The simulation of wave time series or wave elevation histories is of great significance for the accurate study of real wave-action on marine structures. In this paper, a method of simulating multi-directional irregular wave elevations is proposed based on a linear single-summation model. To evaluate the effectiveness of the proposed method, theoretical simulated regular waves, unidirectional and multidirectional irregular waves are deterministically simulated. The consistence between the simulated wave time series and the original ones is verified. The simulated accuracy range is further evaluated based on the quantitative error analysis along the spatial dimension represented by the ratio of rr/L_s (in which, rr denotes the separations of the two wave gauges, and L_s dotes the significant wave length). It is suggested that the optimum relative separations of the wave gauges should be less than 0.12L_s when the proposed method is used to reconstruct multidirectional irregular waves.

Green tide is a high biomass ecological disaster caused by the proliferation of green algae in intertidal zone. Its outbreak is not only driven by environmental factors such as temperature and nutrients, but also closely related to its own photosynthetic capacity. In this study, Ulva intestinalis and Ulva expansa, the two green tide species, were selected for the outdoor culture experiment. The photosynthetic pathway, antioxidant physiological characteristics and their corresponding relationship with photosynthetic products of the two species were detected and compared under the conditions of high temperature and high light intensity in summer. The results showed that there were significant differences in photosynthetic pathway and antioxidant capacity between U. intestinalis and U. expansa. The key enzyme activity of C₄ photosynthetic pathway was highly expressed in the process of photosynthesis of the former, which was significantly correlated with light and temperature. The key enzyme activity of C₃ photosynthetic pathway of U. intestinalis was inhibited by strong light at noon, and the change range of δ¹³C in tissue ranged from −17.1‰ to −15.7‰, which indicated that C₃ and C₄ pathway might be involved in its photosynthetic cooperation. For U. expansa, the expression of key enzymes in C₄ photosynthetic pathway was weak and there was no significant correlation with light and temperature. Also, there was no obvious photoinhibition in C₃ photosynthetic pathway and the range of δ¹³C in tissue is from −23.5‰ to −21.9‰, indicating that the photosynthesis mainly depends on C₃ pathway. In addition, U. intestinalis showed a strong antioxidant capacity in the process of culture, which may be closely related to its C₄ photosynthetic pathway under high temperature and high light conditions. The comparative study between U. intestinalis and U. expansa showed that there were significant differences in the initiation of C₄ photosynthetic pathway between algal species, and the comparative study on the photosynthetic mechanism of different green algal species needs further exploration.

To investigate the spatial and temporal distribution of dinoflagellate cysts in surface sediment of Meizhou Bay, surface sediment was sampled at 7 stations in Meizhou Bay in May 2018 (spring), August 2018 (summer), November 2018 (autumn) and February 2019 (winter) for analysis of dinoflagellate cysts. In total, 42 species representing 6 groups, and 2 uncertain taxa were identified. The species number and abundance of heterotrophic species were higher than those of autotrophic species, and among them the species number and abundance of the protoperidinioid group were the highest. Seasonal difference was not obvious: the species number ranged from 34 to 38, and the abundance varied from 397.8 to 569.5 cysts/g with the annual average of 448.0 cysts/g. The species number and abundance of species at stations near the industrial zone were lower than those near the aquaculture area. There were 16 dominant species, among which the protoperidinioid group had an absolute advantage, but the dominance degree of all these dominant species was not large. Diversity index, richness index and evenness index were high, with the annual average of 3.45, 1.55 and 0.92, respectively. Compared with historical data, 19 new cysts were recognized, but the abundance was not much different. It should also be noted that a total of 6 toxic dinoflagellate cysts were found in the waters of the Meizhou Bay. Although the annual abundance was not high, there is still a risk of toxic red tides, which should be taken seriously.

The phytoplankton water samples were collected in the multidisciplinary investigations in the tropical eastern Indian Ocean (10.0°S−4.0°N, 83.0°−97.5°E) during March to May, 2013. Phytoplankton community structure features were analyzed, including species composition, cell abundance, dominant species. In addition, the species composition and abundance of phytoplankton were compared comprehensively by horizontal and vertical investigation, and the probable causes were also discussed. A total of 306 species (including varieties and forms) were identified, which belonged to 6 phyla (Bacillariophyta, Pyrrophyta, Chrysophyta, Cyanophyta, Euglenophyta and Cryptophyta). The dominant groups were mainly Cryptomonadaceae, Nano-dinoflagellate, Nitzschina spp. (diatoms), Gyrodinium spp. (dinoflagellates), etc., which were smaller cells in size. Horizontally, the cell abundance was similar at different layers with patchy distribution characteristics. The high cell abundance (10⁴ cells/L) was in subsurface water (30 m and 75 m) at south of the equator on 88°E section. However, adjacent to the high abundance area, a larger area of low abundance appeared in the eastern and southeastern parts of the survey area, which extended to the equator. Vertically, diatoms and dinoflagellates were widely distributed at different depths with obvious spatial pattern. At most stations of 0 m and 30 m layers, the proportion of diatoms was 0.2−0.3 or even lower, while that of dinoflagellates was 0.7−0.8; in deeper water layers (75 m, 100 m, 150 m, 300 m), the proportion of diatoms increased to 0.5−0.6, and that of dinoflagellates decreased to 0.4−0.5 inversely. The species richness of diatoms and dinoflagellates were relatively higher at 30 m and 75 m layers. Dinoflagellates were important contributors to the species composition and cell abundance of phytoplankton in the tropical eastern Indian Ocean, especially in low abundance area (80%). This study will greatly enrich the database of phytoplankton community characteristics in the tropical eastern Indian Ocean, and provide data support for quantifying and evaluating the biological resources in this area.

