Analysis of the inter-annual variability and southward expansion of red tides in the Zhejiang coastal waters from 1981 to 2018

A time series dataset spanning 39 years(1981-2018) on red tide events in Zhejiang coastal waters was used to study the characteristics of inter-annual spatial and temporal variations. A distinct inter-annual pattern characterized by low frequency, explosive growth and fluctuating decline stages was found over the studied time scale. Most red tide events occurred in parallel to the bathymetric contour, and 95.4% were located to the west of the 50 m isobath. Additionally, the high-incidence area of red tides is expanding southward. In this paper, local sea surface temperature(SST), mariculture area and secondary industry growth rate are introduced and identified as the main factors influencing the nutrient and hydrometeorological conditions. A multivariate nonlinear regression equation based on these factors was constructed, and the goodness of fit coefficient was 0.907. The causes of the annual variation and high-frequency area in the southward expansion were quantitatively analyzed based on the proposed regression model. Finally, the results indicated that 68.7% of the annual occurrence variation of red tide was due to the SST and mariculture area, which are the main impact factors;however,secondary industry growth could compensate for the nutrient deficiency caused by the sharp mariculture area reduction and decreased SST. The background nutrient level, which is elevated by coastal economic development, especially secondary industry, is the main determinant of the southward expansion. Although the trend of the southward expansion of high-frequency areas has not changed, the red tide frequency in coastal cities has decreased by half and remained at a stable level after 2010 due to substantial economic restructuring and environmental protection.

Microbial Communities in Water during Red Tides along the Coast of China-A Case Study of Prorocentrum Donghaiense Red Tide in the East China Sea

Red tides are a major public hazard in the global oceans.The coast of the East China Sea is the sea area where red tide disasters are the most frequent and serious in China.In order to accurately grasp the occurrence of red tides in the coastal waters of the East China Sea,and to understand the microbial communities in the waters during the occurrence of red tides in the East China Sea,a special survey of red tides in the coastal waters of Zhejiang,China was carried out in June 2018.The results showed that nutrient concentrations of N and P were generally high in this area,DIN concentrations in most areas exceeded the permitted limit of Chinese seawater quality grade I.There were significant differences in dissolved oxygen,pH,COD,chlorophyll and phytoplankton abundance of red tides.During the investigation,red tides were found in the waters near the Yushan Islands.The content of chlorophyll a was 42.12mg/m3,the cell abundance of phytoplankton was 8.16×108/L,and the abundance of Prorocentrum edulis accounted for 98.5%.The Illumina MiSeq sequencing platform was used for 16s high-throughput sequencing of water microorganisms,and a total of 16 bacteria were identified.Proteobacteria is the first dominant phylum,followed by Cyanobacteria and Bacteroides.Some differences in bacterial community compositions between HAB and the nearby seawater were observed.The predominant bacteria in the red tide occurrence area were Proteobacteria,comprising 46.1%of the relative abundance;while the predominant bacteria in the nearby sea area,comprising 42.0%of the relative abundance.

NUMERICAL SIMULATION OF SUMMER CIRCULATION IN THE EAST CHINA SEA AND ITS APPLICATION IN ESTIMATING THE SOURCES OF RED TIDES IN THE YANGTZE RIVER ESTUARY AND ADJACENT SEA AREAS

Based on the COHERENS （a Coupled Hydrodynamical Ecological model for Regional Shelf seas）, a three-dimensional baroclinic model for the summer of East China Sea （ECS） was established with the sigma-coordinate in the vertical direction and spherical coordinate in the horizontal direction. The circulation patterns of the Kuroshio Current, the Taiwan Warm Current （TWC）, the Tsushima Current and the Yangtze Diluted Water （YDW） were successfully simulated with this model. The calculated results are fairly consistent with previous observations and studies. Based on this baroclinic current field, the Lagranian particles tracking was simulated to estimate the possible origins of the red tides frequently occurring in the Yangtze River estuary and its adjacent sea areas. If there are ＂seeds＂ （cysts） of the red tide algae at the seabed of the Taiwan Strait, the offshore of Fujian and Zhejiang Provinces and the northeast Taiwan Island, those are extremely possible sources of the red tides in the Yangtze River estuary and its adjacent sea areas. Field data are needed to confirm it. Numerical simulation to estimate the source of the red tides is a new application of the Lagrangian transport in the marine ecology.

