Marine Phytoplankton Communities Research Articles

Long-Range Transport of a Dust Event and Impact on Marine Chlorophyll-a Concentration in April 2023

Dust aerosols serve as a crucial nutrient source to the oceans and profoundly influence marine ecosystems. This study used satellite and ground observations to explore a strong dust event on 9–13 April 2023, emanating from the Gobi Desert, shared by Mongolia and China’s Inner Mongolia region. We investigated the deposition of dust particles and their effects on marine phytoplankton communities. Our findings revealed that the dust event was intense, enduring, and expansive, illustrated by hourly PM10 concentrations peaking at 5055 µg/m3 near the source and consistently exceeding 1000 µg/m3, even at considerable distances. The dust traveled along two different trajectories and was deposited in the same area of the Northwest Pacific. Total dust deposition in the study area (37°N–42°N, 145°E–165°E) was 79.88 mg/m2 from 13 to 18 April, much higher than the 2019–2022 average deposition of 33.03 mg/m2 for the same period. With dust deposition, the observed mean chlorophyll-a concentrations in the area increased to 2.78 mg/m3 on 14 April, an extraordinary 692% increase above the long-term average. These results highlight the profound impact of dust on the productivity of marine phytoplankton communities by inputting more nutrients into the ocean through different pathways.

Toward a synthesis of phytoplankton community composition methods for global‐scale application

AbstractThe composition of the marine phytoplankton community has been shown to impact many biogeochemical processes and marine ecosystem services. A variety of methods exist to characterize phytoplankton community composition (PCC), with varying degrees of taxonomic resolution. Accordingly, the resulting PCC determinations are dependent on the method used. Here, we use surface ocean samples collected in the North Atlantic and North Pacific Oceans to compare high‐performance liquid chromatography pigment‐based PCC to four other methods: quantitative cell imaging, flow cytometry, and 16S and 18S rRNA amplicon sequencing. These methods allow characterization of both prokaryotic and eukaryotic PCC across a wide range of size classes. PCC estimates of many taxa resolved at the class level (e.g., diatoms) show strong positive correlations across methods, while other groups (e.g., dinoflagellates) are not well captured by one or more methods. Since variations in phytoplankton pigment concentrations are related to changes in optical properties, this combined dataset expands the potential scope of ocean color remote sensing by associating PCC at the genus‐ and species‐level with group‐ or class‐level PCC from pigments. Quantifying the strengths and limitations of pigment‐based PCC methods compared to PCC assessments from amplicon sequencing, imaging, and cytometry methods is the first step toward the robust validation of remote sensing approaches to quantify PCC from space.

Hit or miss? Impact of time series resolution on resolving phytoplankton dynamics at hourly, weekly, and satellite remote sensing frequencies

AbstractCharacterizing marine phytoplankton community variability is crucial to designing sampling strategies and interpreting time series. Satellite remote sensing, microscopy sampling, and flow through imaging systems have widely different resolutions: from weekly or monthly with microscopy sampling to daily when no cloud cover or glint is present with polar‐orbiting satellites, and hourly for autonomous imaging instruments. To improve our understanding of data robustness against sampling resolution at different taxonomic levels, we analyze 2 yr of data from an Imaging FlowCytobot with hourly resolution and resample it to daily, satellite‐temporal, and weekly microscopy sampling resolution. We show that weekly and satellite‐temporal resolutions are sufficient to resolve general community composition but that the randomness of satellite‐temporal resolution can result in overrepresenting or underrepresenting certain categories. While the yearly phytoplankton biomass bloom is detected in late winter by all four resolutions, category‐specific yearly blooms are generally consistent in timing but often underestimated or missed by the weekly and satellite‐temporal resolutions, introducing a bias in year‐to‐year comparisons. A minimum of biweekly sampling, particularly during known bloom periods, would lower the bias in such categories. Similarly, sampling time should be considered as daily variations are category‐specific. Overall, morning and low tide sampling tended to have higher biomass. We provide tables for categories detected by the IFCB in Narragansett Bay with their major bloom characteristics and recorded daily variability to inform future sampling designs. These results provide tools to interpret past and future time series, including possible detection of specific taxonomic groups with targeted satellite algorithms.

