Deciphering environmental factors influencing phytoplankton community structure in a polluted urban river.

Tuojiang River Basin is a first-class tributary of the upper reaches of the Yangtze River-which is the longest river in China. As phytoplankton are sensitive indicators of trophic changes in water bodies, characterizing phytoplankton communities and their growth influencing factors in polluted urban rivers can provide new ideas for pollution control. Here, we used direct microscopic count and environmental DNA (eDNA) metabarcoding methods to investigate phytoplankton community structure in Tuojiang River Basin (Chengdu, Sichuan Province, China). The association between phytoplankton community structure and water environmental factors was evaluated by Mantel analysis. Additional environmental monitoring data were used to pinpoint major factors that influenced phytoplankton growth based on structural equation modeling. At the phylum level, the dominant phytoplankton taxa identified by the conventional microscopic method mainly belonged to Bacillariophyta, Chlorophyta, and Cyanophyta, in contrast with Chlorophyta, Dinophyceae, and Bacillariophyta identified by eDNA metabarcoding. In α-diversity analysis, eDNA metabarcoding detected greater species diversity and achieved higher precision than the microscopic method. Phytoplankton growth was largely limited by phosphorus based on the nitrogen-to-phosphorus ratios > 16:1 in all water samples. Redundancy analysis and structural equation modeling also confirmed that the nitrogen-to-phosphorus ratio was the principal factor influencing phytoplankton growth. The results could be useful for implementing comprehensive management of the river basin environment. It is recommended to control the discharge of point- and surface-source pollutants and the concentration of dissolved oxygen in areas with excessive nutrients (e.g., Jianyang-Ziyang). Algae monitoring techniques and removal strategies should be improved in 201 Hospital, Hongrihe Bridge and Colmar Town areas.

Delineating morphological traits of oceanic micro-phytoplankton as potential ecological indicators.

The micro-phytoplankton (>20 µm) adaptations and resilience were assessed using morphological traits (shape, surface-to-volume ratio; S:V, and greatest-axial-linear-dimension; GALD) from sea-surface and different SCML-depths (shallow:20-50 m, intermediate:50-100 m, and deep:100-140 m) across different bioregions of Indian Ocean. The dominant simple elongated phytoplankton-geometric-shapes (PGSs) and morphological traits showed distinct north-south distribution and varied with light and nutrient availability. Further, SCML and corresponding sea-surface PGS will be similar or dissimilar if the former is located within or deeper than mixed-layer depth. Also, simple and complex PGS contribution gradually decreases and increases with increasing depth. Additionally, shallow SCML-PGS showed low-S:V and high-GALD while vice-versa for intermediate/deep SCML-PGS due to phenotypic plasticity behavior. Overall, only simple-PGS (cylinder, elliptic-prism, and prism-on-parallelogram) showed strong adaptive behavior through phenotypic plasticity and were highlighted as potential ecological tracers to address ecological impact of oceanographic processes (including coastal eutrophication, and aerosol deposition) linked to nutrient and light availability in predicted ocean change scenarios.

Insight into diversity change, variability and co-occurrence patterns of phytoplankton assemblage in headwater streams: a study of the Xijiang River basin, South China.

Phytoplankton has been used as a paradigm for studies of coexistence of species since the publication of the "paradox of the plankton." Although there are a wealth of studies about phytoplankton assemblages of lakes, reservoirs and rivers, our knowledge about phytoplankton biodiversity and its underlying mechanisms in mountain headwater stream ecosystems is limited, especially across regional scales with broad environmental gradients. In this study, we collected 144 phytoplankton samples from the Xijiang headwater streams of the Pearl River across low altitude (< 1,000 m) located in Guangxi province, intermediate altitude (1,000 m < altitude <2,000 m) in Guizhou province and high altitude (> 2,000 m) in Yunnan province of China. Our study revealed high phytoplankton diversity in these streams. Freshwater phytoplankton, including cyanobacteria, Bacillariophyta, Chlorophyta, Rhodophyta, Chrysophyta, Euglenophyta, Glaucophyta, Phaeophyta and Cryptophyta, were all detected. However, phytoplankton alpha diversity exhibited a monotonic decreasing relationship with increasing altitude. High altitudes amplified the "isolated island" effect of headwater streams on phytoplankton assemblages, which were characterized by lower homogeneous selection and higher dispersal limitation. Variability and network vulnerability of phytoplankton assemblages increased with increasing altitudes. Our findings demonstrated diversity, variability and co-occurrence patterns of phytoplankton assemblages linked to environmental factors co-varying with altitude across regional scales.