A relationship between red tide outbreaks and urban development along the coasts of Guangdong Province

Red tides are one of the main coastal catastrophic events in Guangdong Province of southern China. The comparison between the number of red tide events and the development indexes of cities along the coasts of the province shows that the regional differences in red tide outbreaks has close relations with the coastal urban developments. The cause for an initiation of red tide blooms may be natural factors, while wastewater caused by the fast development of population, industry and aquiculture of the coastal cities enhanced the blooms. It may explain why the two periods of frequent outbreaks of the red tides over the last two decades matched the urban developments in the coastal areas of Guangdong not only spatially but also temporally. The red tides in the first period were restricted only to the coasts of middle Guangdong, where urbanization process was at a higher speed than the other coastal areas of the province. In the second period, fast development of the coastal cities in eastern Guangdong led to an increase in the occurrence of red tides in local sea areas of the same coasts.

Notes Effects of four nitrogen substrates on growth of several red tide species

Eight common red tide species including the Dinoflagellates Alejcandrium tamarense,Prorocentrum minimum , Prorocentrum mican , Diatoms Skeletonema costatum , Cerataulina pelag-ica, Leptocylindrus minimus, a Raphidophyte Heterosigma akashiwo and a Chrysophyte Isochrysis galbana were chosen to study the effect of four nitrogen substrates (NOs ?N, NHi - N, Urea ?N, Mixed ?N) on the growth of these algae. After two transfers, the results showed that at N concentration of 550 fano\, NO; - N was the best nitrogen source among these four nitrogen substrates; Urea - N and Mixed ~ N were also good for the growth of most algae, but not as good as NQj ?N for some species; NH??N inhibited the growth of all these species except H. akashrwo. At concentrations of 280 and 50 fimol experiments on the growth of /. galbana , P. minimum and L. minimus in Nri( - N and NO; - N substrates were also performed. The results showed that the growth rates of /. galbana were not significantly different from each other in NO; - N and NH?- N substrates both concentrations of 280 and 50 fonol. In concentration of 280 (anol NHt - N substrate, the growth rates of P. minimum and L. minimus were slower than in same concentration of NO? ~~ N; At concentration of 50 (unol , the growth rate of P. minimum in NH?- N was not significantly different from that in NOj ?N, while the growth rate of L. minimus was only about 30% of that in NQ3 ~ N substrate. The results indicated that each alga had its own preference in N-substrate and concentration, therefore, different nitrogen substrates may play a role in red tide formation.

Secondary pollution from sediment and red tide occurrence

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A new algorithm based on the background field for red tide monitoring in the East China Sea

Remote sensing has been proven to be an effective means of monitoring red tides. The spectral information is an important basis for establishing a model to monitor red tides. The spectral curves of red tide events are analyzed and compared with multiyear monthly averaged spectral curves based on MODIS data from July 2002 to June 2012, as well as spectral differences at the same location during red tide presence and absence. A red tide monitoring algorithm is developed based on the background field to extract the red tide information of the East China Sea （ECS）. With the application of the algorithm in the ECS, the results reveal that the developed model can effectively determine the location of red tides, with good correspondence to the results from an official bulletin. This demonstrates that the algorithm can effectively extract the red tide information.