Deleterious effects of free fatty acids and hydrogen peroxide towards the dinoflagellate Gymnodinium catenatum

Allelopathy refers to biochemical interactions among competing microalgae, it involves a donor species that produces metabolites which can cause inhibitory effects on susceptible species. This phenomenon can participate in the regulation of harmful algal blooms. The dinoflagellate Gymnodinium catenatum is negatively affected by allelopathic interactions with co-occurring microalgae species, like Chattonella marina var. marina, which has been suggested to produce reactive oxygen species (ROS) and free fatty acids (FFA) as nocive and allelopathic agents. This study explored the effect of hydrogen peroxide (H2O2) and the main fatty acids produced by C. marina. An analysis of fatty acids content of C. marina in exponential phase detected 16:0 (12.5 ± 0.01%), 18:4ω-3 (15.4 ± 0.36%) and 20:5ω-3 (35.4 ± 0.71%) as the most abundant. These fatty acids along with H2O2 were used in dose-response bioassays with cultures of G. catenatum in exponential phase. Results suggest that these substances affect cell morphology, including the loss of motility and signs of chlorosis, as well as the chain forming qualities of G. catenatum. Toxicity among these substances varied, suggesting that the polyunsaturated fatty acid 18:4ω-3 can potentially act as a more effective allelochemical (LD50 = 1.7 ± 0.19 mg L-1 at 24 h), followed by 20:5ω-3 (LD50 = 3.6 ± 0.17 mg L-1 at 24 h) and the saturated fatty acid 16:0 (LD50 = 6.2 ± 1.05 at 48 h). Our results suggest these substances can act, at least partially, as allelochemicals, with PUFA being the most effective metabolites. These results contribute in elucidating the potential role of ROS and FFA in allelopathy in marine phytoplankton communities.

Effect of increased pCO2 and temperature on the phytoplankton community in the coastal of Yellow Sea

In order to study the dynamics of marine phytoplankton communities in response to anticipated in temperature and CO2, a shipboard continuous culture experiment (Ecostat) was conducted. The experiment involved simulations under current atmospheric CO2 concentrations (400 ppm) and projected year-2100 CO2 levels (1000 ppm), as well as varying temperature under present (22 °C) versus increased temperature (26 °C) in the Yellow Sea during the summer of 2020. The results showed that both the increased pCO2 and temperature had significant effects on microphytoplankton and picophytoplankton, with the warming effect proving to be more significant. The different responses of various species to acidification and warming and their coupling effect led to the changes in microphytoplankton and picophytoplankton community structure. Elevated temperature and greenhouse treatments promoted the growth of dominant diatoms and Synechococcus, such as Guinardia flaccida and Pseudo-nitzschia delicatissima. This phenomenons widened the ecological niche, and the changes in the growth patterns of dominant species consequently influenced the content of cellular elements. Mantel's analysis further demonstrated that both warming and greenhouse promoted the growth of diatoms and Synechococcus. Projections of marine phytoplankton community trends by the end of the century based on Growth Rate Ratio (GRR), indicated that not only would species with GRR < 1 decrease, but also numerous species with growth rates >1 at elevated pCO2 levels would be ousted from competition. This experiment demonstrates the need to investigate whether extended exposure to increased pCO2 and temperature over more extended time scales would similarly induce shifts in the biological and biogeochemical dynamics of the Yellow Sea.

Phytoplankton thermal trait parameterization alters community structure and biogeochemical processes in a modeled ocean.

Phytoplankton exhibit diverse physiological responses to temperature which influence their fitness in the environment and consequently alter their community structure. Here, we explored the sensitivity of phytoplankton community structure to thermal response parameterization in a modelled marine phytoplankton community. Using published empirical data, we evaluated the maximum thermal growth rates (μmax ) and temperature coefficients (Q10 ; the rate at which growth scales with temperature) of six key Phytoplankton Functional Types (PFTs): coccolithophores, cyanobacteria, diatoms, diazotrophs, dinoflagellates, and green algae. Following three well-documented methods, PFTs were either assumed to have (1) the same μmax and the same Q10 (as in to Eppley, 1972), (2) a unique μmax but the same Q10 (similar to Kremer etal., 2017), or (3) a unique μmax and a unique Q10 (following Anderson etal., 2021). These trait values were then implemented within the Massachusetts Institute of Technology biogeochemistry and ecosystem model (called Darwin) for each PFT under a control and climate change scenario. Our results suggest that applying a μmax and Q10 universally across PFTs (as in Eppley, 1972) leads to unrealistic phytoplankton communities, which lack diatoms globally. Additionally, we find that accounting for differences in the Q10 between PFTs can significantly impact each PFT's competitive ability, especially at high latitudes, leading to altered modeled phytoplankton community structures in our control and climate change simulations. This then impacts estimates of biogeochemical processes, with, for example, estimates of export production varying by ~10% in the Southern Ocean depending on the parameterization. Our results indicate that the diversity of thermal response traits in phytoplankton not only shape community composition in the historical and future, warmer ocean, but that these traits have significant feedbacks on global biogeochemical cycles.

