Globosa Blooms Research Articles

Phaeocystis globosa and diatom blooms promote distinct bacterial communities and associations in a coastal ecosystem.

Phytoplankton and bacteria form the foundation of marine food webs. While most studies on phytoplankton bloom influence on bacteria dynamics focus on diatom-dominated blooms due to their global ecological significance, it is unclear if similar patterns extend to other species that compete with diatoms like Phaeocystis spp. This study aimed to contribute to the understanding of associations between phytoplankton and bacteria in a temperate ecosystem. For this, we studied the dynamics of phytoplankton and bacteria, combining 16S metabarcoding, microscopy, and flow cytometry over 4 years (282 samples). Phytoplankton and bacterial communities were studied throughout the year, particularly during contrasting phytoplankton blooms dominated by the Haptophyte Phaeocystis globosa or diatoms. We applied extended local similarity analysis (eLSA) to construct networks during blooming and non-blooming periods. Overall, the importance of seasonal and species-specific interactions between phytoplankton and bacteria is highlighted. In winter, mixed diatom communities were interconnected with bacteria, indicating a synergistic degradation of diverse phytoplankton-derived substrates. In spring, despite the intensity variations of P. globosa blooms, the composition of bacterial communities remained consistent over several years, suggesting establishing a stable-state environment for bacterial communities. Specific associations between monospecific diatom blooms and bacteria were evidenced in summer.

The micro-ecological feature of colonies is a potential strategy for Phaeocystis globosa bloom formation

Phaeocystis globosa is among the dominant microalgae associated with harmful algal blooms. P. globosa has a polymorphic life cycle and its ecological success has been attributed to algal colony formation, however, few studies have assessed differences in microbial communities and their functional profiles between intra- and extra-colonies during P. globosa blooms. To address this, environmental and metagenomics tools were used to conduct a time-series analysis of the bacterial composition and metabolic characteristics of intra- and extra-colonies during a natural P. globosa bloom. The results show that bacterial composition, biodiversity, and network interactions differed significantly between intra- and extra-colonies. Dominant extra-colonial bacteria were Bacteroidia and Saccharimonadis, while dominant intra-colonial bacteria included Alphaproteobacteria and Gammaproteobacteria. Despite the lower richness and diversity observed in the intra-colonial bacterial community, relative to extra-colonies, the complexity and interconnectedness of the intra-colonial networks were higher. Regarding bacterial function, more functional genes were enriched in substance metabolism (polysaccharides, iron element and dimethylsulfoniopropionate) and signal communication (quorum sensing, indoleacetic acid-IAA) pathways in intra- than in extra-colonies. Conceptual model construction showed that microbial cooperative synthesis of ammonium, vitamin B12, IAA, and siderophores were strongly related to the P. globosa bloom, particularly in the intra-colonial environment. Overall, our data highlight the differences in bacterial structure and functions within and outside the colony during P. globosa blooms. These findings represent fundamental information indicating that phenotypic heterogeneity is a selective strategy that improves microbial population competitiveness and environmental adaptation, benefiting P. globosa bloom formation and persistence.

Responses of microeukaryotic community structure to a Phaeocystis globosa bloom in a semi-enclosed subtropical bay

The occurrence of Phaeocystis globosa, a harmful algal bloom species in Chinese coastal waters, has significant impacts on marine organisms and poses a threat to the safety of coastal nuclear power plants. Although previous studies have established a close association between P. globosa blooms and the bacterial community, the relationship between the microeukaryotic community and P. globosa blooms remains poorly understood. In this study, the variations in the microeukaryotic community resulting from a P. globosa bloom were analyzed using 18S rRNA gene amplicon sequencing. The results indicated that the diversity of the microeukaryotic community during the bloom phase was significantly higher than that during the dissipation phase. The microeukaryotic community compositions varied significantly between the two phases of the P. globosa bloom. During the bloom phase, the dominant microeukaryotic was Viridiplantae, which was then replaced by Dinoflagellata during the dissipation phase. Co-occurrence network analysis showed that the relationship among the microeukaryotic community during the bloom phase was more complex than that during the dissipation phase, and the keystone taxa varied as the bloom progressed. Additionally, microeukaryotic community assembly was primarily driven by stochastic processes during the bloom phase based on the β-nearest taxon distance, whereas it was driven by both deterministic processes and stochastic processes during the dissipation phase. Overall, our findings provide novel insight into the mechanisms and interactions involved in microeukaryotic community dynamics in environments disturbed by P. globosa blooms.

