Relationship between toxic and harmful microalgae and environmental factors in typical mariculture areas of East China Sea

Toxic and harmful algal blooms are usually more frequent in mariculture areas due to the abundant trophic conditions.To investigate the relationship between toxic and harmful microalgae and environmental factors,we set up 12 stations near three mariculture regions(Gouqi Island,Sandu Bay,and Dongshan Bay)in the East China Sea.We collected samples from all four seasons starting from May 2020 to March 2021.We identifi ed 199 species belonging to 70 genera,of which 38 species were toxic and harmful,including 24 species of Dinophyceae,13 species of Bacillariophyceae,and 1 species of Raphidophyceae.The species composition of toxic and harmful microalgae showed a predominance of diatoms in the summer(August),and dinofl agellates in the spring(May),autumn(November),and winter(March).The cell densities of toxic and harmful microalgae were higher in summer(with an average value of 15.34×10^(3) cells/L)than in other seasons,3.53×10^(3) cells/L in spring,1.82×10^(3) cells/L in winter,and 1.0×10^(3) cells/L in autumn.Pseudo-nitzschia pungens,Prorocentrum minimum,Paralia sulcata,and Prorocentrum micans were the dominant species and were available at all 12 stations in the three mariculture areas.We selected 10 toxic and harmful microalgal species with frequency>6 at the survey stations for the redundancy analysis(RDA),and the results show that NO^(-)_(3),water temperature(WT),pH,DO,and NO^(-)_(2) were the main factors on distribution of toxic and harmful microalgae.We concluded that the rich nutrient conditions in the East China Sea mariculture areas increased the potential for the risk of toxic and harmful microalgal bloom outbreaks.

Influences of environmental factors on the spawning stock-recruitment relationship of Portunus trituberculatus in the northern East China Sea

Based on the Ricker-type models,the spawning stock-recruitment(S-R)relationship of Portunus trituberculatus was analysed under the impacts of environmental factors(including red tide area(AORT),sea level height(SLH),sea surface salinity(SSS)and typhoon landing times(TYP))in the northern East China Sea in 2001 and 2014.Besides the traditional Ricker model,two other Ricker-type S-R models were built:Ricker model with ln-linear environmental impact(Ricker-type 2)and Ricker model with ln-quadratic polynomial environmental impact(Ricker-type 3).Results showed that AORT,SLH,SSS and TYP had great influences on the recruitment of P.trituberculatus.When SSS reached 29 and 31,recruitment decreased from 20.7×10^(3) million to 8.3×10^(3) million individuals.In this case,recruitment declined,whereas AORT and TYP increased.Analysis of the S-R model showed that the Akaike information criterion(AIC)value of the traditional Ricker model was 14.619,which remarkably decreased after addition of the environmental factors.Different numbers of environmental factors were added to the Ricker model,and the best result was obtained when four factors were added to the model together.Moreover,Ricker-type 2 model,with the AIC value of-5.307,was better than Ricker-type 3 model(add above four environmental factors at the same time).The findings indicated that the mechanisms by which various environmental factors affect the S-R relationship are different.

Spatio-temporal variability of surface chlorophyll a in the Yellow Sea and the East China Sea based on reconstructions of satellite data of 2001-2020

Chlorophyll-a(Chl-a)concentration is a primary indicator for marine environmental monitoring.The spatio-temporal variations of sea surface Chl-a concentration in the Yellow Sea(YS)and the East China Sea(ECS)in 2001-2020 were investigated by reconstructing the MODIS Level 3 products with the data interpolation empirical orthogonal function(DINEOF)method.The reconstructed results by interpolating the combined MODIS daily+8-day datasets were found better than those merely by interpolating daily or 8-day data.Chl-a concentration in the YS and the ECS reached its maximum in spring,with blooms occurring,decreased in summer and autumn,and increased in late autumn and early winter.By performing empirical orthogonal function(EOF)decomposition of the reconstructed data fields and correlation analysis with several potential environmental factors,we found that the sea surface temperature(SST)plays a significant role in the seasonal variation of Chl a,especially during spring and summer.The increase of SST in spring and the upper-layer nutrients mixed up during the last winter might favor the occurrence of spring blooms.The high sea surface temperature(SST)throughout the summer would strengthen the vertical stratification and prevent nutrients supply from deep water,resulting in low surface Chl-a concentrations.The sea surface Chl-a concentration in the YS was found decreased significantly from 2012 to 2020,which was possibly related to the Pacific Decadal Oscillation(PDO).