The interactions between olivine dissolution and phytoplankton in seawater: Potential implications for ocean alkalinization

Ocean alkalinity enhancement, one of the ocean-based CO2 removal techniques, has the potential to assist us in achieving the goal of carbon neutrality. Olivine is considered the most promising mineral for ocean alkalinization enhancement due to its theoretically high CO2 sequestration efficiency. Olivine dissolution has been predicted to alter marine phytoplankton communities, however, there is still a lack of experimental evidence. The olivine dissolution process in seawater can be influenced by a range of factors, including biotic factors, which have yet to be explored. In this study, we cultivated two diatoms and one coccolithophore with and without olivine particles to investigate their interactions with olivine dissolution. Our findings demonstrate that olivine dissolution promoted the growth of all phytoplankton species, with the highly silicified diatom Thalassiosira pseudonana benefiting the most. This was probably due to the highly silicified diatom having a higher silicate requirement and, therefore, growing more quickly when silicate was released during olivine dissolution. Based on the structural characteristics and chemical compositions on the exterior surface of olivine particles, T. pseudonana was found to promote olivine dissolution by inhibiting the formation of the amorphous SiO2 layer on the surface of olivine and therefore enhancing the stoichiometric dissolution of olivine. However, the positive effects of T. pseudonana on olivine dissolution were not observed in the coccolithophore Gephyrocapsa oceanica or the non-silicate obligate diatom Phaeodactylum tricornutum. This study provides the first experimental evidence of the interaction between phytoplankton and olivine dissolution, which has important implications for ocean alkalinization research.

Seasonal dynamics of phytoplankton community assembly at the Blanes Bay Microbial Observatory (BBMO), NW Mediterranean Sea

The dynamics of phytoplankton biomass and community composition is important for the functioning of marine ecosystems and ocean biogeochemical cycles. However, there is a shortage of studies addressing the interannual seasonal patterns of phytoplankton community assembly due to sampling limitations. Here we study the seasonal dynamics of eight major phytoplankton groups over a 12 year period (2006 to 2018) using a time-series of taxonomic composition from the Blanes Bay Microbial Observatory (BBMO) in the North Western Mediterranean Sea: dinoflagellates, diatoms, coccolithophores, Prochlorococcus, Synechococcus, picoeukaryotes, nanoeukaryotes, and photosynthetic nanoflagellates. We combine the analysis of biotic factors (primary production, phytoplankton taxa, cell abundance, cell size, chlorophyll-a concentration, and phytoplankton biomass) and abiotic factors (nutrients, temperature, and irradiance) to provide a coherent picture of the observed seasonal patterns of phytoplankton community assembly. The BBMO ecosystem is seasonally heterogeneous in community composition, displaying large fluctuating alternations in phytoplankton group dominance throughout the year. The seasonal succession of phytoplankton groups tends to repeat itself every year in a regular fashion, being the seasonal variability of the phytoplankton groups larger than their interannual variability. We compute α-diversity, a measure of the effective richness of phytoplankton groups. The seasonality of α-diversity shows that it is lowest during winter and highest during summer. We compute temporal β-diversity, a measure of compositional heterogeneity of the phytoplankton community. The data show a sinusoidal behavior of β-diversity as a function of the temporal distance between samples, with a period of one year. We use the mirror index (1 - β-diversity) at a temporal distance of one month to compute the phytoplankton group turnover. The seasonality of turnover shows that it is highest during spring and autumn. To evaluate the validity of niche and neutral theories in predicting the interannual sinusoidal behavior of β-diversity, we performed numerical simulations using a mechanistic model. The results provide support to the niche theory for marine phytoplankton ecology and community assembly. The phytoplankton groups appear to follow their specific ecological niches, tracking the seasonal changes in environmental conditions. The ecological implications of these findings are that marine phytoplankton groups appear to fill distinct environmental niches and thus may have different functional roles in the ecosystem. Furthermore, they may be predictable using both mechanistic and species distribution modeling approaches. The climatological time-series presented here can be an excellent testing ground for evaluating the performance of these marine ecosystem models having an explicit representation of different phytoplankton groups.

