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Eutrophication intensifies Harmful Macroalgae Blooms (HMBs) in coastal environments, reducing habitat suitability for organisms and creating significant challenges for small-scale artisanal fishers. Leveraging fishers' memories, we analyzed over 20 years of data on Ulva lactuca blooms and their effects on fishing activities and fish resources in a tropical semi-arid region of Brazil. We estimated the timing, seasonality, and impacts of these bloom episodes on fish catches, fishing gears, and fishery revenues. Since 2010, blooms have become more frequent, particularly during dry seasons in shallow estuaries, likely exacerbated by nutrient enrichment, extended water residence time, and inadequate wastewater treatment. Net-based gear is particularly affected, with fish catches decreasing by up to sevenfold during bloom seasons, leading to income losses of approximately 50 %. Addressing eutrophication through active public policies on effluent treatment is crucial to mitigating economic impacts on vulnerable communities and managing future blooms, which are expected to worsen with climate change., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Carolina Teixeira Puppin Goncalves reports financial support was provided by Coordenação Superior de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). Priscila Fabiana Macedo Lopes reports financial support was provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Macroalgal nitrogen isotope analysis (δ 15 N) is a reliable method for the identification of nitrogen pollutant sources. Understanding δ 15 N geospatial variation within small bays and/or harbour environments can help identify point sources of nitrogen pollution. This study sampled over 300 Fucus vesiculosus and Ulva sp. specimens in September 2022 and May 2023 from Staithes Harbour, North Yorkshire, England. δ 15 N values for Staithes Beck were elevated when compared to sites in Staithes Harbour and the North Sea: this is attributed to sewage effluent and/or agricultural manure. Few sites within Staithes Harbour were significantly different from one another in terms of δ 15 N, suggesting a relatively homogenous nitrogen isotope record of the harbour. Simple harbour environments like Staithes may be relatively well mixed, and thus, sampling one harbour site may be enough to represent the entire harbour. Of course, more complex harbours may require more sample locations to ascertain point sources and mixing in the harbour., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Bloom-induced macroalgal enrichment on the seafloor can substantially facilitate dissolved sulfide (DS) production through sulfate reduction. The reaction of DS with sedimentary reactive iron (Fe) is the main mechanism of DS consumption, which however usually could not effectively prevent DS accumulation caused by pulsed macroalgal enrichment. Here we used incubations to investigate the performance of Fe-rich red soil for buffering of DS produced from macroalgae (Ulva prolifera)-enriched sediment. Based on our results, a combination of red soil additions (6.8 kg/m2) before and immediately after pulsed macroalgal deposition (455 g/m2) can effectively cap DS within the red soil layer. The effective DS buffering is mainly due to ample Fe-oxide surface sites available for reaction with DS. Only a small loss (4 %) of buffering capacity after 18-d incubation suggests that the red soil is capable of prolonged DS buffering in macroalgae-enriched sediments. [Display omitted] • Macroalgae decay on seabed stimulates quick generation of dissolved sulfide (DS). • Low red soil loads can effectively prevent DS release from macroalgae-rich seabed. • Low red soil loads can secure prolonged DS buffering in macroalgae-rich seabed. • Ample reaction Fe surface sites are the key for effective DS buffering by red soil. [ABSTRACT FROM AUTHOR]

The contents of 24 elements were determined in seven species of macroalgae collected in Ceara-Brazil, in the rainy and dry seasons of 2022. The samples were digested, and the analytes were quantified by ICP-OES and Hg by direct analyzer. The CRM CD-200 was analyzed for accuracy and obtained recoveries were higher than 95 %. The seaweed species have different inorganic element profiles with predominant elements being: Ca, K, Na, Mg and P. The Sargassum vulgare species stood out for its Hg and As contents (1.479 ± 0.005 mg kg−1 and 172 ± 6 mg kg−1, both in the rainy seasons). Ulva lactuca attracted attention for its high concentration of V (46.4 ± 3.4 mg kg−1, rainy season). In general, the elemental content levels in the macroalgae samples were higher in the rainy season. Long-term studies to comprehend the effect of seasonality on the elemental composition of seaweed must be carried out. [Display omitted] • Elemental content of 7 seaweed species from Northeast of Brazil was firstly described. • Seasonality had an influence on the elemental content level of all seaweed samples. • High concentrations of As and Hg were found in a brown species of seaweed. [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, a globally prevalent marine ecological anomaly observed in coastal regions, have received substantial attention. However, there is limited research on the burial of Ulva prolifera in sediments during the late stages of green tide outbreaks. This study investigates the effect of temperature on U. prolifera buried in sediment over 30 days. The measurements included the length, biomass, relative growth rate, chlorophyll composition and maximum quantum yield (Fv/Fm) of PS II at different stages. The results indicate that at −20 °C, numerous seedlings emerged after 14 days of recovery culture, suggesting the release of spores or gametes; survival was possible from −2 °C to 15 °C; but at 20 °C and 30 °C, all U. prolifera died. The U. prolifera buried in sediment during the late stage of green tide outbreaks may serve as one of the sources for the subsequent year's green tide eruption. This research provides insights into the origins of green tide outbreaks in the southern Yellow Sea. [Display omitted] • The study investigated the physiological responses of Ulva prolifera in sediments under seven temperature conditions. • The research found Ulva prolifera in sediments could still disperse after 30 days at -20°C. • At 20°C and 30°C, Ulva prolifera buried in sediments for 30 days decayed and died, with no microscopic propagules. [ABSTRACT FROM AUTHOR]

