Picophytoplankton Community Structure Research Articles

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.

Latitudinal and meridional patterns of picophytoplankton variability are contrastingly associated with Ekman pumping and the warm pool in the tropical western Pacific.

Marine picophytoplankton plays a major role in marine cycling and energy conversion, and its effects on the carbon cycle and global climate change have been well documented. In this study, we investigated the response of picophytoplankton across a broad range of physicochemical conditions in two distinct regions of the tropical western Pacific. Our analysis considered the abundance, carbon biomass, size fraction, distribution, and regulatory factors of the picophytoplankton community, which included the cyanobacteria Prochlorococcus and Synechococcus, and small eukaryotic phytoplankton (picoeukaryotes). The first region was a latitudinal transect along the equator (142-163° E, 0° N), characterized by stratified oligotrophic conditions. The second region was a meridional transect (143° E, 0-22° N) known for its high-nutrient and low-chlorophyll (HNLC) conditions. Results showed that picophytoplankton contributed >80% of the chlorophyll a (Chl a), and was mainly distributed above 100 m. Prochlorococcus was the dominant organism in terms of cell abundance and estimated carbon biomass in both latitudinal and meridional transects, followed by Synechococcus and picoeukaryotes. In the warm pool, Prochlorococcus was primarily distributed below the isothermal layer, with the maximum subsurface abundance forming below it. The maximum Synechococcus abundance was restricted to the west-warm pool, due to the high temperature, and the second-highest Synechococcus abundance was associated with frontal interaction between the east-warm pool and the westward advance of Middle East Pacific water. In contrast, picoeukaryotes formed a maximum subsurface abundance corresponding to the subsurface Chl a maximum. In the mixed HNLC waters, the cell abundance and biomass of the three picophytoplankton groups were slightly lower than those in the warm pool. Due to a cyclonic eddy, the contours of the maximum subsurface Prochlorococcus abundance were uplifted, evidently with a lower value than the surrounding water. Synechococcus abundance varied greatly in patches, forming a weakly high subsurface peak when the isothermal layer rose to the near-surface (<50 m). The subsurface maximum picoeukaryote abundance was also highly consistent with that of the subsurface Chl a maximum. Correlation analysis and generalized additive models of environmental factors showed that nutrient availability had a two-faceted role in regulating the spatial patterns of picophytoplankton in diverse latitudinal and meridional environments. We concluded through regression that temperature and light irradiance were the key determinants of picophytoplankton variability in the tropical western Pacific. This study provides insights into the changing picophytoplankton community structure with potential future changing hydroclimatic force.

Water column stratification governs picophytoplankton community structure in the oligotrophic eastern Indian ocean

Under the background of global warming, the area extent of the oligotrophic tropical oceans has growing due to increased water-column stratification over the past decades. Picophytoplankton is usually the most dominant phytoplankton group in oligotrophic tropical oceans and substantially contribute to carbon biomass and primary production three. Understanding how vertical stratification governs the community structure of picophytoplankton communities in oligotrophic tropical oceans is important for comprehensively understanding the plankton ecology and biogeochemical cycle in these areas. In this study, the distribution of the picophytoplankton communities in the eastern Indian Ocean (EIO) was investigated during a period of thermal stratification in the spring of 2021. Prochlorococcus contributed most (54.9%) to picophytoplankton carbon biomass, followed by picoeukaryotes (38.5%) and Synechococcus (6.6%). Vertically, the three picophytoplankton groups showed quite different distribution pattern: the abundance of Synechococcus was highest in the surface layer, while Prochlorococcus and picoeukaryotes were usually located between 50 m and 100 m. The relationship between the abundance of picophytoplankton and environmental factors was analyzed, and the results revealed that picophytoplankton distribution was strongly correlated with the degree of vertical stratification of the water column. The density of Synechococcus was higher in strongly stratified waters, while Prochlorococcus was more abundant in regions of weaker stratification. This is mainly attributed to variation of physicochemical parameters such as nutrient structures and temperature resulted from water column stratification. Understanding the distribution patterns of these organisms and their relationship with stratification in the oligotrophic EIO is essential for comprehensive understanding on oligotrophic tropical ecosystem with increasing stratification in future.