Tetrodotoxin in bivalve mollusks: An integrated study towards the comprehension of the influencing factors of a newly native phenomenon

Tetrodotoxins (TTXs) are potent neurotoxins named after the Tetraodontidae fish family. The ingestion of TTX-contaminated flesh can cause neurotoxic symptoms and can lead to death. In 2017 symptoms the European Food Safety Authority (EFSA) recognized the threat to food safety resulting from TTX exposure via food consumption and, thus, proposed a safety limit of 44 μg/kg of TTX in marine gastropods and bivalves. To date, however, TTXs have not yet been included in the list of biotoxins to be monitored within the European Union, even though, in a few cases, levels of TTX found were higher than the EFSA limit. The origin of TTX production is debated and the roles of both biotic and abiotic factors on TTX-mediated toxic events remain unclear. In order to meet these knowledge requests the present study was aimed to investigate the role of seawater temperature, pH, water conductivity, and oxygen saturation, along with the marine phytoplankton community and the bacterial community of mussels and oysters on the accumulation of TTX and analogues in the bivalves. Abiotic parameters were measured by means of a multi-parametric probe, phytoplankton community was analyzed by optic microscopy while microbial community was described by amplicon metataxonomic sequencing, TTXs concentration in the collected matrices were measured by HILIC-MS/MS.A possible role of seawater pH and temperature, among the investigated abiotic factors, in regulating the occurrence of TTXs was found. Regarding biotic variables, a possible influence of Vibrio, Shewanella and Flavobacteriaceae in the occurrence of TTXs was found. Concurrently, Prorocentrum cordatum cell numbers were correlated to the incidence of TTX in mussels. The results herein collected suggest that environmental variables play a consistent part in the occurrence of TTX in the edible bivalve habitats, and there are also indications of a potential role played by specific bacteria taxa in association with phytoplankton.

Response of the Coastal Phytoplankton Community to the Runoff from Small Rivers in the Northeastern Black Sea

River runoff is an important source of nutrients as well as suspended and dissolved organic matter that in coastal zones and on the shelf are transformed due to local production cycles. River runoff affects the hydrological regime, salinity, temperature, and irradiance in river–seawater mixing zone. Our study focuses on the response of phytoplankton to the impact of small Caucasian rivers in the Northeastern (NE) Black Sea, as one of the most sensitive components of marine ecosystems with respect to the changes in abiotic factors. The leading role of marine species of diatoms, dinoflagellates, and coccolithophores in the structure and functioning when impacted by runoff from small rivers is demonstrated in comparison to the freshwater community. Variability of the taxonomic composition and quantitative and productive characteristics of marine phytoplankton communities impacted by small rivers were comparable to or exceed the seasonal and interannual variability on the NE Black Sea shelf. This indicates the significant role of runoff from small Caucasian rivers in maintaining of a high production level of phytoplankton overall and of the coccolithophore Emiliania huxleyi in particular in the coastal zone.

Phylogenomics shows that novel tapeworm-like traits of haplozoan parasites evolved from within the Peridiniales (Dinoflagellata)

Haplozoans are intestinal parasites of marine annelids with bizarre traits, including a differentiated and dynamic trophozoite stage that resembles the scolex and strobila of tapeworms. Described originally as “Mesozoa”, comparative ultrastructural data and molecular phylogenetic analyses have shown that haplozoans are aberrant dinoflagellates; however, these data failed to resolve the phylogenetic position of haplozoans within this diverse group of protists. Several hypotheses for the phylogenetic position of haplozoans have been proposed: (1) within the Gymnodiniales based on tabulation patterns on the trophozoites, (2) within the Blastodiniales based on the parasitic life cycle, and (3) part of a new lineage of dinoflagellates that reflects the highly modified morphology. Here, we demonstrate the phylogenetic position of haplozoans by using three single-trophozoite transcriptomes representing two species: Haplozoon axiothellae and two isolates of H. pugnus collected from the Northwestern and Northeastern Pacific Ocean. Unexpectedly, our phylogenomic analysis of 241 genes showed that these parasites are unambiguously nested within the Peridiniales, a clade of single-celled flagellates that is well represented in marine phytoplankton communities around the world. Although the intestinal trophozoites of Haplozoon species do not show any peridinioid characteristics, we suspect that uncharacterized life cycle stages may reflect their evolutionary history within the Peridiniales.

