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It has been 16 years since the world's largest Ulva bloom appeared in the Yellow Sea. However, it remains unclear how the floating Ulva prolifera developed into the immense green tide within two months especially considering that source control measures have been conducted since 2019. In this study, we investigated the growth mechanism of the floating population by examining the production and regeneration of U. prolifera explants and constructing a growth model. The results showed that U. prolifera explants exhibited rapid regeneration mainly through branches at 15, 20 and 25 °C. Algivore feeding and sporulation (at 20–25 °C) contributed to mass production of explants. The growth of floating population could be attributed to the coupling of mass production and rapid regeneration of explants through multiple cycles, which accounted for the outbreak of floating green tide. This finding presented a novel population growth model to elucidate macroalgal bloom occurrences. [Display omitted] • Polarity loss stimulated the growth of Ulva prolifera explants through uncontrolled branching. • Algivore feeding and sporulation contributed to the mass production of U. prolifera explants. • Mass production and rapid regeneration of explants contributed to green tide outbreak. [ABSTRACT FROM AUTHOR]

Over the past 18 years, green tides have persistently occurred in the Yellow Sea. Micropropagules of these algae are key to bloom formation, yet their species composition and succession during dissipation remain underexplored. During the dissipation process of accumulated green tide algae, a large number of micropropagules are released. This study monitored the dissipation of green tide algae at a coastal site, tracking micropropagules in water and sediment using an internal transcribed spacer (ITS) and 5S rDNA primers. Results showed that the dissipation lasted about one month, with significant micropropagule release. Initially, micropropagules matched 5S-II Ulva prolifera , but later species like Ulva torta , Ulva simplex , Ulva flexuosa , and Ulva meridionalis emerged. Ulva meridionalis dominated sediment in July and August, while U. torta was prevalent in water, and U. flexuosa was dominant in other months. Accumulated U. prolifera in the intertidal zone may not contribute to the seeding of the next year's bloom. This study sheds light on the dissipation process and succession patterns of micropropagules in coastal environments. [Display omitted] • Green macroalgae naturally dissipate in intertidal zones in about a month. • During green tide dissipation, many Ulva micropropagules are released. • Micropropule species in water and sediment differ slightly. • Accumulated Ulva prolifera in the intertidal zone may not seed the next year's bloom. [ABSTRACT FROM AUTHOR]

The world's largest green tide, caused by the nuisance green algae Ulva prolifera , has occurred in the southern Yellow Sea for 16 consecutive years. It is puzzling why the extensive floating green tide occurs exclusively in the southern Yellow Sea, rather than other waters. We speculate that the transition of U. prolifera from a sessile state to a surface-floating one is the underlying cause of the floating green tide. Here we founded that the floating of U. prolifera was attributed to detachment from substrata and appropriate desiccation. The convergence of unreasonable green algae disposal, geographical features and farming patterns of Porphyra (economic red algae) in Subei Shoal contributed to mass production of floating U. prolifera , resulting in the exclusive occurrence of the floating green tides. Inducing the natural inactivation of green algae to prevent the floating of U. prolifera may effectively mitigate the extensive Ulva bloom at zero cost. [Display omitted] • Desiccation significantly augmented the surface hydrophobicity of the thalli. • The floating of Ulva prolifera was attributed to detachment and desiccation. • The convergence of multiple factors contributed to mass production of floating U. prolifera. • Inducing the natural inactivation of green algae may mitigate the green tide at zero cost. [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]

