Spatial-temporal variation of phytoplankton community structure in Jiaozhou Bay,China

To better understand the spatial-temporal variation in phytoplankton community structure and its controlling factors in Jiaozhou Bay,Qingdao,North China,four seasonal sampling were carried out in 2017.The phytoplankton community structure and various environmental parameters were examined.The phytoplankton community in the bay was composed of mainly diatoms and dinoflagellates,and several other species of Chrysophyta were also observed.Diatoms were the most dominant phytoplankton group throughout the year,except in spring and winter,when Noctiluca scintillans was co-dominant.High Si/N ratios in summer and fall reflect the high dominance of diatoms in the two seasons.Temporally,the phytoplankton cell abundance peaked in summer,due mainly to the high temperatures and nutrient concentrations in summer.Spatially,the phytoplankton cell abundance was higher in the northern part of the bay than in the other parts of the bay in four seasons.The diatom cell abundances show significant positive correlations with the nutrient concentrations,while the dinoflagellate cell abundances show no correlation or a negative correlation with the nutrient concentrations but a significant positive correlation with the stratification index.This discrepancy was mainly due to the different survival strategies between diatoms and dinoflagellates.The Shannon-Wiener diversity index(H')values in the bay ranged from 0.08 to 4.18,which fell in the range reported in historical studies.The distribution pattern of H' values was quite different from that of chlorophyll a,indicating that the phytoplankton community structure might have high biomass with a low diversity index.Compared with historical studies,we believe that the dominant phytoplankton species have been changed in recent years due mainly to the changing environment in the Jiaozhou Bay in recent 30 years.     

DISTRIBUTION AND POPULATION DYNAMICS OF PARACALANUS PARVUS, PARACALANUS CRASSIROSTRIS, AND ACARTIA BIFILOSA (COPEPODA, CALANOIDA) IN THE BOHAI SEA

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Effects of Lugol's iodine solution and formalin on cell volume of three bloom-forming dinoflagellates

Fixatives are traditionally used in marine ecosystem research.The bias introduced by fixatives on the dimensions of plankton cells may lead to an overestimation or underestimation of the carbon biomass.To determine the impact of traditional fixatives on dinoflagellates during short-and long-term fixation,we analyzed the degree of change in three bloom-forming dinoflagellates(Prorocentrum micans,Scrippsiella trochoidea and Noctiluca scintillans) brought about by Lugol's iodine solution(hereafter Lugol's) and formalin.The fixation effects were species-specific.P.micans cell volume showed no significant change following long-term preservation,and S.trochoidea swelled by approximately 8.06% in Lugol's and by 20.97% in formalin as a percentage of the live cell volume,respectively.N.scintillans shrank significantly in both fixatives.The volume change due to formalin in N.scintillans was not concentration-dependent,whereas the volume shrinkage of N.scintillans cells fixed with Lugol's at a concentration of 2% was nearly six-fold that in cells fixed with Lugol's at a concentration of 0.6%-0.8%.To better estimate the volume of N.scintillans fixed in formalin at a concentration of 5%,we suggest that the conversion relationship was as follows:volume of live cell=volume of intact fixed cell/0.61.Apart from size change,damage induced by fixatives on N.scintillans was obvious.Lugol's is not a suitable fixative for N.scintillans due to high frequency of broken cells.Accurate carbon biomass estimate of N.scintillans should be performed on live samples.These findings help to improve the estimate of phytoplankton cell volume and carbon biomass in marine ecosystem.     

