Owing to its high toxicity, recalcitrance, and bioaccumulation potential, heavy metal cadmium (Cd) bioaccumulates through the food chain and threatens the stability of aquatic ecosystems and human health. It poses a challenge in current aquatic environmental remediation. Against the backdrop of global warming, high-temperature-tolerant macroalgae-based bioremediation technologies have potential for treating aquaculture effluents. Here, Gracilariopsis heteroclada, a characteristic high-temperature-tolerant species in southern China, was selected as the research object. Physiological experiments with gradient Cd2+ concentrations were designed to study the growth and physiological response mechanisms and tolerance thresholds of G. heteroclada to Cd, while quantifying its Cd biosorption capacity. The results showed that Cd concentrations >= 0.5 mg/L significantly inhibited algal growth, with the growth rate decreasing to-0.14%/d at 10 mg/L. Elevated cadmium levels also markedly affected photosynthetic pigment contents and chlorophyll fluorescence parameters, with the initial concentrations causing significant inhibition being 0.5, 1, 7, and 7 mg/L for Chl a, Car, PE, and PC, respectively. In addition, G. heteroclada exhibited strong cadmium purification capacity, achieving a maximum adsorption rate of 3904.87 & micro;g/(g center dot h) and removal efficiencies exceeding 40% after 72 h of treatment. In summary, G. heteroclada shows strong potential for cadmium remediation and biomonitoring in aquaculture systems, providing practical implications for sustainable aquaculture and the effective utilization of red algal resources.

Several small, unidentified specimens of the Laurencia complex were collected from mangrove forests in Qinzhou, Guangxi, China. To characterize these specimens, we performed detailed morphological observations and phylogenetic analyses based on chloroplast rbcL and mitochondrial cox1 gene sequences. The results revealed that these specimens represent a previously undescribed species within the genus Palisada. Given that the species was discovered in Xiandao Park (also known as Yat-sen Park), we name it P. yatsenii sp. nov. to honor Dr. Sun Yat-sen, the great forerunner of China's modern democratic revolution. This species is endemic to the high intertidal mangrove habitat, a niche where no known congeneric species have been previously documented-thus expanding our ecological understanding of the genus Palisada. Key diagnostic traits of this species include a predominantly pale-yellow thallus, prostrate growth habit, and the formation of irregular to subcircular cushion-shaped clumps. Phylogenetic analyses based on the rbcL and cox1 makers separately confirmed that the studied specimens form a clade within Palisada, with strong support recovered in the rbcL phylogeny. The rbcL and cox1 genetic distances between the new species and other members of the genus Palisada ranged from 6.3% to 9.7% and from 5.8% to 8.4%, respectively-values that exceed the minimum threshold for species delimitation in Palisada. The discovery of P. yatsenii sp. nov. underscores the gaps in our knowledge of coastal macroalgae and emphasizes the urgency of macroalgal diversity research for the sustainable management and conservation of these biological resources.