Metabarcoding analysis identifies high diversity of harmful algal bloom species in the coastal waters of the Beibu Gulf.

Harmful algal blooms (HABs) have occurred more frequently in recent years. In this study, to investigate their potential impact in the Beibu Gulf, short-read and long-read metabarcoding analyses were combined for annual marine phytoplankton community and HAB species identification. Short-read metabarcoding showed a high level of phytoplankton biodiversity in this area, with Dinophyceae dominating, especially Gymnodiniales. Multiple small phytoplankton, including Prymnesiophyceae and Prasinophyceae, were also identified, which complements the previous lack of identifying small phytoplankton and those unstable after fixation. Of the top 20 phytoplankton genera identified, 15 were HAB-forming genera, which accounted for 47.3%-71.5% of the relative abundance of phytoplankton. Based on long-read metabarcoding, a total of 147 OTUs (PID > 97%) belonging to phytoplankton were identified at the species level, including 118 species. Among them, 37 species belonged to HAB-forming species, and 98 species were reported for the first time in the Beibu Gulf. Contrasting the two metabarcoding approaches at the class level, they both showed a predominance of Dinophyceae, and both included high abundances of Bacillariophyceae, Prasinophyceae, and Prymnesiophyceae, but the relative contents of the classes varied. Notably, the results of the two metabarcoding approaches were quite different below the genus level. The high abundance and diversity of HAB species were probably due to their special life history and multiple nutritional modes. Annual HAB species variation revealed in this study provided a basis for evaluating their potential impact on aquaculture and even nuclear power plant safety in the Beibu Gulf.

Direct Air Capture of CO2 through Carbonate Alkalinity Generated by Phytoplankton Nitrate Assimilation.

Despite the consensus that keeping global temperature rise within 1.5 °C above pre-industrial level by 2100 reduces the chance for climate change to reach the point of no return, the newest Intergovernmental Panel on Climate Change (IPCC) report warns that the existing commitment of greenhouse gas emission reduction is only enough to contain the warming to 3-4 °C by 2100. The harsh reality not only calls for speedier deployment of existing CO2 reduction technologies but demands development of more cost-efficient carbon removal strategies. Here we report an ocean alkalinity-based CO2 sequestration scheme, taking advantage of proton consumption during nitrate assimilation by marine photosynthetic microbes, and the ensuing enhancement of seawater CO2 absorption. Benchtop experiments using a native marine phytoplankton community confirmed pH elevation from ~8.2 to ~10.2 in seawater, within 3-5 days of microbial culture in nitrate-containing media. The alkaline condition was able to sustain at continued nutrient supply but reverted to normalcy (pH ~8.2-8.4) once the biomass was removed. Measurements of δ13C in the dissolved inorganic carbon revealed a significant atmospheric CO2 contribution to the carbonate alkalinity in the experimental seawater, confirming the occurrence of direct carbon dioxide capture from the air. Thermodynamic calculation shows a theoretical carbon removal rate of ~0.13 mol CO2/L seawater, if the seawater pH is allowed to decrease from 10.2 to 8.2. A cost analysis (using a standard bioreactor wastewater treatment plant as a template for CO2 trapping, and a modified moving-bed biofilm reactor for nitrate recycling) indicated that a 1 Mt CO2/year operation is able to perform at a cost of ~$40/tCO2, 2.5-5.5 times cheaper than that offered by any of the currently available direct air capture technologies, and more in line with the price of $25-30/tCO2 suggested for rapid deployment of large-scale CCS systems.

Marine phytoplankton community data and corresponding environmental properties from eastern Norway, 1896–2020

Time series are essential for studying the long-term effects of human impact and climatic changes on the natural environment. Although data exist, no long-term phytoplankton dataset for the Norwegian coastal area has been compiled and made publicly available in a standardised format. Here we report on a compilation of phytoplankton data from inner Oslofjorden going back more than a century. The database contains 605 sampling events from 1896 to 2020, and environmental data has also been provided when available. Although the sampling frequency has varied over time, the high taxonomic quality and relatively similar methodology make it very useful. For the last 15 years (2006–2020), the sampling frequency has been almost monthly throughout the year. This dataset can be used for time series analysis to understand community structure and changes over time. It can also be used to study common taxa’ responses to environmental variables and changes, seasonal or annual species diversity and be useful for developing ecological indicators.

