The Change Of Fish Community Structure And Its Stress Factors Analysing In Zhangjiang Estuary Mangrove Area

In this study,the annual seasonal survey of the fish community in Zhangjiang Estuary Mangrove area(Fujian province)was conducted in December 2017,March,June,September and December 2018.The species composition,ecological group as well as the status of the taxonomic biodiversity of the fish community in this area were described.Meanwhile,it was further compared and tested with the survey data(species number,individual number,body mass,dominant species(standard length distribution of dominant species),biodiversity and spatial and temporal pattern)between 2013-2014 and 2017-2018 in this region,so as to better understand the changes of fish community structure during these years.Based on this,combined with the main pressure factors faced by the region(such as biological invasion,pond cultivation,overfishing,discharge of pollutants into the sea,etc.),a comprehensive analysis is carried out to provide theoretical basis and rationalization.Suggestions for the protection of fish resources and the management of mangrove reserve in the region in the future are provided.The main findings are as follows:(1)A total of 81 species of fish were collected from the survey in 2017-2018 belonging to 36 families,11 orders and 1 class,all of which were teleostean.The species of Perciformes were the most,accounting for 69.14%of the total species.Gobiidae had the most species,up to 25 species.The species-number relationship of fish presented an anti-J-type distribution,in which the number of individuals collected ranged 1-10 was the highest,accounting for 53.09%of the total number of species.In terms of ecological groups,the dominant species of the perching water level,thermophilic and dietary habits are demersal species(65.43%of the total species),warm-water species(88%of the total species)and carnivorous species(65%of the total species).(2)The overall changes of fish community structure in the region between 2018 and 2014 were not obvious,and remain relatively stable.The specific analysis results are as follows:A.Relative richness index:Among the two annual survey results,the relative richness indices of Order and Family were dominated by Perciformes and Gobiidae,respectively.The relative richness of Perciformes was not Significantly different(P>0.05),while the relative richness of Family was significantly different(P<0.05),which mean the number of species of the order in the period did not change much,but the changes of the Family were obvious.B.Similarity coefficient index:The similarity coefficient indices of Order,Family and Genus between two years were all beyond 0.70,while the similarity coefficient index between the species was the lowest,0.63,and the total number of species is up to 53.It showed that the fish community structure in the Zhangjiang Estuary mangrove area was relatively stable in the past few years,and the similarity coefficient index of species level is relatively low,indicating that the change of species was more obvious,which was consistent with the change of the number of species in the family.C.The taxonomic distinctness index:The average taxonomic distinctness △＋in 2018 is 51.80,significantly less than the value(52.83)in 2014(P<0.01),which indicated that the average path length between two fish species connected by phylogenetic trees decreased significantly in 2018,that is,relative kinship was relatively close.The variations in taxonomic distinctness index A＋(273.12)in 2018 was slightly greater than the value(264.43)in 2014,that is,the evenness of fish community species distribution in 2018 is relatively poor,but not obvious(P>0.05).The 95%confidence funnel curve further showed that the above-observed values were within the confidence interval,indicating that there was no significant change in the taxonomic distinctness index for each year.D.The inclusion index:The inclusion index at each taxonomic level in 2018 was slightly less than the value surveyed in 2014,that is,the stability of the species(genus,family,and order)belonging to the genus(class,order)was slightly weak,but not significant.(3)To better compare with the survey data in 2014,and avoid the influence of factors such as differences in research methods,the sampling method consistent with 2018 and 2014 was selected(Using cage nets at Creek section,fyke nets at Flat section),and the sampling period(three seasons in winter,spring and summer,and representative month of each season lasts 5 consecutive days in tidal circle)was compared and studied(the same below).A.Biodiversity analysis:compared with that in 2014,the total number of fish species and the three biodiversity indices in the three seasons increased,but the total number of individuals and overall body mass collected from sampling decreased significantly.The comparison results of different sections show that the number of individuals and body mass at Creek sections in 2018 increased significantly,while the number of individuals and body mass at two flat sections decreased significantly.In 2018,the indexes at Flat 1 decreased,while others increased at Flat 2 and Creek.This indicated that the fish community structure at Creek was more stable,and the fish resources were also significantly increased.The fish resources at two flat sections reduced significantly,and to some extent,the fish community structure at Flat 1 became worse,while it was relatively stable at Flat 2.The comparison results of different seasons showed that the number of individuals and body mass of fish sampling in different seasons in 2018 was much less than that in 2014.The number of individuals and