A model study on dynamical processes of phytoplankton in Laizhou Bay

A three-dimensional ecosystem model, using a PIC (Particle-In-Cell) method, is developed to reproduce the annual cycle and seasonal variation of nutrients and phytoplankton biomass in Laizhou Bay. Eight state variables, i.e., DIN (dissolved inorganic nitrogen), phosphate, DON (dissolved organic nitrogen), DOP (dissolved organic phosphorus), COD (chemical oxygen demand), chlorophyll-a (Chl-a), detritus and the zooplankton biomass, are included in the model. The model successfully reproduces the observed temporal and spatial variations of nutrients and Chl-a biomass distributions in the bay. The nutrient concentrations are at high level in winter and at low level in summer. Double-peak structure of the phytoplankton (PPT) biomass exists in Laizhou Bay, corresponding to a spring and an autumn bloom respectively. Several numerical experiments are carried out to examine the nutrient limitation, and the importance of the discharges of the Yellow River and Xiaoqinghe River. Both DIN limitation and phosphate limitation exist in some areas of the bay, with the former being more significant than the latter. The Yellow River and Xiaoqinghe River are the main pollution sources of nutrients in Laizhou Bay. During the flood season, the algal growth is inhibited in the bay with the Yellow River discharges being excluded in the experiment, while in spring, the algal growth is enhanced with the Xiaoqinghe River excluded.     

DISTRIBUTION AND POPULATION DYNAMICS OF PARACALANUS PARVUS,PRACALANUS CRASSIROSTRIS,AND ACARTIA BIFILOSA（COPEPODA,CALANOIDA）IN THE BOHAI SEA

Paracalanus parvus,Paracalanus crassirostris,and Acartia bifilosa are dominant and widely distributed in the Bohai Sea,and comprise an important part of zooplankton in terms of biomass as well as production rate.In order to understand their seasonal distribution and population dynamics,their stage-specific abundance in different months of the year were analyzed based on the never analyzed yet samples collected in 1959.The three species showed clear and remarkable seasonal variation in abundance,which maximized in spring and summer,when they formed high biomass patches or concentrations in the nearshore area.For Paracalanus parvus,two peaks were observed in the annual circle,one in June and the other in September,For Paracalanus crassirostris,one peak occurred in summer and a small one in December.The seasonal pattern of Acartia bifilosa was different in different regions.In Bohai Bay it had a two-peak pattern,with the first large peak occurring in May and the second one in October.In Laizhou Bay,a winter peak in December and January could be observed besides the spring one.The number of generations during the reproductive season for the three species was estimated based on the annual cycle in abundance and ambient temperature.     

Zooplankton community structure,abundance and biovolume in Jiaozhou Bay and the adjacent coastal Yellow Sea during summers of 2005–2012: relationships with increasing water temperature

Zooplankton abundance, biovolume and taxonomic composition in Jiaozhou Bay and the adjacent coastal Yellow Sea were evaluated using ZooScan measurement of samples collected by net towing every August from 2005 to 2012. Zooplankton abundance and biovolume ranged from 1 938.5 to 24 800 ind./m~3 and 70.8 to 1 480.1 mm~3/m~3 in Jiaozhou Bay and 73.1 to 16 814.3 ind./m~3 and 19.6 to 640.7 mm~3/m~3 in the coastal Yellow Sea. Copepods were the most abundant group in both regions, followed by N octiluca scintillans and appendicularians in Jiaohzou Bay, and chaetognaths and N octiluca scintillans in adjacent coastal Yellow Sea. Over the study period, the most conspicuous hydrographic change was an increase in water temperature. Meanwhile, a general decrease in zooplankton abundance was observed, particularly in copepod populations. Based on redundancy analysis(RDA), the warming trend was the key environmental factor influencing to decrease of copepod abundance. The proportion of small-sized copepods increased while the mean size of all copepods decreased, in significant correlation with water temperature. Our results indicate that zooplankton, particularly copepods, are highly sensitive to change in water temperature, which is consistent with predicted impacts of warming on aquatic ectotherms. Due to their dominance in the zooplankton, the decline in copepod size and abundance could lead to an unfavourable decrease in energy availability for predators, particularly planktivorous fish.     

