Dinoflagellate Blooms Research Articles

Metaproteomics reveals metabolic activities potentially involved in bloom formation and succession during a mixed dinoflagellate bloom of Prorocentrum obtusidens and Karenia mikimotoi.

Understanding metabolic activities involved in bloom formation during a single-species algal bloom has improved greatly. However, little is known about metabolic activities during a multi-species algal bloom. Here, we investigated protein expression profiles at different bloom stages of a mixed dinoflagellate bloom caused by Karenia mikimotoi and Prorocentrum obtusidens (syn. Prorocentrum donghaiense) using a metaproteomic approach. Our results indicated that both P. obtusidens and K. mikimotoi cells highly expressed proteins associated with essential cellular metabolisms such as cell growth and nutrient acquisition before their respective bloom occurrence. P. obtusidens preferentially enhanced uptake and utilization of ammonium, amino acid and organophosphorus-like phospholipid at the early bloom stage, and expressed highly abundant chloroplast peridinin-chlorophyll a-binding protein at the early and the P. obtusidens-dominated bloom stages, indicating their important roles in preferential occurrence and maintenance of P. obtusidens bloom. While absorption and utilization of nutrients, especially ammonium, urea, cyanate, phospholipid, and nucleotide, as well as endocytosis, in K. mikimotoi cells, were enhanced. Notably, both species increased photosynthesis, energy generation, cell proliferation, cell motility and cell defense before their respective blooms, which were beneficial to dealing with adverse external stresses, enabling them to be more competitive and advantageous in complex environments. Interestingly, diatom groups (Skeletonema, Pseudo-nitzschia, and Thalassiosira) decreased uptake and utilization of ambient nutrients and cell proliferation during the bloom period. This study demonstrates that niche differentiation and functional complementarity among phytoplankton species regulate bloom formation and succession during the mixed bloom.

Assessing optical water types in Asian coastal ocean waters from space using GCOM-C/SGLI observations

ABSTRACT Human activities and climate change exert environmental and ecological pressures on the Asian coastal ocean waters through dramatic changes in optical water types. This necessitates the development of methods to observe and monitor optical water types with optimal spatiotemporal resolution, which can only be achieved through remote sensing techniques, particularly for optically detectable water properties. This study utilized 250-mresolution ocean colour data retrieved from the Second-Generation Global Imager (SGLI), covering waters across Asia, to develop a common optical water type algorithm for Asian coastal ocean waters. The algorithm is based on relationships among optical properties, threshold values, and criteria, classifying the waters into eight optical water types: turbid, high-coloured-dissolved organic matter (CDOM), mixed, oligotrophic, coccolithophore bloom, mesotrophic, diatom bloom, and dinoflagellate bloom waters. The values of remote sensing reflectance (Rrs) slope between 490 and 530 nm (3.0 × 10−6) and the Rrs at 490 nm (0.0013 sr−1) serve as optimal thresholds for distinguishing dinoflagellate blooms, diatom blooms, and high-CDOM waters. The proposed method performs well in classifying most water bodies, though some artefacts suggest that refinements are needed to improve the method’s robustness. The ability to classify optical water types provides a valuable tool for marine ecosystem and biogeochemical studies, especially in optically complex water bodies where land–ocean interactions are particularly strong.

Organic matter accumulation driven by land-sea interactions during the Late Cretaceous: A geochemical study of the Nenjiang Formation, Songliao Basin

The Late Cretaceous Nenjiang Formation in the Songliao Basin presents a unique setting to examine how climate change and sea-level rise influenced organic matter accumulation. This study combines TOC analysis, Rock-Eval pyrolysis, GC–MS, GC–MS-MS, and elemental geochemistry on core samples from two wells to assess organic matter deposition before and after transgressive events. TOC values range from 0.18 to 14.63 wt%, with significant variations in hydrocarbon potential and thermal maturity. Periodic warm and cool climates triggered intermittent seawater intrusions that created anoxic conditions conducive to marine diatom and lacustrine dinoflagellate proliferation. Extended warm periods, however, suppressed dinoflagellate development and reduced paleo-productivity. The activity of methanogenic bacteria further contributed to the degradation of sedimentary organic matter, hindering its accumulation. While warm climates facilitated flood events that transported terrigenous nutrients, enhancing dinoflagellate blooms and expanding the oxygen minimum zone. These findings highlight the bio-environmental interactions that governed organic matter accumulation during transgressions, offering insights for exploration in similar sedimentary environments.

