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In recent years, the frequent outbreaks of Ulva prolifera in the South Yellow Sea have become the largest-scale green tide disasters in the world. The causes of its outbreaks have garnered widespread attention, particularly the coupled effects of multiple factors. Leveraging the Google Earth Engine (GEE) platform, this study conducted a long-term investigation of the Yellow Sea green tide disaster and the factors using multi-source satellite imagery. Finally, the combined effects of natural environmental changes and human activities on Ulva prolifera were analyzed by redundancy analysis (RDA) and variation partitioning analysis (VPA). The results indicate: (1) Since 2018, the scale of Ulva prolifera in the South Yellow Sea has shown a distinct "biennial" trend. (2) Regarding environmental factors, SST, PAR, precipitation, and windspeed have certain effects on the growth of Ulva prolifera. However, they cannot be considered as determining factors for the outbreak of Ulva prolifera (0.002 < R2 < 0.14). Regarding anthropogenic factors, the recycle time of Pyropia yezoensis culture rafts has a relatively minor influence on the extent of Ulva prolifera. There exists a certain positive correlation (R2 = 0.45) between the human footprint index (HFI) of Jiangsu Province and the annual variation in Ulva prolifera area in the South Yellow Sea. (3) The combined effects of multiple factors influence green tide outbreaks. The Ulvatotal explanatory power of SST, PAR, precipitation, windspeed, HFI, and the recycle time of Pyropia yezoensis culture rafts for the annual variation in the Ulva prolifera area is 31.8%, with these factors interweaving and mutually influencing each other. This study offers important insights into quantifying the driving forces behind Ulva prolifera in the South Yellow Sea, providing valuable information for a deeper comprehension of the complexity of marine ecosystems and sustainable management. [ABSTRACT FROM AUTHOR]

The Neopyropia aquaculture area located in Subei Shoal has garnered considerable attention due to the green tide in the Yellow Sea. Acid treatment is widely used in Neopyropia culture, both in the seedling and mature stages. In light of this, we propose the implementation of acid treatment technology in the Neopyropia aquaculture area within Subei Shoal, with the primary aim of mitigating the proliferation of green macroalgae on the rafts. This, in turn, is anticipated to elevate the yield and overall quality of Neopyropia. In this paper, we provide a comprehensive overview of the application of acid treatment technology in Neopyropia aquaculture, elucidating the key acid solutions used and the underlying mechanisms governing acid treatment. Furthermore, we delve into early prevention strategies for countering the green tide within the Neopyropia aquaculture region of northern Jiangsu Province, ultimately striving to augment the quality of Neopyropia cultivation and propose effective measures for curtailing the scale of green tide. [Display omitted] • Introducing the acid treatment in the Neopyropia aquaculture. • Introducing the damage mechanism of acid solution to green macroalgae. • Providing suggestions for further research on green tide prevention. • Acid treatment will not have harmful effects on marine environment. [ABSTRACT FROM AUTHOR]

We conducted continuous monitoring at 13 stations along the Jiangsu coast to study the spatiotemporal distribution, population succession of micropropagules of green algae, and their impact on the outbreak of Southern Yellow Sea green tide. The study discovered that: 1) Green algae micropropagules had obvious temporal and spatial distribution and population changes along the Jiangsu coast. The monthly average abundance of micropropagules of green algae at station BH1, which was the high-value area, was 1230 inds/L. Station XS2 had the second-highest value area. Green algae micropropagules had an average monthly abundance of 836 inds/L. Between stations XS2 and BH1, the amount of green algae micropropagules steadily declined in comparison to other stations. The abundance was greatest from spring to early summer, and Ulva prolifera micropropagules predominated; 2) Compared with salinity, temperature had a more obvious effect on the micropropagules of green algae along the Jiangsu coast; 3) Green algae micropropagules on the Jiangsu coast could be a potential additional source on the outbreak of Southern Yellow Sea green tide. More data are needed to corroborate this conclusion. For the purpose of preventing and managing green tide, it is crucial to investigate the Southern Yellow Sea's potential supplementary source. This study analyzes the spatiotemporal distribution and population changes of green algae micropropagules along the Jiangsu coast, as well as their impact on green tide outbreaks, providing scientific data support for the prevention and control of green tides in the Southern Yellow Sea. • Analysis of spatial and temporal distribution and population composition of green algae micropropagules along the coast of Jiangsu. • The temperature has an important effect on the distribution of micropropagules of green algae along the Jiangsu coast. • Green algae micropropagules along the Jiangsu coast have little impact on the green tide in the Southern Yellow Sea. [ABSTRACT FROM AUTHOR]