Understanding the prolonged spatiotemporal evolution and identifying the underlying causes of Ulva prolifera green tides play pivotal roles in managing such occurrences, restoring water ecology, and fostering sustainable development in marine ecosystems. Satellite remote sensing represents the primary choice for monitoring Ulva prolifera green tides due to its capability for extensive, long-term ocean monitoring. Based on multi-source remote sensing images, ecological and environmental datasets, and machine learning algorithms, therefore, this study focused on "remote sensing modelling - evolution history - change trends - mechanism analysis" to elucidate both the remote sensing monitoring models and the underlying driving factors governing the spatiotemporal evolution of Ulva prolifera green tides in the highly impacted South Yellow Sea of China. With the use of GOCI Ⅰ/Ⅱ images, an hybrid remote sensing extraction model merging the robustness of the random forest (RF) model and the optical algae cloud index (ACI) was established to map Ulva prolifera distribution patterns. The ACI-RF method exhibited exceptional performance, with an F1 score surpassing 0.95, outperforming alternative methods such as the support vector machine (SVM) and K-nearest neighbour (KNN) methods. On the basis, we analysed the evolutionary trends and the driving factors determining these distribution patterns using meteorological data, runoff data, and data on various water quality parameters (SST, ocean current speed, wind speed, precipitation, DO, PAR, Si, NO 3 -, PO 4 3-and N/P). Over the period from 2011 to 2022, excluding 2021, there was a notable decline in the area of Ulva prolifera green tides, varying between 397 and 2689.9 km2, with an average annual reduction rate of 3%. The maximum annual biomass varied between 0.12 and 15.9 kt. Notably, more than 75% of the area of Ulva prolifera green tides exhibited northward drift, which was significantly influenced by northern currents and wind fields. The analysis of driving factors indicates that factors such as average sea surface temperature, eastward wind speed, northward wind speed, precipitation, PO 4 3- and N/P/Si significantly influence the biological growth rate of Ulva prolifera. Furthermore, coastal land use change and surface runoff, particularly surface runoff in June, significantly impacted the growth rate of Ulva prolifera, with Pearson correlation coefficients of 0.74 and 0.67, respectively. Against the background of global warming and severe deterioration in the marine environment, Ulva prolifera blooms persist. Consequently, two distinct management strategies were proposed based on the distribution patterns and cause analysis results for addressing Ulva prolifera green tides: establishing a continuous protection framework for rivers, lakes, and nearshore areas to mitigate pollutant inputs and implementing precise environmental monitoring measures in urban expansion areas and farmlands to combat overgrowth-induced green tides. This methodology could be applied in other regions affected by marine ecological disasters, and the criteria for selecting influencing factors offer a valuable reference for designing tailored and proactive measures aimed at controlling Ulva prolifera green tides. • A hybrid model of random forest and Algae Cloud Index(ACI) was developed to extract Ulva prolifera green tides. • The spatial-temporal evolutions of Ulva prolifera green tides in the South Yellow Sea from 2011 to 2022 were analyzed. • The effects of 11 natural factors and 2 human factors on the blooms of Ulva prolifera green tides were analyszed. • Surface runoff in June, nutrient input, and land use changes are three major driving factors of Ulva prolifera green tides. [ABSTRACT FROM AUTHOR]

Photoperiod and temperature are two main factors in the growth of macroalgae, and changes in photoperiod and diurnal temperature difference exist in natural condition. In order to study the effects of photoperiod and diurnal temperature difference on the growth of green algae Ulva prolifera , we cultured this species under three light/dark cycles (light: dark = 10:14, 12:12 and 16:08) with constant (22 °C for light and dark period, noted as 22-22 °C) and diurnal temperature difference (22 °C and 16 °C for light and dark period, respectively, noted as 22-16 °C) conditions. The results showed that: 1) Compared with 10:14 light/dark cycle, the growth of U. prolifera under 12:12 light/dark cycle was significantly enhanced by 39% and 16% for 22-22 °C and 22-16 °C treatments, respectively, while the increase proportion decreased when the daylength increase from 12 h to 16 h. 2) The enhancement in growth induced by diurnal temperature difference was observed under 10:14 light/dark cycle, but not for 12:12 and 16:08 light/dark cycle treatments. 3) The Chl a content and photosynthetic rate increased under short light period and 22-22 °C conditions, while under 22-16 °C conditions, higher photosynthetic rate was observed under 12:12 light/dark cycle and no significant difference in Chl a content was observed. 4) Under 22-22 °C conditions, compared with 10:14 (L:D) treatment, the expression levels of proteins in light-harvesting complexes, PSII and carbon fixation were down regulated, while the photorespiration and pentose phosphate pathway (PPP) were up regulated by 16:08 light dark cycle. Then we speculate that the higher photosynthetic rate may be one compensation mechanism in short photoperiod, and under long light period condition the up regulations of photorespiration and PPP can be in charge of the decrease in enhancement growth induced by longer daylength. • The growth of U. prolifera was enhanced by diurnal temperature difference under short daylength, but not for long daylength. • With the increase of daylength, the growth of U. prolifera increased, but the proportion of this enhancement decreased. • The photosynthetic rate increased under short light period. • The photorespiration and pentose phosphate pathway (PPP) were up regulated by longer daylength. [ABSTRACT FROM AUTHOR]

To aid early warning and prevent the outbreak of green tides in the Yellow Sea, both the growth and photosynthetic performance of Ulva prolifera were studied after culture in different temperatures (18, 22, and 26 °C) and light intensities (44, 160, and 280 μmol m −2 ·s −1 ). Furthermore, their instantaneous net photosynthetic performance (INPP) was studied to determine the resulting environmental acclimation. The relative growth rates of U. prolifera significantly decreased in response to increasing temperature, while they increased with increasing light intensity. Culture at higher light intensities significantly increased INPP, while higher temperatures decreased the INPP. Culture at lower temperatures lowered INPP, while increased growth temperature increased the effect. These results suggest that high temperatures during the cold season inhibited U. prolifera growth. However, low temperatures during the warm season increase biomass and may cause a large-scale green tide. These results help to understand the correlation between U. prolifera blooms and extreme weather. [ABSTRACT FROM AUTHOR]