Analysis of the development and causes of formation of Eucampia zoodiacus red tide in Xiamen Harbor

The red tide event of 11￣28, May in 1987 was caused by Eucampia zoodiacus, a coastal eurythermic phytoplanktou. Results from the field monitoring indicated that during the red tide occurrence the optimal temperature and salinity for the multiplication of the red tide organism were 20￣25℃ and 26￣28. During the red tide event cell densities in two peak values both reached 3 000×103ind. /din3. Organism number in horizonal distribution increased from the harbour mouth to the inner harbour. Average number of the organism at the monitoring stations in the inner harbour was 2 930×103 md. /dm3 which was 3. 7 and 61 times higher than that at the two control monitoring stations. The organism number in vertical distribution apparently showed stepwise, day and night changes. Daily change of the phytoplankton number with spring and ebb tides exhibited a negative relativity.Major reasons for this red tide event included species competition of red tide organisms, sudden increment in water temperature in short time, sharp decrement in salinity by rainfall, water eutrophication, high contents of stimulating materials such as Fe and Mn, poor water exchange condition and stable synoptic condition, etc.High content of dissolved oxygen and high pH value was resulted from the photosythesis of a great quantity of the red tide organisms.

Influence of the concentration ratio of nitrogen to phosphorus on the growth and interspecies competition of two red tide algae

The growth and interspecies competition of two red tide algal species Thalassiosira pseudonana Hasle et Heimdal and Gymnodinium sp. were studied under different concentration ratios of nitrogen to phosphorus, and the algal hatch culture experiments were conducted. The physiological and biochemical indexes were measured periodically, including the maximum comparing growth rate, relative growth rate, average double time and chlorophyll a concentration. The results showed that when the concentration ratio of nitrogen to phosphorus was 16： 1, the maximum comparing growth rate, relative growth rate and chlorophyll a concentration of Thalassiosira pseudonana all reached the highest,and average double time was the shortest. This implied that the optimal concentration ratio of nitrogen to phosphorus of Thalassiosira pseudonana is 16： 1. When the concentration ratio of nitrogen to phosphorus was 6：1, the maximum comparing growth rate, relative growth rate and the chlorophyll a concentration of Gymnodinium sp. reached the highest, and average double time was the shortest, so the optimal concentration ratio of nitrogen to phosphorus of Gymnodinium sp. is 6： 1. From the growth curves as indicated both in the cell density and the chlorophyll a concentration, it is suggested that the influence of concentration ratio of nitrogen to phosphorus on the chlorophyll a concentration and the cell density are almost the same. Different concentration ratios of nitrogen to phosphorus had weak influence on community succession and the competition between the two algae. Gymnodinium sp. may use the phosphorus in vivo for growth, so it is important to pay attention to the concealment of phosphorus, in order to avoid the outbreak of red tide. On the basis of the importance of nitrogen and phosphorus and the ratio of their concentration, the possible outbreak mechanism of red tide of the two algae was also discussed.

3-D observations of a red tide event in the offshore water along the western Guangdong coast

From November 24 to 26, 2014, a red tide event occurred in the offshore water off the Hailing Island located at the western Guangdong coast. The red tide appeared as pink strips distributed within 3 km in the offshore water and extended for about 10 km along the shoreline. During the flood tide, the pink seawater rushed to the beach with breaking waves, forming foam strips on the beach. Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction Technologies, Guangdong Ocean University, emergently responded to the event and organized three-dimensional observations from the air, onboard and on beach. The preliminary analyses of the cruise data and water samples indicate that the event was induced by non- toxic Noctiluca scintillans, of which the concentration reaches as high as 4 200 cells/L near the surface and 2600 cells/L at the bottom.

Ecological features of phytoplankton in red tide outburst area in the Xiamen Harbor

The results from the 38 cruises of phytoplankton surveys in the red tide outburst area in the XiamenHarbor in 1987 indicate 41 species of red tide organisms among 110 species of phytoplankton identified. Species composition was dominant by eurytopic species and warm water species. Species diversity apparently changed with (coldand warm) seasons. There was a high diversity in warm seasons, 63 species in August. Average annual number ofphytoplankton reached 1 119 × 103 ind. /dm3 which was 2 to 2. 6 times that in 2 control monitoring stations. Thenumber of phytoplankton in horizonal distribution displayed an obvious increasing tendency from the harbour mouthto the inner harbor. The phytoplankton number always changed with time, but with 3 peak values in the year round.The daily change of the phytoplankton number with tide exhibited a negative relativity. Moreover phytoplanktonspotes and their number showed a vertical movement during day and night. Futhermore, 10 predominant specieschanged with seasons was noted in the present paper.