Seasonal distribution of macrobenthos and its relationship with environmental factors in Yellow Sea and East China Sea

Macrobenthos samples were collected from the Yellow and East China Seas in four seasons during 2011 to 2012. The seasonal distribution of macrobenthos and its relationship with environmental factors were analyzed. A total of 562 macrobenthic species were identified, with polychaetes and mollusks accounting for 67% of the total number of species. A similarity percentage(SIMPER) analysis showed that the dominant species were bivalve mollusks in the Yellow Sea and small-sized polychaetes in the East China Sea. A two-factor analysis of variance showed significant seasonal variations in species number, density and diversity index, and significant regional differences of biomass and density. Two-factor community similarity analysis also showed significant seasonal and regional differences in macrobenthic communities. Canonical correspondence analysis indicated that the main environmental factors af fecting the macrobenthic communities were water depth, temperature, dissolved oxygen, and inorganic nitrogen. The results demonstrate significant regional differences and seasonal variations in macrobenthos in the two seas. Sediment properties and water mass characteristics are speculated to be the causes of regional differences.

Distribution of chlorophyll a, photosynthesis and their relations to the environmental factors in the Central South China Sea

Some studies have been made on the variation of primary productivity in the Central South ChinaSea. This paper studies comprehensively the characteristics of chlorophyll a distributions in time andspace and the primary productivity, as well their relations to the environmental factors.Materals and methods During the comprehensive investigation in the Central South China Sea from September 1983 toDecember 1984, the distributions of chlorophyll a and primary productivity were studied. Figure 1shows the sampling stations and their range of investigation.

Organic Carbon Deposition on the Inner Shelf of the East China Sea Constrained by Sea Level and Climatic Changes Since the Last Deglaciation

The East China Sea(ECS),which is located in the transitional zone between land and ocean,is the main site for the burial of sedimentary organic carbon.Despite good constraints of the modern source to the sinking process of organic carbon,its fate in response to changes in climate and sea level since the last deglaciation remains poorly understood.We aim to fill this gap by presenting a high-resolution sedimentary record of core EC2005 to derive a better understanding of the evolution of the depositional environment and its control on the organic deposition since 17.3 kyr.Our results suggest that sedimentary organic carbon was deposited in a terrestrial environment before the seawater reached the study area around 13.1 kyr.This significant transition from a terrestrial environment to a marine environment is reflected by the decrease in TOC/TN and TOC/TS ratios,which is attributed to deglacial sea level rise.The sea level continued to rise until it reached its highstand at approximately 7.3 kyr when the mud depocenter was developed.Our results further indicate that the deposition of the sedimentary organic carbon could respond quickly to abrupt cold events,including the Heinrich stadial 1 and the Younger Dryas during the last deglaciation,as well as‘Bond events'during the Holocene.We propose that the rapid response of the organic deposition to those cold events in the northern hemisphere is linked to the East Asian winter monsoon.These new findings demonstrate that organic carbon deposition and burial on the inner shelf could effectively document sea level and climatic changes.

Phosphorus forms in sediments of the East China Sea and its environmental significance

By means of SEDEX, ASPILA and XRF, depth-dependent changes of different phosphorus forms in sediment cores from specific areas of the offshore Changjiang Estuary (Yangtze Estuary) in 1998 were analyzed. Results show that contents of total phosphorus (TP), organic-phosphorus (OP) and iron-phosphorus (Fe-P) decreased down-core, while those of absorbed-phosphorus (Ad-P) and calcium-phosphorus (Ca-P) increased. The distribution tendency of detritus-phosphorus (De-P) is not obvious. Results also show that TP, Fe-P and OP contents at Meso station of the Changjiang Estuary and Hangzhou Bay are higher than that of the other stations. This suggests that the pollutants carried by the Changjiang and the Qiantang rivers from inland have affected the natural environment in offshore area. TP, Fe-P and OP contents of each station become higher from bottom to top, indicating the amount of the terrestrial pollutants carried by the two rivers has been enhanced since the last 30-50 years. Ad-P, Ca-P, Fe-P and OP are all active phosphorus in sediments, and their re-cycling in sediment is closely related to each other.