Large numbers of Amphipoda feed on floating green tide macroalgae in the Yellow Sea, among which Ampithoe valida has a high abundance in the stable and decline periods. Amphipoda preferentially feed on Ulva. Under different temperatures, salinities, and pH, the physiological responses of A. valida and its feeding potential on Ulva prolifera were investigated, along with its physiological responses during green tide blooms in the Southern Yellow Sea. Ampithoe valida could survive within a temperature range of 5–30 °C, salinity of 5–40, and pH of 4–10. Optimal environmental conditions for growth were temperature 15–25 °C, salinity 10–40, and pH 6–10. At temperatures of 5–30 °C, salinities of 5–35, and pH of 4–9, A. valida could effectively reduce U. prolifera biomass. The feeding ability of A. valida was greatest in 25–30 °C, 10–25 salinity, and neutral seawater, exceeding 5 mg·ind.−1·d−1. During green tide outbreaks in the Southern Yellow Sea from May to August, the monthly average sea surface temperature, salinity, and pH range is 17.5–27.3 °C, 23.8–29.6, and 7.87–8.17, respectively, within which A. valida showed well growth and could effectively reduce U. prolifera biomass. Finally, this study further discussed the possibility of A. valida as a biological method to control green tide. • Optimal environmental factors for growth of Ampithoe valida were temperature 15–25 °C, salinity 10–40, and pH 6–10. • A. valida had a stronger feeding ability (>5 mg·ind.−1·d−1) at temperature 25–30 °C, salinity 10–25, and neutral pH. • The potential of A. valida used for the biological control of green tides in the Southern Yellow Sea is discussed. [ABSTRACT FROM AUTHOR]

Many studies have documented the responses of Ulva prolifera to environmental factors. However, the diurnal temperature differences and interactive effects of eutrophication are usually ignored. In this study, we selected U. prolifera as material to examine the effects of diurnal temperature on growth, photosynthesis and primary metabolites under two nitrogen levels. We cultured U. prolifera seedlings under two temperature conditions (22-22 °C: 22 °C during day and night; 22-18 °C: 22 °C during day and 18 °C at night) and two nitrogen levels (LN: 0.1235 mg L−1; HN: and 0.6 mg L−1). The results showed that 1) HN-grown thalli had higher growth rates, the chlorophyll a (Chl a) content, photosynthesis, superoxide dismutase (SOD) activity, soluble sugar, and protein contents under the two temperature conditions; 2) The growth of thalli was enhanced by 22–18 °C condition compared with 22-22 °C, but the increase was only significant under HN condition; 3) 22-18°C-grown thalli had a lower net photosynthetic rate, maximal quantum yield (F v /F m), and dark respiration rate (R d) than those grown at 22-22 °C; 4) No significant effects of diurnal temperature difference were detected on the SOD activity and soluble sugar content under LN and HN conditions, while the soluble protein content was enhanced by 22–18 °C under LN condition; 5) The nitrogen affected metabolite variations in U. prolifera more significantly than the diurnal temperature difference. The metabolite levels in the tricarboxylic acid cycle, amino acid, phospholipids, pyrimidine, and purine metabolism pathways increased under HN condition. The levels of glutamine, γ-aminobutyrate (GABA), 1-aminocyclopropane-1-carboxylate (ACC), glutamic acid, citrulline, glucose, sucrose, stachyose, and maltotriose were enhanced by 22–18 °C, especially under HN condition. These results identify the potential role of the diurnal temperature difference and offer new insight into the molecular mechanisms for U. prolifera responses to eutrophication and temperature. • The combined effects of diurnal temperature difference and eutrophication on Ulva prolifera were investigated. • Both diurnal temperature difference and high nitrogen enhanced the growth. • The reasons for the growth enhancement by the diurnal temperature may not be because of photosynthesis. • Positive correlation between RGR and most amino acids. [ABSTRACT FROM AUTHOR]

