Study On Zooplankton Community Structure With Image Analysis Technology

Zooplankton play a central role in marine ecosystem.Moreover,zooplankton can indicate global climate change and ocean circulation.As one of the marginal sea of the Western Pacific Ocean,China Sea was influenced by the pacific western boundary currents.Western Pacific develops a unique ecosystem owing to the extraordinary geographical environment and complex current system and is regarded as a center of origin with high species diversity.Thus,it is of great significance to carry on zooplankton research.In the present study,zooplankton community structure in the Yellow Sea,the East China Sea and the Pacific western boundary currents of the North Pacific was evaluated based on the ZooScan Integrated System and the normalized biomass size spectra.It aims to provide basic data for the study on large scale changes in zooplankton community structure from Chinese Coastal Regions to Western Pacific.In the Yellow Sea,based on the samples collected during August of 2013,significant correlations were detected between zooplankton biovolume calculated by ZooScan Integrated System and dry mass,carbon content,nitrogen content calculated by traditional measurement.Moreover,zooplankton communities based on ZooScan Integrated System was consistent with the results of previous studies.Thus,ZooScan Integrated System was proved to provide an efficient and feasible method to study the zooplankton community structure in China Sea.In the Yellow Sea and the East China Sea,samples were collected during autumn of 2014.Zooplankton were sorted into 17 diverse taxonomic groups: Copepoda,Euphausiacea,Chaetognatha,Medusa,Tunicata,Ostracoda,Amphipoda,Gastropoda,Polychaeta,Fish larvae,Nauplius,Noctiluca scintillans,Cladocera,Foraminifera,Radiolaria,Fish eggs,and other zooplankton.Zooplankton abundance ranged from 571.4 to 65995.1 ind.m^-3(average 6988.0±11008.1 ind.m^-3),and the dominant groups were Copepoda,Noctiluca scintillans,and Tunicata.Zooplankton biovolume ranged from 62.7 to 13050.2 mm³ m^-3(average 1468.3±2364.8 mm³ m^-3),and the dominant groups were Copepoda,Medusa,and Chaetognatha.According to the normalized biovolume size spectra,zooplankton communities were classified into four groups: the Yellow Sea group,the Yellow Sea and East China Sea Mixed group,the East China Sea Neritic group,and the East China Sea Shelf group,which were influenced by the water mass,sea temperature,and the latitude.For the Yellow Sea and the East China Sea,the slopes of the normalized biovolume size spectra for each group were slightly flatter than-1,which indicates that zooplankton communities in the Yellow Sea and the East China Sea were characterized by high energy transfer efficiency.The slopes for the Yellow Sea group and the Yellow Sea and East China Sea Mixed group were-0.66,while those for the East China Sea Neritic group and the East China Sea Shelf group were-0.72,which indicated that zooplankton communities in the Yellow Sea was more efficiently in energy transfer than that in the East China Sea.The intercepts of the normalized biovolume size spectra were in order of the East China Sea Neritic group > the East China Sea Shelf group > the Yellow Sea and East China Sea Mixed group > the Yellow Sea group,which indicated that the production for small size zooplankton was highest in the East China Sea Neritic group and lowest in the Yellow Sea group.In the western boundary currents of the North Pacific（0—200 m）,samples were collected during winter of 2012 and autumn of 2014,respectively.Zooplankton were sorted into 13 diverse taxonomic groups: Copepoda,Euphausiacea,Chaetognatha,Medusa,Tunicata,Ostracoda,Amphipoda,Gastropoda,Luciferida,Polychaeta,Fish larvae,Nauplius,and other zooplankton.In winter,the dominant groups were Copepoda,Tunicata,and Chaetognatha.Zooplankton abundance and biovolume ranged from 35.1 to 456.8 ind.m^-3(average 206.6 ± 128.6 ind.m^-3)and 4.3 to 231.7 mm³ m^-3(average 55.2 ± 55.5 mm³ m^-3),respectively.According to the normalized biovolume size spectra,zooplankton communities were classified into four groups,which basically coincided with the geographical patterns of different currents: the North Equatorial Current,the North Equatorial Counter Current,the Kuroshio Current,and the Mindanao Eddy,respectively.In autumn,zooplankton abundance ranged from 51.7 to 505.1 ind.m^-3(average 181.9±113.5 ind.m^-3),and the dominant groups were Copepoda,Ostracoda,and Chaetognatha.Zooplankton biovolume ranged from 4.1 to 138.1 mm³ m^-3(average 46.2±38.0 mm³ m^-3),and the dominant groups were Copepoda,Chaetognatha,and Euphausiacea.According to the normalized biovolume size spectra,zooplankton communities were classified into two groups: the Pacific North group and the Pacific South group.Seasonal variation was detected for the zooplankton communities.For the western boundary currents of the North Pacific（0—200 m）,the slopes of the normalized biovolume size spectra for each group were slightly flatter than or close to-1,which indicates that zooplankton communities in the western boundary currents of the North Pacific were characterized by high energy transfer efficiency.The slopes for groups in winter were flatter than those for groups in autumn,which indicated that zooplankton communities in winter was more efficiently in energy transfer,while that in autumn was more stable.According to the order of the intercepts of the normalized biovolume size spectra,the highest production for small size zooplankton were observed in the North Equatorial Counter Current group（in winter）and the Pacific South group（in autumn）,while the lowest production for small size zooplankton were detected in the North Equatorial Current group（in winter）and the Pacific North group（in autumn）.For the vertical distribution of zooplankton communities in the North Pacific,samples were collected down to 3000 m depths during autumn of 2014.Zooplankton were sorted into 13 diverse taxonomic groups: Copepoda,Euphausiacea,Chaetognatha,Medusa,Tunicata,Ostracoda,Amphipoda,Gastropoda,Polychaeta,Fish larvae,Nauplius,Foraminifera,and other zooplankton.The taxa composition of zooplankton varied greatly with increasing depths.Both the zooplankton abundance and biovolume decreased as the depth increased.The pattern of declining zooplankton abundance with depth was described better by a power regression model,whereas that of the biovolume fitted better to an exponential regression model.The slope of the normalized biovolume size spectra became flatter with increasing depths,which indicated that larger body size was observed with greater depth.According to the normalized biovolume size spectra,zooplankton communities were classified into three groups,which basically coincided with the vertical patterns of the optical layers of water,i.e.,the epipelagic zone,the mesopelagic zone,and the bathypelagic zone,respectively.For the North Pacific down to 3000 m depths,the slopes of the normalized biovolume size spectra for each group were lower than-1,which indicates that the zooplankton communities down to great depths（3000m）of North Pacific were characterized by high energy transfer efficiency.The slope for the epipelagic zone group was the most steep and that for the bathypelagic zone group was the most flat,while the intercept was highest in the epipelagic zone group and was lowest in the bathypelagic zone group,which indicated that zooplankton communities in the epipelagic zone was characterized by relatively high production and low energy transfer efficiency,while that in the bathypelagic zone was characterized by relatively low production and high energy transfer efficiency.