Green tides occurrence has increased in coral reefs, yet few reference values have been documented to support bloom management in these ecosystems. Here, we took advantage of recent Ulva green tides that occurred in New Caledonia to (i) identify the elements limiting the growth of Ulva spp. during these blooms; and (ii) validate the use of isotopic markers for identifying sources of nutrients that generated blooms. N/P ratios highlighted a stronger limitation of algae by phosphorus than by nitrogen on sites under oceanic influence, while the proportions of N and P were optimal for algal growth at sites where green tides occurred. Macroalgae highly exposed to sewage water was characterized by higher δ15N than macroalgae collected in areas exposed to synthetic inorganic fertilizers. From these results, we established a new set of threshold values for using δ15N in Ulva species as an indicator of nitrogen source type in coral reefs. • N/ P values were optimal for algal growth at sites where green tides occurred. • δ15N in Ulva spp. varied between areas exposed to different nutrient sources. • Similar trends in δ15N at area scales were found for Ulva spp. and Halimeda cylindracea. [ABSTRACT FROM AUTHOR]

We investigated spatial heterogeneity and diel variations in bacterioplankton and pico-nanoeukaryote communities, and potential biotic interactions at the extinction stage of the Ulva prolifera bloom in the Jiaozhou Bay, Yellow Sea. It was found that the presence of Ulva canopies significantly promoted the cell abundance of heterotrophic bacteria, raised evenness, and altered the community structure of bacterioplankton. A diel pattern was solely significant for pico-nanoeukaryote community structure. >50 % of variation in the heterotrophic bacterial abundance was accounted for by the ratio of Bacteroidota to Firmicutes, and dissolved organic nitrogen effectively explained the variations in cell abundances of phytoplankton populations. The factors representing biotic interactions frequently contributed substantially more than environmental factors in explaining the variations in diversity and community structure of both bacterioplankton and pico-nanoeukaryotes. There were higher proportions of eukaryotic pathogens compared to other marine systems, suggesting a higher ecological risk associated with the Ulva blooms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Seawater samples were collected from April 6 to September 6, 2017 in the Southern Yellow Sea, China where green tides often occurred, and analyzed for nutrients, dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM). The DOC concentrations increased significantly in the green tide areas by approximately 1.2 times compared to those in the non-green tide areas. From the large-scale outbreak to the complete dissipation of the green tide, the fluorescence intensities of the four FDOM fluorescent components identified in the green tide areas were significantly higher than those in the non-green tide areas. During the extinction period, the fluorescence intensities of the three humus-like components and one protein-like component were approximately 1.8 and 1.3 times higher than those in the non-green tide areas, respectively. These findings suggested that the outbreak of green tide could release DOM into water and affect the biogeochemical cycle in green tide regions. • DOC increased 20% in the green tide areas during the outbreak of Ulva prolifera. • The fluorescent components were significantly higher in the green tide areas. • DON in the green tide areas increased 30% than those in the non-green tide areas. • When Ulva decayed, it released FDOM and DON into the water. [ABSTRACT FROM AUTHOR]

Green algal blooms have occurred in the Yellow Sea for 13 consecutive years since 2007. However, little is known about the reproductive strategy of the dominant species Ulva prolifera in the field. In particular, it is not clear whether the floating Ulva species are sporophytes or gametophytes, and if their life history is sexual or asexual. In this study, the life history type was determined based on the size, phototactic response, and flagella number for the zoids in at least two successive generations. In addition, chromosome observations were conducted to distinguish the gametophytes and sporophytes in the floating Ulva species. The results showed that the floating Ulva species were all sporophytes with sexual reproductive patterns, thereby indicating that this Ulva species always maintains vegetative growth from April to June during the early stage of the blooms. In addition, we found that the chromosome numbers were 18 for the diploid sporophytes and nine for the haploid male and female gametophytes. These results provide useful information to help understand the explosive growth of these green algal blooms. • Chromosome number 18 for diploid Ulva prolifera sporophytes • Chromosome number nine for haploid male and female gametophytes • Floating Ulva species all sporophytes with sexual reproductive patterns • Ulva species maintain vegetative growth from April to June during early blooming. [ABSTRACT FROM AUTHOR]