body masses captured at both flat sections in each season were significantly reduced,while the number was reversed at Creek,which indicated that the fish resources at two flat sections decreased significantly,while the fish resources at Creek increased.The biodiversity index of the different seasons in the region increased mostly,while a few showed little fluctuation.At Flat 1:In winter,the richness index decreased,but the evenness index and diversity index both increased.In spring,three indices were significantly reduced.In summer,although the richness index increased significantly,the evenness index and diversity index are significantly reduced.At Flat 2:The three indices increased significantly in different seasons.At Creek:The richness index and diversity index increased significantly among different seasons,but the evenness indices decreased in spring and summer.In conclusion,the biodiversity and resources of fish community at Creek both increased.The change of biodicersity indices at two flat sections was not consistent,but both of resources were decreased.This indicated that the increase of the biodiversity index did not illustrate the state of change of resources,which mean the fish community structure can still be in a relatively stable and only quantity-change state when the resources of the species declined.B.Analysis of dominant species:In comparison with the surveys in 2018 and 2014,the dominant species of fish communities were more abundant.In addition to the pelagic fish,the near demersal species(Lateolabrax japonicus)and the demersal species(Solea ovata,Amoya chusanensis,and Bostrychus sinensis)were newly added.Clupanodon thrissa,Liza carinata,Osteomugil cunnesius and Tilapia sp.were dominant species of two years.As indicated above,the dominant species of fish in the region was more abundant,and other changes were not obvious except for the addition of near demersal and demersal species.The comparison results of different sections show that the number of dominant species at Flat 1 decreased relatively,but the species composition did not change much.Among them,Liza carinata,Clupanodon thrissa,Tilapia sp.and Osteomugil cunnesius were the dominant species between two years.The number of dominant species at Flat 2 was relatively increased,and the Solea ovata and Ambassis gymnocephalus were newly added.Among them,Clupanodon thrissa and Osteomugil cunnesius were the dominant species.The number of dominant species in the tidal section was relatively increased,mostly Gobiidae.Tilapia sp.,Liza carinata and Bostrychus sinensis are the dominant species at the tidal section of two years.This indicated that the composition of dominant species at the different sections had different change.However,in terms of Family,the change is not obvious.For the Genus,the of demersal species increased,especially at the Creek.The comparison results of different seasons showed that the number of dominant species increased in winter,and new species of Acanthogobius hasta,Glossogobius giuris and S.chinensis were added.Clupanodon thrissa,Osteomugil cunnesius and Liza carinata were the dominant species.The number of dominant species in spring increased,and Bostrychus sinensis,Amoya chusanensis,and Acentrogobius viridipunctatus newly added,among which Osteomugil cunnesius,Clupanodon thrissa and Tilapia sp.are common dominant species.The dominant species in summer did not change significantly,and Solea ovata were added,but Acanthopagrus latus was missing.As can be seen from the above that the number of dominant species in winter and spring increased,most of which were demersal species represented by Gobiidae.(4)Via comparing the body length distribution of dominant species or economic species in 2018 and 2014,except for Liza carinata,the average body length distribution of Clupanodon thrissa(P=0.04),Osteomugil cunnesius(p=0.00)and Acanthopagrus latus(P>0.05)decreased,and the number of fish caught was also significantly reduced,which indicated that the resources of some dominant species or economic species in the region were decreasing,and there was a possibility of miniaturization.(5)According to cluster analysis and non-metric multi-dimensional scaling,the fish communities in Zhangjiang Estuary mangrove area were divided into two groups in 2014 and 2018:Group 1:CG(Creek)Winter,CG(Creek)Spring,CG(Creek)Summer;Group 2:HC(Flat 1)Winter,HC(Flat 1)Spring,HC(Flat 1)Summer,DT(Flat 2)Winter,DT(Flat 2)Spring,DT(Flat 2)Summer,and the results of the non-metric multidimensional scaling(nMDS)analysis in 2014 and 2018 show that Stress=0.01 and Stress=0.05,respectively,indicating that the above results were credible.Differences between Group 1 and Group 2 in 2014 and 2018 were tested by the analysis of similarity(ANOSIM).The results showed that there were significant differences in fish community composition among three sections and three seasons in the region(R=1,P<0.05;R=0.981,P<0.05),that is,the difference between Group 1 and Group 2 was significant,which meant the distribution of species affected by habitat was greater than that of seasons.In short,the spatial and temporal distribution between two years was basically the same,which also indicated that habitat was the main factor affecting the distribution of species.(6)Combined with the results of the fish community change,identified biological invasion(like Spartina alterniflora),pond culture,overfishing and surrounding engineering construction as the main stress factors in the regions via consulting the bulletin,yearbook and related literature,using questionnaires and taking a visiting,and provided some advice on the protection and management of fish resources in the region.