Ulva prolifera blooms have occurred every summer in the South Yellow Sea since 2008. U. prolifera blooms appeared in the area near the Jiangsu shoal and then were driven to the Shandong Peninsula by the prevailing summer winds. The blooms covered a maximum area of more than 50000 km2 and had an aggregate estimated biomass of 3.64 × 105 tons. Large number of U. prolifera dissipation in the natural degradation and this cause a serious impact on the marine environment. We used MODIS, HJ-1A/B and GF-1 remote sensing image data to conduct large-scale monitoring of U. prolifera. Combined with sea surface monitoring station data from Haiyang city, Shandong province, we analyzed the impact of U. prolifera death on the coastal sea environment of Haiyang city from 2012 to 2016 using multiple regression analysis. It showed that chlorophyll-a concentration was related to sea surface temperature (SST), salinity, dissolved inorganic nitrogen (DIN) and phosphate (R2 = 0.50, P < 0.001). Among these, DIN and phosphate were important factors affecting chlorophyll-a concentration. There was a significant positive correlation between chlorophyll-a concentration and DIN, but a significant negative correlation between chlorophyll-a concentration and phosphate. The nutrients released by the decomposition of U. prolifera enhanced the growth of planktonic microalgae, and increased the mean chlorophyll-a concentration from 1.398 μmol/L to 2.819 μmol/L during May to August in the study area. This increased the Level of eutrophication in the coastal area and contributed to blooms of secondary algae such as red tides. [ABSTRACT FROM AUTHOR]

To develop an effective method to eliminate green macroalgae attached to Neopyropia aquaculture nets, we explored the influence of mixed acid solution on the photosynthetic fluorescence characteristics of Ulva spp. (green macroalgae) and Neopyropia yezoensis (red macroalgae) from Dafeng and Rudong aquaculture areas in Jiangsu Province, China. Treatment with mixed acid solution (0.0475 % hydrochloric acid:citric acid (pH 2.0) at a ratio of 4:3) for 60 s caused death of Ulva spp., but did not affect N. yezoensis. Additionally, a mixed acid solution effectively eliminated green macroalgae from Neopyropia aquaculture rafts and the marine environment remained unaffected. Hence, the application of mixed acid solution treatment has demonstrated significant efficacy in eradicating green macroalgae adhered to Neopyropia aquaculture rafts, thus presenting a promising strategy for mitigating green macroalgae proliferation in Neopyropia aquaculture areas and curbing their contribution to green tides. [Display omitted] • Ulva spp. was completely killed with a mixed acid (4:3 HCl to citric acid). • Neopyropia yezoensis treated with the mixed acid can get back. • This method will not have harmful effects on marine environment. [ABSTRACT FROM AUTHOR]

