Search Results (23)

Understanding macroalgal bloom development is crucial for managing eutrophication and protecting estuarine ecosystems. In this study, brown macroalgal blooms (i.e., golden tides) were identified in a potentially eutrophic temperate estuary (NW Ireland). Pylaiella littoralis (Phaeophyceae, Ectocarpales) was monitored at low tide over seven sampling occasions between June 2016 and August 2017. In situ biomass, tissue nutrients (nitrogen (N) and phosphorus (P)), and isotopic signature (δ¹⁵N contents) were measured, and relations with environmental drivers were explored. Difference Vegetation Index (NDVI) values from Sentinel-2 satellite imagery were used to assess the spatiotemporal dynamics of P. littoralis biomass (2016–2022). The results indicated that NDVI attributed to golden tides were lowest in 2022, during summer (coinciding with high temperatures and high rainfall) and at the lower shore on the right margin of an entering river. The highest tissue P content was recorded in April 2017, coinciding with in situ biomass peaks (spring–early summer), suggesting elevated P demand. Tissue N content (>2%) and N:P ratios (10–30) indicated occasional P limitation but no N limitation. δ¹⁵N data were very low and it was not possible to identify any primary N source. These findings highlight the importance of nutrient management in mitigating golden tides, addressing eutrophication, and preserving estuarine ecosystems. Full article

The invasion of the golden mussel has resulted in considerable environmental and socioeconomic alterations, which present a considerable threat to the native biodiversity and sustainability of the region. Understanding the distribution and biological characteristics of this Asian mussel, as well as its interaction with human activities, is of the utmost importance to developing effective strategies for mitigating and preventing its further spread. This study examines the dispersal route and incidence of golden mussels, tracing their movement from initial populations in Argentina to their arrival in the São Francisco River Basin (SFR). The presence of the mussel was confirmed through an integrative assessment that included shell taxonomic analyses and mitochondrial DNA signatures. This assessment identified populations located 7.5 km from the river’s mouth, close to the Atlantic Ocean, in areas such as shrimp farms, artisanal ports, and marinas. The analysis of mitochondrial DNA revealed the presence of South-American-specific and shared ancestral haplotypes in the SFR, Grande River, and Argentina. These findings indicate that intracontinental colonization toward the northeast region of South America originated from Asian populations that entered South America via Argentina. The absence of Asian-specific signatures in the SFR, combined with a geomorphological structure unsuitable for large ports or transoceanic vessels, supports the hypothesis of the intracontinental dispersal of Limnoperna fortunei. Full article

Harmful algal blooms (HABs) represent a significant global marine ecological disaster. In the Yellow Sea, green and golden tides often occur simultaneously or sequentially, suggesting that interspecific competition involves not only spatial and resource competition but also allelopathy. This study investigated the allelopathic interactions between Ulva prolifera and Sargassum horneri using physiological and biochemical parameters, including relative growth rate (RGR), cell ultrastructure, chlorophyll fluorescence, enzyme activity, and metabolomics analysis. The results showed that S. horneri filtrate significantly inhibited U. prolifera growth, while U. prolifera filtrate had no significant effect on S. horneri. Both algal filtrates caused cellular damage and affected photosynthesis, enzyme activities, and metabolism. However, their allelopathic responses differed: U. prolifera may rely on internal compensatory mechanisms, while S. horneri may depend on defense strategies. These findings provide insights into the dynamics of green and golden tides and support the scientific control of HABs through allelopathy. Full article