Ecological Characteristics of Phytoplankton in Qinhuangdao Waters during Red Tide Period

The spatio-temporal distribution of phytoplankton is influenced by physical and chemical factors such as water temperature, salinity, dissolved oxygen, Ph and nutrients. Nitrogen （N） and phosphorus （P） are essential for the growth of phytoplankton, which play a key role in determining the abundance of phyto- plankton. The species composition, community similarity and diversity of phytoplankton affect the structure and function of ocean ecosystems. Marine phytoplankton can be used as a rapid and sensitive indicator reflecting environmental changes. The offshore area of Qinhuangdao is a spawning and feeding ground for fish, shrimp and crabs. However, this region has experienced an increase in frequency of red tides as a result of pollution and marine development. In 2010, red tides began in late May and ended in August. We evaluated the species composition, spatio-temporal distribution, community structure of phytoplankton and the relationship be- tween phytoplankton abundance and environmental factors based on data collected from May to September in 2010. The phytuplankton , belonging to 96 species, 46 genera, were identified. The phytoplankton community was primarily composed of Bacillariophyta and Pyrrophyta. The majority were neritic species or eurythermal and euryhaline cosmopolitan species, while the remainders were oceanic warm species or polagic species. The dominant species included Noctiluca scintiUans, Rhizosolenia stolterfothii, Ghaetoceros spp. , Goscinodiscus spp. , and Bacteriastrum spp.. A total of 48 red tide causative species were observed, accounting for 50% of total phytoplankton species. The average phytoplankton abundance ranged from 6.20 × 10^4 cells/m^3 to 4 129.53 × 10^4 cells/ms. Abundance peaked in September 2010 and reached the lowest value in July 2010. The diversity index values were all greater than 1.0, suggested that biodiversity and community structure was healthy. The highest indices of community structure and biodiversity were observed in September, and biediversity was the lowest in June. The community similarity of phytuplankton was relatively high and the similarity range was 40% -70% from May to September. The community similarity of phytoplankton successively were September 〉 July 〉 August 〉 May 〉 June. The average abundance of phytoplankton had significant negative correlation with salinity（ r = - 0. 734, P 〈 0. 01, N = 37 ） and significant positive correlation with inorganic nitrogen nutrients （ r = 0. 753, P 〈 0. 01, N = 37 ）. We concluded that inorganic nitrogen was the primary factor explaining the increase in phytoplankton abundance during the survey period. A canonical correspondence analysis of the relationship between phytoplankton species and environmental factors indicated that N/P, salinity, nitrate, silicate, nitrite and water temperature were the main environmental factors influencing community structure of phytoplankton in Qinhuangdac waters.

Red Tide Information Extraction Based on Multi-source Remote Sensing Data in Haizhou Bay

[Objective] The aim was to extract red tide information in Haizhou Bay on the basis of multi-source remote sensing data.[Method] Red tide in Haizhou Bay was studied based on multi-source remote sensing data,such as IRS-P6 data on October 8,2005,Landsat 5-TM data on May 20,2006,MODIS 1B data on October 6,2006 and HY-1B second-grade data on April 22,2009,which were firstly preprocessed through geometric correction,atmospheric correction,image resizing and so on.At the same time,the synchronous environment monitoring data of red tide water were acquired.Then,band ratio method,chlorophyll-a concentration method and secondary filtering method were adopted to extract red tide information.[Result] On October 8,2005,the area of red tide was about 20.0 km2 in Haizhou Bay.There was no red tide in Haizhou bay on May 20,2006.On October 6,2006,large areas of red tide occurred in Haizhou bay,with area of 436.5 km2.On April 22,2009,red tide scattered in Haizhou bay,and its area was about 10.8 km2.[Conclusion] The research would provide technical ideas for the environmental monitoring department of Lianyungang to implement red tide forecast and warning effectively.

