Demersal Fish Biodiversity In Bering And Chukchi Sea And Its Responses To Environmental Changes

The Bering Sea and Chukchi Sea are located at high latitudes,one of the most significant areas affected by climate change.In marine ecosystem,the temporal and spatial distributions of fishes are closely related to environmental characteristics.This thesis synthesizes data from demersal fishes surveys in the Bering Sea continental shelf,the Bering Strait,the Chukchi Sea continental shelf area and the Chukchi Sea continental slope from the 4th(July-September,2010),5th(July-September,2012),6th(July-September,2014),7th(July-September,2016)and 8th(September,2017)Chinese Arctic Scientific Expedition.The analyses of fish composition,biodiversity,and community are conducted.Relationship between fish and environment is illustrated basing on the environmental data,such as depth,bottom temperature and salt in the study areas.Furthermore,the adaptations and feedbacks of demersal fishes under the background of increasing environmental disturbance in the study area are discussed.The main contributions are as follows:(1)The total fishes identified are composed of 65 species within 15 families,8 orders.Among them,53 species are identified from samples collected in the Bering Sea,belonging to 14 families,8 orders,with the largest number of species collected during the 6th Chinese Arctic Scientific expedition(36 species).In the Chukchi Sea,43 fish species are identified,belonging to 11 families,6 orders,with the largest number of species collected during the 7th Chinese Arctic Scientific expedition(25 species).Meanwhile,there are 31 common species in these two seas.There are 5 species identified in every expedition except for the 8th: Liparis fabricii,Enophrys diceraus,Gymnocanthus tricuspis,Ulcina olrikii,Boreogadus saida and Hippoglossoides robustus.The top 3 fishes of the largest number are Gymnocanthus tricuspis,Hippoglossoides robustus and Boreogadus saida,and their resource abundance has been evaluated maintaining at a high level in recent years according to our surveys.Among them,Boreogadus said is one of the key species in the Arctic ecosystem(FEC,Focal Ecosystem Component),which is responsible for transmitting energy to upper predators,and can be considered as an indicator species to observe changes in the Arctic.(2)In the Bering Sea,Margalef richness index ranges from 0 to 3.11,the ShannonWiener diversity index ranges from 0 to 2.18,and the Pielou evenness index ranges from 0 to 1.While in the Chukchi Sea,Margalef richness index ranges from 0 to 2.28,the Shannon-Wiener diversity index ranged from 0 to 1.87,and the Pielou's evenness index ranged from 0 to 1.The data shows that the average value of Margalef richness index in the Bering Sea is larger than in the Chukchi Sea and the difference is significant(P<0.05).However,there is no significant difference between Shannon-Wiener diversity index and Pielou evenness index(P>0.05).In terms of taxonomic diversity,the average taxonomic distinctness(?+)of the 65 demersal fish species in the study area is 74.18,the variation in taxonomic distinctness(?+)is 318.27;while the ?+ of 53 demersal fish in the Bering Sea is 74.26 and the ?+ is 302.40;the ?+ of the 43 species in the Chukchi Sea is 71.45,and the ?+ is 296.35.Statistical data shows that the fish biodiversity in the Bering Sea is higher,while the genetic relationship of fishes in the Chukchi Sea is closer.Analyses of Pearson correlation coefficient indicates that,in the Bering Sea,the Margalef richness has significantly negativecorrelation with the depth;the taxonomic distinctness and the average taxonomic distinctness have significantly positive correlation with the salinity.In the Chukchi Sea,the biomass has significantly positive correlation with the depth;the number of species and the variation in taxonomic distinctness have significantly positive correlation with bottom temperature.(3)Demersal fishes in the study areas can be divided into four communities:(1)The outer marginal of the continental shelf in the northern Bering Sea(Community I),represented by the results from 4th and 6th expeditions.The factor analysis shows that the variance of water depth is the highest and the main predominant species are Lycodes palearis and Icelus spatula.(2)The St.Lawrence Island-Bering Strait(Community II),represented by the results from 4th,5th and 6th expeditions,as the depth and bottom temperature are the highest value in the factor analysis,where the average bottom temperature is close to 0°C.The main predominant species are Hippoglossoides robustus,Ulcina olrikii and Liparis fabricii.(3)The coastal area in the eastern Chukchi Sea(Community III),represented by the results from 6th and 7th expeditions,as the depth is the highest value in the factor analysis.And that the T test show that the depth has significantly difference with the community I and the community II(P<0.05).The main predominant species are Gymnocanthus tricuspis,Hippoglossoides robustus and Boreogadus saida.(4)The continental slope in the northern Chukchi Sea(Community IV),the only communities with an average bottom temperature below 0°C.The T test shows that the bottom temperature is significantly lower than that of community I and community III(P<0.05),and the bottom salinity is significantly higher than the other three communities(P<0.05).The main predominant species is Boreogadus saida.(4)Climate change has caused changes of species distribution.In our study,8 species that which mainly distributed in other Arctic waters appeared in our expeditions and 12 species that the distribution extend northward or close to the north boundary are recorded.The analyses of trophic level show that the latitude 60°N to 62°N in the Bering Sea experienced an increase in weighted trophic levels,which may be the area most disturbanced.The response of different species to climate change in community composition is different,which leads to the reconstruction of community structure.At the same time,climate change could amplify the influence of human factors(such as overfishing,habitat destruction and water pollution)to the marine biodiversity.So research on fish could help countries and interest groups reach on consensus about the climate warming effects on marine ecosystems.