous group--middle trophic level omnivorous group--low trophic level planktonivorous group.No seasonally stable top predators were found in the Min Estuary.