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Ocean acidification (OA), caused by the rising concentration of atmospheric CO2, leads to changes in the marine carbonate system. This, in turn, affects the physiological processes of phytoplankton. In response to increased pCO2 levels, marine microalgae modulate their physiological responses to meet their energy and metabolic requirements. Nitrogen metabolism is a critical metabolic pathway, directly affecting the growth and reproductive capacity of marine microorganisms. Understanding the molecular mechanisms that regulate nitrogen metabolism in microalgae under OA conditions is therefore crucial. This study aimed to investigate how OA affects the expression profiles of key genes in the nitrogen metabolic pathway of the marine diatom Skeletonema costatum. Our findings indicate that OA upregulates key genes involved in the nitrogen metabolic pathway, specifically those related to nitrate assimilation and glutamate metabolism. Moreover, pCO2 has been identified as the predominant factor affecting the expression of these genes, with a more significant impact than pH variations in S. costatum. This research not only advances our understanding of the adaptive mechanisms of S. costatum in response to OA but also provides essential data for predicting the ecological consequences of OA on marine diatoms. [ABSTRACT FROM AUTHOR]

Phytoplankton samples were collected both inside and outside a large scale raft mussel culture area of Gouqi island in September 2023. The diurnal variation characteristics of phytoplankton community inside and outside the culture area were analyzed by using abundance and diversity index and multivariate statistical methods. A total of 7 phyla and 158 species of phytoplankton were collected(103 species inside and 98 species outside the area), including 104 species of diatom(accounting for 65.82%), 30 species of Pyrrophyta(accounting for 18.99%), and 15.19% for the rest species. During the daytime, 94 species were collected in the inner area, while 103 species were collected at night. In the outer area, 93 species were collected during the daytime, and 98 species were collected at night. The dominant species of phytoplankton in the aquaculture area were 9 species, while in the outer area, there were 12 dominant species. Among them, Skeletonema costatum and Noctiluca scintillans were dominant species throughout the day in both areas. The average abundance of phytoplankton in the inner area was (1.77×107±2.5×106) cells/L during the daytime and (1.64×107±2.31×106) cells/L at night, while in the outer area, it was (1.87×107±3.36×106) cells/L during the daytime and (1.75×107±2.72×106) cells/L at night. The abundance variation in the inner area showed a multi-peak pattern, with peak values occurring during the rising and falling tides and the high tide. In contrast, the abundance variation in the outer area showed a single-peak pattern, closely related to tidal changes, with the peak value only occurring during the high tide.Non-metric multidimensional scaling (nMDS) analysis showed that there was no significant difference in phytoplankton community between day and night in the aquaculture area (P>0.05), but there was significant difference in phytoplankton community outside the area (P<0.05), which was significantly correlated with tidal changes (P<0.01). Temperature, dissolved oxygen and salinity were significantly correlated with the number and abundance of phytoplankton (P<0.05), the number of phytoplankton species was significantly negatively correlated with phosphate and nitrate (P<0.05), and the abundance was significantly positively correlated with ammonia nitrogen and silicate (P<0.05). The results showed that the impact of large-scale raft culture on phytoplankton community in local waters could present a more positive result at the stage of red tide organism aggregation. [ABSTRACT FROM AUTHOR]

This study emphasises the importance of environmental filters in the dynamics of the zooplankton community and the ecological relationships with phytoplankton in three zones of a tropical mesotidal estuary.Thus, sampling was carried out in six different locations strategically positioned along the Preguiças River estuary, with the following objectives: to characterise the abundance of zooplankton and, through this, determine changes in the community's α‐ and β‐diversity indices depending on variables environmental; to define environmental filters that affect the indicator species of ecosystem zones; and to identify the interaction between phytoplankton and zooplankton along the estuarine gradient.The zooplankton community contained 80 species, including 14 phyla, with Arthropoda being the most diverse, followed by Ciliophora and Mollusca. The class Copepoda stood out, with Paracalanus crassirostris, Pseudodiaptomus gracilis, and Oithona nana dominating the community. In total, 21 species were selected as indicators, including Temora turbinata in the coastal zone, Rhizodomus tagatzi in the mixing zone, and Moina micrura in the tidal river zone. The environmental heterogeneity showed significant spatial differences, with variations governed mainly by salinity, temperature, and suspended organic matter, which acted as the principal environmental filters. The coastal zone and mixing zone species demonstrated direct ecological relationships with the blooms of the diatoms Skeletonema costatum and Asterionellopsis glacialis, in which the abundance of zooplankton was favoured by their occurrence, denoting top‐down control of the trophic network. For the partitioning of β diversity, the turnover component was responsible for the diversity value due to environmental heterogeneity, which distinguished communities across zones.Our findings represent the first comprehensive investigation into the relationship between environmental heterogeneity and zooplankton within this tropical ecosystem, subject to mesotides. These discoveries are pivotal in identifying environments highly susceptible to degradation (low β diversity) and those acting as dispersal centres (high β diversity), thereby facilitating targeted conservation efforts and more efficient management of estuarine systems. Therefore, our results provide a crucial basis for the sustainable management of similar coastal ecosystems in different parts of the world. [ABSTRACT FROM AUTHOR]

Siliceous diatoms are one of the most prominent actors in the oceans, and they account for approximately 40% of the primary production and particulate organic carbon export flux. It is believed that changes in carbon flux caused by variations in diatom distribution can lead to significant climate shifts. Although the fundamental pathways of diatom-driven carbon sequestration have long been established, there are no reports of CaCO3 precipitation induced by marine diatom species. This manuscript introduces novel details regarding the enhancement of aragonite precipitation during photosynthesis in Skeletonema costatum in both artificial and natural seawater. Through direct measurements of cell surfaces via a pH microelectrode and zeta potential analyzer, it was determined that the diatom-mediated promotion of CaCO3 precipitation is achieved through the creation of specific microenvironments with concentrated [CO32−] and [Ca2+] and/or the dehydrating effect of adsorbed Ca2+. Based on this mechanism, it is highly plausible that diatom-mediated calcification could occur in the oceans, an assertion that was supported by the significant deviation of total alkalinity (TA) from the conservative TA-salinity mixing line during a Skeletonema costatum bloom in the East China Sea and other similar occurrences. The newly discovered calcification pathway establishes a link between particulate inorganic and organic carbon flux and thus helps in the reassessment of marine carbon export fluxes and CO2 sequestration efficiency. This discovery may have important ramifications for assessing marine carbon cycling and predicting the potential effects of future ocean acidification. [ABSTRACT FROM AUTHOR]

A comparative assessment of phytoplankton dynamics during low tide (LT) and high tide (HT) was conducted from February 2022 to January 2023 in a tropical mesotidal creek, Manori, Mumbai, India. In total, 124 phytoplankton species were recorded. The HT resulted in greater species richness (124 species) and diversity indices (Shannon–Wiener's index) than the LT (102 species). The Pielou's evenness (Jʹ) and Simpson's dominance index (1-D) did not show significant fluctuations with the tides due to the marine phytoplankton species moving rhythmically in and out of the creek with the tides. Overall, the seasonal abundance was maximum during pre-monsoon at HT (5.79 × 103 u/L) and lowest in monsoon at LT (0.45 × 103 u/L), whereas spatial abundance was maximum at S1 (HT- 4.04 × 103 u/L) at HT and lowest at S3 (LT- 0.75 × 103 u/L) at LT. The diatoms dominated in their abundance (1.83 × 103 u/L and 3.82 × 103 u/L in HT) and diversity (77 in LT and 92 in HT). The species such as Coscinodiscus centralis, Coscinodiscus granii, Coscinodiscus radiatus, Triops furca, Melosira varians, Nitzchsia palea, Chaetoceros affinis, Skeletonema marinoi, Stephanocyclus meneghinianus, Planktoniella sol and Skeletonema costatum were the dominant native residents in the creek. SIMPER analysis revealed that the maximum similarity was during the monsoon (47.65%), and the minimum was during the pre-monsoon (38.10%) at LT. However, in HT, the maximum similarity of phytoplankton shifted to post-monsoon (63.85%) and the minimum during the pre-monsoon (46.71%). The mean value of richness (dʹ) and Shannon's diversity (Hʹ) showed a moderate phytoplankton diversity in the system. The environmental parameters (water temperature > pH > nitrate > salinity > DO > Alk > silicate) have a greater influence on the distribution of the phytoplankton community with tides as revealed by the Canonical correspondence analysis. Therefore, it has been found that tides play a significant role in the distribution and abundance of the phytoplankton community in a mesotidal creek environment. [ABSTRACT FROM AUTHOR]