Early warning and monitoring of the safety risk of coastal nuclear power plant cold source under the stress from Phaeocystis globosa blooms

Context In recent years, Phaeocystis globosa has become a typical red tide species in the Beibu Gulf, posing a safety hazard to the cold-water intake system of the Guangxi Fangchenggang Nuclear Power Plant. Aims To establish an effective early risk-warning monitoring and ensure the safety of nuclear power plant cold-water intakes. Methods In this study, a multifactor and multilevel early risk-warning monitoring system was established using the early warning idea of ‘risk grading’. Key results The results showed that this method can analyse the influence trend of marine-environment changes on the growth of P. globosa and improve the timeliness of early warning and forecasting. Conclusions The method established in this paper can effectively guide coastal nuclear power enterprises to conduct early risk warning and monitoring of P. globosa and improve the accuracy of early warning and forecasting. Implications The methed is of great significance to coastal nuclear power enterprises dealing with red tide disasters caused by P. globosa blooms.

Morphological, molecular, and life cycle characteristics of Phaeocystis globosa Scherffel (Prymnesiophyceae) in the Southeast China Sea

Phaeocystis globosa blooms frequently occur in the Southeast China Sea and cause significant negative impacts on coastal ecology and mariculture. The P. globosa blooms in southeastern China are very different compared to those of European strains, suggesting that differences may exist in their morphological, phylogenetic, and life history traits. In this study, seven strains of P. globosa isolated from Southeast China Sea that were typical strains of algal blooms in the region, in addition to one strain from the Gulf of Mexico (CCMP629), were comprehensively evaluated to better understand region-specific differences of the species. Significant differences were not observed in the internal cell structures and other characteristics compared to those of European strains, while differences in cell surface structures were apparent. For example, small and large flagellated Chinese P. globosa cells exhibited two flagella with slightly unequal lengths and a short haptonema, the surfaces of small flagellated cells were not covered by scales, and colony cell diameters were smaller. 18S rRNA sequence phylogenetic analysis also revealed that P. globosa comprised a species complex with two ecotypes (warm- and cold-water types), of which the strains from the southeastern coast of China and CCMP629 belonged to the warm-water type. In addition, the life cycles and variable modes of P. globosa colony formation were evaluated in detail. The algal bloom may be due to the rapid colonies formation by budding and colony fragments. These results provide new insights into the life cycle of P. globosa and highlight the differences in morphological and phylogenetic relationships between strains from the southeast coast of China and those from coastal European regions.

Responses of bacterioplankton, particle- and colony-attached bacterial communities to Phaeocystis globosa blooms in Mirs Bay, China

Microalgae blooms are a frequent occurrence in coastal waters worldwide. It is reasonable to assume that these blooms have various influences on bacterial communities, which in turn may affect the development and dissipation of the bloom. However, the bacterial community characteristics, particularly of attached bacteria, associated with microalgae blooms remain unclear. In this study, we investigated the community profiles of bacteria using high-throughput sequencing during a Phaeocystis globosa bloom in Mirs Bay, southern China, in January 2021. Bacteria living in three habitats, i.e., bacterioplankton, particle-attached bacteria, and colony-attached bacteria, were studied from the exponential growth phase to the decline growth phase of the bloom. Distinct variations in bacterial community composition existed among the three habitats. Bacteroidota, Proteobacteria, and Cyanobacteria were the dominant phyla of bacterioplankton, particle–attached bacteria, and colony-attached bacteria, respectively. Richness and diversity were significantly highest (p < 0.01) in particle-attached bacteria, followed by bacterioplankton, and lowest in colony-attached bacteria. The community diversities of bacterioplankton and particle-attached bacteria decreased significantly (p < 0.05) as the bloom shifted from the exponential to the decline phase. During the decline growth phase of the bloom, Bacteroidota and Verrucomicrobiota were the dominant remarkably abundant bacteria in the bacterioplankton community, whereas Verrucomicrobiota was dominant in the particle-attached bacteria community. No significant difference was observed in the colony-attached bacterial community between the exponential and decline phases of the P. globosa bloom owing to their complex network. The results of this study suggest that P. globose bloom has a profound impact on marine bacteria, particularly species that can decompose organic matter, which could play a crucial role in the dissipation of algal blooms.