Methodological 'lenses' influence the characterization of phytoplankton dynamics in a coastal upwelling ecosystem.

New technologies enable the opportunity to improve our monitoring and understanding of marine phytoplankton communities. However, careful consideration for how different methodological approaches, or 'lenses', influence our interpretation of phytoplankton ecology is important, particularly when drawing conclusions about change over time or space. Using both high-throughput 18S rRNA gene sequencing and microscopy, we explored how phytoplankton community structure varied over the course of a year within a nearshore semi-enclosed coastal embayment along the Central Coast of California. The seasonal shift in the relative community dominance (i.e., diatom vs. dinoflagellate dominance) was captured in the microscopy results but not effectively captured in the molecular-based findings. However, the molecular approach explained more of the variability in composition across seasons relative to the microscopy approach. Temporal dynamics of specific bloom-forming taxa also differed between the molecular and microscopy results. Overall, the observed differences between the molecular- and microscopy-derived characterization of phytoplankton dynamics suggest that the approaches are best suited to answer different research questions. Moreover, the approaches complement each other for a more comprehensive perspective of a coastal phytoplankton ecosystem. Therefore, identifying the biases of each approach within natural communities is necessary to effectively and accurately characterize phytoplankton communities.

Primary analysis of the phytoplanktonic community of the water capture channel of a thermal electric plant in Northeast Brazil

In the environmental policy of the Pernambuco Thermoelectric Power Plant, there are plans for monitoring the environmental quality. This study is about the marine phytoplankton community, in the area of ​​influence it has followed a regularity of studies in its catchment channel and in the area of ​​disposal of the submarine outfall. Collections were made every three months, between March 2020 and October 2021. Collections were carried out by trawling 20 µm nets in the area of the submarine outfall and using a Van Dorn oceanographic bottle, inside the catchment channel. from the plant. The taxonomic analyzes showed that in the water catchment channel the genera Chaetoceros and Navicula stood out for their abundance, being represented by 956 and 283 individuals, respectively. At the collection point, the most abundant genera were Pinnularia and Oscillatoria, with 1978 and 559 representatives, respectively.

Dissipation of a Polykrikos geminatum Bloom after Wind Events in Pearl River Estuary

Dinoflagellates is one dominant group in coastal marine phytoplankton communities and, on occasion, form blooms in estuaries and coastal ecosystems. While relationships between dinoflagellate bloom dynamics and nutrients are well-studied, information regarding bloom dissipation in estuaries is limited. We studied the dissipation of dinoflagellate Polykrikos geminatum blooms in the Pearl River Estuary, South China Sea, during August of 2011 using ecological, molecular, and satellite remote sensing data. We found that the dinoflagellate bloom was associated with water temperatures of 29.2–31 °C, salinities ranging 16.4–20, and ambient water nutrient concentrations that were not limited. The abundance of the ciliate Euplotes rariseta, which feeds on P. geminatum cell debris and bacteria, functions as an indicator species of P. geminatum bloom dissipation. In situ and satellite data indicate that bloom water masses were transferred from the central to inner estuary near Shenzhen Bay, driven by continuous, strong southerly winds; at which point in time, P. geminatum blooms dissipated to a high-salinity area near the estuary mouth driven by northerly winds and freshwater discharge, whereupon the blooms rapidly vanished. A low tolerance to low or high salinities resulted in P. geminatum bloom demise in the Pearl River Estuary. We propose that interactions among salinity, wind, and freshwater incursion result in P. geminatum bloom dissipation in the Pearl River Estuary.

Molecular fossils and calcareous nannofossils reveal recurrent phytoplanktonic events in the early Toarcian