Nitrogen source and availability regulate plastic population dynamics in the marine diatom Thalassiosira weissflogii.

Variation in nitrogen (N) availability significantly influences population dynamics and the productivity of marine phytoplankton. As N availability in the ocean is conditioned by the N source, it is important to understand the capacity of phytoplankton organisms to adjust their physiology and dynamics under different N conditions. We investigated the growth dynamics of Thalassiosira weissflogii, a coastal diatom, in response to different N sources (Nitrate, NO3-; Ammonium, NH4+; urea, CH4N2O) and availabilities (45 and 5 µM). Our findings demonstrate that T. weissflogii can display plastic adjustments in population dynamics to different N sources. These responses evidenced a greater preference for NH4+ and urea than NO3-, particularly under high N availability. The relative growth rate (µ) is higher (1.18 ± 0.01) under NH4+-high treatment compared to NO3--high (1.01 ± 0.01). The carrying capacity (K) varied only among concentrations, indicating equal N utilization efficiency for biomass production. No effects of N source were detected under the low concentration, suggesting that the preference for NH4⁺ and urea was diminished by limited nitrogen supply due to potential interactions. These results provide valuable insights into the physiological flexibility of T. weissflogii to varying N conditions, shedding light on the ecological success and resilience of this species in highly variable coastal environments.

Modeling freshwater plankton community dynamics with static and dynamic interactions using graph convolution embedded long short-term memory.

Given the frequent association between freshwater plankton and water quality degradation, several predictive models have been devised to understand and estimate their dynamics. However, the significance of biotic and abiotic interactions has been overlooked. In this study, we aimed to address the importance of the interaction term in predicting plankton community dynamics by applying graph convolution embedded long short-term memory networks (GC-LSTM) models, which can incorporate interaction terms as graph signals. Temporal graph series comprising plankton genera or environmental drivers as node features and their relationships for edge features from two distinct water bodies, a reservoir and a river, were utilized to develop these models. To assess the predictability, the performances of the GC-LSTM models on community dynamics were compared those of LSTM and GCN models at various lead times. Moreover, GNNExplainer was used to examine the global and local importance of the nodes and edges for all predictions and specific predictions, respectively. The GC-LSTM models outperformed the LSTM models, consistently showing higher prediction accuracy. Although all the models exhibited performance degradation at longer lead times, the GC-LSTM models consistently demonstrated better performance regarding each graph signal and plankton genus. GNNExplainer yielded interpretable explanations for important genera and interaction pairs among communities, revealing consistent importance patterns across different lead times at both global and local scales. These findings underscore the potential of the proposed modeling approach for forecasting community dynamics and emphasize the critical role of graph signals with interaction terms in plankton communities.

How does increasing temperature affect the toxicity of bisphenol A on Cryptomonas ovata and its consumer Daphnia magna?

The global rise in plastic production has led to significant plastic deposition in aquatic ecosystems, releasing chemical compounds as plastics degrade. Among these, bisphenol A (BPA) is a major global concern due to its endocrine-disrupting effects and widespread presence in aquatic environments. Furthermore, the toxicity of BPA on aquatic organisms can be modulated by global change stressors such as temperature, which plays an essential role in the metabolism of organisms, including the degradation and accumulation of toxic compounds. In this study, we aimed to understand how temperature can modulate the toxic effect of BPA on a phytoplankton species (Cryptomonas ovata) and how this effect can be transferred to its herbivorous consumer (Daphnia magna). To do this, we first determined the sensitivity of C. ovata over a BPA gradient (0-10 mg L-1). Subsequently, we experimentally determined how the increase in temperature (+5ºC) could modify the toxic effect of BPA on the physiology, metabolism and growth of the phytoplankton. Finally, we investigated how this effect transferred to the growth rate of D. magna through food. Our results show a negative effect of BPA on C. ovata from 5 mg BPA L-1, affecting its photosynthetic yield of photosystem II, net primary production, respiration, and growth. This effect was accelerated when the temperature was higher. Additionally, the growth rate of D. magna also decreased when fed on C. ovata grown in the presence of BPA and high temperature. Our results indicate that high temperature can accelerate the toxic effects of BPA on organisms located at the base of the food web and this effect could be transferred to higher levels through food.