Abundance, biomass and composition of spring ice algal and phytoplankton communities of the Laptev Sea （Arctic）

Abundance,biomass and composition of the ice algal and phytoplank-ton communities were investigated in the southeastern Laptev Sea in spring 1999.Diatoms dominated the algal communities and pennate diatoms dominated the dia-tom population.12 dominant algal species occurred within sea ice and underlyingwater column,including Fragilariopsis oceanica,F.cylindrus,Nitzschiafrigida,N.promare,Achnanthes taeniata,Nitzschia neofrigida,Naviculapelagica,N.vanhoef fenii,N.septentrionalis,Melosira arctica,Clindrothecaclosterium and Pyrarnimonas sp.The algal abundance of bottom 10 cm sea icevaried between 14.6 and 1562.2×10~4 ceils l~(-1)with an average of 639.0×10~4cells l~(-1),and the algal biomass ranged from 7.89 to 2093.5μg C l~(-1)with an av-erage of 886.9μg C l~(-1),which were generally one order of magnitude higherthan those of sub-bottom ice and two orders of magnitude higher than those ofunderlying surface water.The integrated algal abundance and biomass of lower-most 20 cm ice column were averagely 7.7 and 12.2 times as those of upper 20 mwater column,respectively,suggesting that the ice algae might play an importantrole in maintaining the coastal marine ecosystem before the thawing of sea ice.Icealgae influenced the phytoplankton community of the underlying water column.However,the“seeding”of ice algae for phytoplankton bloom was negligible be-cause of the iow phytoplankton biomass within the underlying water column.     

Winter Phytoplankton Assemblages of Coastal Yellow Sea Connected to Jiaozhou Bay,China

I Introduction Phytoplankton play an important role in the primary production of ocean (Ning et al., 1995). They are impor-tant biological mediators of carbon turnover in seawater ecosystems (Zhu et al., 1993). Phytoplankton in Jiaozhou Bay have been preliminarily studied on the subjects of community structure, primary productivity and carbon budget (Qian et al., 1983; Guo et al., 1992; Jiao et al., 1994). It has been found that seasonal variation of phytoplankton cell abundance presents w…     

Seasonal variations of organic carbon and nitrogen in the upper basins of Yangtze and Yellow Rivers

The profound impacts exerted by climate warming on the Tibetan Plateau have been documented extensively, but the biogeochemical responses remain poorly understood. This study was aimed at seasonal variations of total organic carbon (TOC) and total organic nitrogen (TON) in stream water at two gauging sections (TTH, ZMD) in the upper basin of Yangtze River (UBYA) and at four gauging sections (HHY, JM, JG, TNH) in the upper basin of Yellow River (UBYE) in 2013. Results showed that concentrations of TON exhibit higher values in spring and winter and lower values in summer. TOC exhibits higher concentrations in spring or early summer and lower concentrations in autumn or winter. Seasonal variations of TOC and TON fluxes are dominated by water flux. In total, the UBYE and UBYA delivers 55,435 tons C of organic carbon and 9,872 tons N of organic nitrogen to downstream ecosystems in 2013. Although the combined flux of TOC from UBYA and UBYE is far lower than those from large rivers, their combined yields is higher than, or comparable with, those from some large rivers (e.g. Nile, Orange, Columbia), implying that organic carbon from the Tibetan Plateau may exert a potentially influence on regional and/or global carbon cycles in future warming climate.     

Spatial and temporal variations of Synechococcus and picoeukaryotes in the Taiwan Strait,China

The size-fractionated phytoplankton biomass, and the spatial and temporal variations in abundance of Synechococcus (SYN) and picoeukaryotes (PEUK) were measured in the Taiwan Strait during three cruises (August 1997, February-March 1998, and August 1998). The results show that picophytoplankton and nanophytoplankton dominate the phytoplankton biomass, in average of 38% and 40%, respectively. SYN and PEUK varied over time in abundance and carbon biomass, greater in summer than in winter, in range of (7.70–20...     

