Variations Of Macrofaunal Diversity In The Yellow Sea And East China Sea And The Influence Of Kuroshio Current

The aims of this thesis are: exploring the temporal and spatial variations of macrobenthic diversity among seasons,periods,and regions in the southern Yel ow Sea,and mainly discussing the influence of anthropogenic activities to the macrobenthos;studying the temporal and spatial variations of macrobenthic diversity among months,seasons,and regions in the East China Sea,and mainly discussing the influence of Kuroshio Current to the macrobenthos.The main results were listed as follows.1.Seasonal and spatial characteristics of the macrobenthic community in the southern Yel ow Sea were studied based on data from three voyages carried out in spring,summer and autumn,2012.A total of 218 species were obtained with Polychaeta and Crustacea being the predominant groups.Abundance showed an increasing trend with season.Biomass and secondary productivity had lowest values in spring and highest values in summer.Biomass was significantly different among seasons,and number of species,secondary productivity and Shannon-Weiner index had significant differences among regions.Abundance,Pielou's evenness index and average taxonomic distinctness were not significantly different among seasons nor regions.Overall significant differences of community structure among both seasons and regions were detected.2.To detect large,temporal-and spatial-scale variations in the macrofaunal community in the southern Yel ow Sea,data collected along the western,middle and eastern(i.e.the deep water)regions of the southern Yellow Sea from 1958 to 2014 were organized and analyzed.The abundance of polychaetes increased in the western region but decreased in the eastern region from 1958 to 2014,whereas the abundance of echinoderms showed an opposite trend.For the entire macrofaunal community,Margalef's richness(d),the Shannon-Wiener index(H')and Pielou's evenness(J')were significantly lower in the eastern region when compared with the other two regions.No significant temporal differences were found for d and H',but there were significantly lower values of J' in 2014.Considerable variation in the macrofaunal community structure over the past several decades and among the geographical regions at the species,genus and family levels were observed.The most conspicuous pattern was the increase in the species Ophiura sarsii vadicola in the eastern region.In the western region,five polychaetes(Ninoe palmata,Notomastus latericeus,Paralacydonia paradoxa,Paraprionospio pinnata and Sternaspis scutata)increased consistently.The dominance curves showed that both the species diversity and the dominance patterns were relatively stable in the western and middle regions.Environmental parameters such as depth,temperature and salinity could only partially explain the observed biological variation in the southern Yel ow Sea.Anthropogenic activities such as demersal fishing and other unmeasured environmental variables may be more responsible for the long-term changes in the macrofaunal community.3.Decadal variations(2000-2013)in the macrobenthic community of the southern Yel ow Sea and its relationship with climate indices were investigated based on the analysis of the community at two stations located basically along the 70 m depth contour.Significant decadal variations in community structure were found.The decadal community variations could be roughly attributed to the decrease of two species of mollusks(Thyasira tokunagai and Nucula tenuis)and the increase of one echinoderm(Ophiura sarsii vadicola),one polychaete(Notomastus latericeus)and one bivalve(Portlandia japonica)at both stations.Redundancy analysis showed that the Pacific Decadal Oscillation(PDO)and the Southern Oscillation Index(SOI)were significant climate indices influencing the macrobenthic community structure in the southern Yel ow Sea.4.In spring and summer 2011,the macro-and megabenthic fauna in two sections of the East China Sea were investigated using an Agassiz net trawl to detect the seasonal and spatial variations of benthic community characteristics and the relation to environmental variables.The index of relative importance(IRI)indicated that the top five important species changed completely from spring to summer.Species number,abundance and biomass in summer were significantly higher than in spring,but no significant difference was observed among areas(coastal,transitional and oceanic areas,divided basically from inshore to offshore).Species richness(d),diversity(H')and evenness(J')showed no significant seasonal or spatial variations.Cluster analysis and nMDS ordination identified three benthic communities from inshore to offshore,corresponding to the three areas.Analysis of Similarity(ANOSIM)indicated the overall significant difference in community structure between seasons