Seasonal variation of phytoplankton community structure and nitrogen uptake regime in the Indian Sector of the Southern Ocean

The subsurface chlorophyll maximum (SCM) is increasingly recognised as an important but understudied locus of primary production particularly in shelf seas. Here we report the results of a 4 year, repeat station, summer sampling programme (2013–2016) of a seasonally recurrent SCM in the Western English Channel. Interannual variability in phytoplankton community structure and chlorophyll distribution and intensity was strongly related to water column stability at the depth interval of the SCM and also to water temperature. The phytoplankton community was statistically distinct in each year. High stability, as evidenced by large Richardson numbers and a well-developed strong thermocline appeared to favour the growth of larger dinoflagellates (autotrophs or mixotrophs) and diatoms. Such conditions led to development of the most intense SCMs and these were sometimes dominated by a single or a few key species most prominently in 2015 with near monospecific concentrations of the dinoflagellate Tripos fusus with average peak SCM chlorophyll concentrations of 7.3 ± 4.4 μg l−1. By contrast, in years with low water column stability and intermittent turbulence at the thermocline (2014, 2016) there was greater chlorophyll dispersal and less intense SCM. In these low stability conditions, red fluorescent nano-phytoplankton, such as naked dinoflagellates, chlorophytes and prymnesiophytes, made a greater contribution to the community, possibly as a result of the advantages that motility and enhanced light utilisation efficiency confer within an SCM exposed to turbulence. It is also likely that turbulence disrupted the stability required by the larger dinoflagellates and diatoms. Several of the key SCM taxa were absent from surface waters including the dinoflagellates Tripos fusus, Tripos lineatus, and most of the Rhizosolenia/Proboscia diatoms, consistent with adaptations more suited to survival at depth in stratified waters. These traits include luxury nutrient uptake and storage and survival in low light (both groups) and mixotrophy (dinoflagellates). On the other hand, in 2013, diatoms including Pseudo-nitzschia spp. were abundant in both surface, SCM and bottom waters. The relatively cooler waters (11.6–12.1 °C on average in 2013 and 2016) were characterised by smaller diatoms (Chaetoceros spp. and Pseudo-nitzschia spp.) whereas the warmer waters (13.1 °C on average in 2014) contained larger diatoms (large Rhizosolenia spp., Lauderia annulata and Leptocylindrus danicus). There did not appear to be continuity of key species between years, other than for the dinoflagellate Tripos lineatus, which was significant in both 2013 and 2014 and present in 2015. In any given year, there was no correspondence between the key spring bloom phytoplankton species as monitored in the nearby Western Channel Observatory L4 station and the key SCM taxa.

The Ross Sea is a critical region for understanding phytoplankton dynamics and their role in polar marine ecosystems in the west Antarctica, particularly in the context of rapid environmental change. Investigating the spatial variability of phytoplankton biomass and community structure is essential for assessing ecosystem productivity and biogeochemical cycling in this vulnerable area. From January to February 2023, a field survey of the Ross Sea was conducted onboard the icebreaker research vessel Araon, utilizing high-resolution, continuous observations of surface seawater with the Algae Online Analyzer and Imaging FlowCytoBot. These observations provided precise spatial distribution data on phytoplankton biomass and species abundance. The results revealed intricate spatial variability in phytoplankton community structure and biomass across the eastern and western Ross Sea, spanning coastal to offshore gradients, and in the dynamic waters near polynyas and ice shelves. The phytoplankton community was predominantly composed of diatoms, especially Fragilariopsis spp., and/or Phaeocystis spp., with their dominance varying across spatial gradients. The observed patterns suggest that multiple interacting environmental factors, including sea ice concentrations, water masses, and ocean currents, influence on phytoplankton distribution in the region. These findings highlight the critical role of physical and biological interactions in phytoplankton distributions and offer valuable insights into their potential responses to environmental changes in the Ross Sea ecosystem.