In order to understand how darkness/irradiance and low nighttime temperature might alter physiology of Ulva prolifera under lower salinity conditions, we analyzed the growth rates, water content, superoxide dismutase (SOD) activity, total soluble proteins (SPs) and carbohydrates content at the end of dark and light period under three temperature levels (25–25 °C treatment: 25 °C for day and night; 15–15 °C treatment: 15 °C for day and night; 25–15 °C treatment: 25 °C for day with 15 °C for night) and two salinity conditions (15, 25), meanwhile, the pigment content (chlorophyll a and b), chlorophyll fluorescence and photosynthetic oxygen evolution also were determined during light phase. We found that the U. prolifera showed higher growth rate and SOD activity during dark phase at 25 °C, but this dark-induced increase could not be observed at 15 °C. The reasons for this increase varied, however, maybe not included water content and SPs for no significant difference in water content observed under all the treatments, as well as lower SPs content for dark period aside that at 15 °C and salinity 15. Compared to other two temperature treatments, the thalli grown at 25–15 °C showed higher growth rate and the photosynthetic oxygen evolution rate in light phase under salinity 15 conditions, although the maximum relative electron transport rate (rETR max) showed higher value under 25 °C treatment. These results indicate that the darkness and the lower nighttime temperature maybe responsible reason for the rapid growth of these green tide algae. Unlabelled Image • The effects of darkness and low nighttime temperature under low salinity were studied. • The higher growth and SOD activity at the dark phase were observed at 25°Crather than 15 °C. • Low nighttime temperature enhanced the growth and photosynthesis in light phase at lower salinity. • The darkness and low nighttime temperature maybe the midwife for the rapid growth of this alga. [ABSTRACT FROM AUTHOR]

This baseline study highlights the 210Po and 210Pb concentration in seven macroalgae species from the northern Gulf that are frequently washed ashore during the bloom season from February to April. The highest concentrations of 210Po and 210Pb were 2.947 ± 0.032 and 1.057 ± 0.145 Bq kg−1 wwt, respectively, in brown algae Sargassum boveanum, and the lowest in green algae Ulva prolifera with 1.533 ± 0.058 and 0.170 ± 0.069 Bq kg−1 wwt, respectively. A 210Po enrichment was observed in both brown and green algae species , with the 210Po/210Pb ratio being >1 for all the samples. The mean concentration of 210Po in all species was an order of magnitude higher than 210Pb, and the difference in mean concentration is statistically significant (p < 0.001). At the same time, the mean concentration of dissolved 210Po and 210Pb in seawater was 0.28 ± 0.01 and 0.52 ± 0.01Bq m−3 with a 210Po/210Pb ratio of 0.54 ± 0.02 indicating that 210Po was absorbed from water and more concentrated by macroalgae. The measured concentration factor (CF) for 210Po in these macroalgae for the northern Gulf varied between 5 × 103–1 × 104, higher than the IAEA recommended value of 1 × 103 which suggests that a revision of that value may be needed. The field derived CFs for 210Pb vary between 3 × 102–1.8 × 103, comparable to the ICRP recommended value of 2 × 103. • This paper establishes the baseline for 210Po and 210Pb in macroalgae from northern Gulf. • Brown algae has higher 210Po and 210Pb concentration than green algae. • Difference in 210Pb and 210Po concentrations in seven macroalgae was statistically significant. • The concentration factor in both green and brown macroalgae is higher than IAEA recommended value. [ABSTRACT FROM AUTHOR]

We investigated how elevated CO 2 affects the responses of Gracilariopsis lemaneiformis and Ulva lactuca to NH 4 + enrichments. All algae were incubated under four nutritional conditions (zero addition, 100, 500, and 2500 μM NH 4 +), and two CO 2 levels (390 ppm and 1000 ppm). The growth, photosynthesis, and soluble protein contents of both species increased under the eutrophication condition (100 μM NH 4 +). However, the growth and carotenoid contents of the two species declined when NH 4 + concentration increased. Under the super eutrophication condition (2500 μM NH 4 +), all indexes measured in G. lemaneiformis were suppressed, while the growth and photosynthesis in U. lactuca changed indistinctively, both compared with the control. Moreover, under the super eutrophication condition, elevated CO 2 reduced the suppression in the growth of G. lemaneiformis , but decreased the growth of U. lactuca. Nonetheless, G. lemaneiformis displayed much lower growth rates than U. lactuca under the super eutrophication and elevated CO 2 condition. • Responses of two algal species to NH 4 + and CO 2 enrichments were investigated. • 100 μmol L−1 NH 4 + enhanced growth and photosynthesis in both algal species. • 2500 μmol L−1NH 4 + was toxic to Gracilariopsis lemaneiformis but not Ulva lactuca. • Elevated CO 2 reduced the toxicity of 2500 μmol L−1 NH 4 + to G. lemaneiformis. [ABSTRACT FROM AUTHOR]

Abstract To investigate bioavailability of dissolved organic nitrogen (DON) and its contribution to nitrogen demand for Ulva prolifera , a cruise was conducted during a bloom of U. prolifera in Qingdao coastal waters, China, dissolved inorganic nitrogen (DIN) and DON components were investigated. Uptakes of both DIN and DON by U. prolifera were synchronously measured onboard using stable isotope techniques. The contribution of DON to total dissolved N (TDN) was >50% and that of labile components (urea and to amino acids, AA) to DON exceeded 30%. Both DIN and DON were utilized by U. prolifera , which uptake NH 4 -N preferentially, then urea, NO 3 -N and AA in turn; whereas the ranking of turnover times from short to long was AA, NH 4 -N, urea and NO 3 -N. The high uptake rates and short turnover time of AA and urea indicated that DON may play an important role in the nutrition of U. prolifera. Highlights • Dissolved organic nitrogen showed high bioavailability in a green macroalgal bloom. • Urea and dissolved amino acids contributed >30% of the organic nitrogen pool. • Ulva prolifera absorbed ammonium most, followed by urea, nitrate and amino acids. • Dissolved organic nitrogen contributed significantly to support the green bloom. [ABSTRACT FROM AUTHOR]