Spatiotemporal dynamics of dinoflagellate communities in the Taiwan Strait and their correlations with micro-eukaryotic and bacterial communities

Dinoflagellate blooms have negative adverse effects on marine ecosystems. However, our knowledge about the spatiotemporal distribution of dinoflagellate communities and their correlations with micro-eukaryotic and bacterial communities is still rare. Here, the sediment micro-eukaryotic and bacterial communities were explored in the Taiwan Strait (TWS) by 16S and 18S rRNA gene high-throughput sequencing. We found that the dinoflagellates were the most abundant algal group in TWS, and their relative abundance was higher in spring and autumn than in summer. Moreover, the species richness and community composition of dinoflagellates showed strong seasonal patterns. NO3-N and NH4-N had the strongest correlations with the spatiotemporal dynamics of community composition of dinoflagellates. The dinoflagellates had a significantly wider niche breadth than other algal groups for NH4-N, NO3-N and NO2-N, and therefore potentially contributed to a wider distribution range and high abundance in TWS. In addition, the dinoflagellates had stronger impacts on microeukaryotes than on bacteria for both community composition and species richness. However, the dinoflagellates showed close coexistence with bacteria but loose coexistence with microeukaryotes in spring co-occurrence networks. This close coexistence suggests the potentially strong synergy effects between dinoflagellates and bacteria in spring dinoflagellate blooms in TWS. Overall, this study revealed the distribution mechanisms of dinoflagellates in TWS based on niche breadth and also unveiled the different effects of dinoflagellates on micro-eukaryotic and bacterial communities.

The occurrence patterns and alternative host use of the generalist parasitoid Parvilucifera infectans (Alveolata, Perkinsozoa) of marine dinoflagellates revealed by a high-frequency time series microscopic data at a temperate coastal site

Species belonging to the genus Parvilucifera (Alveolata, Perkinsozoa) are known as generalist parasitoids that can infect a variety of marine dinoflagellates and ultimately kill the host cell. Despite the accumulation of knowledge on Parvilucifera parasitoids over the last twenty years, the occurrence pattern and use of alternative hosts for persistent transmission within fluctuating natural dinoflagellate host communities have received relatively little attention. To address this, high-frequency (i.e., daily) time series protist monitoring was conducted for 411 days, from April 2020 to May 2021, at a temperate coastal site in Jinhae Bay, Republic of Korea. This site was characterized by frequent blooms of mixed dinoflagellates throughout most of the year. Nonetheless, Parvilucifera infections were detected only in the spring seasons, and its occurrence pattern was primarily governed by the presence and cell density of its primary dinoflagellate host, Akashiwo sanguinea. As long as the primary host was present at high densities (greater than 104 cells L-1), this primary host alone could support the transmission and persistence of the parasitoid. However, if the cell density of the primary host started to decline, then Parvilucifera searched for and exploited alternative hosts for its continued survival. Taken together, this study suggests that the presence and cell density of its preferred primary host species and the duration for which the density remains above the threshold level are key factors that regulate the timing of Parvilucifera occurrence and alternative host use.

Quantitative real-time PCR assays for species-specific detection and quantification of Baltic Sea spring bloom dinoflagellates.

In the Baltic Sea, the dinoflagellates Apocalathium malmogiense, Biecheleria baltica, and Gymnodinium corollarium are important contributors to the spring bloom. However, their relative contribution to the bloom community cannot be unambiguously determined by conventional light microscopy due to a lack of resolution of distinctive morphological features of the three species. Here, we describe a molecular approach based on a quantitative real-time polymerase chain reaction (qPCR) primer and probe system, targeting the ITS1 and ITS2 regions of the rRNA gene for all three species and enabling their quantification. The specificity of the method was demonstrated using monocultures of A. malmogiense, B. baltica, G. corollarium as well as three other dinoflagellate species co-occurring in the Baltic Sea during spring and validated using field-collected phytoplankton samples.