Recent sedimentary records in the East China Sea inner shelf and their response to environmental change and human activities

The East China Sea continental shelf is a unique area for the study of land-sea interactions and paleoenvironmental change because it receives a large amount of terrestrial material inputs. In recent decades, human activities and global climate change have greatly aff ected river discharges into the sea. However, changes in the deposition process caused by these factors in the East China Sea continental shelf are unclear. We collected eight short sediment cores from the East China Sea inner shelf(ECSIS) using a box core sampler in 2012 and 2015. The grainsize, 2 10 Pb, and 1 37 Cs of these cores were analyzed in order to reconstruct the deposition history since the 1950 s, and to reveal human activity and climate change influences on sediment deposition in the ECSIS. Results indicated that sediment grain size became finer after 1969, turned coarser after 1987, and then further coarser since 2003, corresponding well to the three steps of sediment load drop in the Changjiang(Yangtze) River, which are mainly caused by human activities(particularly the closure of the Three Gorges Dam). Simultaneously, the East Asian Monsoon influenced the deposition process in the ECSIS by changing the intensity of coastal currents. Mean grain size variations in the fine-grained population(divided by grain size vs. standard deviation method) coincided with that of the East Asian Winter Monsoon strength and reflected its weakness in 1987. Abrupt changes in sediment grain size over a short time scale in these sediment cores were generally caused by floods and typhoons. Spectral analyses of the sediment cores showed periodicities of 10–11 and 20–22 years, corresponding to the periodicity of solar activity(Schwabe cycle and Hale cycle). Mean grain size time series also displayed a 3–8 year periodicity corresponding to El Ni?o Southern Oscillation periodic change.

Environmental anomalies in the northeastern East China Sea during the last 3 000 years:implications for El Nio activity in the Holocene

To reconstruct the productivity changes for the last 10 500 a in the northeastern East China Sea （ECS）, biogenic compounds （such as carbonate, organic carbon and opal）, marine micropaleontological fossils （planktonic foraminifera, benthic foraminifera, radiolarian and silicoflagellate） and the compositional characters of benthic foraminifera fauna analyses were carried out on a sediment core DOC082 obtained from the western slope of Okinawa Trough （29°13.93′N, 128°08.53′E; 1 128 m water depth）. The long-term changes of biogenic and micropaleontological proxies display some similarities through the last 10 500 a, which show three different phases： lower values are recorded during the early and middle ttolocene （before about 4 000 a BP）, followed by an abrupt and remarkable increase at about 4 000 a BP, the late Holocene （after about 3 000 a BP） is characterized by continuously high values. The multi-proxy data of paleoproductivity and percents of benthic foraminifera genera （Uvigerina and Bulimina） show that during the early and middle Holocene （10 500-4 000 a BP） productivity was relatively low with a sudden and distinct increase at about 4 000 a BP, and the late Holocene （3 400-0 a BP） is marked by significantly higher productivity. Also, the radiolarian-based sea surface temperature （SST） records reveal a distinct decline in SST in the late Holocene after 3 200 a BP, very different from the early and middle Holocene. For the last 3 000 a, the enhanced biological productivity and distinctly lower SST indicate a major change of oceanographic conditions in the northeastern ECS. These marine environmental anomalies are consistent with other paleoclimatic records for the late Holocene in the Chinese continent and its surrounding regions. After analyzing the mechanisms of modern productivity and SST changes in the northeastern ECS, and based on the climatic anomalies in the Chinese continent and variations in the Kuroshio Current during modern El Nino periods, we suggest that the anomalous environmental conditions in the northeastern ECS may imply intensified El Nino activity during the late Holocene.

Relationships between daily growth of different groups of swordtip squid(Uroteuthis edulis)and environmental variables in the East China Sea

Swordtip squid(Uroteuthis edulis)is one of the important economical fishing target species in the East China Sea.Uroteuthis edulis is characterized by rapid growth,extensive migration,and long spawning period and sensitive to surrounding environment.In order to assess its stock status,it is necessary to explore its spawning season,growth patterns of different populations and their relationship with the environment in advance.In this paper,based on the samples of U.edulis collected in the East China Sea from September 2017 to March 2018,we explored the relationships between daily growth of statolith microstructure and environmental variables by gradient forest method and generalized additive model.The spawning season of U.edulis was found to be nearly one year,and two dominant season groups were found:the spring group with the peak period of April and the summer group with the peak period of August.Water temperature in the depth of 25 m(Temp_25),sea surface temperature(SST)and zonal velocity were the key environmental variables for the daily growth of April-spawning group.The most suitable environmental conditions for the growth of April-spawning group were water temperature(24-27℃)and velocity(0.1-0.3 m/s).SST,Temp_25 and mixed layer depth were the key environment variables for the daily growth of August-spawning group.The most suitable environmental conditions for the growth of Augustspawning group were water temperature(21-28℃)and water depth(0-50 m).Key environmental variables of different groups suggested that early growth was significantly affected by seasonal changes of water temperature,current velocity and prey abundance.This study explored the relationships between early growth and environmental variables and provided the scientific guidance for the management and conservation of U.edulis.