Since 2007, the annually Yellow Sea green tide (YSGT) have caused significant economic losses and serious social impacts in China. Previous research indicated that the floating green algal was originated from Subei Shoal, southwestern Yellow Sea, while the early development of floating green algae in the shoal remains unclear. Using Sentinel-2 high-resolution images, we extracted the floating green algae information in 2018. The effects of topography, sea surface temperature and sea surface wind on the distribution and development of floating green algae were studied using CCMP sea wind data and Microwave+IR Signal Fusion SST sea surface temperature data. The results showed that the first sign of floating green algae by satellites was detected in the south of Subei Shoal on May 23. The floating green algae expanded northwards in June, and decayed on July 13. The floating green algae could be traced back to the edge of Prophyra aquaculture area, aggregated and formed stripes along the sand grooves in the Subei Shoal. These stripes stretched tens of kilometers with width of 10–200 m and existed throughout the development of YSGT. In the region of north to Subei Shoal, the distribution and drifting of floating green algae were highly associated with wind directions. Based on our research, it is feasibleand cost-effective to collect and remove the floating algae in the Subei Shoal.

In recent years, the eutrophication of seawater has led proliferation of large seaweeds in offshore waters, becoming a worldwide environmental problem. Since 2007, the green tide of Ulva prolifera has continuously broken out in the Yellow Sea, causing huge economic losses. In order to investigate the relation between macroalgae and the ratio of nitrogen to phosphorus (N/P), and the competition mechanism with other macroalgae, we studied the growth of U. prolifera and U. lactuca when pure culture and co-culture. The results showed that: (1) When U. prolifera was pure cultured, the higher or lower N/P can promote the growth of U. prolifera. (2) When U. lactuca was pure cultured, the effect of the N/P on U. lactuca is not obvious. (3) U. prolifera growth was inhibited to some extent under the different N/P conditions when U. prolifera and U. lactuca were co-cultured, and the lowest N/P group was affected the most. (4) The N/P in the Subei Shoal is more suitable for the growth of U. prolifera, which may be one of the main reasons for the large-scale outbreak of U. prolifera green tide.

In the autumn of 2014, a comprehensive survey of hydrology, chemistry and biology in the Bohai Sea was carried out. The structure characteristics of phytoplankton community in the Bohai Sea were studied. The historical data were combined to analyze the formation of phytoplankton community structure. Three classes, including 42 genera, 96 species were found in the survey. Among of them, diatoms are the main species, with 34 genera and 79 species, accounting for 82% of the total species; 16 species of 7 genera of the dinoflagellates account for 17% of the total species; and 1 species of 1 genera of the Chrysophyta. Among them, the genera of Chaetoceros has the most species, a total of 17 species, followed by the genera of Coscinodiscus, a total of 13 species. The total cell abundance of phytoplankton is between 0.71×10⁴ cells/m³ to 72.15×10⁴ cells/m³, with an average of 13.88×10⁴ cells/m³. The cell abundance ratio of diatom to dinoflagellate is 2∶1. The abundance of diatoms in the Laizhou Bay is significantly higher than that in other sea areas. The cell abundance of dinoflagellates in the central Bohai Sea is significantly higher than that in other sea areas. The dominant species of phytoplankton are mainly Coscinodiscus asteromphalus, C. wailesii, Paralia sulcata, Ceratium fusus and Noctiluca. Scintillans. Horizontal distribution of phytoplankton community diversity in the Bohai Sea is uneven in autumn, and the diversity of local sea area is reduced due to the overproduction of single dominant species, the low value areas in autumn are distributed in the Liaodong Bay and the Bohai Strait. Compared with the historical data, the phytoplankton community in the Bohai Sea have obvious species succession. The genara of Ceratium has gradually emerged, its dominance in the central Bohai Sea and Liaodong Bay have surpassed the genara of Chaetoceros and Coscinodiscus. The phytoplankton community structure transforms from dominating by diatoms to dominating by diatoms and dinoflagellates.