Observation of a red tide event in the Western Harbour, Xiamen

Measurements of red tide organism cell counting, chlorophyll a, water temperat-ure, salinity, pH, DO, COD, NH~+, NO, NO, active phosphate, dissolvable siliconwere made in a follow-up observation of a red tide event which occurred in the western harbourof Xiamen from 18th June to 3rd July in 1986.

Automatic Red Tide Algae Recognition

This paper presents a real-time alga classifier designed for flow-cytometry-based marine alga monitoring systems.The difficulties of such classification include:1)the shape of the same algae category is deformable,and largely variant due to the individual differences and mature stage;2)the image of algae may vary due to different 3D positions to the imaging plane and partial occlusion;3)the images also contain unknown algae and contaminations.In the proposed method,several shape features were developed,a naive Bayes classifier(NBC)was trained to reject the contaminative objects and unknown algae,and a support vector machine(SVM)was used to classify the algae to taxonomic categories.Our approach achieved greater 90%accuracy on a collection of algal images.The test on contaminated algal image set(containing unknown algae and non-algae objects such as sands)also demonstrated promising results.

Increased diversity and environmental threat of harmful algal blooms in the Southern Yellow Sea,China

Harmful algal blooms(HABs)in the Southern Yellow Sea(SYS)have shown a trend of increasing diversity and detrimental ef fects.While the Bohai Sea,East China Sea,and South China Sea have experienced a high incidence of HABs since the 1980s,the Yellow Sea provides a relatively healthy ecological environment in which fewer HABs have been documented before the 21s t century.Yet largescale blooms of the green macroalga Ulva prolifera(so-called“green tides”)have occurred annually since 2007 in the Yellow Sea.Six people were poisoned and one person died in Lianyungang in 2008 due to ingestion of algal toxins.Moreover,the Yellow Sea experienced co-occurrence of harmful red tides,green tides,and golden tides in 2017.This combination of events,rare worldwide,indicates the potential for further deterioration of the marine environment in the Yellow Sea,which may be related to climate change,aquaculture,and other human activities.Using the SYS as an example,we collected data of the frequency and scale of HABs over the years,as well as that of marine algal toxins,and analyzed the trend in the diversity of HABs in the SYS,to explore the causes and impacts of HABs,as well as the interrelationships among dif ferent types of HABs,including harmful red tides,green tides,and golden tides.We also attempted to improve our understanding of HAB evolution under the influence of global climate change and intensified human activities.

Toxic effect of dinoflagellate Alexandrium species on Cladocera Moina mongolica Daday

The main objective of this study was to investigate toxic effects of the dinoflagellate Alexandrium species, on cladocera Moina mongolica in the laboratory. Ten strains of Alexandrium species, including Alexandrium tamarense （AT-6, ATHK, ATCI02, ATCI03 and AT5-1）, A. catenella （ACDH）, A. affine （AC-1 and AS-1）, A. lusitanicum and A A. tamarense （ATHK, ATCI02 and AT5-1） and A minutum were tested. The results showed that affine （AC-1 and AS-1）, but not A. tamarense （AT-6 and ATCI02）, A. catenella （ACDH）, A. lusitanicum and A. minutum had significantly negative effects on the survival of M. mongoliea; when exposed to these ten strains of Alexandrium species in densities of 3 000 cells/cm^3 for 7 d, respecyively. M. mongolica could feed on A. tamarense （AT-6, ATHK, ATCI02, ATCI03 and AT5-1）, A. eatenella, A. lusitanieum and A. minutum, but exhibited little or no grazing on A. affine （AC-1 and AS-1）, based on the changes in gut pigment af- ter exposure to alga for 1 and 12 h. A. affine AC-1, which had the strongest toxicity on the survival of M. mongolica, was chosen to further study the negative effects on M. mongolica. The results showed that the effect of A. affine AC-1 on the survival of M. mongolica was density-dependent, and its lethal effects on one-day, two-day and three-day old M. mongolica were exacerbated with increasing age; The whole algal culture, re-suspended algal cells, cell fragments and cell contents all had adverse impacts on the survival of M. mongolica. Moreover, both juvenile numbers and life-span time of M. mongolica were decreased significantly when they were cultured in A. affine AC-1 of 10 and 50 cells/cm^3, combined with 3×10^6 cells/cm^3 of Chlorella spp., respectively. As a non-PSP producer, A. affine may produce other toxins, responsible for the strong negative effects on M. mongolica.