Resting Cysts of the Toxic Dinoflagellate Gymnodinium catenatum (Dinophyceae) Ubiquitously Distribute along the Entire Coast of China, with Higher Abundance in Bloom-Prone Areas

Blooms of Gymnodinium catenatum have occurred occasionally in different areas of China and caused tremendous economic loss and even threatened human health. Not only is G. catenatum an important harmful-algal-bloom (HAB)-causing species, but also the only gymnodinioid dinoflagellate known to produce paralytic shellfish poisoning toxins (PSTs). Due to the germination of resting cysts, which often initiates blooms, the distribution and abundance of cysts in sediments and particularly the confirmation of cyst beds are important information for understanding and predicting dinoflagellate blooms. In this research, 199 sediment samples were collected from China’s coastal seas, ranging from the Beidaihe in the Bohai Sea (BS) to the southernmost sample from the Nansha Islands of the South China Sea (SCS). TaqMan quantitative PCR (qPCR) assays with species-specific primers and probes were developed to specifically detect the distribution and abundance of cysts in the 199 samples. The detection revealed that G. catenatum cysts were widely present in the sediments (126 of the 199 samples), with 93.55%, 74.65%, 42.37%, and 50% of the samples detected positively from the BS, YS, ECS and SCS, respectively, and covering the vast sea area from Nansha Islands to the Beidaihe area. The single-cyst morpho-molecular identification in the samples from Beidaihe confirmed the existence of G. catenatum cysts in the BS, and the positive detections of G. catenatum cysts using the qPCR methods. While G. catenatum cysts were widely distributed in all four seas of China, the average abundance was relatively low (1.0 cyst per gram of wet sediment). Three samples from the East China Sea (ECS), however, contained G. catenatum cysts at a relatively higher level (23 cysts g−1 wet sediment) than other sea areas, suggesting a pertinence of cyst abundance to the frequent occurrences of G. catenatum blooms in the area during recent years. Collectively, for G. catenatum being such an important toxic and HAB-causing species globally, the ubiquitous distribution of its cysts along the coastal waters of China and higher abundance in the bloom-prone areas warns us of a risk that cyst beds, although currently low in abundance, may seed HABs in any and many sea areas of China at any forthcoming year, and particularly those areas with records of frequent HABs outbreaks in the past.

High and fine resolution of bloom dynamics using HPLC analysis in a semi-enclosed harbour

Chemotaxonomic analysis, a functionally efficient method, was performed every week over a year in the semi-enclosed Jangmok Bay to determine the composition of major phytoplankton assemblages, including small phytoplankton. Multiple blooms occurred through a year: two in summer and one in fall. The high abundance of diatoms in summer resulted in an intensive bloom of cryptophytes with a one-week time lag, followed by a dinoflagellate bloom in the fall. Additional microscopic analysis revealed an ecological succession of major phytoplankton species: a bloom of fast-growing Pseudo-nizschia sp. in summer was replaced by a bloom of Cryptomonas sp. one week after the diatom bloom, and then further succeeded to an Akashiwo sanguinea bloom in fall. The dominance of relatively small-sized Cryptomonas sp. led to a mismatch between the microscopic and chemotaxonomic results during the second bloom, indicating size dependence. In contrast, for the Akashiwo bloom, the microscope analysis was significantly underestimated by the chemotaxonomic analysis. Additionally, the ecological traits inherited by bloom-forming species play a role in their bloom dynamics. This study highlighted that the frequent sampling with the rapid HPLC analysis is effective for accurately understanding spatiotemporal variations of blooms, and can be an invaluable strategy for early warning and understanding bloom patterns in changing coastal ecosystems.

An unusual winter bloom of dinoflagellates with notable damage to kelp cultivation around Shandong peninsula, China

In the coastal waters around Shandong peninsula, an unprecedented winter bloom of dinoflagellates Gonyaulax polygramma and Akashiwo sanguinea occurred in 2021 from late November to early December. The bloom affected a wide area of coastal waters extending from west to east along the northern Shandong peninsula and had a devastating blow to the kelp cultivation industry. Based on the remote-sensing data, the initiation of the bloom was traced back to the region adjacent to the mouth of the Yellow River in Laizhou Bay, where enhanced freshwater discharge from the Yellow River was recorded from September to November. It's proposed that the increased precipitation in the Yellow River basin associated with northward extension of the precipitation band in China could be an important reason for this winter bloom. This unusual winter bloom around Shandong peninsula highlights the potential risks of harmful algal blooms and their impacts on coastal ecosystems under the background of climate change.