Macroalgal biomass blooms, including those causing the green and golden tides, have been rising along Chinese coasts, resulting in considerable social impacts and economic losses. To understand the links between the ongoing climate changes (ocean warming and acidification) and algal tide formation, the effects of temperature (20 and 24 °C), pCO₂ concentration (Partial Pressure of Carbon Dioxide, 410 ppm and 1000 ppm) and their interaction on the growth of Ulva prolifera and Ulva lactuca (green tide forming species), as well as Sargassum horneri (golden tide forming species) were investigated. The results indicate that the concurrent rises in temperature and pCO₂ level significantly boosted the growth and nutrient uptake rates of U. lactuca. For U. prolifera, the heightened growth and photosynthetic efficiency under higher CO₂ conditions are likely due to the increased availability of inorganic carbon. In contrast, S. horneri exhibited negligible responsiveness to the individual and combined effects of the increased temperature and CO₂ concentration. These outcomes indicate that the progressive climate changes, characterized by ocean warming and acidification, are likely to escalate the incidence of green tides caused by Ulva species, whereas they are not anticipated to precipitate golden tides. Full article

Massive accumulations of invasive brown algae Rugulopteryx okamurae are exacerbating environmental and socio-economic issues on the Mediterranean and potentially Atlantic coasts. These golden tides, likely intensified by global change processes such as changes in wind direction and intensity and rising temperatures, pose increasing challenges to coastal management. This study employs the Normalized Difference Vegetation Index (NDVI), with values above 0.08 from Level-2 Sentinel-2 imagery, to effectively monitor these strandings along the coastline of Los Lances beach (Tarifa, Spain) in the Strait of Gibraltar Natural Park from 2018 to 2022. Los Lances beach is one of the most affected by the R. okamurae bioinvasion in Spain. The analysis reveals that wind direction determines the spatial distribution of biomass accumulated on the shore. The highest average NDVI values in the western patch were observed with south-easterly winds, while in the eastern patch, higher average NDVI values were recorded with south-westerly, westerly and north-westerly winds. The maximum coverage correlates with elevated temperatures and minimal rainfall, peaking between July and October. Leveraging these insights, we propose a replicable methodology for the early detection and strategic pre-shore collection of biomass, which could facilitate efficient coastal cleanup strategies and enhance biomass utility for biotechnological applications. This approach promises cost-effective adaptability across different geographic areas impacted by golden tides. Full article

Sargassum horneri golden tides are increasingly becoming a marine ecological problem in the Yellow Sea (YS) and East China Sea. To understand the genetic relationship between the attached S. horneri along the China coast and the floating biomass in the YS, we used partial rbcL, ITS2, cox1, cox3, and cob-cox2 to analyze the population genetic evolution of 165 Sargassum samples. The results showed that all samples were a single species of S. horneri. Partial sequences of each gene had major haplotypes, and other haplotypes evolved from the occurrence of base mutations. The cob-cox2 gene haplotype research showed only the attached samples from ZJ, LN, and KR contained Hap3, and the distribution proportions of Hap2 and Hap4 in SS and the YS were closest to the distribution of the attached samples from SD. These novel findings provided information about the genetic evolutionary relationship between attached S. horneri along the coast of China and floating S. horneri in the YS, as well as new ideas for tracing the source of floating S. horneri in the YS from a molecular biological perspective. Full article

Converting Sargassum horneri (SH)—a harmful marine stranding that can cause golden tide—to highly porous bio-adsorbent material (via one-step catalytic oxidative pyrolysis with K₂FeO₄) can be a strategically useful method for obtaining low-cost materials suitable for CO₂ capture. In this manuscript, the behavior of different mass ratios of K₂FeO₄/SH precursor acting on the surface physicochemical properties of carbon materials are reported. The results suggest that specific surface area and total pore volume first increased to the mass ratio of K₂FeO₄/carbon precursor, then decreased. Among the samples prepared, the highest specific surface area was obtained with a K₂FeO₄/SH precursor ratio of 1:4 (25%-ASHC), and the CO₂ adsorption performance was significantly increased and faster compared with the original biochar. The fitted values of the three kinetic models showed that the double exponential model provided the best description of carbon adsorption, indicating both physical and chemical adsorption; 25%-ASHC also exhibited excellent cyclic stability. The improved CO₂ adsorption performance observed after K₂FeO₄ activation is mainly due to the increase in material porosity, specific surface area, and the enrichment of nitrogen and oxygen functional groups. Full article