Distribution patterns of phytoplankton in the Changjiang River estuary and adjacent waters in spring 2009

The Changjiang River estuary and adjacent waters are one of the most notable regions for red tides/harmful algal blooms in China's coastal waters.In this study,phytoplankton samples were collected and analyzed during the outbreak stage of red tides in May 2009.It was found that dinoflagellates,Prorocentrum donghaiense and Karenia mikimotoi,and diatoms,Skeletonema spp.and Paralia sulcata,were the major taxa dominating the phytoplankton community.Cluster analysis,non-metric multidimensional scaling(NMDS) and analysis of similarities(ANOSIM) was conducted on a data matrix including taxa composition and cell abundance of the phytoplankton samples.The analyses categorized the samples into three groups at a similarity level of 30%.Group Ⅰ was characterized by estuarine diatoms and distributed mainly in the highly turbid estuarine region.Group Ⅱ,which was dominated by the diatom Skeletonema spp.and represented the red tide of Skeletonema spp.,was situated around Group Ⅰ in the sea area west of 122°50'E.Group Ⅲ was characterized by a high proportion of dinoflagellates and was found further offshore compared with Groups Ⅰ and Ⅱ.Group Ⅲ was further divided into two subgroups(Ⅲ-S1 and Ⅲ-S2) at a similarity level of 40%.Group Ⅲ-S1 was characterized by the presence of the benthic diatom P.sulcata,representing phytoplankton samples collected either from the bottom or from the sea area affected by upwelling.GroupⅢ-S2 was dominated by dinoflagellates and represented red tides formed by P.donghaiense and K.mikimotoi.A gradual change of red-tide causative species was observed from the estuary to the offshore sea area,from diatoms to armored dinoflagellates and then unarmored dinoflagellates.Environmental factors associated with each group,and thus affecting the distribution of phytoplankton and red tides,are discussed.

Physical Hydrography and Algal Bloom Transport in Hong Kong Waters

In sub-tropical coastal waters around Hong Kong, algal blooms and red tides are usually first sighted in the Mirs Bay, in the eastern waters of Hong Kong. A calibrated three-dimensional hydrodynamic model for the Pearl River Estuary （Delft3D） has been applied to the study of the physical hydrography of Hong Kong waters and its relationship with algal bloom transport patterns in the dry and wet seasons. The general 3D hydrodynamic circulation and salinity structure in the partially-mixed estuary are presented. Extensive numerical surface drogue tracking experiments are performed for algal blooms that are initiated in the Mirs Bay under different seasonal, wind and tidal conditions. The probability of bloom impact on the Victoria Harbour and nearby urban coastal waters is estimated. The computations show that： i） In the wet season （May - August）, algal blooms initiated in the Mirs Bay will move in a clockwise direction out of the bay, and be transported away from Hong Kong due to SW monsoon winds which drive the SW to NE coastal current; ii） In the dry season （November- April）, algal blooms initiated in the northeast Mirs Bay will move in an anti-clockwise direction and be carried away into southern waters due to the NE to SW coastal current driven by the NE monsoon winds; the bloom typically flows past the east edge of the Victoria Harbeur and nearby waters. Finally, the role of hydrodynamic transport in an important episodic event -- the spring 1998 massive red tide -- is quantitatively examined. It is shown that the strong NE to E wind during late March to early April, coupled with the diurnal tide at the beginning of April, significantly increased the probability of bloom transport into the Port Shelter and East Lamma Channel, resulting in the massive fish kill. The results provide a basis for risk assessment of harmful algal bloom （HAB） impact on urban coastal waters around the Victoria Habour.