Study on spatial and temporal distribution of planktonic amphipoda in the East China Sea

Quantitative distribution of planktonic amphipoda in the East China Sea is analyzed and the relation with environmental factors and mackerel and scad fishing grounds is studied. The result shows that the characteristic of biomass is great seasonal and interannual variety during the passing three decades. The distribution of planktonic amphipoda basically reflects the movement, decay and intensification of the different water systems in the survey area.

A New model to forecast fishing ground of Scomber japonicus in the Yellow Sea and East China Sea

The pelagic species is closely related to the marine environmental factors, and establishment of forecasting model of fishing ground with high accuracy is an important content for pelagic fishery. The chub mackerel（Scomber japonicus） in the Yellow Sea and East China Sea is an important fishing target for Chinese lighting purse seine fishery. Based on the fishery data from China＇s mainland large-type lighting purse seine fishery for chub mackerel during the period of 2003 to 2010 and the environmental data including sea surface temperature（SST）, gradient of the sea surface temperature（GSST）, sea surface height（SSH） and geostrophic velocity（GV）, we attempt to establish one new forecasting model of fishing ground based on boosted regression trees. In this study, the fishing areas with fishing effort is considered as one fishing ground, and the areas with no fishing ground are randomly selected from a background field, in which the fishing areas have no records in the logbooks. The performance of the forecasting model of fishing ground is evaluated with the testing data from the actual fishing data in 2011. The results show that the forecasting model of fishing ground has a high prediction performance, and the area under receiver operating curve（AUC） attains 0.897. The predicted fishing grounds are coincided with the actual fishing locations in 2011, and the movement route is also the same as the shift of fishing vessels, which indicates that this forecasting model based on the boosted regression trees can be used to effectively forecast the fishing ground of chub mackerel in the Yellow Sea and East China Sea.

Distribution of meiofaunal abundance in relation to environmental factors in Beibu Gulf,South China Sea

This study aims to explore the distribution of meiofaunal abundance in relation to environmental factors in the Beibu Gulf, a natural semi-enclosed part of the South China Sea, surrounded by China and Vietnam. Meiofauna and ten benthic environmental factors were determined at 27 sampling stations in the Beibu Gulf in four surveys during 2006 2007. The results show a clear geographical trend in meiofaunal abundance, water depth, salinity and clay content. The meiofaunal abundance and the clay content decreased, whereas the water depth and the salinity increased from the north to the south of the Gulf. The percentage of meiofaunal abundance in the 0 2 cm layer increased, whereas in the 2-5 cm and 5 10 cm layers it decreased from the north to the south of the Gulf. Correlation analysis show significant negative correlations between meiofaunal abundance and water depth, benthic temperature, salinity and pH, but significant positive correlations between meiofaunal abundance and dissolved oxygen, chlorophyll a and clay content.

Sedimentary Environment Analysis of Ancient Sand Ridges from Zk23 Hole in the East China Sea

Abstract： Based on the analysis of core samples from the hole of Zk23 in the East China Sea Continental Shelf and by means of sedimentary stratigraphy, biostratigraphy and chronostratigraphy, the authors consider that the fine-sand deposition in borehole was part of buried ancient estuary sand ridges of the Yangtze River. The deposition history of study area around the hole before and after the glacial period as well as postglacial period is made clear after our research： （1） the estuarine sublayer -undersea delta facies strata was deposited under the fast sea level rise about 15 kaB.P; （2） sand ridges mostly consisting of fine-sand, were formed when the sea level was the fluctuant range of 60 - 80 m of isoba during the deglacial period around 15 - 12 kaB.P; （3） first silty clay and clay silt strata above the sand ridges were deposited during the period when the sea level rose fast from 12 to 7 kaB.P, and then it keeps stable to the present.

Factors controlling the development of tight sandstone reservoirs in the Huagang Formation of the central inverted structural belt in Xihu sag, East China Sea Basin

By means of thin section analysis, zircon U-Pb dating, scanning electron microscopy, electron probe, laser micro carbon and oxygen isotope analysis, the lithologic features, diagenetic environment evolution and controlling factors of the tight sandstone reservoirs in the Huagang Formation of Xihu sag, East China Sea Basin were comprehensively studied. The results show that: the sandstones of the Huagang Formation in the central inverted structural belt are poor in physical properties, dominated by feldspathic lithic quartz sandstone, high in quartz content, low in matrix, kaolinite and cement contents, and coarse in clastic grains;the acidic diagenetic environment formed by organic acids and meteoric water is vital for the formation of secondary pores in the reservoirs;and the development and distribution of the higher quality reservoirs in the tight sandstones of the Huagang Formation are controlled by sediment source, sedimentary facies belt, abnormal overpressure and diagenetic environment evolution. Sediment provenance and dominant sedimentary facies led to favorable initial physical properties of the sandstones in the Huagang Formation, which is the prerequisite for development of reservoirs with better quality later. Abnormal high pressure protected the primary pores, thus improving physical properties of the reservoirs in the Huagang Formation. Longitudinally, due to the difference in diagenetic environment evolution, the high-quality reservoirs in the Huagang Formation are concentrated in the sections formed in acidic diagenetic environment. Laterally, the high-quality reservoirs are concentrated in the lower section of the Huagang Formation with abnormal high pressure in the middle-northern part;but concentrated in the upper section of Huagang Formation shallower in burial depth in the middle-southern part.