and among areas.K-dominance curves revealed the high intrinsic diversity in the offshore area.Canonical correspondence analysis showed that the coastal community was positively correlated to total nitrogen and total organic carbon in spring,but negatively in summer;oceanic community was positively correlated to total nitrogen and total organic carbon in both seasons.Species such as Coelorhynchus multispinulosus,Neobythites sivicola,Lepidotrigla alata,Solenocera melantho,Parapenaeus fissuroides,Oratosquilla gonypetes and Spiropagurus spiriger occurred exclusively in the offshore oceanic area.The distribution of these species may reflect the influence of the Kuroshio Current to the benthic community structure in this area.5.Kuroshio Current intrudes the East China Sea continental shelf in the bottom from the northeast of Taiwan via two bottom branches named as Nearshore Kuroshio Branch Current(NKBC,along the ?60 isobaths)and Offshore Kuroshio Branch Current(OKBC,along the ?100 isobaths).However,knowledge of macrofaunal response to the bottom branches is limited.This study examined the benthic macrofaunal community in a section under the influence of NKBC.During 9 months from February to November,2015(except August)in this section,a total of 270 macrofaunal species were collected.Cluster analysis and nMDS ordination revealed three communities named as Inshore,Kuroshio Branch and Offshore Community,roughly corresponding to the west,middle and east of NKBC route.Significant differences in species composition(One-way PERMANOVA)and diversity indices(One-way ANOVA)among regions and communities were detected,while no difference among months was revealed.Indicator species also varied among communities,with Sternaspis scutata and Odontamblyopus rubicundus dominated in Inshore Community,Camatopsis rubida,Schizaster lacunosus and Craspidaster hesperus in Kuroshio Branch Community,and Portunus argentatus,Champsodon snyderi and Coelorinchus multispinulosus in Offshore Community.However,some rare species(e.g.Neobythites sivicola)may indicate the pass of NKBC rather than indicator species.Redundancy analysis was used to describe the relationship between macrofaunal species and environmental variables in this study.Water depth and turbidity play important roles in the distribution of macrofauna.S.scutata and O.rubicundus were associated with high turbidity and shal ow depth,while Plesionika izumiae and P.argentatus were opposed.Because the existence of NKBC had not been detected in those investigations carried out since 1950 s and the Kuroshio Branch Community had no significant seasonal variations throughout the year,it could be speculated that the forming time of the Kuroshio Branch Community which has been stable may be not long.It could be further speculated that the NKBC has been a stable branch of the Kuroshio Current.6.To examine the diversity and distribution of demersal fish in the East China Sea(ECS)and access the impact of the bottom branch of Kuroshio,we investigated the demersal fish using the Agassiz trawl in forty sites in the ECS shelf in summer,2015.A total of 72 species were collected with Amblychaeturichthys hexanema,Champsodon snyderi,Odontamblyopus rubicundus,Cynoglossus interruptus,and Caelorinchus multispinulosus being the top 5 most abundant species.Cluster analysis and nMDS ordination identified three demersal fish groups(the coastal group,the transitional group and the kuroshio group)and ANOSIM indicated the overall significant difference among the three groups.Gobies were the representative species in the coastal group,Neobythites sivicola,C.interruptus and Aseraggodes kobensis in the transitional group,C.snyderi,Callionymus beniteguri and Ostorhinchus fasciatus in the kuroshio group.Most of the diversity indices showed an increasing trend from inshore to offshore.CCA revealed that turbidity,fine silt sediment content,fluorescence,dissolved oxygen and salinity were the most active environmental variables affecting the demersal fish community.RDA found that turbidity and temperature showing significant associations with biodiversity matrix.These environmental variables were all related to the intrusion of the Kuroshio Current.The important results in this thesis includes that: the long term variations of macrobenthos in the southern Yel ow Sea were mainly influenced by anthropogenic activities;the evolution orientations of macrobenthos were different in the regions with different anthropogenic stress,such as the downsizing and simplification in the coastal region and the invariance in the offshore region;the macrobenthos in the East China Sea could reflect the influence of Nearshore Kuroshio Branch Current,especially for the distribution pattern of the demersal fish;some rare species(such as Neobythites sivicola)could act as the indicator species of the intrusion of Kuroshio Current.