The outbreak and scale of harmful algal blooms (HABs) have been on the rise in recent years, mainly attributed to the effects of worsening seawater eutrophication and climate-change-related temperature increases. Yet, current approaches for detecting HABs fail to meet the requirements of rapid qualification and on-site quantification of the algae species and early warning of the outbreaks. Herein, an electrochemical biosensor based on In2O3/NC/Au NP nanomaterials was developed for the dynamic detection of Skeletonema costatum (S. costatum), one of the typical HABs. Specifically, the biosensor demonstrated a lower limit of detection (LOD, 671 fg/μL or 3528 cells/L) and had been confirmed to be accurate and reliable when compared to droplet digital PCR (ddPCR) and traditional microscope techniques. Moreover, for actual sample analysis, the concentrations of S. costatum were determined as 3.8 × 103 to 2.1 × 105 cells/L by the biosensor, which demonstrated a lower risk of S. costatum bloom outbreak in the sampling region and was consistent with the standard survey method. Therefore, the biosensor has great potential in the early stage qualitative analysis and on-site quantification of S. costatum and serves as an ideal warning technology of HAB outbreaks. [ABSTRACT FROM AUTHOR]

As two significant pollutants, the increased concentrations of copper ions and microplastics in coastal waters pose a substantial threat to the health of marine ecosystems. This study explored the individual and combined toxic effects of copper ions and microplastics on the marine diatom Skeletonema costatum. The results indicated that copper ions at a concentration of 0.05 mg/L exerted a negative impact on the growth of S. costatum; however, the influence of microplastics on algal cell growth was more complex: there was no significant inhibition of algal cell growth observed within the first 72 h of cultivation, but a pronounced negative effect on cell growth was noted between 72 and 96 h, with high concentrations (10.00 mg/L) of microplastics even causing a premature stagnation phase in algal cell growth. When both pollutants were present simultaneously, their impact on cell growth was similar to that of the microplastic pollution group, yet the growth condition was better than that of the copper ion pollution group. Through investigation of adsorption rates and toxicity mitigation rates, it was found that the adsorption of copper ions by microplastics was a significant reason for the improved growth condition of algal cells in the mixed pollution group compared to the copper ion pollution group. However, in the later stages of cultivation, the inhibitory effect of microspheres on algal cell growth counteracted their mitigating effect on copper ion toxicity. This study provides a reference for evaluating the impact of microplastics and heavy metals on coastal ecosystem health and for revealing the interactions between different pollutants. [ABSTRACT FROM AUTHOR]

Increasing the marine carbon dioxide (CO 2) absorption capacity by adding alkaline minerals into the world's oceans is a promising marine carbon dioxide removal (mCDR) approach to increase the ocean's CO 2 storage potential and mitigate ocean acidification. Still, the biological impacts of dispersion of alkaline minerals need to be evaluated prior to its field deployment, especially the impacts of the initial discharge causing local and temporary extreme alkalinity/pH changes. In this study, the toxicity effect on marine microalgae of two commonly used alkaline minerals, calcium hydroxide (Ca(OH) 2) and magnesium hydroxide (Mg(OH) 2), was determined by adding the same equivalent molar concentration of hydroxyl ions. Cultures of marine green microalgae Tetraselmis suecica were exposed to Ca(OH) 2 or Mg(OH) 2 , in concentrations mimicking the initial high concentrations following a dispersion scenario from a ship. A short-term exposure with high-alkaline mineral concentration called "dispersion phase" was followed by a dilution step and a "regrowth" phase over 6 d. There was no detectable effect of Mg(OH) 2 treatment on algae growth either after the dispersion phase or during the regrowth phase, compared to control treatments. The Ca(OH) 2 treatment resulted in very few living algal cells after the dispersion phase, but a similar growth rate was observed during the regrowth phase as was for the Mg(OH) 2 and control treatments. Standardized whole effluent toxicity (WET) tests were carried out with a range of Mg(OH) 2 concentrations using a sensitive marine diatom, Skeletonema costatum, which confirmed the relatively low toxicity effect of Mg(OH) 2. Similar biological effects were observed on natural microalgae assemblages from a local seawater source when applying the same Mg(OH) 2 concentration range and exposure time used in the WET tests. The results suggest that Mg(OH) 2 is relatively safe compared to Ca(OH) 2 with respect to marine microalgae. [ABSTRACT FROM AUTHOR]

Phytoplankton blooms have become a global concern due to their negative impacts on public health, aquaculture, tourism, and the economic stability of coastal regions. Therefore, elucidating the shifts in phytoplankton community structure and abundance, as well as their environmental drivers, is crucial. However, existing studies often fail to capture the detailed dynamics of phytoplankton blooms and their environmental triggers due to low temporal observation resolution. In this study, high temporal resolution (daily) samples were collected over 43 days to investigate the influence of environmental factors on phytoplankton in Qinhuangdao in the summer. During the observation period, a total of 45 phytoplankton species were identified, comprising 26 Bacillariophyta species, 16 Dinophyta species, 2 Euglenophyta species, and 1 Chromophyta species. Interestingly, a lag bloom pattern of phytoplankton behind freshwater input was observed across day-to-day samples. Phytoplankton blooms typically lagged 1-3 days behind periods of decreased salinity and nutrient input, suggesting that freshwater influx provides the foundational materials and benefits for these blooms. Moreover, the phytoplankton blooms were triggered by six dominant species, i.e., Chaetoceros spp., Pseudo-nitzschia delicatissima, Skeletonema costatum, Protoperdinium spp., Leptocylindrus minimus, Pseudonitzschia pungens, and Thalassiosira spp. Consequently, the succession of phytoplankton showed a predominant genera shift in the following sequence: Nitzschia, Protoperdinium, and Prorocentrum - Skeletonema - Pseudonitzschia - Gymnodinium - Leptocylindrus. Besides that, a deterministic process dominated phytoplankton community assembly across time series, and DIP is a key factor in shifting the phytoplankton community structures in this area. In summary, our study offers high-resolution observations on the succession of phytoplankton communities and sheds light on the complex and differentiated responses of phytoplankton to environmental factors. These findings enhance our understanding of the dynamics of phytoplankton blooms and their environmental drivers, which is essential for the effective management and mitigation of their adverse impacts. [ABSTRACT FROM AUTHOR]

Phytoplankton are photosynthetic microscopic organisms that inhabit the upper sunlit layer (euphotic zone) of marine and fresh water bodies. Phytoplankton, as the primary producer of the aquatic ecosystem’s food chain and are very sensitive to environmental changes as energy stored up in them determine the basic primary productivity of an ecosystem. There is dearth of information on the phytoplankton community of the Festac creek and thus the need for this study which aims at microscopically investigating the phytoplankton community of the Festac creek. The Phytoplankton diversity and distribution of the Festac creek, Lagos, Nigeria. was investigated for 12 months (November 2021 – October, 2022). Phytoplankton samples were collected monthly for 12 months, using a 55 μm mesh size standard plankton net towed horizontally from a motorized boat for 5 mins at < 4 Km/h and preserved by adding 4% unbuffered formalin. The drop count microscopic analysis method was used to study the phytoplankton species. A total of 34 phytoplankton species from 7 algal classes namely Bacillariophyceae (16 species), Cyanophyceae (9 species), Chlorophyceae (2 species), Conjugatophyceae (3 species), Dictyochophyceae (2 species), Tintinnid (1 species) and Dinophyceae (1 species) were recorded. Notable species were recorded such as: Lyngbya sp, Prorocentrum lima, Navicula sp. Nitzschia lineola, Phormidium bohneri, Oscillatoria limosa, Oscillatoria nigro viridis, Oscillatoria formosa and some other known marine species such as Coscinodiscus radiatus, Coscinodiscus marginatus Skeletonema costatum, Odontella sinensis, Thalassionema nizschoides, Fragillaria oceanica, Spirulina subsalsa and Tintinnopsis radix. The most abundant class was the Cyanophyceae (Blue-green algae) with Oscillatoria limosa being the most abundant species. This could be attributed to the constant addition of nutrient particularly nitrate and phosphate run offs from industries around the study area which enhances cyanobacterial growth and indicates that the Festac creek is eutrophic. [ABSTRACT FROM AUTHOR]