This 30-day experiment evaluated the multifaceted effects of integrating the red alga Gracilaria fisheri into the recirculating aquaculture of pearl gentian grouper (Epinephelus fuscoguttatus female x Epinephelus lanceolatus male), focusing on the microbiota of the culture water, fish intestine, and phycosphere (the microenvironment surrounding the algae, which encompasses associated microorganisms). 16S rRNA high-throughput sequencing demonstrated that G. fisheri significantly enhanced microbial diversity in all three communities, evidenced by respective Shannon index increases of 0.4, 1.3, and 0.5. Concurrently, the abundance of dominant phyla and genera shifted: within the aquatic microbiota, Bacteroidetes increased by 16.3 % while Proteobacteria, Bacteroidetes, and Verrucomicrobia declined; in the gut microbiota, Firmicutes and Bacteroidetes rose by 7 % and 17.3 %, inversely proportional to reductions in Proteobacteria and Actinobacteria; the phycosphere microbiota exhibited a 13 % Proteobacteria increase with decreases in Bacteroidetes and Desulfobacterota. Specific genus-level successions occurred: Edaphobaculum was succeeded by Nautella in water; Pseudomonas and Ralstonia were replaced by Photobacterium and Lachnospiraceae_NK4A136_group in the gut; Pelomonas and Ralstonia were supplanted by Ruegeria and Psychroserpens in the phycosphere. Functionally, ecological functional abundance decreased in the aquatic microbiome, whereas metabolic functions for terpenoids and polyketides and the abundance of genetic information and cellular processes increased in the phycosphere and intestinal microbiota, with other functions waning. Statistical analysis revealed the strongest correlation between the aquatic and phycosphere microbiota (p < 0.01), followed by the aquatic and intestinal microbiota (p < 0.01), while the intestinal and phycosphere microbiota exhibited a weaker positive correlation (p = 0.05). Overall, G. fisheri optimized the aquaculture water environment and regulated fish intestinal microbiota structure. Therefore, addition of this alga to the culture environment is a viable strategy for enhancing aquaculture sustainability through the improvement of water microbial quality, enhancement of fish intestinal health, and potential strengthening of host disease resistance.

Ulva ohnoi forms harmful green tides and a large population has recently been recorded in Zhanjiang, China, where its strong growth and reproduction favor its large-scale commercial cultivation. Understanding its biology at different growth stages is essential to maximize its aquaculture potential. We first confirmed the generational identity of our samples to eliminate potential biological variations due to generation type. We used an orthogonal experimental approach to investigate three factors (temperature, light intensity, and salinity) at three different levels, to identify optimal cultivation conditions for each developmental stage, and documented the maturation and early development processes. All of our samples were female gametophytes or apomicts, which produced biflagellate female gametes or apomictic zoids, without undergoing sexual reproduction. The optimal growth conditions for U. ohnoi from Zhanjiang were 20 °C, 90 μmol·m⁻²·s⁻¹ light intensity, and 25 salinity; the optimal reproductive conditions were 25 °C, 60 μmol·m⁻²·s⁻¹ light intensity, and 35 salinity; and the optimal development conditions were 25 °C, 90 μmol·m⁻²·s⁻¹ light intensity, and 25 salinity. Temperature dominated in determining U. ohnoi from Zhanjiang growth and early development, while light intensity was most influential in governing reproduction. Growth, reproduction, and early development were almost unaffected by salinity values between 15 and 35. These findings provide essential baseline information for the large-scale aquaculture of U. ohnoi in the coastal waters of southern China.

Gracilariaceae species are among the most economically important seaweeds, with a wide range of applications. Large‐scale cultivation of Gracilariopsis lemaneiformis has already been established along the eastern coast of China. However, as global demand for Gracilariaceae species rises, it is crucial for China to expand large‐scale cultivation of these species to other coastal regions. Although the South China Sea harbors rich macroalgal resources, including Gracilariaceae, large‐scale cultivation of these species has yet to be implemented in the region. To identify heat‐tolerant Gracilariaceae species suitable for large‐scale cultivation in the South China Sea, we conducted surveys between June and August from 2021 to 2024. Several heat‐tolerant species were identified. Taxonomic identity was confirmed through detailed morphological examination and molecular analysis of rbc L and cox1 gene sequences. We identified eight species of Gracilariaceae, including one Gracilariopsis ( Gp .) species and seven Gracilaria ( G .) species. Morphologically, the species were characterized as follows: Gp. heteroclada (long secondary branches with short or spiny tertiary branches), G. salicornia (club‐shaped segments), G. vermiculophylla and G. tenuistipitata (slender‐branched), G. edulis (broom‐like appearance with red‐tinged branch bases), G. firma (highly constricted branch bases), and two unclassified species, Gracilaria sp.1 and Gracilaria sp.2. This study contributes to the taxonomic knowledge of Gracilariaceae and provides valuable information for the development of heat‐tolerant species suited for large‐scale cultivation in the South China Sea.