The annual outbreak of green tides since 2007 has destroyed coastal waters' ecological environment and caused substantial economic losses. Ulva prolifera , known as the dominant species of green tides, is influenced by temperatures. Omics-based technology was used to analyze U. prolifera under 12 h of treatment at 30 °C in the work. High temperature has the following advantages, e.g., activating the abscisic acid signaling pathway, improving the heat tolerance of U. prolifera , up-regulating metabolites such as glycolipids, glyceroyl, and glutamic acid to maintain the stability and fluidity of cells, and reducing the stimulatory effect of external stress on cells. The key genes and proteins of the tricarboxylic acid cycle, glycolysis, and pentose phosphorylation pathways were inhibited; however, the key enzyme pyruvate phospho-dikinase of the C4 pathway was up-regulated. The C4 pathway was activated in U. prolifera in response to high-temperature stress and may play a key role in photosynthesis. Besides, U. prolifera metabolizing amino acids was active. High temperature inhibited genes and proteins related to DNA replication and cell cycle in the transcriptome and proteome as well as the growth and reproduction of U. prolifera. • Analyzed the response mechanism of Ulva prolifera by omics. • The C4 pathway was activated in response to high-temperature stress and may play a key role in photosynthesis. • Molecules related to DNA replication, cell cycle, growth and reproduction was inhibited. [ABSTRACT FROM AUTHOR]

Large-scale outbreaks of green tides in the Yellow Sea affect the development of local tourism and aquaculture and significantly damage the coastal ecological environment. To study the distribution characteristics of green tides and to explore their impact on the environment, a coupled physical-ecological model (LTRANS-GT) based on the Lagrangian TRANSport model (LTRANS) was constructed in this paper to simulate the growth and dissipation process of Ulva prolifera and to obtain its drift trajectory and biomass. The results show that the tracks of the green tide are mainly divided into three categories, namely, northwestward, northward, and eastward. The green tide biomass showed a single-peak with seasonal variation in most years (entering a rapid proliferation period in May–June, reaching a peak biomass after developing for approximately 30 days, then dying out rapidly and basically disappearing by August), and showed a double-peak only in a few years due to extreme weather effects. In 2017, the biomass of U. prolifera was the lowest, with a maximum wet weight of only 24600 tons, while the largest biomass occurred in 2013, with a maximum wet weight of more than 560,000 tons. The interannual difference in the biomass of U. prolifera was mainly due to its initial biomass and the difference in nutrient concentration in the area where it was located. The year in which U. prolifera absorbed the most dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) was 2013, with absorption values of 3973 tons and 114 tons, respectively; and the year in which U. prolifera absorbed the least DIN and DIP was 2017, with absorption values of 172 tons and 5 tons, respectively. During the period of U. prolifera outbreak, the consumption of DIN and DIP in the sea area where it occurred accounted for approximately 43.65% and 0.6% of the total discharge of the rivers, and 26.86% and 6.1% of the atmospheric deposition, respectively. The impact of green tide outbreaks on the annual nitrogen and phosphorus nutrient budget of the entire Yellow Sea was relatively small, but the impact on the area where U. prolifera grows and decays can not be ignored. In dissipation period, the decay of U. prolifera may make DON and DOP double near Shandong coast. • A coupled physical-ecological model (LTRANS-GT) was constructed to simulate the growth and dissipation process of Ulva prolifera. • In several years, the short-term extreme weather were the main reasons for the double-peak distribution in green tide biomass. • The impact of green tide outbreaks on the nutrient budget of the entire Yellow Sea is small, but the impact on the sea area where U. prolifera occurs cannot be ignored. [ABSTRACT FROM AUTHOR]

To understand how seasonal factors could drive the formation of green tide blooms and their flotation and decay, we cultured the green tide algal species Ulva prolifera at various temperatures (5, 10, 15, 20, 25, 30, and 35 °C) and light intensities (40, 80, 140, 240, and 400 μmol photons m−2 s−1). The results showed that the ratio of floating U. prolifera increased with increasing light and temperature, which was accompanied by morphological changes. The net photosynthetic rate and the proportion of floating U. prolifera thalli showed a nonlinear relationship. Furthermore, an enclosure experiment confirmed that the flotation of U. prolifera was influenced by light intensity via the regulation of photosynthesis of the thalli. These results suggest that seasonal factors control the photosynthesis of U. prolifera , which drives the flotation and decay of green tide algae in the Yellow Sea. • Seasonal temperature and light changes drove green tide algae flotation and decay. • Increasingly adaptive temperature and light resulted in the formation of air sacs. • Supra-optimal temperature resulted in the settlement of Ulva prolifera. [ABSTRACT FROM AUTHOR]