Environmental controls on bioluminescent dinoflagellate density, in Laguna Grande, Fajardo, Puerto Rico

Introduction: Bio bays in Puerto Rico play an important socio-economic role and declines in dominant bioluminescent dinoflagellate Pyrodinium bahamense are concerning. Studies show erratic blooms with is weak correlation to in situ environmental factors. Our study examines shorter field and longer proxy records on dinoflagellate density at Laguna Grande de Fajardo (LGF). Objectives: To quantify temporal changes in dinoflagellate density in a long-term monitoring study, understand how the marine environment modulates those changes, and determine the wider impacts of a fluctuating climate and extreme events on proxies for dinoflagellate density. Methods: Bimonthly samples were collected from 2016 to 2021 at three sampling sites in LGF. Dinoflagellates density was estimated by Sedgewick Rafter counting cells. Environmental conditions were obtained from Rio Fajardo 5007100 station and NOAA buoy 41056. Marine climate and biotic proxies were obtained from remote sensing measurements. Kruskal Wallis, Spearman correlations and cross-correlations in the shorter field and longer proxy records were used to evaluate environmental controls on LGF dinoflagellate blooms. Results: Six years of field monitoring densities found a low period in 2016-2017, frequent and intense blooms in 2018-2021 punctuated by hurricanes. Generally low values were recorded in late winter in contrast with higher values in late summer (Aug-Nov). Light winds and mixed layer response to seasonal warming in the form of high tides and low salinity, were found to sustain dinoflagellate reproduction. Conclusions: Bioluminescent dinoflagellates are vital to coastal tourism and require resource management. LGF results show that: 1) dinoflagellate counts fluctuate widely, 2) fluorescing dinoflagellates are sensitive to environmental conditions because of limited seasonality and narrow physiological range, 3) hurricanes play a role by ‘raking and refreshing’ the coastal lagoon for subsequent biotic reproduction, and 4) intra-seasonal fluctuations of density and proxies relate to air-sea thermodynamic conditions, the salinity budget and sea level.

Emergency control of dinoflagellate bloom in freshwater with chlorine enhanced by solar radiation: Efficiency and mechanism

Dinoflagellate requires a lower temperature and blooms frequently in the spring and autumn compared to regular cyanobacteria. The outbreak of dinoflagellate bloom will also lead to the death of some aquatic organisms. However, research on freshwater dinoflagellates is still lacking due to the challenges posed by classification and culture in laboratory. The removal effect and mechanism of Peridinium umbonatum (P. umbonatum, a typical dinoflagellate) were investigated using solar/chlorine in this study. The effect of simulated solar alone on the removal of algae was negligible, and chlorine alone had only a slight effect in removing algae. However, solar/chlorine showed a better removal efficiency with shoulder length reduction factor and kmax enhancement factor of 2.80 and 3.8, respectively, indicating a shorter latency period and faster inactivation rate for solar/chlorine compared to solar and chlorine alone. The removal efficiency of algae gradually increased with the chlorine dosage, but it dropped as the cell density grew. When the experimental temperature was raised to 30 °C, algal removal efficiency significantly increased, as the temperature was unsuitable for the survival of P. umbonatum. Attacks on cell membranes by chlorine and hydroxyl radicals (•OH) produced by solar/chlorine led to a decrease in cell membrane integrity, leading to a rise in intracellular reactive oxygen species and an inhibition of photosynthetic and antioxidant systems. Cell regeneration was not observed in either the chlorine or solar/chlorine systems due to severe cell damage or cysts formation. In addition, natural solar radiation was demonstrated to have the same enhancing effect as simulated solar radiation. However, the algal removal efficiency of solar/chlorine in real water was reduced compared to 119 medium, mainly due to background material in the real water substrate that consumed the oxidant or acted as shading agents.