Green tides have long occurred in the Yellow Sea for 17 years, with 5S-II Ulva prolifera being the dominant species. Previous studies indicate the Neopyropia aquaculture area in Jiangsu to be the main source of green tides in the Southern Yellow Sea. Little is known regarding the occurrence of this species in coastal dykes in Jiangsu Province. We investigated the species composition, diversity, and biomass of green macroalgae in these dykes during 2022 using internal transcribed spacers and 5S rDNA and identified U. prolifera , Ulva linza , Blidingia spp., Ulva meridionalis , Ulva torta , Ulva flexuosa , Ulva compressa , Ulva aragoensis , Ulva australis , and Ulva simplex. Ulva prolifera occurred in every month of the survey. Species diversity was highest in October, and the Ulva spp. biomass was highest in February. Attached 5S-II U. prolifera occurred in the coastal dykes in February, April, and June 2022. Dyke characteristicsand elevations may affect the biomass and species of Ulva spp. observed. Green tide blooms in the Yellow Sea have enabled 5S-II U. prolifera to colonize the Jiangsu coast dykes. • Ulva prolifera, a dominant sp. in green tides, was found in Jiangsu coastal dykes. • Attached and floating 5S-II U. prolifera bear close affinities. • Different dyke types may affect the Ulva spp. species present. • Ten species of green macroalgae were found in Jiangsu coastal dykes. [ABSTRACT FROM AUTHOR]

Green tides in the Yellow Sea have occurred periodically since 2007, impacting the ecological environment and green algal communities along the coasts of Jiangsu and Shandong provinces in China. To investigate the morphological characteristics and genetic diversity of Ulva prolifera , we conducted surveys and comparative analyses of both its floating and attached forms along the coastal areas of Jiangsu and Shandong. The results revealed that the external morphology of the floating U. prolifera was multibranched. The attached U. prolifera displayed significant morphological variation among individuals. Based on the analysis of the amplified characteristic bands of the chloroplast gene, it was shown that both floating and attached U. prolifera could hybridize with Ulva linza. The genetic diversity of U. prolifera was studied using mitochondrial and chloroplast genome fragments. All floating U. prolifera and three strains of attached U. prolifera belonged to the same haplotype. The genetic diversity of floating U. prolifera was low, and there were some genetic differences with attached U. prolifera. The attached U. prolifera displayed a higher level of genetic diversity with abundant sites of variation and haplotypes. • Floating and attached Ulva prolifera displayed significant morphological variation. • Floating and attached U. prolifera could hybridize with Ulva linza. • All collected floating U. prolifera belonged to the same haplotype. • Attached U. prolifera showed high genetic diversity with abundant sites of variation. • Attached U. prolifera genetic information varied primarily within populations. [ABSTRACT FROM AUTHOR]

The massive pelagic Sargassum horneri (Turner) C. Agardh, 1820 has increasingly occurred in the Yellow Sea and East China Sea. Significant intrusion of floating S. horneri into the southwestern Yellow Sea, the major bloom region of the green tides, has aroused speculations on the blooming mechanism and confounded concurrent prevention practices of green tides. The floating S. horneri were surveyed and sampled throughout its distributional range to study the diversity and abundance of sympatric macroalgae, including the epiphytes and non-epiphytes. The study showed that both types of macroalgae commonly coexisted with the pelagic S. horneri and showed distinct distribution patterns. The non-epiphytic green macroalgae, primarily Ulva prolifera , were free floating with S. horneri. They were initiated from the nearshore water of Jiangsu in late April followed by a rapid accumulation and expansion as the green tide developed. The non-epiphytic green algae were mostly restricted in the western coast of southern YS with biomass decreasing evidently toward offshore. Four species in Phaeophyta were commonly detected epiphytic on the pelagic S. horneri in the survey region and Proselachista taeniiformis was dominant. Unlike the co-occurring green algae, the species composition and abundance of epiphytes have no significant variation in the distributional range of the pelagic S. horneri. High frequency (80%) and abundance (0.25 ± 0.17 g Epi /g Sar) of epiphytes indicated significant biological interactions with their hosts and ecological functions of this pelagic system, which deserves further investigation. • Epiphytic and co-occurring macroalgae of pelagic S. horneri in YS and ECS showed distinct distribution patterns. • U. prolifera was not attaching to pelagic S. horneri and restricted in the coasts of southwestern YS. • High frequency and abundance of algae in Phaeophyta was observed epiphytic on the pelagic S. horneri. • Proselachista taeniiformis was the dominant epiphyte of S. horneri in the survey region. [ABSTRACT FROM AUTHOR]