On the conditions promoting Pseudo-nitzschia spp. blooms in the eastern English Channel and southern North Sea

This study investigated the drivers of the blooms of Pseudo-nitzschia seriata and Pseudo-nitzschia delicatissima complexes in the eastern English Channel and southern North Sea. Phytoplankton data series acquired from 1992 to 2020 were analyzed with a multivariate statistical approach based on Hutchinson's niche concept. P. seriata and P. delicatissima complexes were found to be typically present year round, but they bloomed at different periods because they occupied different realized ecological niches. P. delicatissima complex occupied a more marginal niche and was less tolerant than P. seriata complex. P. delicatissima complex typically bloomed in April-May at the same time as Phaeocystis globosa while P. seriata complex blooms were more frequently observed in June during the decline of low intensity P. globosa blooms. P. delicatissima and P. seriata complexes were both favored by low-silicate environments and relatively low turbulence but they responded differently to water temperature, light, ammonium, phosphate and nitrite + nitrate conditions. Niche shifts and biotic interactions played important roles in the control of the blooms of P. delicatissima and P. seriata complexes. The two complexes occupied different sub-niches during their respective low abundance and bloom periods. The phytoplankton community structure and the number of other taxa presenting a niche overlapping the niches of P. delicatissima and P. seriata complexes also differed between these periods. P. globosa was the taxa contributing the most to the dissimilarity in community structure. P. globosa interacted positively with P. delicatissima complex and negatively with P. seriata complex.

Succession and controlling factors of phytoplankton assemblages during a period with recurrent outbreaks of Phaeocystis globosa blooms in Qinzhou Bay, China

Qinzhou Bay is a tropical semiclosed bay with the highest phytoplankton diversity and a high frequency of harmful algal blooms (HABs) in the Guangxi coastal area, located north of the Beibu Gulf. Phaeocystis globosa is a typical HAB species in the Guangxi coastal area, and blooms mainly occur in autumn and winter. The causes of these blooms and the succession of phytoplankton assemblages related to the blooms are complicated and not fully understood. Therefore, a continuous survey was conducted monthly from October 2018 to March 2019 to study the succession of the phytoplankton community in Qinzhou Bay and its relationship with environmental variables in this area. The results revealed that the dynamics of the phytoplankton assemblages varied significantly with time, and P. globosa was the most frequent dominant species in five of these voyages, with the highest cell density of 3.79 ± 1.34 × 106 cells/L in January. Chaetoceros species had a high density and were a dominant species associated with P. globosa in the early stage, while they were replaced by Guinardia striata when the density of P. globosa increased rapidly in January, and the abundance of dinoflagellates increased after the decline in P. globosa. The diversity index indicated that the community structure was more stable from October to December, while the sharp increase in P. globosa in January caused a decline in phytoplankton diversity. The redundancy analysis (RDA) results revealed that the phytoplankton community structure and its variation were mainly affected by hydrological and chemical factors, including DIN/DIP, temperature, DSi, DIP and DSi/DIP. Furthermore, we inferred that phosphorus (P) was the key factor limiting the colony formation of P. globosa, and P limitation prevented the outbreak of blooms. This research may provide more insight into the mechanisms driving and prevention of P. globosa blooms.