Abstract Large-scale green tides caused by Ulva prolifera , occurred for 12 consecutive years in the Yellow Sea of China. To resolve the abrupt shift in species composition between attached and floating macroalgal assemblages, field experiments were conducted from May to July 2017 to quantify the net buoyancy force and compare the floating potential of the common green macroalgae from the red algal seaweed Pyropia yezoensis rafts. At the same time, U. prolifera from different sampling locations were tested to study variable buoyancy of this species and the associated influencing factors. Our results illustrated a stronger positive buoyant force and a proportionally greater buoyancy capacity of U. prolifera , compared to the other co-occurring species. Buoyancy is a dynamic trait and is closely correlated with light intensity, morphology and physiological status. The positive buoyancy of U. prolifera is an important factor that helps explain its predominance in the Yellow Sea's large-scale green tides. Highlights • U. prolifera has a stronger buoyant force relative to other co-occurring green algae. • Buoyancy is closely correlated with irradiance, morphology and physiological status. • U. prolifera 's buoyancy helps explain its dominance in the Yellow Sea's green tides. [ABSTRACT FROM AUTHOR]

Abstract Since 2007, green tide blooms with Ulva prolifera as the dominant species have occurred every summer in the Yellow Sea. Biomass is a critical parameter used to describe the severity of green tide blooms. In this study, we analyzed the relationships between several indices (normalized difference vegetation index (NDVI), floating algae index (FAI), ratio vegetation index (RVI), enhanced vegetation index (EVI), ocean surface algal bloom index (OSABI), Korea Ocean Satellite Center (KOSC) approach) and the biomass per unit area of Ulva prolifera by using the in situ measurements from a water tank experiment. EVI, NDVI, and FAI showed strong exponential relationships with Ulva prolifera biomass per unit area. In order to apply the relationships to satellite remote sensing data, the impacts of the atmosphere (different aerosol optical depth at 550 nm) and mixed pixels to the relationships were analyzed. The results show that atmosphere has little effect on the relationship between EVI and Ulva prolifera biomass per unit area with R2 = 0.94 and APD (the average percentage deviation) = 19.55% when EVI is calculated from R rc (Rayleigh-corrected reflectance), and R2 = 0.95 and APD = 17.53% when EVI is calculated from R toa (top-of-atmosphere reflectance). Due to the low sensitivity to the atmosphere, the EVI relationship can be directly utilized in the top-of-atmosphere (TOA) reflectance without atmospheric correction. In addition, the EVI was slightly affected by mixed pixels with the APD only increased by ~10%. The EVI relationship was then applied to a long MODIS image time series to obtain the maximal total biomass of floating Ulva prolifera in the Yellow Sea from 2007 to 2016. The results showed that the maximum and minimum total biomass occurred in 2016 (~1.17 million tons) and 2012 (~0.074 million tons), respectively. The main factors that caused the inter-annual biomass variability were analyzed. The total amount of nutrients from Sheyang River which was the largest river on the northern coast of Jiangsu Province, and Porphyra cultivation in the Radial Sand Ridges of Jiangsu Province had both strong correlation with Ulva prolifera total biomass. Highlights • A new algorithm is proposed based on EVI which is most sensitive to biomass. • EVI is proved to be insensitive to aerosol optical thickness and mixed pixels. • The changes and influencing factors of biomass in recent ten years are revealed. [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]

Since 2007, green tides have occurred almost every year in the Yellow Sea, and a method to prevent them and to control levels of attached Ulva prolifera is urgently needed. In this study, we measured the effects of different concentrations of citric acid-activated chlorine dioxide solution (0, 50, 100, 150, 200, and 250 mg/L of chlorine dioxide) on the morphology (macrostructure and microstructure), chlorophyll a content, chlorophyll b content, carotenoid content, and chlorophyll fluorescence parameters (Fv/Fm, Y (II), NPQ, and ETRmax) of U. prolifera. Micropropagules in the treatment filtrate were cultured to determine whether the solution reduced the number of micropropagules released during the treatment process. The results showed that citric acid-activated chlorine dioxide at the appropriate concentration can be applied to remove U. prolifera from Neopyropia cultivation rafts. Because U. prolifera and its micropropagules died in the 250 mg/L chlorine dioxide group, we recommend that the appropriate concentration of chlorine dioxide for removing green macroalgae is ≥250 mg/L. Our results provide a scientific basis for convenient collection of accurate data for the U. prolifera prevention trial organized by the Ministry of Natural Resources of the People's Republic of China. • Providing a new chemical control method on Ulva prolifera. • The experiment was carried out using a mixed solution of citric acid and chlorine dioxide. • Micropropagules were taken into consideration during the process of killing macroalgae. [ABSTRACT FROM AUTHOR]