Annual Cycle of the Synechococcus spp. and Picoeukaryotic Growth and Loss Rates in a Subtropical Coastal Ecosystem

Seasonal variations in the picophytoplankton community structure (Synechococcus spp. and picoeukaryotes) were studied by flow cytometry in the coastal ecosystem of the subtropical western Pacific from October 2019 to September 2020. Synechococcus spp. was dominant in abundance during the study period, with its density ranging from 0.05 to 5.6 × 104 cells mL−1; its maximum occurred in July 2020. Picoeukaryotes were less abundant, with their density ranging from 0.2 to 13.6 × 103 cells mL−1. Their highest abundance was recorded in January 2020. The growth rates of Synechococcus spp. and picoeukaryotes ranged from −0.39 to 1.42 d−1 and 0.38 to 2.46 d−1, respectively, throughout the study period. Overall, the growth rate of the picoeukaryotes was significantly higher than that of Synechococcus spp. It is interesting to note that the grazing mortality of Synechococcus spp. and picoeukaryotes during the warmer period (April to September) was relatively low. Based on this study, we suggest that mixotrophic nanoflagellates lowered their feeding activity that obtained nutrients from prey and instead used additional nutrients during the incubation experiments. Our study demonstrated that a shift in the picophytoplankton community composition and grazing activity of predacious nanoflagellates in cold and warm periods can impact on the seasonal dynamics of the microbial food web.

Estimation of cell abundances of picophytoplankton based on the absorption coefficient of phytoplankton in the South China sea

Picophytoplankton are essential components of phytoplankton in the oligotrophic South China Sea (SCS). Understanding the variation in the picophytoplankton community structure will provide important information about primary production and the biogeochemical cycling of carbon in the SCS. Based on a field dataset from the SCS, we developed empirical algorithms using the absorption coefficient of phytoplankton at 443 nm [aph(443)] as the input to estimate the cell abundances of picophytoplankton, including Prochlorococcus (Pro), Synechococcus (Syn), and autotrophic picoeukaryotes (PE), in the SCS. Evaluation of algorithm performances demonstrated good agreement with field measurements. The root mean square errors and the mean absolute errors (MAEs) between the algorithm derivations and measurements were 0.44, 0.35, and 0.29, and 2.67, 2.02, and 1.88 for the cell abundances of Pro, Syn, and PE, respectively. The match-up comparisons showed that the satellite-derived cell abundances of picophytoplankton (e.g., MAEs ranged from 1.73 to 2.76) also agreed with the field data. We also analyzed the influences of both temperature and nutrient concentration on algorithm performance. The influence of temperature on the algorithms was not significant because the data were mainly collected in the summer, and the analysis should be repeated in the future with data from other seasons. The algorithm for estimating cell abundance of Syn was sensitive to variations in nutrient levels and herbivory pressure in coastal waters where nano- or microphytoplankton dominated. The input of our algorithms, aph(443), was easily obtained from field measurements and remote sensing. These algorithms provide a relatively easy way to estimate the cell abundances of picophytoplankton and provide data for studying the picophytoplankton community structure in the SCS.

Environmental influence on the picophytoplankton community structure in the central and northern Bay of Bengal

The Bay of Bengal (BoB) is a low productive, oligotrophic ecosystem. The picophytoplankton (Pico; <3μm) play a significant role in the biogeochemistry of such ecosystems. The information on the Pico is exiguous from this Bay. Here, the seasonal and spatial variations in abundance and carbon biomass of the Pico groups were investigated (July’08 to April’09) in the central and northern BoB in relation to the environmental conditions. Surface samples were collected from twenty-two stations across the Chennai–Port Blair–Kolkata sector. The Synechococcus group was dominant during most of the year, both in abundance and biomass, with few exceptions when Prochlorococcus dominated the Pico community. The Synechococcus abundance and carbon biomass were higher in the nutrient-rich coastal regions and correlated negatively with salinity. The picoeukaryotes exhibited a distribution pattern similar to Synechococcus, although relatively lower in numbers and biomass. The Prochlorococcus abundance and biomass were higher in the open ocean regions of the central BoB (CBoB). The relatively lower abundance of Prochlorococcus in the northern BoB implies an influence of the freshwater influx, as depicted from the positive correlation with salinity. During the winter monsoon, a cyclonic storm coincided with a deep mixed layer characterized by high concentrations of nutrients and chlorophyll-a in the CBoB. The Pico abundance and biomass were relatively higher during this period, with the Prochlorococcus dominating the former and Synechococcus, the latter. The real-time observations of the surface distribution of Pico abundance and carbon biomass in the BoB revealed seasonal variations that were modulated by the episodic mesoscale features.