Evaluating physiological responses of microalgae towards environmentally coexisting microplastics: A meta-analysis.

Microplastics (MPs) are abundantly present in aquatic environments, where the phytoplankton-microalgae, are now inevitably bound to a long-term coexistence with them. While numerous studies have focused on the toxicological effects of high-concentration MPs exposure, there remains controversy over whether and how MPs affect microalgae at environmentally relevant concentrations. This study aims to draw conclusions that narrow the gap from 52 studies with varying results. Overall, MPs can inhibit growth and photosynthesis, induce oxidative damage, from which microalgae can recover after an appropriate period. Cyanobacteria exhibit greater vulnerability than chlorophyta. The relative size of MPs to algal cells potentially governs their coexistence behavior, thereby altering the mechanisms of impact. Pristine MPs may increase the production of extracellular polymeric substances (EPS) and microcystins (MCs), while aged MPs have the opposite effect. Additionally, relevant factors are systematically discussed, offering insights for future research.

Cross-frontal variability of phytoplankton productivity in the Indian sector of the Southern Ocean during austral summer of 2010-2018.

Oceanic phytoplankton productivity, which regulates atmospheric CO2, is crucial for unraveling the complexities of the global carbon cycle. Despite its substantial contribution to the global carbon budget and its critical role in anthropogenic carbon sink, the Southern Ocean (SO) remains under-sampled due to logistical challenges. The present study attempts to elucidate the variability of water column primary production (PP) in the Indian Sector of the Southern Ocean (ISSO) by examining associated physicochemical parameters and physiological conditions of phytoplankton that drive this variability. The study revealed the nutrient limitation in the region north of the Subantarctic Front (SAF) and light limitation coupled with intense zooplankton grazing in the region south of the SAF. Coastal waters exhibit higher PP, characterized by the prevalence of large phytoplankton. The SAF displayed maximum productivity among the fronts, while the Polar Front 2 (PF-2) recorded the lowest. The water column PP varies from 27.01 to 960.69 mg C m-2 d-1 in the frontal region, while the coastal waters recorded productivity up to 1083.56 mg C m-2 d-1. Phytoplankton in the frontal regions indicated a stable surface abundance, except north of the Subtropical Front (STF), where the oligotrophic condition fosters the growth of picoplankton, subjected to high grazing by microzooplankton. Conversely, in the colder coastal waters, the phytoplankton experienced physiological acclimation. Model-based estimates of PP highlighted the efficacy of the Carbon-based Production Model (CbPM) in estimating net PP (NPP) in these polar waters, surpassing the Vertically Generalized Production Model (VGPM) and Eppley-VGPM. Notably, all model-based PP estimates significantly improved with in situ chlorophyll as input instead of satellite-retrieved chlorophyll. While the models performed well in the coastal water, their performance was suboptimal in the frontal region. This study advances our understanding of the intricate dynamics of phytoplankton productivity in the SO, offering valuable insights for future research endeavors.

Climate-driven decline in water level causes earlier onset of hypoxia in a subtropical reservoir.

Hypoxia, especially in the bottom water, is occurring in deep and stratified reservoirs worldwide, threatening aquatic biodiversity, ecosystem functions and services. However, little is known about the timing of onset and ending of hypoxia, especially in subtropical reservoirs. Based on five-year (from April 2015 to January 2020) sampling of a subtropical monomictic deep reservoir (Tingxi Reservoir) in southeast China, we found the evidence of about 40 days earlier onset of hypolimnion hypoxia during low water level periods in dry years compared to wetter high water level years. We explored the effects of stratification and mixing conditions on hypoxia, cyanobacterial biomass, and nutrient dynamics; and revealed the physical and biochemical conditions that drove hypoxia. The results indicated that 1) The decline in water level increased the intensity of thermal stratification, resulting in 40 days earlier onset of hypolimnion hypoxia in dry years than in wet years; 2) The decline in water level expanded the extent of hypoxia by promoting nutrient accumulation and phytoplankton biomass growth; 3) Warmer climate and less precipitation (drought) significantly promoted the risk of hypoxic expansion and endogenous phosphorus release in subtropical reservoirs. We suggest that more attention needs to be paid to the early onset of hypoxia and its consequences on water quality in subtropical stratified reservoirs during low water level periods in a changing climate.

Assessing ecological status using phytoplankton functional groups in three urban rivers in Hainan Island, China.