The effects of turbulence on phytoplankton growth have received considerable attentions. However, the complexity of turbulence poses a significant challenge to its systematic characterization in the laboratory, resulting in relatively limited data on the effects of turbulence on several algal species. Here, a laboratory turbulence simulation system was set up to systematically investigate the growth of three common diatom species (Thalassiosira pseudonana, Skeletonema costatum, and Phaeodactylum tricornutum) under stationary and turbulent conditions (at 60, 120, 180 rpm), and measurements were taken for the algal biomass, algal photosynthetic activity, and nutrients consumption. By comparing the growth of three algae species under different turbulence exposure intensities, this study found that different algae exhibit varying sensitivities to turbulence, and therefore have different shear thresholds. Meanwhile, cell morphology is the key factor influencing the different shear threshold values observed in the three diatom species. Additionally, turbulence could impact algal aggregation and light availability, and dramatically improve nutrient uptake by phytoplankton. Our study will provides theoretical support for future endeavors in using turbulence to cultivate phytoplankton or combat algal blooms. [ABSTRACT FROM AUTHOR]

In our recent investigations of diatom diversity, we studied three species, namely, Skeletonema costatum, Skeletonema subsalsum, and Skeletonema potamos. Although they have been found frequently in Changjiang (Yangtze) River Basin, their morphological and molecular identification is difficult in taxonomy. Therefore, to integrate morphological and molecular biological approaches, we compared systematically their morphological characters and performed phylogenetic analysis. Twelve strains of Skeletonema were collected and isolated from Shanghai and Jiangsu, China, and their morphological characteristics were examined by light microscopy (LM) and the scanning electron microscopy (SEM). Based on morphological comparison, we determined that S. potamos is easy to distinguish from the other two species. The heavily silicified areolae, undulated or cleft distal ends of terminal fultoportula processes (TFPPs), absence of basal pores of fultoportula processes (FPPs), the root-like protrusions of FPPs, and no interlocking connection are the stable characteristics that can be used to identify S. potamos. However, there are only two features that can distinguish S. costatum from S. subsalsum, namely the location of terminal rimoportulae (TRPs) and the distal shape of TFPPs. In addition, we amplified and sequenced nine common genetic markers from the strains, from which 101 sequences were obtained, constructed phylogenetic trees based on the nine genes and evaluated that seven genes can be used to identify S. potamos, and revealed that S. subsalsum is the closest known relative of S. costatum, and only ATP synthetase beta-subunit gene (atpB) is able to distinguish them from each other, which strongly support that it is an effective molecular marker for Skeletonema. This work provided a theoretical basis for the taxonomic study of Skeletonema. [ABSTRACT FROM AUTHOR]

The dinoflagellate Noctiluca scintillans is a globally distributed bloom-forming species. Previous studies have shown that the primary reason for the frequent occurrence of N. scintillans blooms may be the proliferation of microalgae due to eutrophication, which provides a sufficient source of food. Meanwhile, N. scintillans may release nutrients into the environment, thus affecting the population dynamics of microalgae. Thus, to investigate the interaction between N. scintillans and co-occurring microalgae, this study examined the population dynamics of N. scintillans and their interaction with three representative microalgae species in response to varying nutrient levels. The findings indicate that the growth of N. scintillans is slow when co-cultured with diatom Skeletonema costatum. Moreover, a high density and rapid growth rate of S. costatum may have an inhibitory effect on the growth of N. scintillans. Conversely, the population abundance of N. scintillans increased with the rise in the population density and nutritional level of Heterocapsa steinii (dinoflagellate) and Heterosigma akashiwo (raphidophyceae). Notably, N. scintillans can discharge specific nutrients into the aquatic environment, which can subsequently be assimilated and exploited by H. steinii. Thus, the interaction between the species and population dynamics of plankton, as well as changes in nutrient levels within the ecosystem, played a significant role in influencing the growth and population dynamics of N. scintillans. The mutualistic association between N. scintillans and microalgae may establish a transient closed loop, thereby fostering the sustained proliferation and subsequent expansion of N. scintillans. [ABSTRACT FROM AUTHOR]

This study investigated the effects of levofloxacin (LEV) and norfloxacin (NOR) on Skeletonema costatum, focusing on cell growth, chlorophyll a (Chla) content, maximal quantum yield of PSII (Fv/Fm), protein content, enzyme activities of superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GSH-PX), and the membrane lipid peroxidation product malondialdehyde (MDA) content were conducted to analyze the responses of S. costatum under LEV and NOR exposure. Cell growth, Chla content, Fv/Fm, protein content, enzyme activities, and MDA content were assessed to elucidate physiological changes. Both LEV and NOR inhibited S. costatum growth, except for 10 mg/L NOR, which promoted growth. Algal cells exhibited higher sensitivity to LEV, with 96h-IC50 values of 14.770 mg/L for LEV and 44.250 mg/L for NOR. Low NOR concentration (10 mg/L) increased Chla content, while high antibiotic concentrations (>20 mg/L for LEV, >100 mg/L for NOR) decreased Chla content and Fv/Fm, indicating an impact on photosynthesis. Elevated LEV and NOR levels reduced protein and MDA content but increased GR, SOD, and GSH activities, indicating induced oxidative stress. The study provides a comprehensive analysis of LEV and NOR effects on marine microalgae growth and underlying physiologicalmechanisms, shedding light on potential ecological risks posed by antibiotics inmarine ecosystems. [ABSTRACT FROM AUTHOR]

Despite management efforts, anthropogenic nutrient enrichments continue to enhance phytoplankton blooms worldwide. Release of nitrogen and phosphorus compounds not only provides surplus of nutrients but also disbalances their stoichiometry. Declines in the relative availability of dissolved silicon might induce limitation in diatoms, major primary producers with silicified shells. We studied experimentally how nutrient enrichment and resulting decline in dissolved silicon to nitrogen ratios (Si:N) affect the structure and functioning of natural plankton communities. Nitrate was added to create a range of Si:N ratios and phosphate was supplied in Redfield ratio to nitrogen. We also manipulated copepod abundance to understand the top-down effects on communities experiencing nutrient enrichment. Nitrogen and phosphorus additions resulted in a steep phytoplankton biomass increase, followed by a post-bloom decline. Phytoplankton bloom biomass was higher in high nitrogen treatments but during the post-bloom period this trend switched. Biomass was sustained longer in high Si:N treatments, indicating that silicon limitation terminates the bloom. Many diatom species did not benefit from nitrogen and phosphorus enrichment and diatom dominance ceased below Si:N of 0.4:1. Under high grazing pressure, silicate was taken up faster suggesting that silicification is important in diatom defense. Copepods shaped plankton communities via feeding on dinoflagellates, chlorophytes and the diatom Skeletonema costatum but there was no significant effect of nitrogen and phosphorus enrichment on copepod abundance. Our results, combined with previous studies, show that while nutrient concentrations define the total phytoplankton bloom biomass, resource ratios are important in sustaining biomass and determining community structure and composition. [ABSTRACT FROM AUTHOR]

Under global change scenarios, the sea surface temperature is increasing steadily along with other changes to oceanic environments. Consequently, marine diatoms are influenced by multiple ocean global change drivers. We hypothesized that temperature rise mediates the responses of polar and temperate diatoms to UV radiation (UVR) to different extents, and exposed the temperate centric diatoms, Thalassiosira weissflogii and Skeletonema costatum, and a polar pennate diatom Entomoneis sp., to warming (+5°C) for 10 days, then performed short‐term incubations under different radiation treatments with or without UVR. The effective quantum yields of the three diatoms were stable during exposure to PAR, but decreased when exposed to PAR + UVR, leading to significant UV‐induced inhibition, which was 3% and 9%, respectively, for T. weissflogii and S. costatum under ambient temperature but increased to 12% and 17%, respectively, in the cells acclimated to the warming treatment. In contrast, UVR induced much higher inhibition, by about 45%, in the polar diatom Entomoneis sp. at ambient temperature, and the warming treatment alleviated the UV‐induced inhibition, which dropped to 36%. The growth rates were significantly inhibited by UVR in S. costatum under the warming treatment and in Entomoneis sp. under ambient temperature, while there was no significant effect for T. weissflogii. Our results indicate that the polar diatom was more sensitive to UVR though warming could alleviate its impact, whereas the temperate diatoms were less sensitive to UVR but warming exacerbated its impacts, implying that diatoms living in different regions may exhibit differential responses to global changes. [ABSTRACT FROM AUTHOR]