Spatiotemporal distribution of protozooplankton and copepod nauplii in relation to the occurrence of giant jellyfish in the Yellow Sea

The occurrence of the giant jellyfish, Nemopilema nomurai, has been a frequent phenomenon in the Yellow Sea. However, the relationship between the giant jellyfish and protozoa, in particular ciliates, remains largely unknown. We investigated the distribution of nanoflagellates, ciliates, Noctiluca scintillans, and copepod nauplii along the transect 33~N in the Yellow Sea in June and August, 2012, during an occurrence of the giant jellyfish, and in October of that year when the jellyfish was absent. The organisms studied were mainly concentrated in the surface waters in summer, while in autumn they were evenly distributed in the water column. Nanoflagellate, ciliate, and copepod nauplii biomasses increased from early June to August along with jellyfish growth, the first two decreased in October, while N. scintillans biomass peaked in early June to 3 571 pg C/L and decreased in August and October. In summer, ciliate biomass greatly exceeded that of copepod nauplii （4.61-15.04 ~tg C/L vs. 0.34-0.89 pg C/L）. Ciliate production was even more important than biomass, ranging from 6.59 to 34.19 ~tg C/（L.d） in summer. Our data suggest a tight and positive association among the nano-, micro-, and meso-zooplankton in the study area. Statistical analysis revealed that the abundance and total production of ciliate as well as loricate ciliate biomass were positively correlated with giant jellyfish biomass, indicating a possible predator-prey relationship between ciliates and giant jellyfish. This is in contrast to a previous study, which reported a significant reduction in ciliate standing crops due to the mass occurrence ofN. nomurai in summer. Our study indicates that, with its high biomass and, in particular, high production ciliates might support the mass occurrence of giant jellyfish.     

Seasonal changes in phytoplankton biomass and dominant species in the Changjiang River Estuary and adjacent seas: General trends based on field survey data 1959–2009

The characteristics of seasonal variation in phytoplankton biomass and dominant species in the Changjiang River Estuary and adjacent seas were discussed based on field investigation data from 1959 to 2009. The field data from 1981 to 2004 showed that the Chlorophyll-a concentration in surface seawater was between 0.4 and 8.5 μg dm-3. The seasonal changes generally presented a bimodal trend, with the biomass peaks occurring in May and August, and Chlorophyll-a concentration was the lowest in winter. Seasonal biomass changes were mainly controlled by temperature and nutrient levels. From the end of autumn to the next early spring, phytoplankton biomass was mainly influenced by temperature, and in other seasons, nutrient level(including the nutrient supply from the terrestrial runoffs) was the major influence factor. Field investigation data from 1959 to 2009 demonstrated that diatoms were the main phytoplankton in this area, and Skeletonema costatum, Pseudo-nitzschia pungens, Coscinodiscus oculus-iridis, Thalassinoema nitzschioides, Paralia sulcata, Chaetoceros lorenzianus, Chaetoceros curvisetus, and Prorocentrum donghaiense Lu were common dominant species. The seasonal variations in major dominant phytoplankton species presented the following trends: 1) Skeletonema(mainly S. costatum) was dominant throughout the year; and 2) seasonal succession trends were Coscinodiscus(spring) →Chaetoceros(summer and autumn) → Coscinodiscus(winter). The annual dominance of S. costatum was attributed to its environmental eurytopicity and long standing time in surface waters. The seasonal succession of Coscinodiscus and Chaetoceros was associated with the seasonal variation in water stability and nutrient level in this area. On the other hand, long-term field data also indicated obvious interannual variation of phytoplankton biomass and community structure in the Changjiang River Estuary and adjacent seas: average annual phytoplankton biomass and dinoflagellate proportion both presented increased trends during the 1950 s-2000 s.     

Variations in the lower level of the PBL associated with the Yellow Sea fog-new observations by L-band radar

The Chinese east coastal areas and marginal seas are foggy regions.The development of effective forecasting methodsrests upon a comprehensive knowledge of the fog phenomena.This study provides new observations associated with the sea fogsover the northwestern Yellow Sea by means of L-band radar soundings with a high vertical resolution of 30 m.The monthly tem-perature lapse rate,the Richardson Numbers,and the humidity show obvious seasonal variations in the lower level of the planetaryboundary layer (PBL) that are related to the onset,peak and end of the Yellow Sea fog season.The typical pattern of stratification forthe sea fog season in the northwestern Yellow Sea is that a stable layer of about 400 m thick caps a 150 m conditionally unstable layer.Besides,the differences between fogs and stratus clouds in terms of humidity,turbulence and temperature are analyzed,which is ofsignificance for sea fog forecast and detection by satellites.The thickness of the sea fogs varies in different stages of the fog season,and is associated with the temperature inversion.The numerical simulation proves that the seasonal variations obtained by the radarwell represent the situations over the Yellow Sea.     