Sargassum horneri, a prevalent species of brown algae found along the coast of the northwest Pacific Ocean, holds significant importance as a valuable source of bioactive compounds. However, its rapid growth can lead to the formation of a destructive “golden tide”, causing severe damage to the local economy and coastal ecosystems. In this study, we carried out de novo whole-genome sequencing of S. horneri using next-generation sequencing to unravel the genetic information of this alga. By utilizing a reference-guided de novo assembly pipeline with a closely related species, we successfully established a final assembled genome with a total length of 385 Mb. Repetitive sequences made up approximately 30.6% of this genome. Among the identified putative genes, around 87.03% showed homology with entries in the NCBI non-redundant protein database, with Ectocarpus siliculosus being the most closely related species for approximately one-third of these genes. One gene encoding an alkaline phosphatase family protein was found to exhibit positive selection, which could give a clue for the formation of S. horneri golden tides. Additionally, we characterized putative genes involved in fucoidan biosynthesis metabolism, a significant pathway in S. horneri. This study represents the first genome-wide characterization of a S. horneri species, providing crucial insights for future investigations, such as ecological genomic analyses. Full article

In recent years, golden tides caused by drifting Sargassum horneri (Turner) C. Agardh have caused serious ecological disasters in coastal areas of China. Eutrophication is an important cause of the formation of the golden tide. Additionally, the drifting population on the surface of the ocean is exposed to more ultraviolet radiation (UVR) than the attached population on the sea floor. In this study, the thalli of S. horneri were cultivated under two levels of nitrogen (LN: natural seawater, in which the concentration of NO₃⁻-N was 1 µmol L⁻¹; HN: NO₃⁻-enriched seawater, in which the concentration of NO₃⁻-N was 200 μmol L⁻¹) for 6 days with low photosynthetically active radiation (PAR), and then exposed to three levels of radiation (P: photosynthetically active radiation (PAR), 400–700 nm; PA: PAR + UVA, 320–700 nm; PAB: PAR + UVA + UVB, 280–700 nm) under each level of nitrogen for 2 h to investigate the effects of high UVR and nitrogen on photosynthesis. The results showed that the high level of N (HN) only enhanced the synthesis of pigments after 6 days of pre-cultivation under low PAR. After 2 h of high UVR exposure, high P, PA, and PB decreased the maximum photochemical quantum yield (F_v/F_m) and increased non-photochemical quenching (NPQ) in S. horneri regardless of the N level, and PAB significantly decreased F_v/F_m compared to PA under the LN condition alone. Under the LN condition, compared to the P group, PA and PAB significantly promoted the synthesis of carotenoids. Under the HN condition, compared to the P group, PAB increased the absorbed flux by active RCs (ABS/RC) and dissipated the energy flux by active RCs (DI₀/RC) in S. horneri alone. Furthermore, HN increased F_v/F_m, ABS/RC, and DI₀/RC more in S. horneri with PAB in comparison to those in the LN and PAB group. However, no significant differences in these parameters were observed between the LN and HN conditions under the same UVR treatments. These results demonstrate that drifting S. horneri on the surface of seawater could be inhibited by the high P; however, S. horneri living in eutrophic high-nitrogen seawater may have a stronger ability to resist high UVR damage, especially with regard to PAB radiation, which may be one of the reasons for the formation of golden tides in coastal seawater. Full article

Golden tide macroalgae have been accumulating in the Southern Yellow Sea (SYS) for several years, causing serious damage to local coastal economy and ecosystems. However, little is known about the environmental and ecological significance of the epizoans drifting on the floating macroalgae. In this study, floating macroalgae collected from four stations were identified as Sargassum horneri. Furthermore, morphological and molecular (based on the Cytochrome C Oxidase Subunit I, COI) identification revealed that the 28 epizoans on the macroalgae consisted of four crustacean (Ampithoe lacertosa, Idotea metallica, Apohyale sp., and Peramphithoe tea). Apohyale sp. and P. tea were found at all stations, while A. lacertosa is found at only one station. The weight range of Apohyale sp., P. tea, I. metallica, and A. lacertosa is 0.0037~0.0420 g, 0.0057~0.0304 g, 0.0222~0.6592 g, and 0.0047 g, respectively. The specific roles of these epizoans in the golden tide in SYS deserve further study. Our results provide a reference for future studies of invasive macroalgae and epizoans. Full article