ABSTRACT Skeletonema costatum, a cosmopolitan diatom primarily inhabiting coastal ecosystems, exhibits a typically close yet variable relationship with heterotrophic bacteria. The increasing temperature of surface seawater is expected to substantially affect the viability and ecological dynamics of S. costatum, potentially altering its relationship with bacteria. However, it remains unclear to what extent the elevated temperature could change these relationships. Here, the relationship between axenic S. costatum and natural seawater bacteria underwent a dramatic shift from mutualism to antagonism as the co-culture temperature increased from 20°C to 25°C. The co-occurrence network indicated significantly increased complexity of interaction between S. costatum and bacteria community after temperature elevation, especially with Flavobacteriaceae, implying their potential role in eliminating S. costatum under higher temperatures. Additionally, a Flavobacteriaceae isolate, namely MS1 identified as Tamlana genus, was isolated from the co-culture system at 25°C. MS1 had a remarkable ability to eliminate S. costatum, with the mortality rate at 25°C steadily rising from 30.2% at 48 h to 92.4% at 120 h. However, it promoted algal growth to some extent at 20°C. These results demonstrated that increased temperature promotes MS1 shifts from mutualism to antagonism with S. costatum. According to the comparative genomics analysis, changes in the lifestyle of MS1 were attributed to the increased gliding motility and attachment of MS1 under elevated temperature, enabling it to exert an algicidal effect through direct contact with alga. This investigation provided an advanced understanding of interactions between phytoplankton and bacteria in future warming oceanic ecosystems.IMPORTANCEOcean warming profoundly influences the growth and metabolism of phytoplankton and bacteria, thereby significantly reshaping their interactions. Previous studies have shown that warming can change bacterial lifestyle from mutualism to antagonism with phytoplankton, but the underlying mechanism remains unclear. In this study, we found that high temperature promotes Tamlana sp. MS1 adhesion to Skeletonema costatum, leading to algal lysis through direct contact, demonstrating a transition in lifestyle from mutualism to antagonism with increasing temperature. Furthermore, the gliding motility of MS1 appears to be pivotal in mediating the transition of its lifestyle. These findings not only advance our understanding of the phytoplankton-bacteria relationship under ocean warming but also offer valuable insights for predicting the impact of warming on phytoplankton carbon sequestration.

Diatom sinking plays a crucial role in the global carbon cycle, accounting for approximately 40% of marine particulate organic carbon export. While oceanic models typically represent diatoms as microphytoplankton (> 20 mm), it is important to recognize that many diatoms fall into the categories of nanophytoplankton (2-20 mm) and picophytoplankton (< 2 mm). These smaller diatoms have also been found to significantly contribute to carbon export. However, our understanding of their sinking behavior and buoyancy regulation mechanisms remains limited. In this study, we investigate the sinking behavior of a nanoplanktonic diatom, Phaeodactylum tricornutum (P. tricornutum), which exhibits rapid changes in sinking behavior in response to varying nutrient concentrations. Our results demonstrate that a higher sinking rate is observed under phosphate limitation and depletion. Notably, in phosphate depletion, the sinking rate of P. tricornutum was 0.79 ± 0.03md-1, nearly three times that of the previously reported sinking rates for Skeletonema costatum, Ditylum brightwellii, and Chaetoceros gracile. Furthermore, during the first 6 h of phosphate spike, the sinking rate of P. tricornutum remained consistently high. After 12 h of phosphate spike, the sinking rate decreased to match that of the phosphate repletion phase, only to increase again over the next 12 hours due to phosphate depletion. This rapid sinking behavior contributes to carbon export and potentially allows diatoms to exploit nutrient-rich patches when encountering increased nutrient concentrations. We also observed a significant positive correlation (P< 0.001) between sinking rate and lipid content (R = 0.91) during the phosphate depletion and spike experiment. It appears that P. tricornutum regulates its sinking rate by increasing intracellular lipid content, particularly digalactosyldiacylglycerol, hexosyl ceramide, monogalactosyldiacylglycerol, and triglycerides. Additionally, P. tricornutum replaces phospholipids with more dense membrane sulfolipids, such as sulfoquinovosyldiacylglycerol under phosphate shortage. These findings shed light on the intricate relationship between nutrient availability, sinking behavior, and lipid composition in diatoms, providing insights into their adaptive strategies for carbon export and nutrient utilization. [ABSTRACT FROM AUTHOR]

In the context of global change, the stressors of warming and eutrophication have significant ecological implications in coastal waters. In order to examine the diversity of phytoplankton and its relationship with water quality, we conducted a survey of phytoplankton community compositions and their correlation with environmental changes over four seasons in a eutrophic bay located in the East China Sea. Through a systematic analysis, we identified diatoms and dinoflagellates as the primary dominant groups, with the species Skeletonema costatum, Skeletonema marinoi, Biddulphia sinensis, Thalassiosira eccentrica, Leptocylindrus danicus, Coscinodiscus oculus-iridis, Coscinodiscus jonesianus, and Chaetoceros knipowitschi as the most abundant species in all seasons. Significant seasonal alterations were observed in both environmental settings and phytoplankton species richness, dominance, and abundance. The phytoplankton community varied in its response to diverse aquatic environments and was principally affected by temperature, silicic acid concentrations, and suspended solids. Elevated temperatures were found to promote an increase in phytoplankton abundance. However, no clear evidence of diatom and dinoflagellate succession in relation to N:P ratio was observed across seasons. Water quality analysis illustrated that the majority of the study area exhibited a mid-eutrophic with severe organic pollution. The abundance of phytoplankton was significantly influenced by eutrophication and organic pollution. The accelerated warming process related to coastal nuclear power plants and nutrient regime alterations significantly affect the temporal shift of the phytoplankton community. These findings contribute valuable insights into the effects of eutrophic environments on the structure of phytoplankton communities in coastal aquatic systems. [ABSTRACT FROM AUTHOR]

In order to improve the understanding of the environmental impacts of polymetallic nodule mining, ecotoxicological studies were conducted on the growth of model phytoplankton species Skeletonema costatum and Prorocentrum donghaiense using cobalt and nickel. This study evaluated various physiological and ecological indicators, such as cell proliferation, chlorophyll a, pigments, total protein, and antioxidant enzyme markers. The results show that the introduction of low amounts of cobalt or nickel increased the growth rate of phytoplankton. The phytoplankton benefited from low concentrations of cobalt and nickel stress. The increased protein levels and decreased activity of antioxidant enzymes considerably impacted physiological responses during the promotion of cell abundance. High concentrations of cobalt or nickel resulted in decreased light-absorbing pigments, increased photoprotective pigments, an inactive chlorophyll content, decreased total proteins, and maximal antioxidant enzyme activity in phytoplankton. Throughout the experiment, both the phytoplankton protein and enzyme activity declined with prolonged stress, and the cells underwent age-induced damage. Thus, seabed mining's repercussions on phytoplankton could result in both short-term growth promotion and long-term damage. These consequences depend on the impurity concentrations infiltrating the water, their duration, and the organism's physiological responses. [ABSTRACT FROM AUTHOR]

As two significant pollutants, the increased concentrations of copper ions and microplastics in coastal waters pose a substantial threat to the health of marine ecosystems. This study explored the individual and combined toxic effects of copper ions and microplastics on the marine diatom Skeletonema costatum. The results indicated that copper ions at a concentration of 0.05 mg/L exerted a negative impact on the growth of S. costatum; however, the influence of microplastics on algal cell growth was more complex: there was no significant inhibition of algal cell growth observed within the first 72 h of cultivation, but a pronounced negative effect on cell growth was noted between 72 and 96 h, with high concentrations (10.00 mg/L) of microplastics even causing a premature stagnation phase in algal cell growth. When both pollutants were present simultaneously, their impact on cell growth was similar to that of the microplastic pollution group, yet the growth condition was better than that of the copper ion pollution group. Through investigation of adsorption rates and toxicity mitigation rates, it was found that the adsorption of copper ions by microplastics was a significant reason for the improved growth condition of algal cells in the mixed pollution group compared to the copper ion pollution group. However, in the later stages of cultivation, the inhibitory effect of microspheres on algal cell growth counteracted their mitigating effect on copper ion toxicity. This study provides a reference for evaluating the impact of microplastics and heavy metals on coastal ecosystem health and for revealing the interactions between different pollutants.