Seasonal variability of phytoplankton community structure in relation to different nitrogen-phosphorus ratios in the southern coastal waters of Zhejiang, China

With the rapid development of economy and increase of population in the drainage areas, the nutrient loading has increased dramatically in the Changjiang estuary and adjacent coastal waters. To properly assess the impact of nutrient enrichment on phytoplankton community, seasonal microcosm experiments were conducted during August 2010–July 2011 in the coastal waters of Zhejiang Province. The results of the present study indicated that the chl a concentration, cell abundance, diversity indices, species composition and community succession of the phytoplankton varied significantly with different N/P ratios and seasons. Higher growth was observed in the 64:1 (spring), 32:1 (summer), 16:1 (autumn) and 128:1, 256:1 (winter) treatments, respectively. The values of Shannon-Wiener index (H′) and Pielou evenness index (J) were lower in the 8:1 and 16:1 treatments in autumn test, while H′ value was higher in the 128:1 and 8:1 treatments in winter test. A definite community succession order from diatoms to dinoflagellates was observed in the autumn and winter tests, while the diatoms dominated the community throughout the culture in the spring and summer tests.     

Macrobenthic community structure and species composition in the Yellow Sea and East China Sea in jellyfish bloom

To understand the characteristics of macrobenthic structures and the relationship between environment and benthic assemblages in jellyfish bloom, we studied the macrobenthos and related environmental factors in the coastal waters of the Yellow Sea and East China Sea. Data were collected during two seasonal cruises in April and August of 2011, and analyzed with multivariate statistical methods. Up to 306 macrobenthic species were registered from the research areas, including 115 species of Polychaeta, 78 of Crustacea, 61 of Mollusca, 30 of Echinodermata, and 22 of other groups. Nine polychaete species occurred at frequencies higher than 25% from the sampling stations： Lumbrineris longifolia, Notomastus latericeus, Nin6e palmata, Ophelina acuminata, Nephtys oligobranchia, Onuphis geophiliformis, Glycera chirori, Terebellides stroemii, and Aricidea fragilis. Both the average biomass and abundance of macrobenthos are higher in August （23.8 g/m^2 and 237.7 ind./m^2） than those in April （11.3 g/m^2 and 128 ind./m^2）; the dissimilarity ofmacrobenthic structures among stations is as high as 70%. In terms of the dissimilarity values, we divided the stations into four clusters in spring and eight in summer. The ABC curve shows that the macrofauna communities in high jellyfish abundance were not changed. Canonical correspondence analysis showed that depth, temperature, median grain size, total organic carbon of sediment and total nitrogen in sediment were important factors affecting the macrozoobenthic community in the study area.     

Seasonal variations of several main water masses in the southern Yellow Sea and East China Sea in 2011

The seasonal variations of several main water masses in the southern Yellow Sea (SYS) and East China Sea (ECS) in 2011 were analyzed using the in-situ data collected on four cruises. There was something special in the observations for the Yellow Sea Warm Current (YSWC), the Yellow Sea Cold Water Mass (YSCWM) and the Changjiang Diluted Water (CDW) during that year. The YSWC was confirmed to be a seasonal current and its source was closely associated with the Kuroshio onshore intrusion and the northerly wind. It was also found that the YSCWM in the summer of 2011 occupied a more extensive area in comparison with the climatologically-mean case due to the abnormally powerful wind prevailing in the winter of 2010 and decaying gradually thereafter. Resulting from the reduced Changjiang River discharge, the CDW spreading toward the Cheju Island in the summer of 2011 was weaker than the long-term mean and was confined to flow southward in the other seasons. The other water masses seemed normal without noticeable anomalies in 2011. The Yellow Sea Coastal Current (YSCC) water, driven by the northerly wind, flowed southeastward as a whole except for its northeastward surface layer in summer. The Taiwan Warm Current (TWC) was the strongest in summer and the weakest in winter in its northward movement. The Kuroshio water with an enhanced onshore intrusion in autumn was stable in hydrographic features apart from the seasonal variation of its surface layer.     