With global warming, in recent years, golden tides have frequently occurred off the coasts of China. Sargassum horneri, which attach to aquaculture rafts, can float and form small-scale golden tides after falling off. Temperature will affect the growth and reproduction of algae. In order to explore whether the temperature is the potential influence factor of the golden tide outbreak, in this study, the effects of global warming on the growth and proliferation of S. horneri in the mussel aquaculture area of Gouqi Island will be discussed. Samples of the macroalgae were collected monthly from August 2021 to July 2022 at various stages of its life cycle, and the relationship between algal growth and temperature was analyzed based on the concept of effective accumulated temperature, combined with the parameters of sea surface temperature, photosynthetic rate, growth rate, and growth cycle. Based on the continuous temperature variation observed, the growth cycle could be divided into five stages: the decreasing temperature period (October to November), the low-temperature adaptation period (December), the second suitable low-temperature period (January to February), and the high-temperature decay period (February to May). The effective accumulated temperature stored by S. horneri from 2021 to 2022 was 2772.4 °C·d; compared with previous studies, it decreased by about 800 °C·d. The winter temperature in 2022 was higher than the average temperature in the previous 5 years, allowing the macroalgae to enter the reproductive period in advance. This had a significant impact on the blooming time of golden tides and led to an earlier outbreak and extinction. Therefore, in the future, we can set up a monitoring system for the early warning of golden tides according to the change of SST in winter. Full article

The golden tide, a large biomass bloom of the brown macroalgae Sargassum horneri, occurs yearly in the Yellow Sea, where it causes enormous economic and ecologic losses. To investigate the response of S. horneri to global warming and eutrophication, S. horneri was cultured under six conditions of varying temperature combinations (20 and 24 °C) and nitrogen levels (5, 30, and 300 μM). The growth, photosynthetic performance, pigment content, and contents of soluble protein were assessed. The growth of S. horneri followed an increasing trend with increasing N concentration at ambient temperature. Elevated temperatures had an inhibitory effect on growth and photosynthesis in S. horneri, which was further enhanced by eutrophication. This suggests that in the globally warming environment of the future, eutrophication may reduce the frequency and scale of gold tide outbreaks during the hot season. Full article

For several years, industrial damages caused by massive blooming and drifting of Sargassum horneri (S. horneri) called “golden tides” seaweeds have been continuously reported in Korea. National efforts have been made to produce useful cases of application by using the troublesome S. horneri. As a part of that, a CNDs–ZnO nanocomposite with antibacterial and antifungal properties was synthesized through a simple hydrothermal reaction using S. horneri, and the results were verified in this paper. The antibacterial and antifungal activities were mainly determined by the disk diffusion test against five bacterial and fungal strains, respectively. Of note, the inhibitory effect of the CNDs–ZnO on the growth of both Gram-positive (Bacillus cereus and Staphylococcus aureus) and Gram-negative (Escherichia coli, Salmonella typhimurium, and Vibrio alginolyticus) bacteria was highly effective. Moreover, the nanocomposite showed low toxicity compared to chlorine bleach. In addition, the CNDs–ZnO showed antifungal activities against both yeast (Saccharomyces cerevisiae and Rhodotorula mucilaginosa) and mold (Aspergillus flavus, Aspergillus niger, and Aspergillus terreus). This work showed the potential usability in antimicrobial application based on poor marine brown alga considered as useless in Korea. Through this paper, it seems that sufficient utility and possibility can be expected upon various unappreciated and uninterested marine species. Full article