Nutrient removal ability of seaweeds on Pyropia yezoensis aquaculture rafts was studied during the P. yezoensis aquaculture season of 2012–2013 at the offshore farm along the radial sandbanks of Jiangsu Province, China. During the P. yezoensis cultivation season, three Ulva species, including Ulva prolifera , Ulva linza , and Ulva flexuosa , were present on the cultivation rafts. These Ulva spp. were then removed from the rafts or floated away when rafts were recycled in April 2013. The quantities of nitrogen and phosphorus removed by the harvest of P. yezoensis were 3688 and 106 tons, respectively. The nitrogen and phosphorus removal of Ulva were 77 and 3 tons, respectively. These results indicate that P. yezoensis can efficiently remove excess nutrients from coastal waters. The Ulva if harvested can also be utilized as an additional nutrient management tool in eutrophic waters. In addition, introduction of high-temperature adapted seaweeds would be a useful way to continue algal bioremediation during the off season of P. yezoensis aquaculture. [ABSTRACT FROM AUTHOR]

Green tides have occurred in the Southern Yellow Sea (SYS) for 16 consecutive years, causing widespread concern. Attached and floating green macroalgae have been observed in Binhai Harbor, Jiangsu Province, China, in the SYS. This study used morphological analysis, and internal transcribed spacers and rps2- trn L molecular identification methods, to analyze the species composition and biomass of green macroalgae along the Binhai Harbor coast. Six species of green tide algae (Ulva prolifera , Ulva meridionalis , Ulva linza , Ulva flexuosa , Ulva californica , and Ulva intestinalis) were identified, in addition to Blidingia sp. The discovery of U. californica is the first report of this species off the coast of Jiangsu Province. The floating green macroalgae along the Binhai Harbor coast originated from attached green macroalgae in Binhai Harbor, and a small number of the attached algae wer e closely related to the large-scale floating U. prolifera in the SYS. Moreover, in December 2021, February 2022, and April 2022, the total biomass of attached green macroalgae in Binhai Harbor was 25.600, 10.767, and 25.867 t, respectively, of which the U. prolifera biomass was 10.697, 8.709, and 4.185 t, respectively. This study proved Binhai Harbor may not be an important source of green tide in the SYS. • Six species of Ulva were found in Binhai Harbor. • Ulva californica, usually in the Eastern Pacific, now appears in the Yellow Sea. • Floating macroalgae near Binhai Harbor are derived from attached algae in the harbor. • Binhai Harbor may not be a major source of green tides in the Southern Yellow Sea. [ABSTRACT FROM AUTHOR]

From 2008 to 2016, massive floating green macroalgal blooms occurred annually during the summer months in the Yellow Sea. The original source of these blooms was traced based on the spatio-temporal distribution and species composition of Ulva microscopic propagules and settled Ulva vegetative thalli monthly from December 2012 to May 2013 in the Yellow Sea. High quantities of Ulva microscopic propagules in both the water column and sediments were found in the Pyropia aquaculture area along the Jiangsu coast before a green macroalgal bloom appeared in the Yellow Sea. The abundance of Ulva microscopic propagules was significantly lower in outer areas compared to in Pyropia aquaculture areas. A molecular phylogenetic analysis suggested that Ulva prolifera microscopic propagules were the dominant microscopic propagules present during the study period. The extremely low biomass of settled Ulva vegetative thalli along the coast indicated that somatic cells of settled Ulva vegetative thalli did not provide a propagule bank for the green macroalgal blooms in the Yellow Sea. The results of this study provide further supporting evidence that the floating green macroalgal blooms originate from green macroalgae attached to Pyropia aquaculture rafts along the Jiangsu coastline of the southern Yellow Sea. [ABSTRACT FROM AUTHOR]