In aquaculture, high-density seaweed farming brings higher economic benefits but also increases outbreaks of diatom felt.The effective control of diatom felt in high-density seaweed farming has always been a research hotspot.This study selected two potential allelochemicals 2-hydroxycinnamic acid and quinic acid to explore their effects on a diatom Nitzschia closterium and an economic seaweed Monostroma nitidum.The results showed that 2-hydroxycinnamic acid had better inhibitory effects than quinic acid on the growth, pigment content and photosynthetic efficiency of N. closterium.Their half-maximal inhibitory concentrations at 120 h (IC 50-120 h ) were 0.9000 and 1.278 mM, respectively.Additionally, these allelochemicals had limited inhibitory effects on the growth, pigment content and photosynthetic efficiency of M. nitidum before 24 h.To further explore the allelopathic effect of these chemicals, this study focused on the photosystem II energy fluxes of N. closterium.It was found that 3 mM 2-hydroxycinnamic acid could destroy the whole photosynthetic system by devastating the PSII reaction centre (RC) before 24 h; however, the same concentration of quinic acid could only down-regulate the electron transport efficiency by changing the effective antenna size of an active RC and downregulating the PSII reaction centre density.These experimental results are expected to provide a new strategy to control diatom felt blooms on the high-density seaweed farming areas.

Global warming causes great thermal stress to macroalgae and those species that can adapt to it are thought to be better able to cope with warmer oceans. Gracilaria bailinae, a macroalgae with high economic and ecological values, can survive through the hot summer in the South China Sea, but the molecular mechanisms underlying its adaptation to high temperatures are unclear. To address this issue, the present study analyzed the growth and transcriptome of G. bailinae after a 7-day exposure to 15°C (LT: low temperature), 25°C (MT: middle temperature), and 35°C (HT: high temperature). Growth analysis showed that the HT group had the highest relative growth rate (RGR = 2.1%) with the maximum photochemical quantum yield of PSII (Fv/Fm = 0.62) remaining within the normal range. Transcriptome analysis showed more differentially expressed genes (DEGs) in the comparison between MT and HT groups than in that between MT and LT, and most of these DEGs tended to be downregulated at higher temperatures. The KEGG pathway enrichment analysis showed that the DEGs were mainly enriched in the carbohydrate, energy, and lipid metabolisms. In addition, the genes involved in NADPH and ATP synthesis, which are associated with photosynthesis, the Calvin cycle, pyruvate metabolism, and the citrate cycle, were downregulated. Downregulation was also observed in genes that encode enzymes involved in fatty acid desaturation and alpha-linolenic acid metabolism. In summary, G. bailinae regulated the synthesis of NADPH and ATP, which are involved in the above-mentioned processes, to reduce unnecessary energy consumption, and limited the synthesis of enzymes in the metabolism of unsaturated fatty acids and alpha-linolenic acid to adapt to high environmental temperatures. The results of this study improve our understanding of the molecular mechanisms underlying the adaptation of G. bailinae to high temperatures.