The green tides outbreak events seriously threaten the ecological balance of the coastal areas. Quickly and accurately obtaining the spatial distribution and drift state of green tides is key to early warning. Based on Landsat 8 (L8) and Sentinel-2 (S2) image pair, the green tides drift velocity was extracted using the maximum cross-correlation (MCC) method, and windage was calculated by combining ocean current and wind data. The results of the MCC method were validated. Ulva's drift in the Yellow Sea is shaped by both ocean currents and wind, closely aligning with the direction of the currents. Notably, the northward drift velocity of Ulva exhibits a clear boundary around 34°40′N. Windage shows similar characteristics with the Ulva drift velocity, as its values vary with time and space. This study will enhance our comprehension of the dynamic mechanism of green tides drift. • Automated extraction of Ulva drift velocity from medium-resolution imagery pair • The northward drift velocity of Ulva exhibits a distinct boundary around 34°40′N. • Ulva's drift in the Yellow Sea is shaped by both ocean currents and wind. [ABSTRACT FROM AUTHOR]

For 17 consecutive years, the outbreak of Ulva prolifera in the South Yellow Sea area of China has caused significant negative impacts on coastal ecological environment. However, its specific influence on fish immunity is rare. In this study, the juvenile Paralichthys olivaceus was exposed to fresh U. prolifera algae (FU) and decomposing algal effluent (DU). After short-term stress for 14 days, the histopathological and transcriptome analysis were performed to study the effect of U. prolifera decay on P. olivaceus. Histopathological analysis found that the liver, spleen and head kidneys of P. olivaceus were damaged after the short-term stress. The transcriptome results showed that the steroid biosynthesis signaling pathway and the PI3K-Akt signaling pathway were significantly enriched. Some immune related genes, including c1qc-like , dusp1 , dusp16 , HSP90 and metabolic related genes serotransferrin , were differentially expressed. These results highlighted the harmfulness of U. prolifera on marine fish, setting a solid foundation for further analyses. • Some immune and metabolic pathways of juvenile P. olivaceus was affected by the degradation of U. prolifera. • Weighted gene co-expression network analysis identified 63 core genes of P. olivaceus responding to U. prolifera. • The liver, spleen and head kidney of P. olivaceus were damaged with U. prolifera stress. [ABSTRACT FROM AUTHOR]

The new velocity fields based on the Generalized Ekman (GE) theory to trace floating algae were derived and verified by drifter observations and compared to reanalysis datasets in the Yellow Sea (YS). Two velocity fields using diagnostic approaches and two velocity fields from reanalysis datasets were examined. The results revealed that the diagnostic velocity fields had comparable accuracy to the reanalysis datasets, even locally better. Then, we applied each velocity field to trace green algae, Ulva prolifera, in July 2011 and brown algae, Sargassum horneri, in May 2017 using particle tracking experiments. In addition, drifter trajectories were simulated, and error accumulation speed was estimated for each velocity field. Simulation results using the diagnostic velocity fields consistently showed better agreement with satellite images and in situ observations than those using reanalysis datasets, demonstrating that the diagnostic velocity could be a superior tool for simulating surface-floating substances and organisms. The approach to derive diagnostic velocity fields can be easily applied instead of relying on heavy computing numerical models., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

We investigated the space-time dynamics of N pollution in a Mediterranean gulf (Gulf of Gaeta) by means of δ 15 N variation in seaweed fronds ( Ulva lactuca ) previously collected from an unpolluted habitat. We used a comprehensive deployment grid that enabled the generation of isotopic seascapes (isoseascapes) describing the topography of N pollution in coastal waters and identifying N input hotspots and their pathways of dispersion at sea. The δ 15 N values of U. lactuca increased during 48 h of exposure to the gulf waters, indicating anthropogenic N inputs from wastewater-derived sources. Comparison of the isoseascapes between two years differing in terms of rainfall identified coastal and offshore areas that were vulnerable to freshwater-transported nutrients, consistent with terrestrial hydromorphology and sea surface-water circulation. Isoseacapes were robust enough to reduce deployment effort, representing a powerful tool for monitoring and management strategies and useful for Environmental Protection Agencies, the main target audience of applied ecological research. [ABSTRACT FROM AUTHOR]

In order to evaluate the effect of the large-scale green tide on micro-propagule community in the coastal waters of Qingdao, a year-round survey was conducted to investigate the abundance and species succession of the green macroalgal micro-propagules. Five Ulva and one Blidingia species were detected and an evident shift on species composition was observed in summer when the large-scale floating biomass of Ulva prolifera approached the coasts of Qingdao. Propagules of U. prolifera were only dominant in summer. Detection of the ‘floating’ type of U. prolifera in summer, a unique strain responsible for the green tide in Yellow Sea, supported that large-scale floating U. prolifera biomass could affect local micro-propagule community. There were, however, no ‘floating’ U. prolifera propagules were detected in the following winter, indicating that influence from the large-scale green tide was transient, and it has not leave prolonged seeds in Qingdao coastal waters. [ABSTRACT FROM AUTHOR]