During the early Toarcian (Early Jurassic, ~183 Ma) global climate and environmental change profoundly impacted biogeochemical cycles and marine ecosystems culminating in the early Toarcian Oceanic Anoxic Event (T-OAE). The T-OAE exhibited a global temperature rise and carbon cycle perturbation that manifested in a stepwise negative Toarcian carbon isotope excursion. While the response of marine invertebrates towards early Toarcian environmental change is well documented, that of marine primary producers is only poorly constrained and is mainly inferred from changes in algae groups producing hard parts, such as calcareous nannoplankton and organic-walled dinoflagellates. Both biotic groups, however, represent only a small part of the marine phytoplankton, the majority of which lack parts with preservation potential in the geosphere. In order to obtain a holistic view on the response of marine primary producers towards the early Toarcian environmental perturbation, we here conducted a high-resolution study based on the combined application of molecular fossils (biomarker) and calcareous nannofossils. Upon the climax of the T-OAE our data indicate that the marine phytoplankton community structure was dominated by eukaryotic algae, which experienced at least five distinct paleoecological events. Each of these was characterized by a demise of red algae groups and shallow- and deep-dwelling calcareous nannoplankton, and a contemporaneous proliferation of opportunistic green algae groups. An increase of poorly developed coccoliths (resembling protococcoliths) during each phytoplankton event attests to periodically harsh environmental conditions in surface waters. Each phytoplankton event was followed by a recovery of pre-event algal communities, indicative of a cyclicity in unstable and fluctuating environmental conditions. During the onset of the T-OAE, phytoplankton events align with negative δ 13 C shifts, suggesting that changes in the global carbon cycle and the climate system impacted on marine primary producers. Phytoplankton events, particularly during the onset of the T-OAE, were accompanied by recurrent freshening of surface waters during warming periods, suggesting these were the most important ecological drivers. Cyclicity in phytoplankton events followed the short eccentricity (100 kyr) orbital frequency, emphasizing the role of orbital forcing in early Toarcian environmental change and ecosystem disturbances. Ecosystem change and extinction were not driven by a single event, but resulted from multiple disturbances that occurred superimposed onto long-term environmental change and culminated in the early Toarcian ecosystem crisis. • Biomarker and calcareous nannofossils reveal recurrent phytoplankton events. • Phytoplankton events record shift from red to green algae communities. • Phytoplankton events forced by high SST, surface water freshening and stratification. • Environmental change and phytoplankton events were paced by orbital cycles.

Environmental DNA Metabarcoding Analysis of Fish Assemblages and Phytoplankton Communities in a Furrowed Seabed Area Caused by Aggregate Mining

To estimate the impact of aggregate mining on a marine ecosystem, fish assemblages and phytoplankton communities were analyzed using environmental DNA metabarcoding. Metabarcoding analysis revealed 152 fish amplicon sequence variants (ASVs) (88 in September and 118 in February), which were assigned to 29 orders, 62 families, 104 genera, and 114 species (73 in September and 89 in February). Heatmap analysis showed that the fish assemblages in the mining area clearly differed from those in the surrounding area and that Pagrus major, Lateolabrax japonicus, Zeus faber, and Eopsetta grigorjewi were significantly more abundant there than in the surrounding area. In the phytoplankton community in September, the phyla Cyanobacteria and Haptophyta differed significantly between the mining area and its surroundings. By contrast, no such significant differences were identified in February, presumably due to the low temperature impeding phytoplankton growth. Taking these findings together, mining activities clearly affect fish and phytoplankton communities, but further long-term study is required to assess their impacts on marine ecosystems.

Two-decadal estimation of sixteen phytoplankton pigments from satellite observations in coastal waters

Knowledge of the marine phytoplankton communities is vital for understanding the carbon cycle, ecological and biogeochemical processes, and climate change. Phytoplankton assemblages contain multiple pigments that play a significant role in describing the phytoplankton communities. Thus, detecting the concentrations of phytoplankton pigments is of great significance. Here, an extensive in situ observation dataset, including the phytoplankton absorption coefficient, concentrations of phytoplankton pigments, and remote sensing reflectance, was collected during seven cruise surveys in the Bohai Sea, Yellow Sea, and East China Sea. This study developed a customized absorption-based remote sensing model using the Gaussian decomposition technique, which closely links phytoplankton absorption characteristics with various pigments. This model was repeatedly assessed to guarantee its stable performance, and was evaluated using the in situ observation dataset and the leave-one-out cross-validation method, yielding results of competitive and acceptable errors (e.g., mean absolute percentage errors (MAPEs) below ∼60% for most pigments). Satellite match-up validation also generated promising predictive errors, with the derived MAPEs in a ∼10%–40% range for most pigments. Another contribution of our study is the application of the developed model to a long time series of satellite data (1998–2019), and the 22-year data record that documents the spatiotemporal variation of 16 pigment concentrations in the study areas. Accordingly, the long-term spatial and temporal evolution rules of 16 pigments are reported for the first time. This work concludes that the pigments (as the second-order delegates of phytoplankton pigments, compared to chlorophyll-a) can be retrieved from satellite data, despite the presence of optically complex turbid coastal waters, thus providing refined characteristics on phytoplankton assemblages for future marine research.