Mechanisms of Phaeocystis globosa blooms in the Beibu Gulf revealed by metatranscriptome analysis

The haptophyceae Phaeocystis globosa is a species responsible for harmful algal blooms in the global ocean, forming blooms in the Beibu Gulf annually since 2011. This species can alternate between solitary free-living cells and colonies. Colonies are the dominant morphotype during blooms. To date, the underlying mechanism of P. globosa blooms in the Beibu Gulf is poorly understood. After combining results of ecological surveys, laboratory studies, and metatranscriptome and bioinformatics analyses, it was found that low temperatures, high nitrate, and low organic phosphorus induced P. globosa blooms in the Beibu Gulf. Additionally, the unique genetic and physiological characteristics that allow P. globosa to stand out as a dominant species in such an environment include (1) several genes encoding high-affinity nitrate transport proteins that could be highly expressed under sufficient nitrate conditions; (2) energy metabolism genes involved in photosynthesis and oxidative phosphorylation that were actively expressed at low temperatures to carry out carbon and energy reversion and produce sufficient ATP for various life activities, individually; (3) abundant glycan synthesis genes that were highly expressed at low temperatures, thus synthesizing large quantities of proteoglycans to construct the mucilaginous envelope forming the colony; (4) cells in colonies exhibited active gene expression in DNA replication contributing to a faster growth rate, which could help P. globosa occupy niches quickly; and (5) the energy and material expenditure was redistributed in colonial cells accompanied with chitin filaments and flagella degraded, more expenditure was used for the synthesis of the mucilaginous envelope and the rapid proliferation.

Spatial and diel variations of the prokaryotic community in the Phaeocystis globosa blooms area of Beibu Gulf, China

Spatial and diel variations of the prokaryotic community in the Phaeocystis globosa blooms area of Beibu Gulf, China

Quantitative Proteomic Analysis Reveals the Key Molecular Events Driving Phaeocystis globosa Bloom and Dissipation.

Phaeocystis globosa is a marine-bloom-forming haptophyte with a polymorphic life cycle alternating between free-living cells and a colonial morphotype, that produces high biomass and impacts ecological structure and function. The mechanisms of P. globosa bloom formation have been extensively studied, and various environmental factors are believed to trigger these events. However, little is known about the intrinsic biological processes that drive the bloom process, and the mechanisms underlying P. globosa bloom formation remain enigmatic. Here, we investigated a P. globosa bloom occurring along the Chinese coast and compared the proteomes of in situ P. globosa colonies from bloom and dissipation phases using a tandem mass tag (TMT)-based quantitative proteomic approach. Among the 5540 proteins identified, 191 and 109 proteins displayed higher abundances in the bloom and dissipation phases, respectively. The levels of proteins involved in photosynthesis, pigment metabolism, nitrogen metabolism, and matrix substrate biosynthesis were distinctly different between these two phases. Ambient nitrate is a key trigger of P. globosa bloom formation, while the enhanced light harvest and multiple inorganic carbon-concentrating mechanisms support the prosperousness of colonies in the bloom phase. Additionally, colonies in the bloom phase have greater carbon fixation potential, with more carbon and energy being fixed and flowing toward the colonial matrix biosynthesis. Our study revealed the key biological processes underlying P. globosa blooms and provides new insights into the mechanisms behind bloom formation.

Monitoring of high biomass Phaeocystis globosa blooms in the Southern North Sea by in situ and future spaceborne hyperspectral radiometry