Abstract: In the summer of 2008, the world’s largest green-tide occurred in the Yellow Sea, China. The hypothesized cause was the expansion of Porphyra yezoensis aquaculture along the Jiangsu coastline and the re-occurrence of a green-tide in 2009 was predicted. In this study, satellite and field images showed the formation of the June 2009 green-tide which again originated from the Jiangsu coast. The responsible species, its source and biomass accumulation were studied to support the previous hypothesis. Morphological and phylogenetic analysis demonstrated the homology of Ulva prolifera in the 2008 green-tide with the U. prolifera from P. yezoensis aquaculture rafts. About 91–505kg/ha of U. prolifera was attached to the P. yezoensis aquaculture rafts and a total biomass of 4956 tonnes was estimated during the harvesting of P. yezoensis. This is sufficient to seed a bloom when they are dislodged from the rafts as a result of harvesting practices. [ABSTRACT FROM AUTHOR]

Green macroalgal blooms have occurred in the Yellow Sea for 13 consecutive years since 2007. However, effective control methods have not yet been successfully developed. Ulva prolifera attached on Pyropia aquaculture rafts was identified as the main source of the blooms, thus, eliminating the attached Ulva from the rafts should be the most efficient method to prevent and control these blooms. In this study, we designed a new molecular marker (rps2- trn L) to identify U. prolifera collected from the aquaculture site. Samples identified as U. prolifera were cultured, and different concentrations of sodium hypochlorite (NaClO) solution (0.2, 0.4, 0.6, 0.8, and 1.0%) were used to kill the alga. The measured chlorophyll content, light quantum yield, and photosynthetic oxygen release rate data from the laboratory experiment suggested that the appropriate concentration of NaClO solution should be 0.6–1.0%. To carry out a small-scale field trial, we developed a device that can spray NaClO on Ulva blades and recycle the residual liquid. Results showed that only the 1.0% NaClO solution could quickly kill the Ulva in outdoor experiments. During the treatment, very little NaClO dripped on the tidal flat, which indicated that the recycling device avoided a potential negative impact of residual solution on the marine ecosystem. By the beginning of November 2019, the Pyropia aquaculture area treated by NaClO was about 13,000 ha, covering about one-third of the total area at the coast of Jiangsu Province. Monitoring by an unmanned aerial vehicle showed that very little attached Ulva was present on the ropes after NaClO treatment, which indicated that it was an effective method to control the green tide. Also, the range of residual active chlorine within seawater during the treatment was only from 0.003 to 0.012 mg/L, which complied with Chinese national standards. However, further monitoring of the formation process of green tides should be conducted in future years to evaluate the effect of NaClO treatment. • A new molecular marker was applied to identify attached Ulva prolifera on the rafts. • The different concentrations of NaClO on killing U. prolifera were tested through laboratory experiment. • A facility was developed to assist spraying NaClO solution on field, and avoided environmental pollution. • Large-scale NaClO treatment was carried out in the Pyropia aquaculture area to kill attached Ulva macroalgae. [ABSTRACT FROM AUTHOR]

The outbreak of a large-scale green tide (Ulva prolifera) will have a serious impact on marine environment, ecological functions, landscape, and coastal social economy. Eutrophication is generally considered to be the most important driving factor of this phenomenon. It is difficult to obtain the pressure-impact relationship between land-based loading and green tides by only surveying or monitoring, whereas modeling can perform this task easily. In this study, therefore, a hydro-biogeochemical model was established and verified by the measured hydrodynamic and water quality variables. In the initial outbreak area of Jiangsu coast, China, we studied the relationship between U. prolifera bloom and the driving factors of nutrient loads and structures by modeling different scenarios of land source inputs. It was found that the ratio of nitrogen to phosphorus could be affected significantly, which triggered the bloom of U. prolifera. When the land-based input doubled or halved, the dissolved inorganic nitrogen concentration increased 20.6% or decreased 9.5%, respectively, which might result in 14.5% increase or 46.3% decrease in the green tide, respectively. It was also found that the nutrient distribution and structure was affected by the land-based load, which caused the outbreak of U. prolifera. Moreover, the total nutrient load must be controlled to prevent the outbreak of green tide in the Jiangsu coast. [ABSTRACT FROM AUTHOR]