In aquatic systems under eutrophic conditions, remobilization of metals from sediment to the overlying water may occur. Consequently, adaptive responses of local organisms could result from the accumulation of metals intermittently released from the sediment. In summer 2007, a field transplantation experiment was performed in the Óbidos lagoon (Portugal) with Ulva spp. comprising three short-term exposures (between 15:30–23:30; 23:30–07:30; 07:30–15:30) during a 24-h period. In each period, Ulva spp. was collected at a reference site located in the lower lagoon (LL) and transplanted to a eutrophic site located at the Barrosa branch (BB), characterized by moderate metal contamination. For comparison purposes, macroalgae samples were simultaneously exposed at LL under the same conditions. Both sites were surveyed in short-time scales (2–4 h) for the analysis of the variability of physical–chemical parameters in the water and metal levels in suspended particulate matter. The ratios to Al of particulate Mn, Fe, Cu and Pb increased during the period of lower water oxygenation at the eutrophic site, reaching 751 × 10−4, 0.67, 12 × 10−4, 9.9 × 10−4, respectively, confirming the release of metals from the sediment to water during the night. At the reference site, dissolved oxygen oscillated around 100%, Mn/Al ratios were considerably lower (81 × 10−4–301 × 10−4) compared to BB (234 × 10− 4–790 × 10−4), and no increases of metal/Al ratios were found during the night. In general, algae uptake of Mn, Cu, Fe, Pb and Cd was significantly higher at the eutrophic site compared to the reference site. The results confirmed the potential of Ulva spp. as bioindicator of metal contamination and its capability to respond within short periods. An induction of SOD, an inhibition of CAT and the increase of LPO were recorded in Ulva spp. exposed at BB (between 23:30 and 7:30) probably as a response to the higher incorporation of Mn, Fe and Pb in combination with the lack of dissolved oxygen in the water. Current findings emphasize the importance of assessing, in eutrophic systems, the relationship between the variability of chemical conditions and its repercussions on autochthonous organisms over day–night cycles. [ABSTRACT FROM AUTHOR]

Abstract: Since 2007, the world's largest macroalgal blooms have occurred along the coastal area of the Yellow Sea for 6 consecutive years. In 2012, shipboard surveying and satellite remote sensing were used to monitor the whole blooming process. The blooms originated in Rudong sea area of the South Yellow Sea where bloom patches were of dark green and filamentous thalli were the dominant morphology. The scale of the blooms reached its peak size in Rizhao sea area of the North Yellow Sea, and decreased promptly and became insignificant in Qingdao coast where the blooms turned yellow, mostly with air sac blades. Meanwhile, vegetative cells of the green tide algae changed into cytocysts gradually from which germ cells were released as the blooms drifted northward. Additionally, chlorophyll contents and fluorescence activity of free-floating thalli in the North Yellow Sea were both significantly lower than that in the South Yellow Sea. Those studies presented here contributed to increasing our understanding about how the green tide declined gradually in the North Yellow Sea. [Copyright &y& Elsevier]

Abstract: In 2008, Qingdao (36°06′N, 120°25′E, PR China) experienced the world largest drifting macroalgal bloom composed of the filamentous macroalga Ulva prolifera. No convincing biologic evidence regarding the algal source is available so far. A series of field collections of both Ulva sp. and waters in various sites along Jiangsu coasts were conducted in March to May of 2009. Density of microscopic Ulva germlings in the waters sampled from different sites ranged from 7 to 3140 individuals L−1, indicating the wide-spreading and long-term existence of the algae in the investigated region. Morphological and the nuclear ribosomal internal transcribed spacer ITS nrDNA and the chloroplast-encoded rbcL gene comparisons of 26 algal samples revealed that the algae collected from land-based animal aquaculture ponds mostly resembled the dominating blooming alga in 2008. Mismatch of Porphyra farming period with the occurrence of the green tide bloom, as well as the negative identification results of the sampled green algae from the Porphyra rafts eliminated Porphyra rafts as the principal and original source of the dominating blooming alga. [Copyright &y& Elsevier]