The multiple-contamination of heavy metals and nutrients worsens increasingly and Ulva sp . green tide occurs almost simultaneously. To reveal the biological mechanism for outbreak of the green tide, Ulva pertusa was exposed to seven-day-multiple-contamination. The relation between pH variation ( V pH ), Chl a content, ratio of ( Chl a content)/( Chl b content) ( R chla / chlb ), SOD activity of U. pertusa ( A SOD ) and contamination concentration is V pH = 1.72 ± 0.38 + 1.68 ± 0.72 × 10 − 4 × C ammonia 2 (p < 0.05), C chla = 0.88 ± 0.09 − 0.01 ± 0.00 × C Cd (p < 0.05), R chla / chlb = 0.72 ± 0.04 − 0.35 ± 0.08 × 10 − 4 × C Cd 2 (p < 0.05), and A SOD = 25.64 ± 2.35 − 0.41 ± 0.09 × 10 − 2 × C Zn 2 + 0.54 ± 0.10 × C Zn (p < 0.05), respectively. C ammonia , C Cd and C Zn is concentration of ammonia, Cd 2 + and Zn 2 + , respectively. Comparing the contamination concentrations of seawaters where Ulva sp. green tide occurred and the contamination concentrations set in the present work, U. pertusa can adapt to multiple-contaminations in these waters. Thus, the adaption to multiple-contamination may be one biological mechanism for the outbreak of Ulva sp . green tide. [ABSTRACT FROM AUTHOR]

Release and microbial degradation of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) from the macroalgae Ulva prolifera were studied in laboratory incubation experiments. The release of DOM and CDOM from Ulva prolifera was a rapid process, and hydrolysis played an important role in the initial leaching of the organic compounds from the algae. Bacterial activity enhanced the release of DOM and CDOM during degradation of the algae and utilization of the released organic compounds. It is calculated that 43 ± 2% of the C and 63 ± 3% of the N from Ulva prolifera 's biomass were released during the 20-day incubation, and 65 ± 3% of the released C and 87 ± 4% of the released N were utilized by bacteria. In comparison, only 18 ± 1% of the algae's C and 17 ± 1% of its N were released when bacterial activities were inhibited. The fluorescence characteristics of the CDOM indicate that protein-like DOM was the major organic component released from Ulva prolifera that was highly labile and biodegradable. Bacteria played an important role in regulating the chemical composition and fluorescence characteristics of the DOM. Our study suggests that the release of DOM from Ulva prolifera provides not only major sources of organic C and N, but also important food sources to microbial communities in coastal waters. [ABSTRACT FROM AUTHOR]

Seaweeds have become an important asset in several sectors, including the food and feed industries, cosmetics, and pharmaceuticals, among others. Whether harvested or reared, interest in algae has been growing worldwide due to the resources they offer, including proteins, vitamins, minerals, carbohydrates, essential fatty acids, and dietary fiber, as well as sources of biologically active compounds. However, given their morphology and physiology, as well as their harvest and cultivation environments, algae are prone to the presence of hazards, including pharmaceuticals taken up from the water. Thus, to ensure human and animal safety as well as environmental health, monitoring is essential. Therefore, this work describes the development and validation of a sensitive screening and confirmatory analytical method based on ultra-high-performance liquid chromatography coupled with time-of-flight mass spectrometry (UHPLC-ToF-MS). This multi-residue method enables the determination of 62 pharmaceuticals distributed between 8 therapeutic classes and was fully validated according to Commission Implementing Regulation (EU) 2021/808. [Display omitted] • The green seaweed Ulva lactuca is an important commodity for several industries. • UHPLC-ToF-MS method developed for 62 pharmaceuticals under 8 therapeutic classes • Fully validated according to Commission Implementing Regulation (EU) 2021/808 • Possibility of revisiting the results in search for different analytes [ABSTRACT FROM AUTHOR]

To better understand the green tide phenomenon impacting French coastline and give guidance to stakeholders to elaborate effective mitigation plan, an extensive survey has been deployed on Brittany hot spots. Based on 18 years monitoring database, the objectives of this work were to investigate the inter-and-intra annual evolutions of Ulva beaching, and to assess the parameters driving green tide annual renewal. The yearly cumulated area of Ulva mat on the Brittany coast averaged 2,42 ± 0,84 ha, of which 55 ± 12 % % was reported within Saint Brieuc-Binic Bay, with a maximal beaching generally observed in July. The renewal of green tide at spring time seems to be correlated with the Ulva bloom from the previous autumn period, particularly in bays with low exposure to swell. The residual stock, defined as Ulva fragments maintained in healthy conditions during the winter season, appears as highly dependent on nitrogen summer flows. • The yearly cumulated area of Ulva mat on the Brittany coast averaged 2,4 ± 0,8 ha. • More than half of Ulva beaching occurred at Saint Brieuc-Binic Bay. • Green tide renewal is tighly linked to the residual algal stock of the last year. • Large nitrate fluxes at the end of summer could promote the renewal of green tides. • The evolution of green tides will be driven by the future mitigation strategies. [ABSTRACT FROM AUTHOR]

Previous studies suggested that the removal of Ulva microscopic propagules (UMP) from cradle water might restrict the formation and expansion of green tides in the Yellow Sea, China. In this study, the distribution characteristics of UMP in the southern Yellow Sea was investigated, and then a flocculation experiment of UMP using modified clay (MC) was conducted at a selected station of the research cruise. The results indicated that the distribution of green algae thalli is one of the main factors that directly influence UMP distribution. UMP density was strongly negatively correlated with the distance between the sampling station and the centre of the area containing floating Ulva (r = − 0.618***, n = 83). > 80% of the UMP was removed from the water column after MC application at a concentration of 0.1 g/L, and MC applied at a concentration of 0.5 g/L reduced the germination rate to 0.3%. [ABSTRACT FROM AUTHOR]

