Changes In Fish Community Structure In Leizhou Bay And Its Adjacent Waters

Marine ecosystems are undergoing important evolution under the influence of human activities and global climate change.Some key water area have even undergone regime shift.The top-down effect and bottom-up effect of fish play an important role in the marine ecosystem.To study the fish community structure ie,species composition,biomass,distribution patterns and its physical drivers in Leizhou Bay,seasonal bottom trawl along with environment monitoring surveys were conducted from 2016 to 2017.The relationships of fish community structure with environmental factors were analyzed using K-means cluster analysis,similarity percentage analysis,and redundancy analysis.The changes of fish richness and biodiversity were study by transforming the number of survey stations through computer simulation.The results were as follows:1)A total of 256 fish species were identified,which belonged to 155 genera in 75 families of 18 orders.Perciformes were the majority during surveys,followed by Pleuronectiformes and Scorpaeniformes.The number of fish species descended as the following: summer(172)> spring(136)> winter(114)> fall(109).The fish species were mainly comprised of demersal fish and warm-water fish.2)The diversity index(H’)ranged from 0.78 to 3.25,with the average value of2.20,whereas the evenness index(J’)ranged from 0.24 to 0.86,with the the average value of 0.65,and the richness index(D)ranged from 2.54 to 10.35,with the average value of 5.57.3)The study sites for each season could be divided into two groups: group I,with water depth of less than 10 m,and group II,with water depth between 10 m and 20 m.Group I showed an average similarity of 38.48%–47.44% across seasons in terms of fish community structure(which was shown as matrixes of sites by species biomass).Three species,Cynoglossus puncticeps,Tachysurus sinensis,and Plotosus lineatus contributed greatly to the average similarity within Group I in summer,fall and winter.Furthermore,Group II showed an average similarity of 41.38%–52.59% across seasons.The Saurida tumbil contributed mostly to the average similarity within Group II in spring,summer and winter.The average dissimilarity between group I and group II in seasons was 57.74%–76.25%.4)Six ecological factors,i.e.depth,dissolved oxygen,water temperature,salinity,pH,and chlorophyll a,explained 41.76%–47.11% of variation in fish biomass.Depth were the major environmental factors affecting the fish community,followed by dissolved oxygen(DO).5)To maintain a 90% fixed percentage of fish species detection and 75%,85%,95% fixed probability of detection within the fishery survey,the required sample sizes were 12,16,19 stations per year.6)In the biological diversity sampling design,the relative estimated error(REE)and coefficient of variation(CV)decreased when the number of survey stations increased in four sampling seasons.The number of stations might be different with the different objectives and precisions in a fishery-independent survey.With the relative estimated error and coefficient of variation are not more than 10% and 5% as the evaluation criteria,the number of stations required is 6 and 13,respectively.Moreover,the fish species richness in Leizhou Bay was obviously higher than in other bays of China.This study provided preliminary data on fish community structure and its relationship with environmental factors in Leizhou Bay,and provides clues for stocking enhancement in the waters.The simulation study provided a clue for the optimization of survey station and reduce the cost of the fishery-independent survey and the negative effects for marine ecosystem.