The green tide disaster is the result of human activities changing the natural environment conditions. What changes have occurred in the environmental factors that affect the green tide outbreak over a long period, and what is the impact of this change on the green tide outbreak? To further understand the outbreak mechanism of green tide, in this study, we used the Google Earth Engine (GEE) platform to extract and analyze the green tide from 2007 to 2021, analyze the long-term trend of various influencing factors (sea surface temperature (SST), sea surface salinity (SSS), photosynthetically available radiation (PAR), precipitation, eutrophication, "nori" aquaculture) in the past 30 years, and explore the impact of each factor on the outbreak of green tide. We found that: 1) SST, seawater eutrophication, and "nori" aquaculture worked together to promote the large-scale outbreak of green tide in 2007; 2) In the context of eutrophication is not effectively controlled, elevated SST, SSS, and PAR will be more conducive to the germination of green tide algae and promote green tide to form a floating state on the sea surface earlier, after that, once there is a year with abundant precipitation, the green tide will break out on a large scale, which is exactly the case in 2021. Exploring the environmental conditions and the long-term regularity of green tide outbreaks to provide a basis for scientific and rational control of green tides., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Continuing global warming and intensification of human activities have substantially disturbed the balance of coastal marine ecosystems, potentially creating favorable conditions for algal blooms. Using serial remote sensing data and various national and provincial statistics, we investigated the spatial and temporal variations of the environmental driving forces for algal blooms in the Southern Yellow Sea between 2003 and 2017. The findings suggest that (1) Continual warming was observed in the Southern Yellow Sea. The study area evidenced more than three times the warming speed (0.41 °C/decade) of the global oceans (0.12 °C/decade) during the same period. There was an apparent warming zone in the region where macroalgal blooms tended to spread, with a heating of 1.0-1.5 °C (May-June). (2) Nutrient loadings have diverse patterns, characterized by fast-growing aquaculture activities and declining nutrients from land-based agriculture fertilizers and sewage discharge (based on published national and provincial statistics). (3) Growing expansion of algal blooms in the Southern Yellow Sea was confirmed by the relative increases in average May-June chlorophyll-a concentration of 46.7% and floating biomass area from 3.3% in 2003 to 13.4% in 2017. (4) While spatial correlation analysis showed a positive influence of the ocean surface temperature on chlorophyll-a, their relatively moderate (r = 0.40, p < 0.15) and declining correlations suggest that nutrient enrichment could be comparatively more influential on macroalgal blooms. Nutrient loading from the discharge of wastewater sourced from coastal aquaculture and organic residuals from land-sourcing sewage and industrial pollution, even though declining as reported, is still upholding a high level of nutrient enrichment in the study area. In addition, the fixed facilities for seaweed mariculture in the region provide vast breeding surfaces for algae. Consequently, the Southern Yellow Sea has become an ideal marine area for algal blooms., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Coastal regions are subjected to degradation due to anthropogenic pollution. Effluents loaded with variable concentrations of heavy metal, persistent organic pollutant, as well as nutrients are discharged in coastal areas leading to environmental degradation. In the past years, many scientists have studied, not only the effect of different contaminants on coastal ecosystems but also, they have searched for organisms tolerant to pollutants that can be used as bioindicators or for biomonitoring purposes. Furthermore, many researchers have demonstrated the capacity of different marine organisms to remove heavy metals and persistent organic pollutants, as well as to reduce nutrient concentration, which may lead to eutrophication. In this sense, Ulva lactuca, a green macroalgae commonly found in coastal areas, has been extensively studied for its capacity to accumulate pollutants; as a bioindicator; as well as for its remediation capacity. This paper aims to review the information published regarding the use of Ulva lactuca in environmental applications. The review was focused on those studies that analyse the role of this macroalga as a biomonitor or in bioremediation experiments. • Macroalgae-based technologies may be a viable option to reduce hazardous substances in waters. • Ulva lactuca can be used for environmental applications. • Ulva lactuca as biomonitor provides a time-integrated measure of nutrient in coastal waters. • Ulva lactuca can be applied in aquaculture systems as a biofilter. • Ulva lactuca can remove heavy metals and different organic pollutants from waters. [ABSTRACT FROM AUTHOR]

The toxicity of heavy metals to coastal organisms can be modulated by changes in pH due to progressive ocean acidification (OA). We investigated the combined impacts of copper and OA on different stages of the green macroalga Ulva linza , which is widely distributed in coastal waters, by growing the alga under the addition of Cu (control, 0.125 (medium, MCu), and 0.25 (high) μM, HCu) and elevated pCO 2 of 1,000 μatm, predicted in the context of global change. The relative growth rates decreased significantly in both juvenile and adult thalli at HCu under OA conditions. The net photosynthetic and respiration rates, as well as the relative electron transfer rates for the adult thalli, also decreased under the combined impacts of HCu and OA, although no significant changes in the contents of photosynthetic pigments were detected. Our results suggest that Cu and OA act synergistically to reduce the growth and photosynthetic performance of U. linza , potentially prolonging its life cycle. • Seawater acidification alleviated the toxicity of low Cu levels on Ulva linza. • Increased Cu concentration would exacerbate toxicity and inhibit the grown of thalli. • Two stages of U. linza have same responses to high CO 2 and Cu concentration. [ABSTRACT FROM AUTHOR]