The golden tide dominated by Sargassum has become a frequently-occurring marine ecological event that may constitute major biotic threats to seaweed aquaculture. In this study, the interaction between cultivated Gracilariopsis lemaneiformis (GL) and floating Sargassum horneri (SH) was investigated by physiological and biochemical measurements under mono-culture and co-culture with different biomass density ratios of 2:1 (2GL:1SH), 1:1 (1GL:1SH), and 1:2 (1GL:2SH). The relative growth rate, net photosynthetic rate, and NO₃-N uptake rate of G. lemaneiformis were significantly greater at the biomass density ratio of 2:1 than at mono-culture. However, these physiological parameters and biochemical composition contents (chlorophyll a and soluble protein) of G. lemaneiformis decreased significantly with increasing biomass of S. horneri. Meanwhile, these physiological and biochemical parameters of S. horneri were greater in all co-culture models than at mono-culture. They decreased significantly with decreasing biomass of G. lemaneiformis. These results indicate that the occurrence of floating S. horneri with low biomass can stimulate the growth of G. lemaneiformis, whereas its outbreak may significantly reduce the production and quality of G. lemaneiformis. G. lemaneiformis cultivation may be beneficial to the increased biomass of floating S. horneri. Full article

Sargassum golden tides (GT) are common in numerous coastal areas all over the world, and it adversely affects local marine life. Eutrophication is critical for Sargassum GT development. However, its physiological and ecological mechanism remains unclear. To investigate the responses of drifting Sargassum horneri, the species causing GT in the western Pacific, to light and enriched nitrogen, we set three light conditions (Low-light (LL), 10 μmol photons m⁻² s⁻¹; Middle-light (ML), 60 μmol photons m⁻² s⁻¹; and High-light (HL), 300 μmol photons m⁻² s⁻¹) and three nitrogen conditions (Natural seawater, the final concentration of N was 31.8 μmol L⁻¹, including 30.5 μmol L⁻¹ of NO₃⁻ and 1.3 μmol L⁻¹ of NH₄⁺; Enrichment of NO₃⁻, final concentration of N was 200 μmol L⁻¹; and Enrichment of NH₄⁺, the final concentration of N was 200 μmol L⁻¹), and grew the thalli under varying conditions for 10 days before determining the growth and utilization of carbon and nitrogen. Based on the accumulated data, the elevated light level led to a higher growth rate of alga. In the LL culture, the higher capacity for carbon utilization, which was reflected by the higher maximum photosynthetic carbon fixation rate (V_max), resulted in the elevated growth rates of thalli in the nitrogen-enriched media as compared with the natural seawater. Furthermore, a higher growth rate was found in the enrichment of NH₄⁺ despite a low affinity for inorganic carbon indicated by a higher value of the half-saturation constant (K_0.5). In the ML treatment, an insignificant difference in growth rate was found in three nitrogen cultures, except for a slight increase in the enrichment of NH₄⁺ than the enrichment of NO₃⁻. In the HL treatment, compared with natural seawater culture, enrichment of NO₃⁻ or NH₄⁺ accelerated the growth of alga, with no significant difference between the two nitrogen sources. Such enhancement in growth was related to the more photosynthetic carbon fixation, indicated by the higher value of V_max and soluble carbohydrates content of alga cultured with NO₃⁻ and NH₄⁺ enrichments. Additionally, the uptake and assimilation products of nitrogen, such as pigments and soluble proteins, remained unaffected by nitrogen source enrichment of NO₃⁻ or NH₄⁺ at all three light levels. In conclusion, enrichment of NO₃⁻ and NH₄⁺ exhibited different influences on the growth of S. horneri at different light levels, which was mainly associated with the capacity and efficiency of photosynthetic carbon utilization. At the HL level, both the enrichment of NO₃⁻ and NH₄⁺ dramatically accelerate the growth of alga by stimulating the photosynthetic carbon fixation. Accordingly, we speculated that drifting S. horneri, exposed to HL level on the surface of the sea, were likely to develop rapidly to form GT in eutrophic oceanic areas with upwelled and river plume NO₃⁻ or NH₄⁺ nutrients. Full article