Spatio-temporal variations in the siphonophore community of the northern South China Sea

To understand how hydrological and biological factors affect near-to off-shore variations in the siphonophore community,we sampled zooplankton at 82 stations in the northern South China Sea during summer,winter,and spring.Forty-one species of siphonophore were collected by vertical trawling.The species richness of siphonophores increased from the nearshore to offshore regions in all three seasons of investigation,with maximum richness in summer and minimum richness in winter.The abundance of siphonophores was also higher in summer than in spring and winter,concentrated in the nearshore region in the warm season and scattered in the offshore region in the cold season.Four siphonophore groups were classified according to the frequency of occurrence:nearshore,near-offshore,offshore,and tropical pelagic.Among them,the nearshore group had higher abundance nearshore compared with the offshore.The tropical pelagic group had higher species number offshore than nearshore.Spatial and temporal fluctuations in taxonomic composition and abundance of siphonophores were due to the influence of the coastal upwelling and surface ocean currents of the South China Sea,driven by the East Asia monsoonal system.     

Seasonal variations in fouling diatom communities on the Yantai coast

Fouling diatoms are a main component of biofilm,and play an important role in marine biofouling formation. We investigated seasonal variations in fouling diatom communities that developed on glass slides immersed in seawater,on the Yantai coast,northern Yellow Sea,China,using microscopy and molecular techniques. Studies were conducted during 2012 and 2013 over 3,7,14,and 21 days in each season. The abundance of attached diatoms and extracellular polymeric substances increased with exposure time of the slides to seawater. The lowest diatom density appeared in winter and the highest species richness and diversity were found in summer and autumn. Seasonal variation was observed in the structure of fouling diatom communities. Pennate diatoms Cylindrotheca,Nitzschia,Navicula,Amphora,Gomphonema,and Licmophora were the main fouling groups. Cylindrotheca sp. dominated in the spring. Under laboratory culture conditions,we found that Cylindrotheca grew very fast,which might account for the highest density of this diatom in spring. The lower densities in summer and autumn might result from the emergence of fouling animals and environmental factors. The Cylindrotheca sp. was identified as Cylindrotheca closterium using18 S rDNA sequencing. The colonization process of fouling diatoms and significant seasonal variation in this study depended on environmental and biological factors. Understanding the basis of fouling diatoms is essential and important for developing new antifouling techniques.     

Community composition,abundance and biomass of zooplankton in Zhangzi Island waters,Northern Yellow Sea

Samples were collected monthly from the sea area around Zhangzi Island,northern Yellow Sea,from July 2009 to June 2010.Vertical net towing was used to examine spatial and temporal variability in zooplankton abundance and biomass.Overall,C alanus sinicus and Saggita crassa were the dominant species found during the study period,while the amphipod T hemisto gracilipes was dominant in winter and spring.Vast numbers of the ctenophore species of the genus Beroe were found in October and November.It was not possible to count them,but they constituted a large portion of the total zooplankton biomass.Zooplankton species diversity was highest in October,and species evenness was highest in April.Zooplankton abundance(non-jellyfi sh)and biomass were highest in June and lowest in August,with annual averages of 131.3 ind./m3and 217.5 mg/m3,respectively.Water temperature may be responsible for the variations in zooplankton abundance and biomass.B eroe biomass was negatively correlated with other zooplankton abundance.Longterm investigations will be carried out to learn more about the infl uence of the environment on zooplankton assemblages.