The seasonal variations in phytoplankton community structure were investigated for the Sanggou Bay (SGB) and the adjacent Ailian Bay (ALB) and Lidao Bay (LDB) in Shandong Peninsula, eastern China. The species composition and cell abundance of phytoplankton in the bay waters in spring (April 2011), summer (August 2011), autumn (October 2011), and winter (January 2012) were examined using the Utermohl method. A total of 80 taxa of phytoplankton that belong to 39 genera of 3 phyla were identified. These included 64 species of 30 genera in the Phylum Bacillariophyta, 13 species of 8 genera in the Phylum Dinophyta, and 3 species of 1 genus in the Phylum Chrysophyta. During the four seasons, the number of phytoplankton species (43) was the highest in spring, followed by summer and autumn (40), and the lowest number of phytoplankton species (35) was found in winter. Diatoms, especially Paralia sulcata (Ehrenberg) Cleve and Coscinodiscus oculus-iridis Ehrenberg, were predominant in the phytoplankton community throughout the study period, whereas the dominance of dinoflagellate appeared in summer only. The maximum cell abundance of phytoplankton was detected in summer (average 8.08 × 103 cells L−1) whereas their minimum abundance was found in autumn (average 2.60 × 103 cells L−1). The phytoplankton abundance was generally higher in the outer bay than in the inner bay in spring and autumn. In summer, the phytoplankton cells were mainly concentrated in the south of inner SGB, with peak abundance observed along the western coast. In winter, the distribution of phytoplankton cells showed 3 patches, with peak abundance along the western coast as well. On seasonal average, the Shannon-Wiener diversity indices of phytoplankton community ranged from 1.17 to 1.78 (autumn > summer > spring > winter), and the Pielou’s evenness indices of phytoplankton ranged from 0.45 to 0.65 (autumn > spring > summer > winter). According to the results of canonical correspondence analysis, phosphate level was the major factor that limited the occurrence of P. sulcata and C. oculus-iridis, whereas optimal temperature and low salinity were responsible for Prorocentrum blooms in summer. The detailed description of seasonal variations in phytoplankton community structure in the three bays provide reference data for future studies on marine ecosystems and mariculture in adjacent areas.

Flood events can significantly affect the physical and biological processes of aquatic ecosystems in a short time, leading to rapid changes in phytoplankton community structure. The Huayanghe Lakes experienced extreme flooding in the summer of 2020, with the water level reaching 16.42 m. In order to understand the effects of flooding on phytoplankton diversity and community structure, eight samples were collected in the Huayanghe Lakes from 2019 to 2020. Water-level disturbance has a significant influence on lake-water quality and phytoplankton community structure. The results showed that the Secchi depth increased from 65.36 to 8.52 cm, while the concentration of total nitrogen (from 0.98 to 0.7 mg/L) and total phosphorus (from 0.04 to 0.031 g/L) decreased. In addition, flooding significantly increased the Shannon–Wiener diversity index, the Pielou index, and the Margalef richness index by an average of 43.5%, 36.7%, and 40.21%, respectively. The phytoplankton community structure in the Huayanghe Lakes changed due to the change of physicochemical environment caused by flood. While in the pre-flood period phytoplankton was composed of large diatoms (e.g., Aulacoseira granulata), cyanobacteria (e.g., Microcystis sp., Anabaena sp., and Aphanizomenon sp.) and other multicellular taxa, the flood period showed an increase in the proportion of chlorophytes and diatoms that quickly adapted to settle in new environments. Pearson correlations and redundancy analyses showed that water level fluctuation was the most significant environmental factor affecting the phytoplankton community between the regular hydrological cycle and flood periods. There are few studies on phytoplankton in the Huayanghe Lakes, and the present study provides basic data on phytoplankton diversity and community structure. In addition, it provides a theoretical basis for controlling water level change in the Yangtze River.

Nitrogen uptake regime and phytoplankton community structure in the Atlantic and Indian sectors of the Southern Ocean

Phytoplankton species were enumerated from 72 samples collected biweekly during the upwelling season (May to August) of 2001�2010 to test for effects of interannual variations in upwelling and decadal basin-scale variability on phytoplankton species composition and commu- nity structure. Cluster analysis of phytoplankton community structure identified 7 groups; 1 group was dominated by dinoflagellates while the other groups were dominated by diatoms but with variable ratios of diatom-to-dinoflagellate abundance ranging from 4 to 847. The most abundant diatoms were Thalassiosira spp., Chaetoceros spp., Asterionellopsis glacialis, Cylindrotheca closterium, Leptocylindrus spp., Nitzschia and Pseudo-nitzschia spp., with dominance varying among the 7 groups. Variations in phytoplankton community structure were not related to the strength of upwelling within a given year; rather, differences were related to when a sample was collected within an upwelling/downwelling cycle. Community structure was also analyzed by non-metric multidimensional scaling ordination. The x-axis scores of the ordination, which is an index of community structure, were correlated with the Pacific Decadal Oscillation (PDO) but not with seasonally averaged coastal upwelling strength. Positive values of the index corresponded with positive PDO years (2002�2007), and negative index values with negative PDO years (2001, 2008�2010). Thus changes in the sign of the PDO seem to be more influential in explaining the interannual variations in phytoplankton community structure than seasonally averaged coastal upwelling.