Characterization and inter-strain variability in ichthyotoxicity of Heterocapsa ovata (Peridiniales, Dinophyceae) from temperate waters of South Australia

IntroductionHarmful algal bloom (HAB)-forming species and populations exhibit substantial intraspecific functional trait variation, which can confer eco-evolutionary advantages. Phenotypic variability among populations can buffer the immediate detrimental effects of environmental fluctuations, with more diverse populations expected to survive changing conditions more efficiently than their uniform counterparts.MethodsIn February 2014, a mixed fish-killing dinoflagellate bloom occurred in the temperate waters of Coffin Bay, South Australia, causing the death of oysters and fish in the area. The bloom was dominated by Karenia mikimotoi and a cryptic species of Heterocapsa. Twenty-one monoclonal Heterocapsa isolates were established from the site and identified as H. ovata using microscopy and universal ribosomal markers (ITS/5.8S and LSU D1/D3 rDNA regions; SSU and cob were used for amplicon sequencing). These isolates were tested for ichthyotoxicity using a bioassay based on cells from the gills of rainbow trout (Oncorhynchus mykiss). Culture fraction preparations (whole cells, supernatant, and lysed cells) were analyzed to determine ichthyotoxicity levels.ResultsThe highest ichthyotoxicity was observed in lysed cells, with surprisingly high inter-strain variability. This suggests that different strains of H. ovata have varying levels of toxicity.DiscussionResults from this study expand our understanding of the adaptive strategies of HAB species and enable predictions of future population dynamics under changing climatic conditions. The substantial phenotypic variability among H. ovatastrains highlights the potential for diverse responses to environmental stressors, underscoring the importance of considering intraspecific variation in ecological and evolutionary studies of HABs.

An Arctic sea ice spring bloom driven and dominated by Dinoflagellates - a harbinger of the future sea ice?

The sea ice spring bloom is crucial for sustaining Arctic marine food webs, with sea ice algae serving as primary carbon sources for higher trophic levels. Despite the prevailing dominance of diatom species in sea ice spring blooms, our study highlights a notable deviation, showcasing a bloom driven by dinoflagellates. Through field sampling of first-year sea ice cores and subsequent analysis of physical and biogeochemical parameters, combined with amplicon sequencing of the 18S rRNA gene, we investigated the occurrence and implications of this significant dinoflagellate bloom, with a particular focus on Polarella glacialis. Our findings reveal that high irradiances at the top of the ice core, coupled with elevated nutrient availability and warm ice conditions, are key drivers of this phenomenon, as elucidated by redundancy analysis. Moreover, our results suggest a potential climate-driven decline in snow cover on sea ice, increased open leads, and thinner sea ice, which may favor the proliferation of dinoflagellates over diatoms. This alternative dinoflagellate-dominated bloom could have profound ecological consequences, given the enriched omega-3 fatty acid content of dinoflagellates, thereby influencing energy transfer within the Arctic marine food web. Furthermore, our study identifies the presence of not only Polarella glacialis but also Chytridinium, an ectoparasite on copepod eggs, and the green algae Ulothrix in relatively high abundances within the sea ice. These findings shed light on the intricate interplay between environmental factors and microbial community dynamics within Arctic sea ice ecosystems.

Dinoflagellate composition and environmental conditions in the Xuan Dai Bay, South-Central Vietnam

The dinoflagellate community was investigated in association with environmental factors using a data set in April 2021 and April 2022 in Xuan Dai Bay, South-Central Viet Nam. Environmental variables, including physical parameters and dissolved inorganic nutrients, were measured in April 2022. Seventy-three dinoflagellate taxa were identified for Xuan Dai Bay. There was a significant difference in the number and abundance of dinoflagellates between two parts of the bay, the upper and lower bay. The study showed that dinoflagellates favored an area with good water exchange and were less affected by aquaculture activities. Principal component analysis (PCA) was used to explore the relative abundances of different phytoplankton groups, their diversity indices, and environmental variables at the surface and bottom layers of the two parts of the bay. The results showed that dinoflagellates correlated to physical parameters (e.g., PAR, salinity, temperature) at the surface layer and nutrients at the bottom layer. Dinoflagellates and diatoms are mixotrophic and strongly correlated at the bottom layer in Xuan Dai Bay. This strong relationship in the bay was because of the dominance of a heterotrophic genus, Protoperidinium. The present study provided characteristics of the dinoflagellates in Xuan Dai Bay and the possible impacts of environmental parameters on their abundance. The results can be used for further studies and possibly managing of dinoflagellate blooms in coastal waters.