Picophytoplankton variability: Influence of Rossby wave propagation in the southeastern Arabian Sea

The westward propagating Rossby waves and associated currents transport low salinity nutrient-rich water mass from the Bay of Bengal into the southeastern Arabian Sea (SEAS) during winter monsoon, and ensuing changes in physicochemical properties of water column regulate phytoplankton distribution in the latter region. Herein, we elucidate the influence of Rossby wave propagation on picophytoplankton community composition in the SEAS. We compare the picophytoplankton community structure between the Rossby front (low saline, high nitrate concentration and strong current) and the surrounding non-frontal regions (high saline, low nitrate and weak current) along a cruise track in the SEAS during early winter monsoon (November 2016). The higher abundance of phycoerythrin-rich Synechococcus (‘dim’ and ‘bright’ types) and lower abundance of Prochlorococcus in the frontal region than the non-frontal regions suggest that salinity and nitrate concentration in the water column significantly influence the picophytoplankton community dynamics. We argue that the advection of low saline water mass from the Bay of Bengal associated with Rossby wave propagation introduces a ‘dim’ phycoerythrin-rich Synechococcus group in the frontal region, and the ensuing physicochemical changes in water column favor their growth, whereas low cell abundance of Prochlorococcus and Phycocyanin-rich Synechococcus suggests restricted growth of both the groups. These inferences indicate that Rossby wave associated circulation pattern and physicochemical changes in the water column regulate picophytoplankton community composition and its contribution to food web dynamics in the SEAS.

Dynamics of size-fractionated phytoplankton biomass in a monsoonal estuary: Patterns and drivers for seasonal and spatial variability

Phytoplankton size-fractionated biomass is an important determinant of the type of food web functioning in aquatic ecosystems. Knowledge about the effect of seasonal salinity gradient on the size-fractionated biomass dynamics is still lacking, especially in tropical estuaries experiencing monsoon. The phytoplankton size-fractionated chlorophyll a biomass (>3 μm and <3 μm) and picophytoplankton community structure were characterized in the monsoonal Zuari estuary, along the west coast of India, from October 2010 to September 2011 across the salinity gradient (0–35). On an annual scale, >3 μm size-fraction was the major contributor to the total phytoplankton chlorophyll a biomass with the ephemeral dominance of <3 μm size-fraction. During monsoon season, freshwater runoff and shorter water residence time resulted in a size-independent response. The lowest annual chlorophyll a biomass concentration of both size-fractions showed signs of recovery with increasing salinity downstream towards the end of the monsoon season. In contrast, the chlorophyll a biomass response was size-dependent during the non-monsoon seasons with the sporadic dominance (>50%) of <3 μm chlorophyll a biomass during high water temperature episodes from downstream to middle estuary during pre-monsoon and at low salinity and high nutrient conditions upstream during post-monsoon. These conditions also influenced the picophytoplankton community structure with picoeukaryotes dominating during the pre-monsoon, phycoerythrin containing Synechococcus during the monsoon and phycocyanin containing Synechococcus during the post-monsoon. This study highlights switching over of dominance in size-fractionated phytoplankton chlorophyll a biomass at intra, inter-seasonal and spatial scales which will likely govern the estuarine trophodynamics.

Picophytoplankton variability: Influence of winter convective mixing and advection in the northeastern Arabian Sea

Abstract The deepening of mixed layer and ensuing changes in optical and physicochemical properties of euphotic zone can influence phytoplankton community dynamics in the northeastern Arabian Sea during winter monsoon. The response of picophytoplankton community to such changes during winter convective mixing is not well understood. Herein, we have compared variations in the picophytoplankton community structure during early (November–December 2012), peak (end-January 2014) and late (mid-February 2015) winter monsoon from three separate cruises in the southern northeastern Arabian Sea. The higher Synechococcus abundance owing to entrainment of nutrients in mixed layer was observed during peak winter monsoon, while the concomitant changes in nitrate concentration, light and oxygen environment restricted Prochlorococcus growth resulting in lower abundance during the same period. This highlights the diverse responses of picophytoplankton groups to physicochemical changes of water column during winter convective mixing. The divinyl chlorophyll b/a ratio (marker for Prochlorococcus ecotypes) indicated prevalence of one low-light adapted ecotype (sensitive to light shock) in sub-surface water, one high-light adapted ecotype in surface water during early winter monsoon and both disappeared during intense mixing period in peak winter monsoon. Subsequently, a distinct low-light adapted ecotype, capable to tolerate light shock, was noticed during late winter monsoon and we argue that this ecotype is introduced to southern northeastern Arabian Sea through advection from north by sub-surface circulation. The total picophytoplankton biomass available to microbial loop is restored during late winter monsoon, when stratification begins, with a higher abundance of Synechococcus and the re-occurrence of Prochlorococcus population in the region. These inferences indicate that variability in picophytoplankton community structure and their contribution to the microbial loop are driven by convective mixing and advection, which in turn influence ecosystem functioning and trophodynamics of the southern northeastern Arabian Sea.