Attempts to control marine invasive alien species (IAS) with native predators gained contrasting results, so far. To explore the feasibility of this approach to control the invasive marine alga Caulerpa cylindracea , we investigated the foraging behaviour of the sea urchin Paracentrotus lividus on three native macroalgae (Ulva sp., Penicillus capitatus and Cystoseira compressa) and on C. cylindracea. The consumption rate of C. cylindracea fresh biomass resulted larger than that of the other algae, when offered separately or in combination. C. cylindracea , however, was not the most attractive food item. The larger consumption rates of C. cylindracea can be explained by its specific caloric content (as assessed by its biochemical composition) that is lower than that of the other algae. Our results confirm that P. lividus can feed on C. cylindracea , but do not fully support its use to control C. cylindracea , unless in conditions where this alga is largely dominant because of other factors. • Caulerpa cylindracea is part of the sea urchin Paracentrotus lividus diet. • Its largest consumption rates depend upon its caloric content. • C. cylindracea is not the most attractive food item. • P. lividus could control C. cylindracea only where this alga is dominant. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) has been identified as a key physiological modulator and signaling molecule in animals and plants. However, due to its high reactivity, our knowledge of its production and consumption pathways in the ocean remain limited. Laboratory experiments showed that Ulva prolifera can produce NO, producing as much as 0.44 ± 0.04 nmol h−1 g−1. During the growth period, U. prolifera released NO, but during the decay period NO was absorbed by U. prolifera and bacteria. Furthermore, field investigations examined NO concentrations in the coastal waters of the Yellow Sea off Qingdao, where the U. prolifera green tide occurred in summer 2018. The average concentrations of NO in the surface seawater were 70.2 ± 38.2 pmol L−1 and 18.9 ± 10.3 pmol L−1 in the late- and after-bloom periods, respectively. NO release by U. prolifera was the primary contributor to the high NO concentrations during the late-bloom period. The study area was a net source of NO to the atmosphere during the study period, with average NO sea-air fluxes from the Qingdao coastal waters being 1.5 × 10−12 mol m−2 s−1 and 0.4 × 10−12 mol m−2 s−1 in the late- and after-bloom periods, respectively. This study concluded that the coastal waters of the Yellow Sea off Qingdao contributed more NO to the atmosphere during the bloom of U. prolifera than afterward. Image 1 • The growing U. prolifera could produce NO with the maximum rate of 0.44 nmol h−1 g−1. • The rate of NO release by U. prolifera was lower than the photoproduction rate. • NO concentration during the late-bloom was 2.7 times higher than after the bloom. • The study area acted as a source of NO to the air with a higher flux during a bloom. [ABSTRACT FROM AUTHOR]

Macroalgal blooms pose a threat to coastal ecosystems worldwide, especially in highly eutrophic environments. Excess nutrients often facilitate the proliferation of opportunistic algae, but in some systems grazing activity counterbalances its effects. I evaluated the regulating role of mesograzers associated with eelgrass (Zostera marina) in Elkhorn Slough, a eutrophic estuary where Ulva spp. blooms are frequent during the upwelling season. I monitored recruitment and transplant success of Ulva spp. along transects placed across the edge of the largest Z. marina bed. Changes in abundance of Ulva spp. on transplants differed spatially and seasonally, and were significantly correlated with density of both small and large invertebrate groups. Grazing affected not only adult Ulva spp. but also its early developmental stages, leading to decreased Ulva spp. abundance on transplants and minimal recruitment inside the Z. marina bed. Image 1 • Grazing is a major factor limiting the spread of Ulva to a temperate eelgrass bed. • Small and large mesograzers both regulate abundance of epiphytic Ulva. • Eelgrass mesograzers exert top-down control on early developmental stages of Ulva. • Eelgrass might indirectly suppress Ulva growth and expansion via recruitment of grazers. [ABSTRACT FROM AUTHOR]

The seagrass Cymodocea nodosa and the chlorophyte Ulva rigida growing in the upper sublittoral zones of the Mediterranean Sea are exposed to air during low tides. We compared the desiccation coefficient (k), and the photosynthetic performance (ΔF/Fm') of C. nodosa leaves with and without epiphytes to that of U. rigida. The recovery ability of these two species was assessed by ΔF/Fm', after re-immersion. The desiccation coefficient (k) significantly (p < 0.01) varied among the three macrophyte materials, while the lowest k values were measured both in C. nodosa leaves with epiphytes and U. rigida. ΔF/Fm' significantly declined with decreasing RWC for all materials, while significant differences in the physiological response were observed between U. rigida and the other two materials. Thallus pieces of U. rigida showed higher desiccation tolerance compared to C. nodosa leaves, with its ΔF/Fm' under 75% degree of dehydration reaching to its initial values thirty (30) minutes after re-immersion, when C. nodosa only reached the 50%. This study provides valuable information on possible changes in the two species distribution under different desiccation scenarios. • Desiccation had a severe effect on PSII for Cymodocea nodosa and Ulva rigida. • Only Ulva rigida showed ability for recovery of ΔF/Fm' after re-immersion. • Desiccation coefficient was lower when epiphytes were present in seagrass leaves. • Seagrass epiphytes decreased the desiccation coefficient. [ABSTRACT FROM AUTHOR]

