Trophic Level Of The Major Species In Coastal Water Of Lvsi Fishing Ground Using Stable Carbon And Nitrogen Isotope Analysis

According to the survey of fishery resources in the coastal waters of Lvsi fishing ground in September 2018,stable isotopic values(?¹³C and?¹⁵N)and trophic levels of main organisms in the waters were compared and analyzed.Iso Source model was used to calculate the contribution values of the three major potential carbon sources?phytoplankton,POM and SOM?of the consumers in the coastal waters of Lvsi fishing ground,and then compared the former and latter trophic levels variation of main organisms by overlapping potential carbon source influence.Using Iso Source model,the trophic ecology of Larimichthys polyactis and Collichthys lucidus were analyzed and compared.The ecological niche and trophic level of two fish were determined by dividing their body length into different groups.The results are as follows:?1?The trophic level of L.polyactis was significantly higher than that of C.lucidus?P<0.05?.The clustering analysis based on?¹³C and?¹⁵N values demonstrated that,the body length of two fishes could be separated into two groups,140-190mm,130-140mm,120-130mm,80-90mm and the rest for L.polyactis,and140-190mm,130-140mm and the rest for C.lucidus.?2?Iso Source model showed that the contribution of phytoplankton to L.polyactis and C.lucidus was 43.38%and 36.38%,respectively,and that of SOM was 40.66%and43.7%,respectively,which determined that phytoplankton and SOM were main potential carbon sources to two fishes.Through Iso Source model,we also found the critical point of body length of diet shift of L.polyactis is 80mm,smaller than C.lucidus?110mm?,reflecting that C.lucidus changed its dietary behavior later than L.polyactis in growth and development stage.?3?The?¹³C and?¹⁵N values ranged from-24.27‰to-13.24‰and 4.30‰to14.61‰,respectively,and the average?¹³C and?¹⁵N values were-17.15±1.85‰and11.21±1.90‰,respectively,in the coastal waters of Lvsi fishing ground.?4?The clustering analysis demonstrated that,TG1?Trophic Group 1?consists mainly of most of middle and small fishes,shrimps and other invertebrates,TG2included the small-sized fishes like Konosirus punctatus,Mugil cephalus,etc.and shrimps like Exopalaemon annandalei,Exopalamon carincauda,etc.,and Phytoplankton in TG3 and Zooplankton in TG4.?5?The range of trophic level of fishes,shrimps,carbs and Shellfish were from 2.7to 4.2,2.8 to 3.7 and 1.5 to 3.6 in the continuous trophic spectrum,respectively,in which most of species belonged to medium and advanced consumers.The average trophic level of species in this survey was 0.6 higher than that in the east yellow sea,and a niche overlap appeared to manifest that the growth and nutrient structure of most species were similar.?6?The contribution of phytoplankton and SOM to major organisms was 58.7%and 28.2%respectively,and the contribution of POM was smaller.Therefore,it is determined that phytoplankton and SOM were main potential carbon source of main organisms in costal water of Lvsi fishing ground in Summer.Trophic position changed little in fishes and cephalopods,but much more in shrimps and carbs in two trophic level spectrums,manifesting that way to overlap potential carbon source could not be accurately express extensive diets of most of fishes.On the opposite,the shrimps and carbs'TLs could be directly reflected using that way.