Spatial-temporal Patterns Of Fish Community And Its Functional Diversities Of The Leizhou Bay Waters,northern South China Sea

The impact biodiversity recession on ecological functions is one of the research hotspots in ecology recently.The functional ecology has became an important way to solve ecological problems.Global fishery resources are facing the threat of overfishing and resources recession.In addition,the destruction of habitats in important fishery waters,deterioration of water quality,eutrophication,invasion of alien species,large-scale sea-related engineering projects and other factors make the sustainable utilization of fishery resources face multiple challenges.The traditional community diversity researches place emphasis on the species composition,species relative abundance and their spatiotemporal variations,while less consideration is given to the functions and status of the species in the community,which is quite different from the actual ecosystem,such as communities functions of the community dominant species(high in abundance and frequency of occurrence)and the predators at the top of the food chain(small in number,but with important regulatory functions)lacked research.Studying the community functional diversities not only help to understand the spatial-temporal pattern changes of the community functional characteristics,but also help to analyze the status and functions of each species in the community,and can provide a scientific bases for the resource management of multi-species at the community level.The bay is greatly affected by human activities,and the relatively closed and stable ecosystem which is one of the ideal experimental fields for marine ecological outdoor research.In my study,the fishes in Leizhou Bay waters were selected as the research object,and eight quarters of bottom trawling fishery resources and ecological environment surveyed in 2016-2018.A functional traits matrix of Leizhou Bay fish was constructed through retrieving literature and actual observation,includes 7 fish functional characteristics: body type,swimming type,mobility,burying ability,trophic level,maximum body length and habitat,describes the functions and status marine fish communities.Furthermore,the temporal-spatial patterns of the traditional diversity and functional diversity were analyzed in Leizhou Bay fish communities.The correlation between traditional diversity indexes and functional diversity indexes of fish communities in Leizhou Bay were analyzed.Finally,through stepwise regression,the relationship between functional diversity and many environmental factors is explored.The results of the study are reflected in the following aspects:(1)Leizhou Bay was rich in species,with the maximum species in summer,followed by spring and autumn and winter.From 2016 to 2018,a total of 306 species of fishes were collected in the waters of Leizhou Bay,belonging to 183 genera,83 families and 19 orders.Among them,the perciformes is the main one,including 150 species,49.02% of the total,followed by the pleuronectiformes and the third is the clupeiformes.(2)Following the seasonal variations,the Margalef diversity index(Dma),ShannonWeaver diversity index(H’)and Simpson diversity index(Dsim)showed a trend of first increase and then decrease,with the highest in summer,and Pielou evenness index(J’)is the smallest in spring,and has little variation in other seasons.The richness index(Dma)range was 0.22-6.18 according to the season,with a value of 3.21±0.99;the ShannonWiener index(H’)had a range of 0.25-3.16,with an average value of 2.18±0.63;The Simpson index(Dsim)range was 0.09-0.94,with an average value of 0.76±0.19;the Pielou evenness index(J’)range was 0.10-0.91,with an average value of 0.65±0.17.(3)The fusiform shape dominated the body shape(37.96%),and the oblong shape appeared in all seasons;The swimming type was mainly subcarangiform,carangiform and anguilliform(96.16%);The motility was dominated by the sedentary or the territorial(58.31%);The majority fish showed no burying ability(69.51%);The largest body length showed there was few large-sized fish(1.09%),and the small-medium-sized body dominated(53.62%);In the trophic level the grade IV accounted for the highest(42.55%);The benthic dominated in the habitat(64.72%).(4)Functional richness(FRic)increased from spring to summer,and then decreased gradually,with an average value of 0.80 ± 0.09,ranging from 0.36 to 0.97;Functional evenness(FEVE)showed no significant seasonal trend,with an average value of 0.63 ± 0.07,ranging from 0.42 to 0.81;Functional divergence(FDiv)in spring and winter > summer and autumn in 2016,but stable in 2017,with no obvious trend of change,with an average value of 0.74±0.17 and a range of 0.22～0.99;Functional dispersion(FDis)in summer and autumn was bigger than spring and winter,with an average of 0.29 ± 0.08,ranging from 0.02 to 0.40;The seasonal variation trend of functional redundancy(Rao)was as same as FDis,with an average of 0.10 ± 0.03,ranging from 0.01 to 0.16.(5)The correlation between the functional diversity of fish communities in this study showed that FDiv and FDis,Rao Q had an extremely significant and moderate positive correlation;FDis,Rao Q and FRic showed a significant weak positive correlation;There was an extremely significant positive correlation between FDis and Rao Q.(6)In this study,FRic was significantly positively correlated with richness index(Dma),Shannonville diversity index(H’),Simpson diversity index(Dsim),and anti-Simpson index(Divn);The dispersion index FDiv,FDis,Rao Q and richness index(Dma),Shannon-Wiener diversity index(H’),Simpson diversity index(Dsim),Pielou evenness index(J’)showed a significant positive correlation(except for functional dispersion FDiv and richness index Dma).There was no significant correlation between other functional diversity indexes and species diversity indexes.(7)In this study,the FRic in Leizhou Bay was significantly affected by water temperature;The FEve was only significantly negatively correlated with water depth;While the functional dispersion FDiv,FDis,Rao Q and water depth were significantly positively correlated,FDiv was significantly positive correlation with p H;There was a significant positive correlation between FDis,Rao Q and DO.