The distribution and variation in environmental factors and the phytoplankton community in the Qiongzhou Strait were investigated in autumn 2015 and spring 2016. The environmental factors were different in the two seasons, as seen when using one-way ANOVA testing, principal component analysis, and cluster analysis. The temperature and levels of dissolved oxygen and soluble solids were higher in autumn, and the ammonia (NH4-N) level was much higher in spring (4.66 ± 0.97 µmol/L), which led to a higher concentration of dissolved inorganic nitrogen in the northeast area. A total of 118 species of phytoplankton were found, with 47 common species in both seasons and more species in spring. Bacillariophyta (diatom) contributed to over 80% of the relative abundance in both seasons. The species of Chrysophyta and Xanthophyta were endemic species in autumn and spring, respectively. Skeletonema costatum and Chaetoceros curvisetus were the common dominant species, with nine dominant species in both seasons. Higher abundance and biodiversity of phytoplankton appeared in spring, and their differences were mostly determined by NH4-N level, hydrodynamic conditions and artificial activities in the coastal area in the Qiongzhou Strait. [ABSTRACT FROM AUTHOR]

With the rapid development of nanotechnology, nanomaterials have been widely utilized in many industries and daily life applications due to their unique properties. However, their potential release and the human health/environmental consequences have raised public concern greatly. In this study, we compared the toxic effects of AgNPs and AgNO3 on Skeletonema costatum in 10, 100, and 500 μg·L−1 Ag treatments. In all the AgNP exposure experiments, cell membrane damage and growth inhibition occurred. However, the cellular damage only obviously appears on exposure to a high concentration of AgNO3. The antioxidant enzyme (SOD and CAT) activities and lipid peroxidation in Skeletonema costatum were also induced significantly in the AgNP treatments. In addition, the percentage of Ag release in seawater increased with the increase in AgNP concentrations (13%, 32% for 100 and 500 μg·L−1 AgNPs). Thus, the biotoxic effects of AgNPs were found to be due to a combination of the solubilization of particles into toxic metal ions and the nature of the nanoparticles. It was worth noting that the induction of oxidative stress and damage to the cell membrane comprised the dominant mechanism of toxicity for AgNPs. Therefore, the behavior of nanometals in seawater affects the biotoxic effect on the phytoplankton. These results shed light on the biological toxicity of nanometals and their possible toxicity mechanism. [ABSTRACT FROM AUTHOR]

We investigated the possible conditions to cryopreserve six marine microalgae that are frequently used in Taiwanese aquaculture: Amphora exigua, Isochrysis galbana, Nannochloropsis oculata, Seminavis gracilenta, Skeletonema costatum, and Tetraselmis elliptica. The approaches for microalgae cryopreservation with cooling from room temperature to −40°C, a rate of approximately −1°C/min, and final storage in liquid nitrogen at −196°C are described. We subsequently assessed the viability of cultures of these microalgae after thawing in a 40°C water bath and evaluated the relative survival rates to compare the suitability of cryoprotectant and cryopreservation conditions. We used four concentrations (5%, 10%, 15%, and 20%) of five cryoprotectants, dimethyl sulfoxide (DMSO), methanol (MeOH), glycerine (GLY), ethylene glycol (EG), and propylene glycol (PG), and found that the individual microalgae required distinct cryoprotectant and concentrations. Only S. costatum was not viable after cryopreservation under any of the conditions tested. Relative survival rates were 87.6% (A. exigua), 70.73% (I. galbana), 87.48% (N. oculata), 91.0% (S. gracilenta), and 57.8% (T. elliptica), when using 20% DMSO, 15% Gly, 20% EG, 20% DMSO, and 20% PG as cryoprotectants, respectively. In summary, we established suitable conditions to cryopreserve these five microalgae that will facilitate conserving their genetic diversity. [ABSTRACT FROM AUTHOR]

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Increasing the marine CO2 absorption capacity by adding alkaline minerals into the world's oceans is a promising marine carbon dioxide removal (mCDR) approach to increase the ocean's CO2 storage potential and mitigate ocean acidification. Still, the biological impacts of dispersion of alkaline minerals needs to be evaluated prior to its field deployment. In this study, the toxicity effect on marine microalgae of two commonly used alkaline minerals, calcium hydroxide (Ca(OH)2) and sodium hydroxide (NaOH), was compared with magnesium hydroxide (Mg(OH)2), by applying the same concentration of hydroxyl radicals (OH-) for each component. Cultures of marine green microalgae Tetraselmis suecica were exposed to NaOH, Ca(OH)2 or Mg(OH)2 in concentrations mimicking dispersion scenarios from a ship which included short-term exposure with high alkaline mineral concentration called "dispersion phase" followed by a dilution and "regrowth" phase over six days. There was no detectable effect of Mg(OH)2 treatment on algae growth either after the dispersion phase or during the regrowth phase, compared to control treatments. The Ca(OH)2 treatment resulted in very few living algal cells after the dispersion phase, but a similar growth rate was observed during the regrowth phase as was for the Mg(OH)2 and control treatments. The NaOH treatment resulted in no surviving algae after the dispersion phase and during the regrowth phase. Standardized whole effluent toxicity (WET) tests were carried out with a range of Mg(OH)2 concentrations using a sensitive marine diatom, Skeletonema costatum, which confirmed the relative low toxicity effect of Mg(OH)2. Similar biological effects were observed on natural microalgae assemblages from a local seawater source when applying the same Mg(OH)2 concentration range and exposure time used in the WET tests. The results suggest that Mg(OH)2 is relatively safe compared to Ca(OH)2 and NaOH with respect to marine microalgae. [ABSTRACT FROM AUTHOR]

This study aims to determine the effect of differences in salinity on the density of phytoplankton (Skeletonema costatum). The method in this study used a completely randomized design with 4 treatments and 3 replications. The parameters tested included the density rate of Skeletonema costatum. Data analysis uses One Way Anova to see the significance of the influence of treatment on the density of Skeletonema costatum and the density results of Skeletonema Costatum was analyzed descriptively. The highest average density of Skeletonema costatum was obtained at a salinity of 30 ppt (90,000 cells/ml), followed by a salinity of 25 ppt (Control) at (42,500 cells/ml), then a salinity of 20 ppt at (37,500 cells/ml) and the lowest at salinity 15 ppt of (32,500 cells/ml). Based on the ANOVA test, salinity had a significant effect on the density of Skeletonema costatum (P<0.05) with the best treatment being 30 ppt salinity. The results of analysis of Skeletonema costatum, a salinity of 30 ppt obtained the highest density. [ABSTRACT FROM AUTHOR]

Structural dynamics of the microphytoplankton community in accordance with the seasonal and inter-annual variations were assessed along the Cochin estuary, a tropical backwater in the southwest coast of India. Field observations were carried out for two years (January 2019 to December 2020) on a weekly basis. The study highlights significant variabilities in the community composition of microphytoplankton with respect to the diversity and abundance during the three seasons (pre-monsoon, monsoon, and post-monsoon). However, inter-annual variations were not much prominent. Although diatoms formed the major taxa for the study site in terms of average numerical abundance, a periodic shift between cyanobacteria (pre-monsoon), green algae (monsoon), and dinoflagellates (post-monsoon) was also observed. Blooms of diatoms, dominated by centrales like Skeletonema costatum, Cerataulina bicornis, Leptocylindrus danicus, Chaetoceros spp., and Thalassiosira spp. and by the dinoflagellate Akashiwo sanguinea were common in both the years. However, blooms of Tripos furca, Peridinium quadridentatum, and Noctiluca scintillans were only reported during the year 2020. The present study emphasized that the estuarine phytoplankton community structure varied significantly with variability in the physical parameters like water temperature and salinity, thus leading to the seasonality of phytoplankton composition in these ecosystems. [ABSTRACT FROM AUTHOR]

Ocean acidification produces significant changes on phytoplankton physiology that can affect their growth and primary production. Among them, a downregulation of the enzymatic activity and the production of different cellular metabolites, including chlorophyll a (Chl a), has been observed in high CO2 cultures under stable conditions. However, the extent of how phytoplankton metabolism regulation under high CO2 conditions affects pigment pools and patterns is unknown. This study shows the effect of the atmospheric CO2 increase on pigment concentration of three important marine primary producers: Thalassiosira pseudonana, Skeletonema costatum, and Emiliania huxleyi. Cultures grown under saturating photosynthetically active radiation were aerated for at least 3 weeks with current concentrations of atmospheric CO2 (0.04% CO2 in air) and with CO2 concentrations expected for future scenarios of climate change (0.1% CO2 in air) to assess the effect of CO2 under acclimated metabolism and stable conditions. Moreover, cultures were also subjected to a perturbation (4 h without aeration) to assess responses under non‐stable conditions. The results showed that light harvesting and photoprotective pigment concentrations (i.e., Chl a, Chl c2, ββ‐carotene, diadinoxanthin, diatoxanthin, fucoxanthin, among others) decreased significantly under high CO2 and stable conditions, but the response reversed after the perturbation. The de‐epoxidation state of xanthophylls, also showed similar patterns, indicating an increase in phytoplankton sensitivity under high CO2 and stable conditions. The results demonstrate the relevance of CO2 concentration and acclimation status for phytoplankton light absorption and photoprotective response. They also identify fucoxanthin and Chl c2 as suitable biomarkers of phytoplankton carbon metabolism under ocean acidification conditions. [ABSTRACT FROM AUTHOR]