The Black Sea's marine ecosystem houses a diverse phytoplankton community crucial for the region's biogeochemical processes. Recent attention has focused on comprehending the taxonomy and community dynamics of Black Sea phytoplankton. High-performance liquid chromatography (HPLC) serves as a potent analytical tool for pigment separation and identification in phytoplankton samples. This study examines HPLC pigment data collected between 2006 and 2019 during 12 oceanographic bio-optic campaigns in the Black Sea. The research investigates taxonomic composition and community structure of the phytoplankton community. Analysis of the dataset involved employing various machine learning and bioinformatics tools. Additionally, the dataset was used for chemotaxonomycal classification and for the development of phytoplankton functional type (PFT) regionalized model. All these methods aimed to identify distinct phytoplankton groups and their relative abundance throughout the campaigns. Results indicate that the Black Sea phytoplankton community is predominantly composed of diatoms and dinoflagellates, with varying contributions from other groups such as prasinophytes, haptophytes (coccolitophores), and chlorophytes. Additionally, the study discerned diverse patterns of community composition and pigment ratios across the campaigns, revealing spatial variations in phytoplankton community structure influenced by factors like nutrient availability and water column stratification. This research significantly contributes to understanding the taxonomy and community structure of Black Sea phytoplankton through the application of advanced multivariate analysis techniques.

Spatial and temporal variation in phytoplankton community structure within a large flood-control reservoir (Sardis Reservoir, MS, USA) was investigated in relation to variation in physicochemical properties, location within the reservoir, hydraulic residence time (HRT), nutrient concentrations, temperature, and light conditions over a 14-month period. During periods of short HRT, phytoplankton communities throughout the reservoir were homogeneous in biomass, composition, and production. With a gradual increase in HRT from spring to summer, spatially heterogeneous phytoplankton communities developed along the longitudinal axis of the reservoir. During this period of longer HRT, diatoms and chlorophytes were a larger proportion of total phytoplankton biomass at shallow and more turbid locations near the head of the reservoir, whereas cyanobacteria were a larger proportion of the community at deeper and less turbid locations closer to the outflow. Seasonal succession of the phytoplankton community was represented by high abundance of diatoms in spring, increasing biomass of cyanobacteria through summer, and a secondary bloom of diatoms in fall. Species of Cyclotella, Asterionella, Nitzschia, and Ankistrodesmus were among the first colonizers in the early growing season, closely followed by Aulacoseira, whereas species of Staurastrum and Tetraedron appeared later in the spring. Species of Synedra, Crucigenia, Selenastrum, Scenedesmus, and Merismopedia occurred throughout the sampling period. As the diatoms started to decrease during mid-spring, cryptophytes increased, prior to dominance of species of Pseudanabaena in summer. Reservoir management of HRT, in combination with spatial variation in reservoir morphology and seasonal variation in temperature and riverine nutrient inputs, creates seasonally variable yet distinct spatial patterns in phytoplankton community biomass, composition, and production.

Phytoplankton abundance and community structure were determined routinely over an annual period and intensively during two storm-runoff events in a small suburban reservoir in northern Virginia, U.S.A. Traditional graphical techniques and a multivariate approach (Principal Components Analysis) were used to demonstrate a seasonal pattern of phytoplankton succession with greens and blue-greens dominant in summer, diatoms and chrysophytes in spring and fall, and cryptophytes in winter. Spatial variations were minor over horizontal and vertical dimensions during spring mixis, but depth variations were substantial during summer stratification. Storm runoff had little effect on phytoplankton composition during the stable summer period, but was associated with a substantial perturbation in community structure during the spring to summer transition.

This study investigated the spatiotemporal distribution of the phytoplankton in the coral habitat of Dongshan Bay (China), along with critical factors affecting the distribution, during June, August, and December 2022. Phytoplankton abundance in Dongshan Bay exhibited considerably temporal variation, peaking in June 2022, gradually decreasing thereafter, and reaching its lowest point in December 2022. The abundance of bottom-layer phytoplankton consistently exceeded that of the surface layer throughout all seasons. The average phytoplankton abundance in the coral habitat of Dongshan Bay was lower than that in non-coral habitat areas. Fluctuations in the Zhangjiang River and coastal upwelling influenced the diversity and community structure of the phytoplankton. Critical factors causing spatiotemporal variability in phytoplankton community structure included nutrient concentrations and seawater temperature. Nutrients played key roles in influencing various phytoplankton groups. Dominant diatom species, such as Thalassionema nitzschioides and Thalassiosira diporocyclus, were positively correlated with ammonia nitrogen, seawater salinity, coral cover, and the number of coral species present. In winter, Calanus sinicus exhibited a negative correlation with harmful algal bloom species. Additionally, it was found that both in the coral habitat and surrounding open sea, currents, nutrients, and zooplankton may play crucial roles in determining the spatiotemporal variability in the phytoplankton community structure.