Phaeocystis globosa (P. globosa hereafter) is a phytoplankton species which commonly blooms at high biomass in April–May in the Southern North Sea and forms undesirable foam which accumulates on the beaches. Monitoring of this species is required by EU directives. Measurement of phytoplankton species composition has historically been made by pigment or microscopic analysis of water samples, which is spatially sparse and temporally infrequent e.g. weekly/monthly. In-water instruments such as flow cytometers can provide very high frequency data but at high acquisition and maintenance cost. Automated in situ above water radiometry has the potential to provide very high frequency data at single locations but requires very careful design of processing algorithms in turbid waters with high non-algal absorption. Spaceborne radiometry could provide both very good spatial coverage and moderate/high frequency of data, e.g. daily/weekly, but accurate determination of phytoplankton species composition is considerably more difficult in turbid waters than in open ocean waters. Prior studies based on a limited number of shipborne reflectance measurements suggested feasibility of P. globosa detection in turbid waters from hyperspectral radiometry. The availability of a new autonomous above water hyperspectral radiometer system has enabled further refinement and intensive testing of these techniques. From a time-series of 4356 water reflectance spectra measured near Ostend harbour in Belgian coastal waters from 2020/04/01 to 2020/08/18, two existing algorithms for P. globosa detection were successfully applied. Results show a high biomass P. globosa bloom occurring in late-April/early-May as found every year in water sample analyses for Belgian coastal waters. The high temporal resolution of the radiometric data allows to capture the evolution of the bloom at time scales sufficiently short (hourly and daily) compared to growth/decay and tidal processes.The challenges of extending the methods to future spaceborne instruments are also tested by simulating the impact of errors in sensor inter-band calibration, atmospheric correction and radiometric noise. Results show that because of their spectral coherence, atmospheric correction errors impact only slightly P. globosa detection whereas inaccuracy in inter-band calibration and radiometric noise are much more problematic as they affect each spectral band independently. Because radiometric noise should be reduced in the new generation of hyperspectral sensors and can always be reduced by spatial binning, the inter-band relative calibration uncertainty appears to be the main challenge for spaceborne mission design. Indeed, it was demonstrated that inter-band calibration error should be <0.25% and ideally 0.1% at top of the atmosphere highlighting the need for particular attention to inter-band calibration in sensor design and post processing treatments including vicarious calibration.

Genetic Analysis of a Large-Scale Phaeocystis globosa Bloom Offshore Qingdao, China.

A sudden large-scale bloom event of the haptophyte Phaeocystis globosa that lasted over one month in the winter of 2021 was observed offshore Qingdao, China. This P. globosa bloom event was unusual as it was the first P. globosa bloom recorded in Qingdao offshore. Furthermore, the temperature at which this event occurred was much lower than that of previous P. globosa blooms in China. We hypothesize that the P. globosa strains that drove the development of this bloom offshore Qingdao were genetically unique and have a competitive advantage in the environmental conditions. To test this hypothesis, we analyzed P. globosa genetic diversity and the temporal dynamics of the bloom, using the high-resolution molecular markers pgcp1 and cox1 that we developed recently. The analysis revealed that the genetic compositions of P. globosa offshore Qingdao were rather limited, containing two dominant genotypes and other rare genotypes with low abundance, representing a small portion of the genetic diversities identified in coastal waters in China, and were rather different from the P. globosa genotypes outside of the Jiaozhou Bay before the P. globosa bloom in the winter of 2021. This suggested only certain strains contribute to the development of blooms under certain environmental conditions. The genetic composition may indicate the unusual timing and scale of this P. globosa event.

Effects of modified clay on the formation of Phaeocystis globosa colony revealed by physiological and transcriptomic analyses

The harmful algal bloom (HAB) species Phaeocystis globosa is commonly observed in global temperate and tropical oceans, and colonies of P. globosa exhibit a dominant morphotype during blooms. The use of polyaluminium chloride modified clay (PAC-MC) is an effective mitigation strategy for P. globosa blooms. Although previous studies have found that PAC-MC can stimulate P. globosa colony formation at low concentrations and inhibit it at higher concentrations, the underlying mechanisms of these effects are poorly understood. Here, we comprehensively compared the physiochemical indices and transcriptomic response of residual P. globosa cells after treatment with two concentrations of PAC-MC. The results showed that PAC-MC induced oxidative stress, photosynthetic inhibition, and DNA damage in residual cells. Moreover, it could activate antioxidant responses and enhance the repair of photosynthetic structure and DNA damage in cells. The biosynthesis of polysaccharides was enhanced and genes associated with cell motility were down-regulated after treatment with PAC-MC, resulting in the accumulation of colonial matrixes. After treatment with a low concentration of PAC-MC (0.1 g/L), the residual cells were slightly stressed, including physical damage, oxidative stress and other damage, and polysaccharide synthesis was enhanced to promote colony formation to alleviate environmental stress. Moreover, the damage to residual cells was slight; thus, normal cell function provided abundant energy and matter for colony formation. After treatment with a high concentration of PAC-MC (0.5 g/L), the residual cells suffered severe damage, which disrupted normal physiological processes and inhibited cell proliferation and colony formation. The present study elucidated the concentration-dependent mechanism of PAC-MC affecting the formation of P. globosa colonies and provided a reference for the application of PAC-MC to control P. globosa blooms.