Pesticides are considered to be toxic pollutants that are harmful to the health of humans and animals or dangerous to the environment. The pesticides chlorpyrifos, acetochlor, and dicofol, representatives of organophosphorus, acyl amide, and organochlorine pesticides, are widely used in agriculture and have been frequently detected in aquatic environments. However, the toxicity of these pesticides to marine microbes is unclear. In this study, the toxic effects of the three pesticides on a representative marine microalga, the diatom Skeletonema costatum (S. costatum), were investigated. Microalgal cell density and chlorophyll-a (Chl-a) content were analyzed to investigate the toxic effects after S. costatum was exposed to the three pesticides both individually and in combination. The N/P ratio in the culture medium and the degradation of the pesticides were also analyzed during exposure. Individual acute toxicity analysis indicated that the growth of S. costatum was significantly inhibited by acetochlor, followed by the effect of dicofol and chlorpyrifos. The cell membrane of the microalgae was impaired by acetochlor. Combined toxicity analysis indicated that the presence of acetochlor increased the toxicity of dicofol and chlorpyrifos. In contrast, the presence of dicofol reduced the toxicity of acetochlor and chlorpyrifos. The N/P ratio in the culture medium was largely increased at late growth stages; however, it was significantly lowered when the microalgae were exposed to chlorpyrifos compared to acetochlor and dicofol. The degradation of the pesticides was promoted by microalgae, suggesting that microalgae might contribute to the removal of these pesticides from the marine environment. The toxic mechanism of the pesticides on the marine microalgae and the fates of pesticides in the ocean need to be further studied. [ABSTRACT FROM AUTHOR]

In order to improve the understanding of the environmental impacts of polymetallic nodule mining, ecotoxicological studies were conducted on the growth of model phytoplankton species Skeletonema costatum and Prorocentrum donghaiense using cobalt and nickel. This study evaluated various physiological and ecological indicators, such as cell proliferation, chlorophyll a, pigments, total protein, and antioxidant enzyme markers. The results show that the introduction of low amounts of cobalt or nickel increased the growth rate of phytoplankton. The phytoplankton benefited from low concentrations of cobalt and nickel stress. The increased protein levels and decreased activity of antioxidant enzymes considerably impacted physiological responses during the promotion of cell abundance. High concentrations of cobalt or nickel resulted in decreased light-absorbing pigments, increased photoprotective pigments, an inactive chlorophyll content, decreased total proteins, and maximal antioxidant enzyme activity in phytoplankton. Throughout the experiment, both the phytoplankton protein and enzyme activity declined with prolonged stress, and the cells underwent age-induced damage. Thus, seabed mining’s repercussions on phytoplankton could result in both short-term growth promotion and long-term damage. These consequences depend on the impurity concentrations infiltrating the water, their duration, and the organism’s physiological responses.

Major anthropogenic activities surround the Port Blair Bay, while Aerial Bay remains as a pristine environment. A field study was carried out during the south-west monsoon season (July - August, 2011) in the two bays to compare the physicochemical parameters and their effect on phytoplankton community structure. Among the physico-chemical parameters, water temperature (p < 0.01, n = 18), DO (p < 0.01, n = 18) and TP (p < 0.05, n = 18) showed significant variation between the Bays. Salinity and Redfield ratio (N:P) was lower in Aerial Bay as compared to Port Blair Bay; while the Si:N ratio was higher in the Aerial Bay. The average chlorophyll-a concentration as well as species richness was found to be higher in the Port Blair Bay as compared to the Aerial Bay. The highest phytoplankton density and centric diatom abundance were observed in Port Blair Bay. In Aerial Bay, the centric diatoms like Dactyliosolen fragilissimus (44.5 %) and Guinardia flaccida (7.1 %) dominated, while in the Port Blair Bay, the centric diatom Skeletonema costatum (25.0 %) and a pennate diatom Nitzschia closterium (24.3 %) dominated the phytoplankton. The phytoplankton community was influenced by the nutrients from the tidal mud flats and rain-fed rivulets in the Aerial Bay; while, in the Port Blair Bay, the phytoplankton abundance was influenced by nutrients from land runoff, inundated areas and anthropogenic sources. [ABSTRACT FROM AUTHOR]

The diatom Skeletonema costatum and the haptophyte Phaeocystis globosa often form blooms in the coastal waters of the South China Sea. Skeletonema costatum commonly dominates in nutrient enrichment coastal waters, whereas P. globosa starts flourishing after the diatom blooms when phosphorus (P) is limited. Therefore, P limitation was proposed to be a critical factor affecting diatom--haptophyte transition. To elucidate the tolerance to P limitation in P. globosa compared with S. costatum, the effect of P limitation on their photosystem II (PSII) performance was investigated and their photosynthesis acclimation strategies in response to P limitation were evaluated. P limitation did not affect the growth of P. globosa over 7 days but decreased it for S. costatum. Correspondingly, the PSII activity of S. costatum was significantly inhibited by P limitation. The decline in PSII activity in S. costatum under P limitation was associated with the impairment of the oxygen-evolving complex (the donor side of PSII), the hindrance of electron transport from QA - to QB (the acceptor side of PSII), and the inhibition of electron transport to photosystem I (PSI). The 100% decrease in D1 protein level of S. costatum after P limitation for 6 days and PsbO protein level after 2 days of P limitation were attributed to its enhanced photoinhibition. In contrast, P. globosa maintained its photosynthetic activity with minor impairment of the function of PSII. With accelerated PSII repair and highly increased non-photochemical quenching (NPQ), P. globosa can avoid serious PSII damage under P limitation. On the contrary, S. costatum decreased its D1 restoration under P limitation, and the maximum NPQ value in S. costatum was only one-sixth of that in P. globosa. The present work provides extensive evidence that a close interaction exists between the tolerance to P limitation and photosynthetic responses of S. costatum and P. globosa. [ABSTRACT FROM AUTHOR]

The present study evaluates the effect of climatic events La Niña and drought on the structure of phytoplankton and hydrological variables in the Amazon estuary. Samples were collected at three sampling stations in the Taperaçu Estuary, on the Brazilian Amazon coast, in 2010 and 2011. During the rainy season of the La Niña (RS-LN) event, salinity reached significantly lower (p < 0.05) than normal values in the upper sector (10.5 ± 5.9), and significant spatial variation (p < 0.05) was recorded in the concentrations of silicate, chlorophyll-a, and phytoflagellates abundance. Significant differences were also found in salinity, turbidity, and the concentrations of dissolved nutrients and chlorophyll-a, as well as the abundance of specific phytoplankton groups, between the dry seasons of the post-drought (DS-PD) and La Niña (DS-LN) periods. During the post-drought dry season (DS-PD), high salinity (37.1 ± 1.3) and reduced precipitation contributed to the development of Psammodictyon panduriforme, a dominant marine species recorded during this period. During periods of higher rainfall (RS-LN and, to a lesser extent, DS-LN), salinity reached its lowest levels, which favored the growth of diatoms such as Cymatosira belgica, Plagiogrammopsis sp., and Skeletonema costatum. The present results indicate that the dynamics of the phytoplankton community of the Taperaçu Estuary is highly influenced by seasonality of rainfall, which is increased (more than 20%) by anomalous climate oscillations and directly affect environmental variables. This pattern would be expected in the dozens of other estuaries that have similar characteristics on the Amazon coast and in other tropical coastal zones around the world. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential nutrient element of phytoplankton, as well as a limiting factor for phytoplankton growth. It controls the succession of blooms from diatoms to dinoflagellates, especially in the East China Sea (ECS), where the eutrophication is serious. Most studies have only considered a single aspect of dissolved inorganic phosphorus (DIP) or dissolved organic phosphorus (DOP). In contrast, we investigated the growth interactions among the major bloom-forming marine diatom Skeletonema costatum and dinoflagellates Prorocentrum donghaiense and Karenia mikimotoi by using bi-algal cultures combined with DIP and DOP. Our results revealed that (1) P. donghaiense and K. mikimotoi have survival strategies that are superior to those of S. costatum in a bi-algal culture, whether under P-sufficient or P-deficient conditions, and (2) P. donghaiense has a slight competitive advantage over K. mikimotoi when P is sufficient, but the reverse is true when P is deficient. The difference in interspecific competition results at different P concentrations with DIP and DOP mainly arises from the variation in the utilization abilities of different species as regards different P sources, a finding which can also provide strong evidence for revealing the succession of diatoms and dinoflagellates blooms in the ECS. [ABSTRACT FROM AUTHOR]