The urban rivers, including Changwang, Meishe, and Wuyuan in Haikou City, Hainan Island, are vital water sources for agricultural production and support industrial and domestic activities. Despite the rivers experiencing anthropogenic impacts, limited studies have assessed their water quality. Accordingly, this study assessed the phytoplankton community structure, utilized the river phytoplankton assemblage index (Qr index) to evaluate the ecological status, and compared its performance with the comprehensive trophic level index (TLI). Sample collection and microscopy analysis was conducted seasonally in 2019. Two hundred ninety-eight phytoplankton species belonging to 8 phyla were identified, predominated by Chlorophyta, Bacillariophyta, and Cyanophyta. The phytoplankton biomass ranged from 0.04 to 34.98 mg L-1, with averages of 3.06 ± 0.71, 5.16 ± 1.92, and 2.70 ± 0.76 mg L-1 in Changwang, Meishe, and Wuyuan, respectively. The phytoplankton biomass varied seasonally, recording the highest and lowest values in summer and autumn, respectively. The phytoplankton species were classified into 26 functional groups, which exhibited spatial and seasonal differences in their biomass and composition. The redundancy analysis (RDA) revealed that NH3-N, TP, CODMn, Chl-a, salinity, and temperature were the main environmental factors influencing phytoplankton functional groups. The average Qr index values in Changwang, Meishe, and Wuyuan were 3.39 ± 0.61, 3.44 ± 0.51, and 3.22 ± 0.67, and all the rivers were rated "good" in status. Seasonally, the Qr index and TLI revealed that the rivers' ecological condition was better in autumn and winter compared to spring and summer. Generally, the Qr index performed better, indicating that parameters such as NH3-N, CODMn, TP, and Chl-a decreased with improving ecological conditions from "poor" to "excellent" status. In addition, the Qr index exhibited a significant negative relationship with TLI, suggesting that low Qr index values may indicate increased eutrophication or deteriorated water quality. Thus, the ecological condition of the urban rivers could be adequately assessed using the Qr index to guide their water quality monitoring and management.

75-Year dynamics of the Black Sea phytoplankton in association with eutrophication and climate change.

Based on a database containing species records obtained from 1948 to 2022 and a hydrochemical database, long-term changes in the biomass and taxonomic structure of phytoplankton in the deep-sea basin of the Black Sea were analysed in the stratified period from April to October. Over 75 years, a significant increase in concentration of nitrate, a weak increase in phosphate and a strong decrease in dissolved silicate were observed in the nutricline. The biomass of diatoms and total phytoplankton increased several times during the peak of eutrophication in 1991-1993, then decreased by the 2000s and has again shown an increasing trend in the last 15 years. The number of species dominant in biomass has halved from the 1940s-60s to the 2010s. The primary beneficiaries were the large- and medium-celled diatoms Pseudosolenia сalcar-avis and Proboscia alata, as well as the coccolithophore Emiliania huxleyi, the main dominant species of the last decade. Most noticeable was the increase in the amplitude and duration of the regular annual May-July bloom of E. huxleyi. Over the past three decades, its biomass has increased by more than an order of magnitude, accounting for about 40 % of the total phytoplankton biomass. Development of the large- and medium-celled diatoms, as well as the decrease in biomass of silicoflagellates, can be, at least partly, associated with the long-term decline in dissolved silicate in the upper layers. The trend towards a decrease in dinoflagellate biomass is probably associated with increased mixing intensity in the water column. Over the study period, the total phytoplankton biomass was positively related to nitrate stock in the water column. Short-term period (from one to several years) interannual variability was influenced predominantly by hydrophysical processes, primarily the intensity of winter convection. After cold winters with intense involvement of deep nutrients in the upper layers, the biomass of diatoms, coccolithophores and total phytoplankton increased. Thus, fluctuations in winter weather or local climate reduced or enhanced the effect of eutrophication, sometimes leading to the time gap between the peak in nitrate stock and phytoplankton biomass. The case of the Black Sea illustrates the complex pattern of the response of a marine ecosystem to the simultaneous impacts of anthropogenic and climate changes, leading to significant alterations in the functioning of the biological carbon pump.

Inter-algal associations and nutrients linked by Scenedesmus and Desmodesmus structure eukaryotic algal communities.