Influence of short-term hydrographic variations during the north-east monsoon on picophytoplankton community structure in the eastern Arabian Sea

The eastern Arabian Sea over the continental margin is a dynamic region subjected to short-term variability in hydrography as a result of various physical forcing such as coastal advection and vertical mixing. In order to assess the influence of hydrography on the picophytoplankton community, a temporal high resolution (every 3h for nine days) study was carried out at a fixed location (15° 18′ 46″N, 72° 41′ 53″E) in the eastern Arabian Sea during the early north-east monsoon (November 2011). The picophytoplankton community comprised of Synechococcus, Prochlorococcus, and picoeukaryotes. Based on the temperature and salinity distribution, the study period was divided into phase I representing a stratified water column and phase II representing a vertically mixed water column. Phase I had higher picophytoplankton abundance with the initial dominance of Prochlorococcus which was later taken over by picoeukaryotes. Towards the end of phase I, with the initiation of vertical mixing, picoeukaryotes were the first to respond to the nutrient influx. As the vertical mixing intensified during phase II, the picophytoplankton abundance declined. Picophytoplankton carbon biomass and their contribution to total phytoplankton biomass was relatively higher during phase I with picoeukaryotes as the major contributors. These transient variations in picophytoplankton abundance highlights the importance of high frequency observations at the single cell level for better understanding the population dynamics in such environments.

CO2 alters picophytoplankton community structure in freshwater ecosystems

CO2 alters picophytoplankton community structure in freshwater ecosystems

Effects of coastal upwelling on picophytoplankton distribution off the coast of Zhanjiang in South China Sea

Abstract Coastal upwelling occurred along the west coast of Guangdong in the northern South China Sea during the summer of 2006. The effects of upwelling on the vertical and horizontal distributions of Prochlorococcus and Synechococcus were investigated. A distinct vertical temperature difference between the surface water and water at a depth of 30 m was observed in the coastal upwelling region. There was a clear spatial variability of temperature, and an increasingly obvious horizontal gradient was created from the coast to offshore waters. Picophytoplankton communities observed from the coast to offshore waters were significantly different. In the coastal upwelling waters, the picophytoplankton community was dominated by Synechococcus within the euphotic zone. Prochlorococcus dominated the picophytoplankton community in the euphotic zone in the non-upwelling region. This difference in the picophytoplankton community structure was due to different hydrodynamics. The results of canonical correspondence analysis demonstrate that temperature, salinity, and phosphate concentration may be important factors affecting the distribution of Prochlorococcus and Synechococcus.

Shifts in picophytoplankton community structure influenced by changing upwelling conditions

The influence of upwelling events on the structure of picophytoplankton communities was assessed at the annual scale from a station within the South Australian shelf region. In this region, local (wind) and global (La Niña/El Niño–Southern Oscillation) hydroclimatic conditions affect the development of upwelling over the austral summer. Using flow cytometry, changes in picophytoplankton community structure were investigated in relation to the properties of the water column when the nature and strength of upwelling event differed for the upwelling seasons of 2008, 2009, and 2010. In 2008, strong upwelling favorable southeasterlies were responsible for extensive upwelling and the dominance of picoeukaryotes. Alternatively, in 2009, the observed dominance of Prochlorococcus reflected the presence of oligotrophic conditions whilst southeasterlies were replaced by downwelling favorable north-westerlies that likely prohibited the full development of upwelling. In 2010, whilst southeasterlies remained relatively weak, particularly cold and low saline upwelled waters indicated enhanced upwelling events. This weak local wind field together with the occurrence of El Niño explained the observation of shallow upwelled waters below the warm surface layer and subsequent enhanced stratification. These conditions led to the dominance of Synechococcus in surface and fluorescence maximum depths, but of Prochlorococcus in bottom upwelled waters. The tight association between upwelling and stratification, i.e. whether upwelled waters reach shallower depths and/or mix with those of the surface as a result of variable climatic conditions, was suggested as the process driving the vertical heterogeneity of picophytoplankton populations. This study brings valuable information for changing picophytoplankton community structure with potential future changing hydroclimatic forcing.

Flow cytometric observation of picophytoplankton community structure in the cascade reservoirs along the Wujiang River, SW China

Picophytoplankton community structure has been seasonally investigated in the cascade reservoirs along the Wujiang River from April 2006 to January 2007. Besides picoeukaryotes, two groups of picocyanobacteria have also been detected by flow cytometry. One is a phycoerythrin-rich picocyanobacteria (PE-rich Pcy), the other is a red-fluorescing cells with lacking orange fluorescence and could be a phycocyanin-rich picocyanobacteria (PC-rich Pcy). The average abundances of PC-rich Pcy, PE-rich Pcy and picoeukaryotes were 103, 104 and 102 cells mL-1, respectively. PE-rich Pcy was the dominant population but showed a reduction with eutrophication, and therefore the community structure of picophytoplankton transformed from dominant PE-rich Pcy to dominant PE-rich Pcy and PC-rich Pcy, which suggested they are excellent indicators for the change of trophic state. Picophytoplankton community structure also presented a seasonal variation, indicating the different response of each picophytoplankton group to water temperature.