Produced water (PW) is a significant byproduct of offshore oil and gas production, constituting a major waste stream in the North Sea. Existing regulations address only the dispersed aliphatic hydrocarbon content in PW, and limited attention is given to other potentially hazardous compounds, including benzene, toluene, ethyl benzene and xylene (BTEX), polycyclic aromatic hydrocarbons (PAHs), phenols, water-soluble petroleum constituents as well as production-related chemicals. In this study, Danish oil production PW samples were subjected to purge and trap extraction on granular activated carbon for volatile compounds identification and quantification by GC-MS analysis. The obtained analytical data correlate with toxicity assessments conducted on three trophic levels, bacteria (Aliivibrio fischeri), algae (Skeletonema costatum) and copepods (Acartia tonsa) on the whole effluent as well as on treated samples. The removal of the PW volatile fraction by purging experiments resulted in a decrease in toxicity response from 37% ± 23–65% ± 16 across the tested species. The chemicals identified in this study and their toxicity response enhance the comprehension of the PW effluent composition and inform the development of strategies for offshore reservoir wastewater. 1) Sampling from acidified samples from Danish offshore platforms. 2) Purge and trap on granular activate carbon (GAC). 3) GC-MS chemical analysis. 4) Ecotoxicological tests with A. fischeri, S. costatum and A. tonsa exposed to produced water. 5) Comparison and evaluation between toxicity tests and identified chemicals. [Display omitted] • Novel Extraction Method: Developed a purge and trap method using granular activated carbon. • Comprehensive Chemical Analysis: Detailed GC-MS analysis to identify and quantify volatile compounds in PW. • Ecotoxicological Impact: Demonstrated the varying toxic effects of PW on marine organisms. • Substance-Based Approach Critique: Questioned the adequacy of the substance-based approach (SBA) for predicting the environmental impact of PW. • Environmental Management Implications: Highlighted the potential of gas purging and GAC to reduce BTEX in PW. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) affect the physicochemical algal-dissolved organic matter properties, indirectly influencing the environmental behavior of contaminants including persistent organic pollutants and heavy metals. Limited research is available on the roles played by intracellular- and extracellular-dissolved organic matter (I-DOM and E-DOM) in the processes that affect the environmental behavior of contaminants. Furthermore, the effects of MPs on the production of I-DOM and E-DOM, as well as their environmental behaviors, remain uncertain. A critical issue lies in the challenge of quantitatively identifying I-DOM and E-DOM in situ. In this work, a new fluorescence ratio method was developed and applied to in situ examine the impacts of polystyrene (PS) MPs (50, 500 nm, and 5 μm) on the I-DOM and E-DOM released by Skeletonema costatum (S. costatum). The experimental results indicated that the detection limits were 0.06 mg L−1, with the respective minimum detectable proportions being 2% for both E-DOM and I-DOM. The suppressive effects of 10–50 mg L−1 of 50 and 500 nm PS MPs on the cell proliferation of S. costatum and the E-DOM secretion were most pronounced on day 6. And the rates of suppression of E-DOM secretion were 10.1%–18.2% and 4.2%–13.9%, respectively. The exposure of algal cells to 50 mg L−1 of 50 and 500 nm PS MPs led to cell rupture and the leakage of I-DOM on day 6. This suggests that the developed method in the laboratory could offer a promising approach for studying the generation of E-DOM and I-DOM in situ , as well as their environmental behaviors affected by MPs. [Display omitted] • A novel method for in situ detection of E-DOM and I-DOM. • The (C1 + C2)/(C3 + C4) ratio revealed high sensitivity and robustness capability. • Effects of PS MPs on E-DOM and I-DOM released by S. costatum were in situ observed. • The growth and E-DOM release of S. costatum were inhibited by 50 and 500 nm PS MPs. • 50 mg L−1 of 50 and 500 nm PS MPs induced I-DOM leakage for S. costatum. [ABSTRACT FROM AUTHOR]

As a new type of environmental pollutant, micro(nano)plastics have become a research hotspot in recent years, and their effects on the full life history of marine microalgae have not been studied. To investigate the effects of micro(nano)plastics on the growth, photosynthesis, physiological morphology and interaction of microalgae during the full life cycle, we selected fluorescently stained polystyrene (PS) plastic microbeads as the target pollutant. By sampling and testing the growth rate, photosynthesis and physiological morphology parameters of algal species, the influence of different concentrations of PS (10, 50 and 100 mg/L) and different particle sizes (0.1, 0.5 and 1 μm) on the full life history of Skeletonema costatum (S. costatum) was investigated. The results showed that after adding PS (particle sizes of 0.5 and 1 μm), the response of S. costatum showed a dual character, while adding the same kind of microplastics (MPs) with a particle size of 0.1 μm inhibited S. costatum throughout the full life cycle. Compared with previous studies, short-term experimental data may overestimate the true ecological risks of MPs. In addition, 0.1 μm fluorescent-stained MPs obviously accumulated around the microalgae, indicating that MPs mainly adhered to the surface of algal cells and may enter the food chain by direct or indirect ways, which can cause negative effects on the aquatic ecosystem. This study supports a more accurate assessment of the true risk of MPs to marine aquatic ecosystems. [Display omitted] • The dynamic effects of PS on Skeletonema costatum on the full life history were revealed. • PS (0.5, 1 μm) have dual effects on microalgae throughout its life cycle. • Short-term studies may overestimate the true ecological risks of microplastics. • PS enter the food chain by sticking or entering microalgae cells. [ABSTRACT FROM AUTHOR]

This study aimed to assess the ecological risks posed by sulfamethoxazole (SMX) at environmentally relevant concentrations. Specifically, its effects on the growth and biochemical components (total protein, total lipid, and total carbohydrate) of two marine microalgae species, namely Skeletonema costatum (S. costatum) and Phaeodactylum tricornutum (P. tricornutum), were investigated. Our findings revealed that concentrations of SMX below 150 ng/L stimulated the growth of both microalgae. Conversely, at higher concentrations, SMX inhibited their growth while promoting the synthesis of photosynthetic pigments, total protein, total lipid, and total carbohydrate (P < 0.05). Transmission electron microscope (TEM) observations demonstrated significant alterations in the ultrastructure of algal cells exposed to SMX, including nuclear marginalization, increased chloroplast volume, and heightened vacuolation. In addition, when SMX was lower than 250 ng/L, there was no oxidative damage in two microalgae cells. However, when SMX was higher than 250 ng/L, the antioxidant defense system of algal cells was activated to varying degrees, and the level of malondialdehyde (MDA) increased, indicating that algae cells were damaged by oxidation. From the molecular level, environmental concentration of SMX can induce microalgae cells to produce more energy substances, but there are almost no other adverse effects, indicating that the low level of SMX at the actual exposure level was unlikely to threaten P. tricornutum , but a higher concentration can significantly reduce its genetic products, which can affect the changes of its cell structure and damage P. tricornutum to some extent. Therefore, environmental concentration of SMX still has certain potential risks to microalgae. These outcomes improved current understanding of the potential ecological risks associated with SMX in marine environments. [Display omitted] • SMX can increase the contents of bioactive substances and photosynthetic pigments of two marine diatoms. • SMX above 250 ng/L will cause chloroplast damage and oxidative damage of algae cells. • SMX above 250 ng/L affects the synthesis of genetic material of P. tricornutum. [ABSTRACT FROM AUTHOR]

With the rapid development of nanotechnology, nanomaterials have been widely utilized in many industries and daily life applications due to their unique properties. However, their potential release and the human health/environmental consequences have raised public concern greatly. In this study, we compared the toxic effects of AgNPs and AgNO3 on Skeletonema costatum in 10, 100, and 500 μg·L−1 Ag treatments. In all the AgNP exposure experiments, cell membrane damage and growth inhibition occurred. However, the cellular damage only obviously appears on exposure to a high concentration of AgNO3. The antioxidant enzyme (SOD and CAT) activities and lipid peroxidation in Skeletonema costatum were also induced significantly in the AgNP treatments. In addition, the percentage of Ag release in seawater increased with the increase in AgNP concentrations (13%, 32% for 100 and 500 μg·L−1 AgNPs). Thus, the biotoxic effects of AgNPs were found to be due to a combination of the solubilization of particles into toxic metal ions and the nature of the nanoparticles. It was worth noting that the induction of oxidative stress and damage to the cell membrane comprised the dominant mechanism of toxicity for AgNPs. Therefore, the behavior of nanometals in seawater affects the biotoxic effect on the phytoplankton. These results shed light on the biological toxicity of nanometals and their possible toxicity mechanism.