In La Paz Bay conspicuous macroalgal blooms of Ulva spp. are recurrent in the waterfront of the city; studies relate its growth to seasonality and nutrient enrichment but their relative influence is not known. We use the δ 15 N to discern amongst nitrogen sources at three sites with different substratum and anthropogenic activities. Ulva blooms were monitored monthly at San Juan de la Costa (SJC), Casa del Marino (CM) and El Tecolote (TE). Species presence varied between sites and months. At SJC Ulva displayed the highest signal of δ 15 N associated with fishing products and local mining wastewaters (19.5‰). CM showed isotopic values related to sewage waters (13‰). The δ 15 N of species at TE were the lowest. We found higher isotopic signatures than in other tropical/subtropical regions, associated with nutrient rich water masses. Ulva species can be used to trace and discern amongst different sources of nitrogen from natural or anthropogenic sources. [ABSTRACT FROM AUTHOR]

The large-scale green tides have been prevailing in the Yellow Sea over a decade. Prevention and control techniques in the source region (Subei Shoal) are urgently needed to minimize its adverse ecological and social impacts. Drifting and spreading mechanism of Ulva mass was investigated in the Subei Shoal in order to develop the early containment measures. The multidisciplinary surveys suggested twelve major waterways transporting the initial Ulva mass which was closely related to the basin topology and water circulation in the shoal. The epiphytic algal mass from the northern and eastern raft regions contributed 82.7 % of the initial floating biomass, and moved out in 4–6 days with an average drifting velocity of 0.28 m s−1. Accordingly, two series of algae-blocking lines were proposed to remove floating mass from the shoal. And the primary field trial in 2018 confirmed the feasibility of this strategy to abate the green tides. • The floating Ulva was transported out of Subei Shoal through 12 major waterways, especially the northern and eastern five. • The movement of initial floating Ulva mass was influenced by the basin topology and accumulated along the sand grooves. • The biomass flux in each waterway was linearly correlated with the source epiphytic Ulva algae from the aquaculture rafts. • Two series of blocking lines were proposed to remove the initial floating mass and mitigate the green tides. [ABSTRACT FROM AUTHOR]

To determine the driving mechanisms between submarine groundwater discharge (SGD) and massive blooms of the green alga Ulva , we examined the magnitude of SGD and SGD-derived nutrient fluxes from November 2019 to July 2020 in Ihotewoo (north) and Bangdu (east) bays, Jeju Island, Korea. The variability of SGD flux at both the sites, where the hydraulic gradient is low, closely followed the daily variability of the tidal range, indicating that SGD flux is primarily driven by tidal pumping. Although the average annual SGD-driven nutrient fluxes were 24–37 % lower in Bangdu Bay than in Ihotewoo Bay, massive Ulva blooms only occurred in Bangdu Bay. A longer residence time (poor water exchange) and continuous SGD input with high dissolved inorganic nitrogen play a significant role in the growth and extentsion of Ulva blooms. • Submarine groundwater discharge (SGD) flux is primarily driven by tidal pumping. • SGD-driven nutrient fluxes are relatively lower in Bangdu Bay than in Ihotewoo Bay. • Poor water exchange and SGD-driven DIN load are important for green tide blooms. [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]

Metal pollution in the marine coastal environment is an important topical issue. In this study, the water quality in five locations along the Alexandria coast (Eastern Harbor, El-Tabia pumping station, El Mex Bay, Sidi Bishir, and Abu Talat) was assessed by measuring physicochemical parameters from water samples. Depending on the morphological classification of macroalgae, the collected morphotypes were related to Ulva fasciata, Ulva compressa, Corallina officinalis, Corallina elongata, and Petrocladia capillaceae. Corallina officinalis and Corallina elongata demonstrated a high capacity for Cd, Pb, and Ni accumulation, and the highest values of Fe, Cu, and Mn were reported in Ulva fasciata and Ulva compressa. Two standard markers were applied, and results showed that the morphological classification matched the molecular data. Moreover, the analysis of algae can only reflect the accumulation of metals. The conclusion is that Ulva compressa and Corallina officinalis are potentially suitable indicators of localized short-term heavy metal pollution., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Green tides attack the Yellow Sea every year since 2007 and have caused substantial financial loss. Based on Haiyang-1C/Coastal zone imager (HY-1C/CZI) and Terra/MODIS satellite images, the temporal and spatial distribution of green tides floating in the Yellow Sea during 2019 was extracted. The relationships between the growth rate of the green tides and the environmental factors including sea surface temperature (SST), photosynthetically active radiation (PAR), sea surface salinity (SSS), nitrate and phosphate during the green tides' dissipation phase has been detected. Based on the maximum likelihood estimation, a regression model that includes SST, PAR and phosphate was recommended to predict the growth rate of the green tides in the dissipation phase (R 2  = 0.63), and this model was also examined using Bayesian information criterion and Akaike information criterion. When the average SST in the study area was above 23.6 °C, the coverage of green tides began to decrease with the increase in temperature under the influence of PAR. The growth rate of the green tides was related to SST (R = -0.38), PAR (R = -0.67) and phosphate (R = 0.40) in the dissipation phase. Compared with HY-1C/CZI, the green tide area extracted using Terra/MODIS tended to be underestimated when the green tide patches were smaller than 11.2 km 2 . Otherwise, the lower spatial resolution of MODIS resulted in larger mixed pixels of water and algae, which would overestimate the total area of the green tides., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The effects of blooms of opportunistic green macroalgae, Ulva prolifera , on the trophic structure of the macrobenthic food web in a temperate intertidal zone on the western coast of Korea were evaluated using carbon and nitrogen stable isotopes. Biomasses of Ulva and microphytobenthos (MPB) increased significantly at the macroalgae-bloom and the non-bloom sites, respectively, from March to September 2011. The δ 13 C values of most the consumers were arrayed between those of MPB and Ulva at both sites, and differed according to feeding strategies at the macroalgae-bloom site. Seasonally increasing magnitudes in δ 13 C and δ 15 N values of consumers were much steeper at the macroalgae-bloom site than at the non-bloom site. Our findings provide evidence that blooming green macroalgae play a significant role as a basal resource supporting the intertidal macrobenthic food web and their significance varies with feeding strategies of consumers as well as the resource availability. [ABSTRACT FROM AUTHOR]