Diagenesis and Diagenetic Evolution of Deltaic and Neritic Gas-Bearing Sandstones in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin: Implications for Depositional Environments and Sequence Stratigraphy Controls

Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.

Study on the dominant species of Pteropoda in East China Sea

Based on the data of four seasonal marine surveys in the East China Sea （23°30′-33°N, 118°30′-128°E）during 1997-2000, the author studied the ecological characters of dominant Pteropoda species in the area. Results showed that there were five dominant Pteropoda species, more in summer, less in autumn and even in other seasons. These species, though belonging warm water species, can be categorized into two different groups in habitability. The first group was acicula, Desmopterus papilio and Creseis virgule, while adapted in summer and autumn, including Creseis the second group in winter and spring, represented by Limacina trochiformis and Agadina syimpsoni. The first group was more abundant than the second one. Besides, the first group contributed more to the Pteropoda abundance having higher occurrence frequency and aggregation intensity than the second. In horizontal distribution, the first group species reside in nearshore, and they could migrate to shallow place near estuary and aggregated in high density, while the second one was different： lower abundance, less occurred and aggregated because they were halophilic warm water species, and they were usually abundant in offshore area.

Three Gorges Dam Controls Sediment Coarsening of the Mud Patch on the Inner East China Sea Shelf

The well-known Three Gorges Dam(TGD) within the Yangtze catchment launched its operation in 2003. The effect of the TGD operation on the sediment size on the East China Sea shelf is rarely known. High resolution(0.5 cm sampling) grain size analysis and 137 Cs and 210 Pb dating of the DH8-1 core were conducted with core collected from the distal part of a main sink for the modern Yangtze sediment entering the sea, the Min-Zhe Coastal Mud Deposits(MZCMD) on the inner East China Sea shelf. The 137 Cs dating results show that the core DH8-1 formed during 1946–2012 with a mean deposition rate of 0.65 cm yr^(-1), indicating that the 0.5 cm sampling for grain size analysis in this local area could reflect environmental changes generally on a one-year time scale. The mean grain size of DH8-1 core sediment that deposited after 2003 is significantly larger than that deposited during 1988–2002. After ruling out other possible factors, we infer that the sediment coarsening of DH8-1 core after 2003 is attributed to the TGD operation which causes the erosion of the Yangtze subaqueous delta. Specifically, the TGD operation significantly intensifies the declining trend of the Yangtze sediment loads to the sea despite no decreased water discharge, which results in extensive erosion of the Yangtze subaqueous delta. The relatively coarse sediment of the subaqueous delta is eroded and resuspended by ocean dynamics and then transported by coastal current, finally depositing on the MZCMD area. In addition, the general sediment fining of core DH8-1 that deposited during 1988–2002, comparing with 1946–1987, is mainly caused by dam construction and soil and water conservation within the Yangtze catchment. Our findings are helpful for better understanding the effects of such a huge dam as the TGD on a sediment sink like the MZCMD of such a large river as the Yangtze River.

Swell Source Analysis of East China Sea Under the Influence of Typical Typhoon Scenarios

The characteristics of swells within the East China Sea have been reported by Tao et al.(2017),while the question of where the swells come from remains unanswered.By using the wave model WAVEWATCH III and the swell tracking method proposed by Hanson(2001),the spatial sources of the swells are investigated during four typical typhoon scenarios,which usually affect the wave environment in the East China Sea,including the Recurving type,the Northward type,the Westward type(striking the East China Sea)and the Westward type(over the South China Sea).The numerical results show that parts of the swells are from the North West Pacific with a long-distance travelling.The moving paths of the swells are affected by the typhoon tracks,which result in various fetches.The Westward type(over the South China Sea)makes one peak in the evolution process.The landing process of the Westward type(striking the East China Sea)could result in swells with low energy.The swell energy depends on swell propagation distance,existence time and wind intensity of generation fetch.The consistent fetch and forceful wind intensity make swell carry more energy.