Opportunistic green macroalgae blooms increasingly affect coastal areas worldwide. Understanding their impacts on organisms that use this zone, such as juvenile flatfish, is critical. By combining stable isotope data, digestive tract contents and community analyses of flatfish and their potential prey (benthic macroinvertebrates) from two North-East Atlantic sandy beaches (one impacted by blooms and one not), we detected similar and species-specific trophic changes among three co-occurring species (sand sole, plaice and turbot). Across flatfish species, juveniles displayed more opportunistic foraging behavior at the impacted site. Differently, plaice and sand sole relied more on the additional basal resource (Ulva spp.) than turbot. Finally, sand sole and turbot presented a stronger diet shift at the impacted site than plaice. We hypothesize that the species-specific response to the blooms are mostly driven by how the flatfish detect their prey (using visual and/or chemical cues) and when they forage (diurnal or nocturnal foraging)., 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 © 2019 Elsevier Ltd. All rights reserved.)

Recent evidence suggests macroalgal blooms may play a role in the worldwide decline in seagrass, but the shape of the functional relationship between seagrass health and dominant bloom-forming macroalgae is poorly characterized. We tested whether the impact of varying abundances of two cosmopolitan bloom-forming macroalgal genera caused linear/quasi-linear or sudden threshold changes in measures of eelgrass, Zostera marina, meadow health. We conducted two caging experiments in a shallow Z. marina bed (∼1 m depth) in Bodega Harbor, California, USA where we maintained six densities within the range of natural abundances of macroalgae, Ulva (0-4.0 kg m -2 ) and Gracilariopsis (0-2.0 kg m -2 ), as well as uncaged controls over a 10-week period. Shoot density, blade growth, and epiphyte load were measured every two weeks and algal treatments reset. We did not find support for threshold transitions between algal abundance and measures of seagrass bed health using sigmoidal and broken-stick regression analyses for each data set; these models are commonly used to identify threshold patterns in ecological shifts. Instead, final measurements of shoot density and epiphyte load were best modelled as linear or slightly non-linear declines with increasing Ulva abundance. A negative linear relationship also existed between shoot density and Gracilariopsis abundance and a trend towards linear negative effects on epiphyte load. The similar shape of these functional relationships across different types of algae suggests the relationship may be generalizable. At algal abundances that are commonly observed, we found smooth and predictable negative impacts to Z. marina by decline in shoot density and potential impacts to food webs by loss of epiphytes rather than sudden threshold shifts or "ecological surprises". Our work contrasts with the growing body of literature suggesting highly non-linear shifts in response to human impact; thus, it is important to broaden understanding of shifts to more than just pattern but to the processes that drive different patterns of shifts., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Coastal ecosystems are subjected to global and local environmental stressors, including increased atmospheric carbon dioxide (CO 2 ) (and subsequent ocean acidification) and nutrient loading. Here, we tested how two common macroalgal species in the Northwest Atlantic (Ulva spp. and Fucus vesiculosus Linneaus) respond to the combination of increased CO 2 and nutrient loading. We utilized two levels of pCO 2 with two levels of nutrients in a full factorial design, testing the growth rates and tissue quality of Ulva and Fucus grown for 21 days in monoculture and biculture. We found that the opportunistic, fast-growing Ulva exhibited increased growth rates under high pCO 2 and high nutrients, with growth rates increasing three-fold above Ulva grown in ambient pCO 2 and ambient nutrients. By contrast, Fucus growth rates were not impacted by either environmental factor. Both species exhibited a decline in carbon to nitrogen ratios (C:N) with elevated nutrients, but pCO 2 concentration did not alter tissue quality in either species. Species grown in biculture exhibited similar growth rates to those in monoculture conditions, but Fucus C:N increased significantly when grown with Ulva, indicating an effect of the presence of Ulva on Fucus. Our results suggest that the combination of ocean acidification and nutrients will enhance abundance of opportunistic algal species in coastal systems and will likely drive macroalgal community shifts, based on species-specific responses to future conditions., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Artificial reefs have been suggested as a tool for conservation and restoration of marine habitats. However, the relationships between coral reef habitats and man-made structures are poorly understood. We experimentally tested whether artificial reefs change grazing patterns in their surrounding environment. We exposed heaps of the macroalgae, Ulva lactuca, to natural grazing, at various distances from three artificial reefs. Results suggest that artificial reefs change grazing patterns in the neighboring area. In all the locations examined grazing was 2-3 times higher near the artificial reefs than in control sites (p < 0.05). We suggest that herbivorous fishes are attracted to the artificial reefs, creating a zone of increased grazing. Therefore, while planning deployment of such artificial reefs it is necessary to consider their overall influence on their natural surroundings, in order to maintain the natural community trophic dynamics.