Spatiotemporal Variation in Phytoplankton and Physiochemical Factors during Phaeocystis globosa Red-Tide Blooms in the Northern Beibu Gulf of China

Phaeocystis globosa blooms frequently in the Beibu Gulf of China. This species has a distinct life cycle that includes colonies and solitary cells. Colonies are formed during a bloom, while solitary cells are produced between blooms. Information about the abundance of solitary cells and other picophytoplankton in the northern Beibu Gulf is limited. To elucidate phytoplankton variation trends during periods of frequent P. globosa blooms and to determine the main physiochemical factors affecting phytoplankton distribution, four cruises were conducted between November 2018 and April 2019. Seawater was collected, and water temperature, salinity, and nutrient concentrations were simultaneously determined. Redundancy analysis was performed to understand the relationship between environmental factors and phytoplankton assemblages. Seven phytoplankton clusters were present during the cruises. Picophytoplankton abundance (including Synechococcus and Picoeukaryote groups I and II) dominated during the four cruises. Synechococcus abundance was restricted by the low temperatures in winter, decreasing from November to February and increasing in April. Picoeukaryote I abundance was almost unaffected by low temperatures and was mainly affected by nutrient concentration. P. globosa solitary cell abundance increased from November to January and decreased in February and April, and phosphorus was the key factor affecting P. globosa blooms. This is the first study to reveal the abundance and distribution of P. globosa solitary cells in this area.

Development of sensitive genotype‐specific quantitative polymerase chain reaction methods for detection of Phaeocystis globosa in the South China Sea

AbstractSince 1997, dense blooms of the alga Phaeocystis globosa have occurred in the South China Sea (SCS), and previous studies have revealed the co‐existence in this sea of two types of P. globosa cell characterized by different marker pigment profiles. However, owing to a lack of quantitative methods for the detection of different types of P. globosa cells, the dynamics of P. globosa blooms in the SCS are still poorly understood. In this study, on the basis of phylogenetic analysis of the mitochondrial atp8 (Mit atp8) gene and pigment profiles, the P. globosa strains from Pacific and Atlantic coastal waters were divided into four genotypes, of which Type I and Type IV strains co‐exist in the SCS. Furthermore, two genotype‐specific quantitative polymerase chain reaction (qPCR) methods were developed targeting the Mit atp8 gene for quantitative determinations of the densities of Type I and Type IV P. globosa cells. Both qPCR methods were reproducible, highly sensitive, and specific with a wide range of detection (from 30 to 1 × 108 cells L−1) for target P. globosa genotypes in the field, thereby facilitating the detection of low cell densities prior to bloom development, as well as high cell densities during bloom periods. Finally, the developed qPCR assays were successfully applied to determine the distribution patterns of Type I and Type IV P. globosa in the Beibu Gulf, a region of the SCS characterized by a high frequency of P. globosa blooms.

Removal effect of algicidal modified clay on Phaeocystis globosa blooms in culturing enclosure experiments: A short communication

With the increased scale of marine aquaculture in the Beibu Gulf, as well as accelerating urbanization and industrialization, frequent harmful algal blooms (HABs) have occurred in this area, especially those formed by Phaeocystis globosa in the past several years. As the P. globosa bloom has been a serious marine ecological disaster in the Beibu Gulf, research on quick and effective methods to eliminate P. globosa blooms is a hot research topic. In this study, the bacteria Streptomyces yatensis B4503 combined with modified diatomite was used to prepare algicidal modified clay, which was then used to study the removal effect on P. globosa blooms in field culture enclosures. The results showed that after 6 h of treatment with algicidal modified clay, compared with the blank control group, the cell density and chlorophyll a content of P. globosa decreased by 26.86% and 64.03%, respectively, and they decreased by 75.23% and 84.81%, respectively, after 24 h. The study indicated that algicidal modified clay can be applied to eliminate HABs caused by P. globosa in coastal water.