Eutrophication reduces the variability of the community composition of plankton. However, the mechanisms underlying the diversity and restructuring of eukaryotic algal communities remain unknown. This study analysed the diversity and compositional patterns of algal communities in shallow eutrophic lakes. It investigated how these communities were modified by key genera through mediating inter-algal associations under the influence of abiotic factors. Inter-algal associations explained more variance in algal communities than environmental variables, and variation in composition and diversity was primarily derived from Scenedesmus, Desmodesmus and Cryptomonas, rather than nutrients. Scenedesmus and Desmodesmus were positively correlated with the genera of Chlorophyta and formed the hub of the algal association network. When the relative abundance of Scenedesmus and Desmodesmus increased from 0.41% to 13.74%, communities enriched in biomarkers of Bacillariophyta, Chrysophyceae and Cryptophyta transitioned to communities enriched in biomarkers of Chlorophyta. Moreover, negative associations between the Chlorophyta hub genera and other non-Chlorophyta genera increased. High concentrations of total phosphorus altered the composition of algal communities by increasing the abundance of Scenedesmus and Desmodesmus, which in turn had cascading effects through inter-algal associations. Additionally, algal communities with higher abundances of Scenedesmus and Desmodesmus were more susceptible to the effects of total phosphorus. Our study suggested that inter-algal associations, centred on Scenedesmus and Desmodesmus, had a greater influence on algal diversity and community structure than other factors. Nutrient levels were not a direct driver of algal diversity and community structure adjustments, but acted indirectly by enhancing the influence of Scenedesmus and Desmodesmus.

The role of predation and pesticides in shaping phytoplankton dynamics in a short microcosms experiment.

Aquatic organisms are subject to various forcing factors that affect their structure, some of which are natural, while others result from human activities, both having variable effects. This study aimed to determine the importance of a natural stressor (zooplankton) and an herbicide (atrazine) on phytoplankton density and morphological composition in a microcosm experiment. A natural phytoplankton assemblage was exposed to two zooplankton predators: a copepod (Argyrodiaptomus falcifer) and a cladoceran (Ceriodaphnia dubia), and to atrazine (27 µg L-1), in three combinations of factors (zooplankton treatments (Z), atrazine treatment (A), the combination of both (ZA)) plus a Control. The experiment lasted 48 h. Samples were taken at the beginning and the end of the experiment, and relevant limnological variables, including inorganic nutrient concentrations, were considered. Results indicated differences in phytoplankton densities when treatments were compared with Control. In this respect, Chlorophyceae, Euglenophyceae, and Bacillariophyceae exhibited more changes than other phytoplankton classes. Chlorophyceae densities tended to be higher in the Control than in the treatments; the combination of zooplankton and atrazine favored Euglenophyceae, while atrazine favored Bacillariophyceae densities. Regarding morphological groups, unicellular and small colonies (<35 µm), showed differences between the Control and particularly with Z treatment, colonial-cenobia forms were negatively affected by atrazine and silica forms were favored by both stressors combined. It is concluded that interactions among natural and anthropogenic stressors could be complex, influencing factors such as phytoplankton taxonomical affinities, morphological groups, and the nature of the stressor applied.

Temporal changes of phytoplankton-derived sterols in suspended particulate matter and their implications as biomarkers for phytoplankton abundance in northern Patagonia, Reloncaví Estuarine System (RES), Chile.

The Northern Patagonia coast, characterized by an intricate interaction among terrestrial and marine systems such as Reloncaví Estuarine System (RES), present highly productive marine and aquaculture activities, having a significant socio-economic importance in Chile. Understanding the composition of Organic Matter (OM) in aquatic ecosystems is crucial for elucidating biogeochemical processes, and the use of lipid biomarkers, has proven valuable in identifying OM sources. This study investigates the relationship between phytoplankton biomass indicators, including phytoplankton abundance, chlorophyll-a, and sterol molecules synthesized in high percentages by phytoplankton cells, also known as phytoplankton-derived sterols at the RES. The RES encompasses the Reloncaví Fjord (RF) and the Reloncaví Sound (RS) and exhibits a high influenced by oceanic waters and freshwater discharge from rivers Spatio-temporal sampling was conducted during the austral spring, summer and winter expeditions of 2018 and 2019, at two sites in RS and RF mouth (RFm). Our findings reveal higher sterol concentration at RFm than RS. Notably, high sterol concentrations during austral summer season coinciding with increased phytoplankton abundances. Furthermore, higher concentrations of terrestrial-derived sterols such as ß-sitosterol (C29Δ5) and stigmasterol (C29Δ5,22), at RFm site suggested an input of OM from the inner RF. Phytoplankton-derived sterols such as 24-methylenecholesterol (C28Δ5,24(28)) provide a reliable estimate of total diatom abundance at both sites (RFm and RS), though they showed a lower relationship with taxonomic subgroups and phytoplankton classes in our study area. Hence, phytoplankton-derived sterols can be considered reliable diatom biomarkers, particularly in the RS, where the primary source of OM is predominantly marine, and even with high sterol degradation values at RES. Our study highlights the importance of interpreting changes in sterol abundances as phytoplankton community shifts. To avoid misinterpretation, it is essential to incorporate direct phytoplankton counts in elucidating the complex biosynthetic sources of sterols within the water column.