In recent years, green tide of Ulva prolifera and red tide of microalgae occurred frequently with increasing marine pollution such as eutrophication in Chinese coastal waters. In this paper, the competitive inhibitory effects of U. prolifera fresh algae, U. prolifera culture filtrate and U. prolifera dry powder in different contents on Prorocentrum donghaiense were studied under laboratory simulation conditions. U. prolifera fresh algae, U. prolifera culture filtrate and U. prolifera dry powder all had inhibitory effects on P. donghaiense under the condition that the initial mass content was greater than 1 g/L, and the inhibitory intensity of U. prolifera dry powder was much higher than U. prolifera culture filtrate and U. prolifera fresh algae. In the co-culture groups, the phenomenon of “low promotion and high inhibition” appeared. Low content of U. prolifera promoted the growth of P. donghaiense, and high content of U. prolifera inhibited the growth of P. donghaiense. In addition, the inhibitory effects increased with the increasing content of U. prolifera. This inhibitory effects of U. prolifera on P. donghaiense may come from the competition and consumption of nutrients. In addition, the effects may also come from the influence of allelopathic substances released by U. prolifera on P. donghaiense. The inhibitory effects of U. prolifera on P. donghaiense can provide ideas and methods for the biological control of red tide.

Based on the nutrients and hydrological environment parameters collected during April (spring, before green tides) and July (summer, later stage of green tides) cruise, and the daily satellite monitoring data of green tides in the southern Yellow Sea (SYS) in 2018, we studied the spatio-temporal variations of the floating Ulva prolifera green tide and it's relationship with nutrients. The results showed that small scales of floating U. prolifera patches were firstly observed in the coastal area of Nantong, Jiangsu Province on April 25, and decomposed and disappeared in the coast of Shandong Peninsula in the mid-August. The trajectory area of floating green tides was mainly in the western of 122°E in the SYS, and the rapid growth phase of green tides existed in the south of 35°N, nearshore area of Jiangsu Province. Nutrients showed regional characteristics of high values in the coastal area of Jiangsu Province and low values in the offshore of the northern and eastern parts of the study area, which influenced by the Yellow Sea Cold Water Mass, freshwater influx, biological uptake and utilization, and other factors. Compared with the development trend of green tides and distributions of nutrients, there were three distinct characteristic zones with different nutrients conditions and stages of green tides: the coastal area of Jiangsu Province (south of 35°N, east of 122°E), characterized with high-value nutrients and rapid growth of green tides; the offshore area of Shandong Peninsula (north of 35°N, east of 122°E), characterized with low nutrients and dissipation phase of green tides; the east sea of 122°E, characterized with no green tides. The nutrients variations in different characteristic zones indicated that rich and sufficient nutrients (${\rm{NO}}_3^- $-N>6.5 μmol/L, ${\rm {PO}}_4^{3-} $-P>0.27 μmol/L), and continuous nutrients inputs were the main factors contributing the germination and rapid growth of U. prolifera, and provided main N, P elements for the development of green tides in the coastal area of Jiangsu Province. The poor nutrients (DIN<2 μmol/L, ${\rm {PO}}_4^{3-} $-P<0.03 μmol/L in summer) might be the limiting factor limiting the continuous development of green tides in the offshore ocean of the Shandong Peninsula.

Based on the daily satellite monitoring data of floating green tides, and the nitrogen nutrients and hydrological environment parameters were collected in spring (April, before green tides) and summer (July, later stage of green tides) cruises in the southern Yellow Sea (SYS) in 2018, we studied the spatio-temporal variation characteristics of the green tides, and the role of nitrogen nutrients in it. The results showed that the small U. prolifera patches were firstly observed in shallow waters off Nantong, Jiangsu Province on April 25, then floated northward and reached its maximum scale on the June 29, followed by decomposition and disappearance in the coast of Shandong Peninsula in the mid-August. The trajectory area of floating green tides was mainly located in the western of 122°E in the SYS, and showed two distinguishable development phases, the rapid growth phase in the south of 35°N, nearshore area of Jiangsu, and the decline phase in the north of 35°N, offshore area of Shandong Peninsula. The nitrogen nutrient components showed regional and seasonal variations, influenced by the freshwater influx, cold water masses, biological activity and other factors. The effects of nitrogen components were different in different development phases of green tides. The rich nitrogen nutrients from a variety of sources (total dissdved nitrogen (TDN) >20 μmol/L and dissolved inorganic nitrogen (DIN) >20 μmol/L) provided sufficient nitrogen for the development of green tides in the dominated form of DIN, and contributed to the fast reproduction and growth of U. prolifera in the rapid growth phase. While the U. prolifera showed a higher affinity for DON in the decline phase area, the urea-N become main nitrogen source for the development of green tides because of the poor bioavailable nitrogen content (DIN<2 μmol/L and urea-N<1.5 μmol/L) condition, which would limit the continuous growth of U. prolifera.