Heterosigma akashiwo blooms have caused severe damage to marine ecosystems, the aquaculture industry and human health worldwide. In this study, Bacillus tequilensis D8 isolated from an H. akashiwo bloom area was found to exert high algicidal activity via extracellular metabolite production. This activity remained stable after exposure to different temperatures and light intensities. Scanning electron microscopy observation and fluorescein diacetate staining indicated that the algicidal substances rapidly destroyed algal plasma membranes and decreased esterase activity. Significant decreases in the maximum photochemical quantum yield and relative electron transfer rate were observed, which indicated photosynthetic membrane destruction. Subsequently, the algicidal compounds were separated and purified by high-performance liquid chromatography and identified as three surfactin homologues by interpreting high-resolution electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy data. Among these, surfactin-C13 and surfactin-C14 exhibited strong algicidal activity against three HAB-causing species, namely, H. akashiwo, Skeletonema costatum, and Prorocentrum donghaiense, with 24 h-LC50 values of 1.2-5.31 mg/ml. Surfactin-C15 showed strong algicidal activity against S. costatum and weak algicidal activity against H. akashiwo but little activity against P. donghaiense. The present study illuminates the algicidal characteristics and mechanisms of action of surfactins on H. akashiwo and their potential applicability in controlling harmful algal blooms. [ABSTRACT FROM AUTHOR]

In estuaries and coastal waters, the flocculation of cohesive sediments is significantly affected by extracellular polymeric substances secreted by microalgae. In this study, laboratory experiments are carried out to explore the role of two typical microalgae (Skeletonema costatum and Cyclotella meneghiniana) on suspended fine‐grained sediments under various turbulent shear and environmental conditions. The results show that the shear rate is a dominant factor in controlling the biomineral flocculation processes, and the existence of microalgae generally enhances the aggregation of mineral sediments with microalgae. It is also found that floc size distributions (FSDs) and mean sizes are clearly influenced by different algal species and concentrations, especially under intensive turbulent environments. Moreover, a quasi‐Monte Carlo (QMC) based bivariate population balance model is developed to simulate the FSDs of sediment‐algae flocs. This model is reasonably validated by two analytical solutions and laboratory observations, and indicates a potential extension for tracking the properties of microalgae‐associated fine sediment flocs due to the discrete nature of the QMC method. Plain Language Summary: The transportation of fine‐grained suspended sediments in estuaries and coastal environments is a factor in many engineering and environmental issues (e.g., siltation, dredging, bed morphology, and water quality). One important characteristic that affects the transport and fate of cohesive sediment particles is flocculation, which is the tendency of particles to aggregate and breakup sequentially to form clusters (flocs) of various sizes, densities, and settling velocities. Since they are abundant in the natural environment, microalgae and their sticky secretions play important roles in the flocculation of cohesive sediment as biological glues. However, few studies have been carried out to reveal the correlation between microalgae and sediment flocculation. Thus, this study aims to investigate the influences of microalgae on the flocculation of cohesive sediment particles in various turbulent environments. We find turbulent shear is dominant in the biomineral flocculation and that biomineral flocs are generally larger than pure sediment flocs. In addition, we develop a bivariate flocculation model to simulate the floc size distribution of biomineral flocs, which is well validated by theoretical solutions and laboratory results. This innovative model offers a preliminary application for multivariate models in biomineral flocculation, which promotes a prospect of future research to develop advanced transportation models. Key Points: The influence of microalgae on the flocculation of cohesive sediments is investigated by laboratory experiments and numerical modelsThe existence of microalgae and their secreted extracellular polymeric substances generally enhances the aggregation of biomineral flocsThe quasi‐Monte Carlo based bivariate population balance model can mimic the biomineral flocculation processes with reasonable accuracy [ABSTRACT FROM AUTHOR]

The nutritional quality of Paracentrotus lividus larvae's feed plays an important role in their survival and development. The lipid profile of microalgae is largely reflected in the successful development of different metamorphoses. Emiliania huxleyi is the most common cocolitophoro in the oceans and the most important microalgae for calcium carbonate sedimentation on the ocean floor. Despite its biological and geological importance, the application of this microalgae in sea urchin larvae feeding is still unknown. In this work, the performance of E. huxley was evaluated as a P. lividus larvae feeding. Three diets were tested: D1: (Rhodomonas marina), D2 (R. marina, Skeletonema costatum, Emiliania huxleyi) and D3 (E. huxley). Larvae fed with the D2 diet (75.8%) and D3 (74.9%) had a survival at 15 DAH higher than D1 (48.7%). Larvae development was significantly higher in larvae fed with more than one species of algae (D1 and D2), compared with larvae fed only with E. huxley. On day 15 DAH, the number of larvae in the pre‐fixation state was much higher in D1 and D2. The analysis of the E. huxley fatty acid profile has a relatively low content of total fatty acids, being, however, rich in DHA (22: 6ω3). The DHA/EPA ratio in these microalgae is significantly higher than the other microalgae used in this work. This research also found that a multiple microalgae species diet promotes optimal development, with the E. huxley species contributing to a high survival rate. [ABSTRACT FROM AUTHOR]

Significant efforts have been made to improve adsorbents capable of eliminating pollutants from aqueous solutions, making it simple and quick to separate from the treated solution. In the current study, the removal of Crystal Violet Dye (CVD) from an aqueous synthetic solution onto a marine diatom alga, Skeletonema costatum, was investigated. Different experiments were conducted as a function of different pH, contact time, adsorbent dosage, temperature, and initial CVD concentration. The highest adsorption efficiency (98%) was obtained at 0.4 g of S. costatum, pH 3, and a contact time of 120 min, at 25 °C. Furthermore, Fourier-transform infrared spectroscopy (FTIR) results display that binding of CVD on S. costatum may occur by electrostatic and complexation reactions. Moreover, the Brunauer–Emmett–Teller surface area analysis (BET) obtained was 87.17 m2 g−1, which, in addition to a scanning electron microscope (SEM), reveals large pores that could enhance the uptake of large molecules. However, the equilibrium adsorption models were conducted by Halsey, Langmuir, Freundlich, Henderson, and Tempkin isotherm. In addition, multilayer adsorption isotherm best described the uptake of CVD onto S. costatum. The maximum monolayer adsorption capacity (qmax) was 6.410 mg g−1. Moreover, thermodynamic parameters of the adsorption studies suggested that the uptake of CVD onto S. costatum was endothermic and spontaneous. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic equations were applied to model the adsorption kinetic data. It was seen that the kinetics of the adsorption may be described using pseudo-second-order kinetic equations. Finally, the present work concluded that the marine diatom alga S. costatum is suitable as a natural material for the adsorption of CVD. [ABSTRACT FROM AUTHOR]

Inorganic nitrogen (N) is an important element for eutrophication and harmful algal bloom (HAB) formation. However, the roles of inorganic N in HAB outbreaks are still unclear. Here, we compared the affinities and abilities for inorganic N uptake and assimilation among three typical bloom-forming algae in the East China Sea (ECS), Skeletonema costatum, Prorocentrum donghaiense and Alexandrium pacificum by investigating the uptake and enzymatic (nitrate reductase (NR) and glutamine synthetase (GS) kinetics for nitrate and ammonia. The Ks of nitrate and ammonium in S. costatum was lower than those in P. donghaiense and A. pacificum. The NR activity of S. costatum and P. donghaiense exhibited a positive relationship with the nitrate concentration, and NR activity of S. costatum was nearly 4-fold higher than that of P. donghaiense at high nitrate concentration. However, the NR activity of A. pacificum could not be detected. The GS activity of three species decreased with the increase of ammonium concentrations, and the highest GS activity was detected in A. pacificum. S. costatum presented the highest affinity for nitrate and ammonium, followed by P. donghaiense and A. pacificum. Moreover, P. donghaiense exhibited the highest affinity for intracellular ammonium. Our results characterized the differences in inorganic nitrogen uptake among the three typical bloom-forming algae, which may contribute to the formation of blooms in the coastal waters of the ECS. [ABSTRACT FROM AUTHOR]