Environmental and Climatic Drivers of Phytoplankton Communities in Central Asia.

Artificial water bodies in Central Asia offer unique environments in which to study plankton diversity influenced by topographic barriers. However, the complexity of these ecosystems and limited comprehensive studies in the region challenge our understanding. In this study, we systematically investigated the water environment parameters and phytoplankton community structure by surveying 14 artificial waters on the southern side of the Altai Mountains and the northern and southern sides of the Tianshan Mountains in the Xinjiang region. The survey covered physical and nutrient indicators, and the results showed noticeable spatial differences between waters in different regions. The temperature, dissolved oxygen, total nitrogen, and total phosphorus of artificial water in the southern Altai Mountains vary greatly. In contrast, the waters in the northern Tianshan Mountains have more consistent physical indicators. The results of phytoplankton identification showed that the phytoplankton communities in different regions are somewhat different, with diatom species being the dominant taxon. The cluster analysis and the non-metric multidimensional scaling (NMDS) results also confirmed the variability of the phytoplankton communities in the areas. The variance partitioning analysis (VPA) results showed that climatic and environmental factors can explain some of the variability of the observed data. Nevertheless, the residual values indicated the presence of other unmeasured factors or the influence of stochasticity. This study provides a scientific basis for regional water resource management and environmental protection.

Molecular diversity and seasonal dynamics of Ostreococcus (Mamiellophyceae, Chlorophyta) in typical mariculture bays based on metabarcoding analysis.

Ostreococcus (Mamiellophyceae, Chlorophyta) is a cosmopolitan genus of marine pico-phytoplankton and the smallest free-living photosynthetic eukaryotes with cell size of 1-2 µm. To understand the diversity and spatio-temporal distribution of Ostreococcus in the Rongcheng coastal regions in northern China, metabarcoding analysis based on the 18S rDNA V4 molecular marker was applied to study the molecular diversity and seasonal dynamics of Ostreococcus in three typical mariculture bays (Rongcheng Bay, Lidao Bay and Sanggou Bay). A total of 103 amplicon sequence variants (ASVs) annotated as Ostreococcus were detected in these three typical mariculture bays throughout the year. The top five ASVs in terms of abundance were ASV4, ASV9, ASV14, ASV28 and ASV109, totally occupying 99.1% of Ostreococcus reads. Phylogenetic analysis showed that these five dominant ASVs represented two Ostreococcus ecotypes (OI and OII) and were grouped into four Ostreococcus clades including Ostreococcus lucimarinus (ASV9) and Ostreococcus tauri (ASV28 and ASV109) in OI, and Ostreococcus sp. RC1 (ASV4) and Ostreococcus sp. RC2 (ASV14) in OII, which provided direct evidence to support the co-existence of two ecotypes in the Rongcheng coastal regions. Five dominant ASVs in OI and OII exhibited two distinct seasonal distribution patterns. Three dominant ASVs (ASV9, ASV28 and ASV109) in OI could be detected in all four seasons of the year, exhibiting native distribution properties, while two ASVs (ASV4 and ASV14) in OII decreased sharply in winter and could not be detected in spring, exhibiting characteristics of alien inputs. The composition, succession and association of Ostreococcus community were mainly driven by water temperature in these mariculture bays. This study helps us systematically understand the molecular diversity and distribution patterns of Ostreococcus in typical mariculture bays in northern China, laying the foundation for understanding and revealing the ecological functions of pico-phytoplankton.

Impact of tropical cyclone Biparjoy on oceanic parameters in the Arabian Sea.