Temperature and nutrients drive distinct successions between diatoms and dinoflagellates over the past 40 years: Implications for climate warming and eutrophication

Diatoms and dinoflagellates are two typical functional groups of phytoplankton, playing important roles in ecosystem processes and biogeochemical cycles. Changes in diatoms and dinoflagellates are thought to be one of the possible mechanisms for the increase in harmful algal blooms (HABs), due to changing hydrological conditions associated with climate change and human activities. However, little is known about their ability to adapt to changing ocean environments, thus making it difficult to know whether and how they are adapting. By analyzing a 44-year monitoring dataset in the central Bohai Sea during 1978–2021, we found that the abundance ratio of diatoms to dinoflagellates showed a decreasing trend seasonally and ecologically, indicating that the phytoplankton community underwent distinct successional processes from diatom dominance to diatom-dinoflagellate co-dominance. These processes exhibited varying responses to temperature, nutrient concentrations and ratios, and their interactions, of which temperature primarily drove the seasonal succession whereas nutrients were responsible for the ecological succession. Specifically, diatoms showed a preference for lower temperatures and higher DIP concentrations, and were able to tolerate lower DIN at lower temperatures. In contrast, dinoflagellates tended to prevail at conditions of warming and high N/P ratios. These different traits of diatoms and dinoflagellates reflected the fact that warming as a result of rising temperature and eutrophication as a consequence of nutrient input would favor dinoflagellates over diatoms. Moreover, the increasing dominance of dinoflagellates indicated that dinoflagellate blooms were likely to become more frequent and intense in the central Bohai Sea.

Effects of bottom‐up factors on growth and toxin content of a harmful algae bloom dinoflagellate

AbstractThe toxin‐producing dinoflagellateAlexandrium pseudogonyaulaxhas become increasingly abundant in northern European waters, replacing otherAlexandriumspecies.A. pseudogonyaulaxproduces goniodomins and lytic substances, which can be cytotoxic toward other organisms, including fish, but we still know little about the environmental conditions influencing its growth and toxicity. Here, we investigated the impacts of different nitrogen sources and light intensities, common bottom‐up drivers of bloom formation, on the growth and toxin content of threeA. pseudogonyaulaxstrains isolated from the Danish Limfjord. While the growth rates were significantly influenced by nitrogen source and light intensity, the intracellular toxin contents only showed strong differences between the exponential and stationary growth phases. Moreover, the photophysiological response ofA. pseudogonyaulaxshowed little variation across varying light intensities, while light‐harvesting pigments were significantly more abundant under low light conditions. This study additionally highlights considerable physiological variability between strains, emphasizing the importance of conducting laboratory experiments with several algal strains. A high physiological plasticity toward changing abiotic parameters points to a long‐term establishment ofA. pseudogonyaulaxin northern European waters.

Full-length transcriptome analysis of a bloom-forming dinoflagellate Prorocentrum shikokuense (Dinophyceae)

Prorocentrum shikokuense (formerly P. donghaiense) is a pivotal dinoflagellate species associating with the HABs in the East China Sea. The complexity of its large nuclear genome hindered us from understanding its genomic characteristics. Full-length transcriptome sequencing offers a practical solution to decipher the physiological mechanisms of a species without the reference genome. In this study, we employed single-molecule real-time (SMRT) sequencing technology to sequence the full-length transcriptome of Prorocentrum shikokuense. We successfully generated 41.73 Gb of clean SMRT sequencing reads and isolated 105,249 non-redundant full-length non-chimeric reads. Our trial has led to the identification of 11,917 long non-coding RNA transcripts, 514 alternative splicing events, 437 putative transcription factor genes from 17 TF gene families, and 34,723 simple sequence repeats. Additionally, a total of 78,265 open reading frames were identified, of them 15,501 were the protein coding sequences. This dataset is valuable for annotating P. shikokuense genome, and will contribute significantly to the in-depth studies on the molecular mechanisms underlining the dinoflagellate bloom formation.