There are species differences in the adaptation of macroalgae to temperature and light intensity. Gracilariopsis bailinae is a large alga that likes high temperature. In order to scientifically guide its application in mariculture and marine ecological restoration, we investigated the photosynthetic physiological responses characteristics of G. bailinae to temperature and light intensity by using chlorophyll fluorescence technology, combined with changes in photosynthetic pigment content and growth rate of algae. We measured various physiological parameters, including specific growth rate (SGR), photosynthetic pigments content [Chlorophyll a (Chl a), carotenoid (Car), and phycobiliprotein], and chlorophyll fluorescence parameters [Maximum photochemical efficiency of PSII (Fv/Fm), actual light conversion efficiency (ΦPSII), electron transfer rate (ETR), photochemical quenching (qP), and non-photochemical quenching (NPQ)] of G. bailinae cultured at five different temperatures (15, 20, 25, 30, 35 ℃) and four different light intensities (1 000, 3 000, 6 000, 9 000 lx). Results reveal that temperatures and light intensities had a significant interaction effect on the parameters measured, except for Car and Fv/Fm (P<0.01). The SGR, phycobiliprotein contents, and chlorophyll fluorescence parameters of G. bailinae increased significantly as temperature increased (P<0.05), whereas high light intensity treatment led to a significant decrease in photosynthetic pigments content and values of Fv/Fm, ΦPSII, ETR, and qP, but a significant increase in NPQ and SGR (P<0.05). These results indicate that G. bailinae can enhance its survival capacity under high temperature conditions by increasing the synthesis of phycobilin, and achieve photoprotection under high light conditions by increasing heat dissipation and decreasing photosynthetic pigment synthesis.

The genera Monostroma and Gayralia belong to the order of monostromatic green algae; however, their taxonomic delimitation remains controversial at the genus level. This study attempts to address this issue through the combined analysis of the morphology and nuclear-encoded Internal Transcribed Spacer region sequences of monostromatic green algal samples collected in the South China Sea. Our phylogenetic data revealed that the monostromatic specimens were separated into the M. nitidum clade, G. brasiliensis clade, and a single Monostroma sp. clade, and that the inter-genera genetic distance between the Monostroma and Gayralia genera was lower than that observed within the Monostroma genus. All the specimens presented similar morphology in their single cell-layered thallus, with irregularly arranged cells, rounded cell corners, a parietal chloroplast, and predominantly one (>90%) pyrenoid. Their most obvious morphological difference was in thallus thickness and size. Moreover, the monostromatic specimens of the M. nitidum clade corresponded to the morphological description of the M. nitidum-type specimens. The genus Monostroma was erected earlier than the genus Gayralia. Therefore, we propose to assign the genus Gayralia to Monostroma based on the morphological and phylogenetic analysis and genetic distance data presented here.

Macroalgae can accumulate a wide array of metals, leading to their appliance as biomonitors of aquatic environments. With the rapid development of industrial and agricultural-based activities, Cd pollution in aquatic environments is considered an increasingly severe problem worldwide. Although La could alleviate the Cd stress in higher terrestrial plants, the response mechanisms of macroalgae to Cd and La are unknown. Along these lines, in this work, Cd significantly affected the growth, internal cellular structure, photosynthesis, pigment content, antioxidant enzyme activity, and lipid peroxidation level of G. bailiniae. However, the presence of La alleviated these adverse effects from Cd. Furthermore, the response mechanism of G. bailiniae to Cd was attributed to the self-antioxidant ability enhancement, membrane defense, and programmed-cellular regulation. However, the presence of La mediated the biosynthesis of both flavonoids and lipids, which inhibited the Cd accumulation, modulated algal stress signalling networks, renewed the impaired chlorophyll molecule, maintained the activity of the crucial enzyme, enhanced antioxidant ability, and maintained the stabilization of redox homeostasis, alleviating the adverse impact from Cd and improve the growth of G. bailiniae. The experimental results successfully demonstrate a new detoxicant to alleviate Cd stress, promoting a more comprehensive array of macroalgal applications.

The monostromatic green macroalga Monostroma nitidum Wittrock is attracting global attention due to its commercial importance. In this study, field Monostroma strains were collected from Dalang, Naozhou Island, on the South China Sea Coast of Zhanjiang City. They were identified as M. nitidum using morphological and developmental characteristics combined with nuclear-encoded internal transcribed spacer sequences. Moreover, the early ontogeny of M. nitidum was observed for the first time in detail under a photomicroscope. The active zoospores had a spherical shape, were 6.88 μm in diameter, and completely settled on the Petri dish 1 day after release. The first transverse division of settled zoospores occurred on the 3rd day; the length of the elongate cells was 15.94 μm. Longitudinal divisions started to occur in the middle and at the top of erect filaments (61.27 μm in length) on the 12th day, and rhizoids began to appear at the posterior end of the microscopic filamentous thallus. The sac-like microthallus (113.79 μm in length) that developed from erect filaments was observed on the 18th day and divided longitudinally towards the rhizoids to produce expanded monostromatic blades (178.96 μm in length) on the 24th day. These data increase our understanding of the ontogeny of M. nitidum.