Climate change is expected to intensify tropical cyclones (TCs), requiring a deeper understanding of their ecosystem impacts. This study investigated TC Biparjoy impact on parameters from June 6 to 19, 2023, using satellite and vertical profiles. Initially, Chlorophyll-a levels remained steady but surged above 4 mg/m3 after the high-intensity phase, indicating increased phytoplankton biomass. Sea surface temperature (SST) initially exceeded 32 °C, favoring cyclone intensification, but dropped below 26 °C post-high-intensity phase due to mixing and upwelling of cooler waters. The SST gradient exceeded 0.15 °C/km post-cyclone. Elevated sea surface height around 0.5 m offshore and over 1 m along the coast was recorded. Wind stress values exceeding 0.4 N/m3 were observed during the high-intensity phase. Vertical profile showed uplifted low-temperature, nutrient-rich waters, enhancing phytoplankton productivity, supported by increased nitrate (>10 mmol/m3) and phosphate (>1.2 mmol/m3) levels. Additionally, slight increase in DIC, and pH during the cyclone period suggested changes in biogeochemical processes.

Mathematical model of oxygen minimum zones in the vertical distribution of oxygen in the ocean.

Processes determining the amount and spatial distribution of dissolved oxygen in the ocean have been a focus of intense research over the last two decades. Anomalies known as Oxygen Minimum Zones (OMZs) have been attracting growing attention, in particular because their growth is believed to be a result of the global environmental change. Comprehensive understanding of factors contributing to and/or controlling the emergence and evolution of OMZs is still lacking though. OMZs are usually thought to result from an interplay between the oxygen transport through the water column from the ocean surface and variable oxygen solubility at different water temperature. In this paper, we suggest a different, novel mechanism of the OMZ formation relating it to the oxygen production in phytoplankton photosynthesis in a stratified ocean. We consider a simple, conceptual model of the coupled phytoplankton-oxygen dynamics and show that the model predictions are in qualitative agreement with some relevant field observations.

Spatiotemporal distribution of neurotoxin ß-N-methylamino-L-alanine and 2,4-diaminobutyric acid in offshore aquaculture area of Shandong province, China.

The neurotoxin ß-N-methylamino-L-alanine (BMAA) has been widely detected in aquatic environments and got the public's attention due to its potential risk to human neurodegenerative diseases. Three cruises in spring, summer and autumn seasons were carried out in Laizhou Bay (LZB), Sishili Bay (SSLB), Sanggou Bay (SGB), Jiaozhou Bay (JZB) and Haizhou Bay (HZB) in 2023. Results showed that the temporal distribution pattern of BMAA in plankton varied in the survey bays. In LZB, the highest average concentration of BMAA in phytoplankton occurred in spring. The highest average concentration of BMAA in phytoplankton was detected in summer in SSLB, JZB and HZB. However, BMAA was only detected in phytoplankton at the R2 station in SGB in spring. The highest average concentration of BMAA in zooplankton was observed in spring in LZB, SSLB and SGB. Zooplankton accumulated the highest average concentration of BMAA in JZB and HZB in summer and autumn, respectively. The BMAA was widely detected in marine mollusks throughout the investigative period. In addition, Mantel test and RDA analysis results indicated that DIN/DIP strongly impacted on the spatiotemporal distribution of BMAA in phytoplankton, in JZB and SSLB. The spatiotemporal distribution of BMAA in plankton was correlated with temperature and DO in JZB. More field cruises should be conducted to explore the environmental drivers of the neurotoxin BMAA in marine ecosystems in future studies.

Evolutionary conservation and metabolic significance of autophagy in algae.

Autophagy is a highly conserved 'self-digesting' mechanism used in eukaryotes to degrade and recycle cellular components by enclosing them in a double membrane compartment and delivering them to lytic organelles (lysosomes or vacuoles). Extensive studies in plants have revealed how autophagy is intricately linked to essential aspects of metabolism and growth, in both normal and stress conditions, including cellular and organelle homeostasis, nutrient recycling, development, responses to biotic and abiotic stresses, senescence and cell death. However, knowledge regarding autophagic processes in other photosynthetic organisms remains limited. In this review, we attempt to summarize the current understanding of autophagy in algae from a metabolic, molecular and evolutionary perspective. We focus on the composition and conservation of the autophagy molecular machinery in eukaryotes and discuss the role of autophagy in metabolic regulation, cellular homeostasis and stress adaptation in algae. This article is part of the theme issue 'The evolution of plant metabolism'.