Impact of natural events on metal bioaccumulation in Anemonia sulcata

Samples of Anemonia sulcata were collected in 2022 from different areas of the Canary Islands affected by different natural contamination sources, such sandstorms, submarine volcanic activity, continuous rainfall, upwelling and dinoflagellate blooms. Significant differences were observed between the zones for the metals and trace elements analyzed (Al, Zn, Cd, Pb, Ni, Co, Fe, B, Cu, Mg and Li). Anemones from volcanic areas showed higher levels of Cd, Pb and Ni. Individuals from sandstorm areas showed elevated levels of Al, Zn and Fe. Samples collected from areas affected by upwelling processes had higher concentrations of Cu, Mg and Li. Finally, the areas affected by dinoflagellates showed lower levels of Zn, Pb, Fe, Mg and Li. The study reveals how natural phenomena dramatically influence metal accumulation in A. sulcata, which is of great value for anticipating and managing potential problems associated with public health.

Preliminary investigation on the causes of red tides in Qinhuangdao coastal areas in 2022.

To explore the causes of red tides in Qinhuangdao coastal water, we conducted surveys on both water quality and red tides during April to September of 2022 and analyzed the relationships between main environmental factors and red tide organisms through the factor analysis and canonical correspondence analysis. The results showed that there were eight red tides along the coast of Qinhuangdao in 2022, with a cumulative blooming area of 716.1 km2. The red tides could be divided into three kinds based on the major blooming organisms and occurrence time, Noctiluca scintillans bloom, diatom-euglena (Skeletonema costatum, Eutreptiella gymnastica, Pseudo-nitzschia spp.) bloom, and dinoflagellate (Scrippsiella trochoidea and Ceratium furca) bloom. Seasonal factor played roles mainly during July to September, while inorganic nutrients including nitrogen and phosphorus influenced the blooms mainly in April and July. The canonical correspondence analysis suggested that N. scintillans preferred low temperature, and often bloomed with high concentrations of ammonium nitrogen and dissolved inorganic phosphorus. S. costatum, E. gymnastica, and Pseudo-nitzschia spp. could tolerate broad ranges of various environmental factors, but favored high temperature and nitrogen-rich seawater. C. furca and S. trochoidea had higher survival rate and competitiveness in phosphate-poor waters. Combined the results from both analyses, we concluded that the causes for the three kinds of red tide processes in Qinhuangdao coastal areas in 2022 were different. Adequate diet algae and appropriate water temperature were important factors triggering and maintaining the N. scintillans bloom. Suitable temperature, salinity and eutrophication were the main reasons for the diatom-euglena bloom. The abundant nutrients and seawater disturbance promoted the germination of S. trochoidea cysts, while phosphorus limitation caused the blooming organism switched to C. furca and maintained the bloom hereafter.

Population dynamics of dominant dinoflagellate species in the North Sea: in situ growth rates, photosynthetic potential, and losses due to parasitism

In the North Sea, Tripos and Dinophysis are commonly occurring mixotrophic planktonic dinoflagellate genera. In order to understand their bloom dynamics, an occurring bloom dominated by T. furca and D. norvegica was followed for several days. High cell abundances of these species were located to estimate: in situ growth rates from cell cycle analyses, depth distributions, growth rates sustained by photosynthesis, and parasite infection prevalence in all T. furca, T. fusus, D. norvegica and D. acuminata. Cell abundances were over 10000 cells L−1 for T. furca and up to 18000 cells L−1 for D. norvegica. Cells accumulated between 15-25 m depth and presented low specific in situ growth rates of 0.04-0.15 d−1 for T. furca and 0.02-0.16 d−1 for D. norvegica. Photosynthesis could sustain growth rates of 0.01-0.18 d−1 for T. furca and 0.02 to 0.14 d−1 for D. norvegica, suggesting that these species were relying mainly on photosynthesis. Parasite infections where generally low, with occasional high prevalence in D. norvegica (by Parvilucifera sp.) and T. fusus (by Amoebophrya sp.), while both parasites showed comparable prevalence in D. acuminata, which could offset in situ growth rates by parasite-induced host mortality. The restructuring effect of parasites on dinoflagellate blooms is often overlooked and this study elucidates their effect to cell abundances and their growth at the final stages of a bloom.