Ulva meridionalis, a green macroalgae, is one of the causal species for green tides in Japan and spread into the coast of China. During this research, we sequenced the complete mitochondrial genome of U. meridionalis. The mitogenome is 62,887 bp in length, including 28 encoding genes and 29 tRNA genes. Compared with the Ulva species from mitogenome, the gene order and organization of this mitogenome are similar to most of other determined Ulva mitogenomes, with the nucleotide base composition of A 33.6%, T 32.2%, C 16.2%, and G 18.0%. Phylogenetic analysis shows U. meridionalis is closely related to Ulva flexuosa.

为探索礁膜(Monostromanitidium)配子体生长的适宜氮、磷浓度需求,以NaNO3为氮源、KH2PO4为磷源,在不同氮(0、10、20、40、60、80μmol/L)、磷(0.5、1、2μmol/L)浓度梯度下,室内培养礁膜配子体7 d,测定各处理组藻体的生长率、光合色素(叶绿素a、b和类胡萝卜素)和可溶性糖.结果表明,藻体生长最适氮、磷浓度比值为20:1;且氮浓度为20μmol/L、磷浓度为1μmol/L时,礁膜配子体生长率取得最大值(13.80％/d);氮浓度为20μmol/L、磷浓度为2μmol/L时,藻体光合色素含量最高(分别为0.3207 mg/g、0.1708 mg/g和0.1036 mg/g);氮浓度为0μmol/L、磷浓度为2μmol/L时,藻体可溶性糖含量最高(19.03 mg/mL).

Abstract Ulva meridionalis is one of the causal green macroalgae for green tides in Japan and exists in coastal areas of China. In the present study, complete chloroplast (cp) genome sequence of Ulva meridionalis was reported, and the total length of this species was 88,653 bp (GenBank accession number MN889540). The overall base composition of cp genome was A (37.1%), T (39.0%), C (11.4%) and G (12.5%), similar to other Ulva macroalgae within cp genome, and the percentage of A + T (76.1%) was higher than C + G (23.9%). U. meridionalis cp genome encoded 113 genes, including 80 protein-coding genes, 27 transfer RNAs genes and 6 ribosomal RNAs genes. The maximum likelihood phylogenetic analysis shows that Ulva linza is the closest sister species of U. meridionalis.

Ulva meridionalis is one of the causal green macroalgae for green tides in Japan and exists in coastal areas of China. In the present study, complete chloroplast (cp) genome sequence of Ulva meridionalis was reported, and the total length of this species was 88,653 bp (GenBank accession number MN889540). The overall base composition of cp genome was A (37.1%), T (39.0%), C (11.4%) and G (12.5%), similar to other Ulva macroalgae within cp genome, and the percentage of A + T (76.1%) was higher than C + G (23.9%). U. meridionalis cp genome encoded 113 genes, including 80 protein-coding genes, 27 transfer RNAs genes and 6 ribosomal RNAs genes. The maximum likelihood phylogenetic analysis shows that Ulva linza is the closest sister species of U. meridionalis.

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.