Annually recurrent green-tides in the Yellow Sea have been shown to result from direct disposal into the sea of fouling Ulva from Pyropia aquaculture. The role abiotic factors play in Ulva biomass accumulation on rafts was studied to find ways to mitigate this problem. Dissolved inorganic nitrogen (DIN) was very high at all sites, but the highest Ulva biomass was associated with the lowest DIN and anthropogenic N. Under luxuriant background nutrient conditions, variability in temperature and periods of emersion, rather than pH, light and salinity determined Ulva biomass. Two dominant species of Ulva displayed differing tolerances to temperature and desiccation which helped explain why Ulva prolifera dominates floating green-tides. Rather than trying to mitigate green-tides only by reducing nutrient pollution, an earlier harvest of Pyropia in southern Jiangsu Province especially before temperatures increase greatly above 10 °C during April, could reduce the biomass of U. prolifera disposed from rafts. [ABSTRACT FROM AUTHOR]

Stable isotope analyses of the abundant infaunal polychaete Hediste diversicolor , recognised as an indicator of sewage pollution, support the hypothesis that nutrient enrichment promotes surface deposit feeding, over suspension feeding and predation. At sewage-polluted sites in three estuaries in SE England Hediste mainly consumed microphytobenthos, sediment organic matter and filamentous macroalgae Ulva spp. At cleaner sites Hediste relied more on suspension feeding and consumption of Spartina anglica . There were no consistent differences in Hediste densities between the polluted and cleaner sites, probably because of increased densities at the cleaner sites too, facilitated by the planting of Spartina and nitrogen enrichment there too, including from agricultural run-off. Increased nutrient enrichment and the artificial availability of Spartina have probably increased densities of, and deposit-feeding by, Hediste in the past half-century and contributed indirectly to saltmarsh losses, since deposit-feeding by Hediste has been implicated in recent saltmarsh erosion in SE England. [ABSTRACT FROM AUTHOR]

Since 2007, Ulva macroalgal blooms have occurred along the coastal areas of the Yellow Sea, China. These blooms are dominated by fragments of Ulva prolifera in the early stages of development. The objectives of this study were to identify the primary mode of asexual reproduction for U. prolifera and to evaluate the contribution of these thalli fragments to the formation of blooms. Four different growth and reproductive strategies of U. prolifera segments were found including: 1) tubular diameter becoming larger; 2) formation of new branches; 3) release of zoids; and 4) polarized growth. This is the first report showing the development of numerous blade-lets from a single segment, which is remarkably different from previous studies on other Ulva species. The results in the present study provide critical information to understand how this species is able to support its explosive growth during a bloom. [ABSTRACT FROM AUTHOR]

Concentrations of 11 elements were quantified in five marine species from different trophic levels of a food web (algae, mussel, shrimp and fish), representative for shallow Senegalese coastal waters, and including species of commercial importance. Significant differences in element concentrations and bioaccumulation were demonstrated, revealing the utility of employing a suite of organisms as bioindicators to monitor metal contamination in coastal areas. There was no clear seasonal pattern in concentration of elements, however inter-site differences were observed. Calculations of transfer factors for all the studied elements showed that transfer factors from water were greater than those from sediments. For shrimp and mussel, the concentrations of Pb and Cd were below the EU's maximum level for human consumption, however high concentrations of arsenic in shrimp were recorded at all sites. [ABSTRACT FROM AUTHOR]

In Penn Cove, ulvoid green algal mats occur annually. To examine seasonal variation in their causes, nitrogen and carbon were measured in Ulva lactuca in May, July, and September and stable nitrogen and oxygen isotope ratios were quantified in U. lactuca , Penn Cove seawater, upwelled water from Saratoga Passage, water near the Skagit River outflow, and effluents from wastewater treatment facilities. Ulvoid growth was nitrogen limited and the sources of nitrogen used by the algae changed during the growing season. Algal nitrogen concentrations were 0.85–4.55% and were highest in September and at sites where algae were abundant. Upwelled waters were the primary nitrogen source for the algae, but anthropogenic sources also contributed to algal growth towards the end of the growing season. This study suggests that small nitrogen inputs can result in crossing a “tipping point”, causing the release of nutrient limitation and localized increases in algal growth. [ABSTRACT FROM AUTHOR]