2010年对菜子湖浮游植物群落结构进行了调查和分析,结果显示:(1)共鉴定浮游植物8门110属285种,不同月份浮游植物的种类组成存在极显著差异,3月份种类数最多,173种,1月份最少,105种.优势度分析显示:蓝藻存在全年高峰;硅藻存在1、5、9、11月的高峰;黄藻存在1、3、5月的高峰;绿藻存在11月的高峰,隐藻存在5月份的高峰;金藻存在1月份的高峰.不同月份浮游植物的细胞密度亦存在极显著差异,7月份最高,为(66.13±8.58)×10⁵ cells/L,1月份最低,为(12.78±0.61)×10⁵ cells/L,夏、秋季较高,冬、春季较低;不同月份浮游植物的生物量差异极显著,9月份最高,为2.80±0.17 mg/L,5月份最低,为0.72±0.03 mg/L.(2)Margalef丰度指数为1.51~3、Shannon-Weaver多样性指数为1.41~3.01、Pielou均匀度指数为0.39~0.66,各指数表现为冬、春季节大于夏、秋季节,3月份最高,7月份最低.(3)聚类分析的结果显示,月份不同影响因素不同,菜子湖水域浮游植物按群落结构特征的分组不同.(4)2007年相比,2010年浮游植物物种数有明显下降,由340种下降到285种,细胞密度明显上升,由(5.91±0.90)×10⁵ cells/L上升到(33.81±10.10)×10⁵ cells/L,群落结构变化较大,贫营养型和固着型藻类都有所减少,富营养型藻类、丝状藻类和浮游性藻类增多.;The annual dynamics of phytoplankton community structure in Lake Caizi has been investigated in 2010. The results indicated that:(1) A total of 285 phytoplankton species from 110 genera of 8 phylum were identified. Phytoplankton species composition in different months showed significant difference. The maximal number of phytoplankton species (173) occurred in March while the minimum (105) in January. The dominant class of phytoplankton changed seasonally. Cyanophyta peaked all the year round; diatoms had an apparent dominance in January, May, September and November; Xanthophyta also played an important role in January, March and May; Chlorophyta dominated in November, Cryptophyta dominated in May while Chrysophyta dominated in January. The cell density and biomass of phytoplankton were higher in summer and autumn than that in winter and spring. The cell density of phytoplankton between different months had significant difference. The maximal density, with the value (66.13 ± 8.58)×10⁵ cells/L occurred in July while the minimal value of (12.78 ± 0.61)×10⁵ cells/L appeared in January. Whereas, the maximal biomass of phytoplankton(2.80 ± 0.17 mg/L) occurred in September and the minimal(0.72 ± 0.03 mg/L) appeared in May, and the biomass in different months was also significant different. (2) Temporal variations of three indices (including Margalef index, Shannon-Wiener index and Pielou evenness index) were obvious. All the indices were higher in winter and spring than those in summer and autumn. The maximal value occurred in March while the minimal one appeared in July. (3) The phytoplankton community structure was influenced by different factors in different months. As a result, the groups of sampling station changed seasonally according to cluster analysis. (4) The obvious variation of phytoplankton community structure was present in 2010 compared with that in 2007. The number of species decreased from 340 in 2007 to 285 in 2010, however, the cell density increased obviously from (5.91 ± 0.90)×10⁵ cells/L in 2007 to (33.81 ± 10.10)×10⁵ cells/L in 2010. At the same time, both the numbers of oligotrophic algae and perphytic algae decreased to the same extent and eutrophic, filamentous and planktonic algae increased.

Influence of sea ice concentration on phytoplankton community structure in the Chukchi and East Siberian Seas, Pacific Arctic Ocean

Inter-annual variability in the phytoplankton abundance and community structure of a tropical monsoonal estuary in response to variable monsoonal patterns

Trace metals Cd, Co, Cu, Ni, and Zn in waters of the subantarctic and Polar Frontal Zones south of Tasmania during the ‘SAZ-Sense’ project

As primary producers, phytoplankton play a pivotal role in the marine environment and are central to many biogeochemical processes. Changes to phytoplankton community composition could have major consequences for wider ecosystem functioning and may occur in response to climate change. Here we describe multi-decadal variability in phytoplankton community structure using taxonomic data from the Continuous Plankton Recorder collected in the North-East Atlantic from 1969-2013, using a total of 42 diatom and dinoflagellate taxa. We considered a range of characteristics of community structure, including taxonomic diversity and community stability and disorder, and how these characteristics change in response to sea surface temperature, mixed layer depth and the North Atlantic Oscillation. We found that phytoplankton community composition was largely stable on interannual timescales. A change in community composition occurred between 1985 and 1995 due to an increased dominance of 2 diatom taxa (Rhizosolenia styliformis and Thalassiosira spp.); however, after this period, the community returned to its previous composition. Further, a community disorder analysis found that phytoplankton compositional structure became more rigid in recent years, which may lead to an eventual community shift in the future. In contrast to previous studies that revealed relationships between total phytoplankton abundance or biomass and environmental forcing, we found that community structure had, at most, a very weak relationship with the environmental parameters tested. Changes to the physical environment may therefore have less influence at interannual timescales on phytoplankton community structure than previously thought.