Effects of Modified Clay on Phaeocystis globosa Growth and Colony Formation.

Phaeocystis globosa is a globally distributed harmful algal blooms (HABs) species dominated by the colonial morphotype, which presents dramatic environmental hazards and poses a threat to human health. Modified clay (MC) can effectively flocculate HAB organisms and prevent their subsequent growth, but the effects of MC on colony-dominated P. globosa blooms remain uncertain. In this paper, a series of removal and incubation experiments were conducted to investigate the growth, colony formation and colony development of P. globosa cells after treatment with MC. The results show that the density of colonies was higher at MC concentrations below 0.2 g/L compared to those in the control, indicating the role of P. globosa colonies in resistance to environmental stress. Concentrations of MC greater than 0.2 g/L could reduce the density of solitary cells and colonies, and the colony diameter and extracellular polysaccharide (EPS) content were also decreased. The adsorption of MC to dissolved inorganic phosphorus (DIP) and the cell damage caused by collision may be the main mechanisms underlying this phenomenon. These results elucidate that the treatment with an appropriate concentration of MC may provide an effective mitigation strategy for P. globosa blooms by preventing their growth and colony formation.

Harmful algal blooms caused by Phaeocystis globosa from 1997 to 2018 in Chinese coastal waters

From 1997 to 2018, Phaeocystis globosa caused harmful algal blooms in Chinese coastal waters almost every year. In this study, the spatial and temporal distribution of P. globosa blooms and its influencing factors were discussed. The results showed that 80.6% of the P. globosa blooms happened in the South China Sea and 72.5% happened in the period from November to March of the following year. But in the Yellow Sea, P. globosa blooms might be limited by green tides. Among the influencing factors, temperature might be an important one that affected the spatial and temporal distribution of P. globosa blooms. Furthermore, eutrophication provided material basis and El Nino events might also stimulate the occurrence of P. globosa blooms. This study is helpful to reveal causes and mechanisms of P. globosa blooms and reduce the negative impacts of blooms on ecological environment, economic development and the safety of nuclear power plants.

Co-occurrence of chromophytic phytoplankton and the Vibrio community during Phaeocystis globosa blooms in the Beibu Gulf

Accumulating research evidence has revealed that harmful algal blooms (HABs) can substantially affect the community structures of phytoplankton and heterotrophic bacteria in marine ecosystems. However, little is known about their species-specific interactions between phytoplankton and heterotrophic bacteria during the HABs period and about their interaction shifts in response to blooms. From this perspective, we investigated the co-occurrence of chromophytic phytoplankton and Vibrio during Phaeocystis globosa blooms in the Beibu Gulf. The results showed that Vibrio communities were distinct during the blooms, and P. globosa blooms resulted in a decline in phytoplankton alpha diversity, revealing that the blooms could affect their community compositions. The regression lines between the Shannon indices and Bray-Curtis distances of phytoplankton and Vibrio showed positive correlations with each other (p < 0.001), suggesting that they may have intrageneric symbiotic interactions overall. In addition, network analysis further demonstrated that relationships between phytoplankton and Vibrio were dominated by positive correlations, and more interaction modules were observed during the blooms, revealing that the blooms intensified synergistic association and mutual symbiotic interactions between them. Environmental factors (SiO32-, NH4+, NO3- and TN,) and P. globosa density more deeply affected network interactions between phytoplankton and Vibrio during the periods of P. globosa blooms than those before the blooms and after the blooms. This study provided new insight to elucidate community structure and interaction relationships between phytoplankton and Vibrio in response to P. globosa blooms and their ecological effects in marine ecosystems.