Since 2007, large-scale blooms have periodically broken out in the Yellow Sea, leading to serious economic and ecological problems in the surrounding coastal environments. Previous studies reported that the blooms originated in the Rudong oceanic area of the southern Yellow Sea and drifted almost 400 km into the Qingdao oceanic area of the northern Yellow Sea. In this study, chlorophyll concentrations, chlorophyll fluorescence, growth rates, and reproductive characteristics of floating Ulva prolifera collected along the Yellow Sea coast were assessed. The results revealed that these four physiological parameters in the Rudong area at the bloom source were considerably higher (2.02 mg/g, 0.68, 28.49% d(-1), and 4 x 10(7), respectively) than in the Qingdao area (0.34 mg/g, 0.31, 5.23% d(-1), and 0.67 x 10 (7), respectively). However, the abundance of microscopic propagules of Ulva in the Qingdao area (3980 ind/l) was significantly higher than that in the Rudong area (667 ind/l). These findings help increase our understanding of the formation of the world's largest Ulva macroalgal blooms.

报道浒苔与缘管浒苔的人工种间杂交技术.利用浒苔属藻类生殖细胞配子与孢子的趋光性差异性,结合其同型世代交替生活史特性,从绿藻群落中分别筛选出浒苔与缘管浒苔的雌雄配子体母本藻体.通过对浒苔雌配子体和缘管浒苔雄配子体进行生殖细胞诱导试验,分别同时获得纯化的雌雄配子液,经均匀混合与显微观察,发现浒苔雌配子和缘管浒苔雄配子快速向彼此游动,接合形成具有负趋光性的合子;接合过程中,雌雄配子鞭毛逐渐消失,运动力逐渐下降,由梭形逐渐转变成为圆形.将纯化合子进行室内培养,获得杂交后代藻体,经凝胶电泳及分子生物学检测,发现杂交种在5S rDNA间隔区序列上同时具有浒苔和缘管浒苔的特异性序列,确认两种浒苔属绿藻成功实现种间杂交.此项技术在国内尚未报道,可为未来开发多种优质性状浒苔品系提供技术示范,为开展浒苔规模化养殖和获得稳定高产浒苔资源提供科学支撑.

Comparative studies of closely related species from different habitats can potentially elucidate mechanisms of adaptation. Hybrids can act as valuable archives, enabling the evaluation of speciation. Brackish Ulva prolifera and marine Ulva linza show partial gamete compatibility and have been identified as closely related Ulva species based on molecular phylogenetic analysis. However, there are few reports on the biological characteristics of hybrids produced by brackish U. prolifera x marine U. linza. This study aimed to compare the morphological and growth characteristics of these two closely related Ulva species and their hybrids. The results showed that hybrid sporophytes had 1.0-3.6 branches per 1 cm of main stem, and the hybrid gametophytes had multiple branching characteristics, including the unbranched flat U. linza type, branched tubular U. prolifera type and branching types that were intermediate between the two. In addition, brackish U. prolifera, marine U. linza and their hybrid sporophytes exhibited high germination rates, approximately 6.6 times greater than hybrid gametophytes (12.7%). The highest daily growth rates of brackish U. prolifera and marine U. linza were 179.2% and 172.7%, respectively, which were significantly higher than those exhibited by hybrids (153.3%). These results demonstrated that the closely related brackish U. prolifera and marine U. linza have a greater capacity to adaptive to their environment than hybrids of the two species.

The world's largest macroalgal blooms caused by Ulva prolifera have occurred in the Yellow Sea for 11 consecutive years. The area covered by blooms has been approximately 500 km2 in previous years, while in 2017, the maximum area decreased significantly to 312 km2. In this study, we concluded that species competition between Ulva and Sargassum (fast rise of the golden tides), extreme high sea surface temperature and harvest for floating Ulva macroalgae were the three critical factors influencing the sharp reduction in covered area for blooms in 2017. In addition, analysis of annual variations of Pyropia aquaculture area in the Southern Yellow Sea over the past two decades revealed that a great expansion in "Sansha" regions was mainly responsible for the initial blooms in 2007, and that this expansion supported the great biomass of the blooms in following years. Based on these findings, we suggest comprehensive utilization of the macroalgal blooms is a feasible way to control them.