Changes In Phytoplankton Community Research Articles

Biomarker evidence of the water mass structure and primary productivity changes in the Chukchi Sea over the past 70 years

The Chukchi Sea has experienced significant changes under global warming in the Common Era, including the shift of primary productivity. However, modern observations are too short to fully investigate the effects of environmental changes in this area. Here, we analyzed lipid biomarkers (e.g. long-chain n-alkanes, n-alkanols, n-alkanoic acids, diols, and sterols) from a sediment core (R07) collected from the Chukchi Sea shelf to determine phytoplankton primary productivity variations and factors influencing these changes over the past 70 years. Similar trends of the abundance of terrestrial ecosystem-derived compounds (e.g. long-chain n-alkanes, n-alkanols, n-alkanoic acids, and C32 1,15-diol) indicate that terrigenous input increased from ca. 1946 towards ca. 1983 and then decreased thereafter. In comparison, biomarkers with marine origin indicate that the ratio of diatoms to dinoflagellates increased after ca. 1983 towards the core-top (ca. 2011). Concurrent changes in terrigenous input and phytoplankton community indicated a shift in water mass structure at ca. 1983 (i.e. the Alaska Coastal Water decreased and the Bering Sea Water increased), which may be attributed to the phase shift of the Arctic Oscillation and/or unsynchronized flow changes in different water masses. Owing to the different water mass properties, the change of water mass structure caused intense water mixing and the resulting high turbidity in the study area, which led to light limitation for phytoplankton growth. These conditions probably account for the reduced phytoplankton primary productivity from ca. 1983 to ca. 2000 in the general trend of increasing. The results indicate that, in addition to global warming and sea ice retreat, other factors, such as change in regional water mass structure (i.e. different water masses), may also have a significant influence on the primary productivity and the phytoplankton community in the Chukchi Sea shelf.

Water and sediment changes and the eco-environment response characteristics in Three Gorges Reservoir after the impoundment

三峡水库举世瞩目,是长江保护与治理的关键性枢纽工程,水库自2003年蓄水运行后库区水沙条件均发生了显著改变,对库区水生态环境产生了深远影响。本文系统综述了三峡水库蓄水运行后库区的水流动力特性和泥沙淤积特性,总结了蓄水后水库的新水沙运动情况;从水库蓄水运行后水质参数特征,营养物质、重金属和典型有毒有机污染物的赋存特征等方面,分析了三峡水库库区新水沙变化条件下的水环境响应特征;基于水库蓄水前后浮游植物、底栖动物等重点生物群落的现存量和群落特征变化规律,探索了三峡水库新水沙变化条件下库区的水生态响应特征;最后对未来三峡水库运行下的水生态环境效应研究提出展望,本文可为三峡水库水生态环境保护科学研究和管理提供新的认识和决策参考。;The water-sediment conditions in the reservoir area had changed significantly after the operation of the Three Gorges Reservoir, which has had a profound impact on the water ecology of the reservoir area. In this paper, the dynamic characteristics of the water flow and sedimentation in the reservoir area before and after the operation of the Three Gorges Reservoir were summarized, and the changes in the water-sedimentation conditions after water storage were analyzed. The water environmental response characteristics under this newly formed water-sediment conditions were evaluated in terms of changes in water quality parameters, nutrients, heavy metals, and toxic organic pollutants after the reservoir storage. The ecological response characteristics of aquatic biotas were also explored based on the community changes of phytoplankton, benthic fauna and other key biological communities before and after the reservoir storage. Finally, the outlook for future research on the water ecological environmental effects of the Three Gorges Reservoir was proposed. This paper can provide support for the water ecological environment protection of the Three Gorges Reservoir.

Assessing the influence of ocean alkalinity enhancement on a coastal phytoplankton community

Abstract. Ocean alkalinity enhancement (OAE) is a proposed method to counteract climate change by increasing the alkalinity of the surface ocean and thus the chemical storage capacity of seawater for atmospheric CO2. The impact of OAE on marine ecosystems, including phytoplankton communities which make up the base of the marine food web, is largely unknown. To investigate the influence of OAE on phytoplankton communities, we enclosed a natural plankton community from coastal Tasmania for 22 d in nine microcosms during a spring bloom. Microcosms were split into three groups, (1) the unperturbed control, (2) the unequilibrated treatment where alkalinity was increased (+495 ± 5.2 µmol kg−1) but seawater CO2 was not in equilibrium with atmospheric CO2, and (3) the equilibrated treatment where alkalinity was increased (+500 ± 3.2 µmol kg−1) and seawater CO2 was in equilibrium with atmospheric CO2. Both treatments have the capacity to increase the inorganic carbon sink of seawater by 21 %. We found that simulated OAE had significant but generally moderate effects on various groups in the phytoplankton community and on heterotrophic bacteria. More pronounced effects were observed for the diatom community where silicic acid drawdown and biogenic silica build-up were reduced at increased alkalinity. Observed changes in phytoplankton communities affected the temporal trends of key biogeochemical parameters such as the organic matter carbon-to-nitrogen ratio. Interestingly, the unequilibrated treatment did not have a noticeably larger impact on the phytoplankton (and heterotrophic bacteria) community than the equilibrated treatment, even though the changes in carbonate chemistry conditions were much more severe. This was particularly evident from the occurrence and peak of the phytoplankton spring bloom during the experiment, which was not noticeably different from the control. Altogether, the inadvertent effects of increased alkalinity on the coastal phytoplankton communities appear to be rather limited relative to the enormous climatic benefit of increasing the inorganic carbon sink of seawater by 21 %. We note, however, that more detailed and widespread investigations of plankton community responses to OAE are required to confirm or dismiss this first impression.

The role of nutrients, wind speed, and rainfall in determining the composition of the algal community of shallow lakes in the Taoge water system, upstream from Lake Taihu, China.

Gaining a deeper understanding of factors that influence changes in phytoplankton community has significant implications for shallow lake management. The present study examined changes in the algae community of three shallow eutrophic lakes of the Taoge water system between 2008 and 2018 and the related factors influencing these changes. The composition of the algal community varied significantly during this period with the relative diatom biomass in lakes Changdanghu and Gehu increasing between 2014 and 2016 and again decreasing after 2017. However, relative cyanobacteria biomass initially decreased and later increased; meanwhile, the proportion of biomass of other phyla decreased continuously in the study period. Lake Zhushanhu showed similar trends, although it eventually returned to its initial state with absolute Microcystis dominance. Furthermore, the analysis of driving factors revealed that the concentrations of total nitrogen (TN), nitrate (NO3), and orthophosphate (PO4) were significantly associated with a significant increase in Microcystis biomass. Meteorological conditions also influenced changes in total algal and diatom biomasses, which were inversely related to the daily mean and daily maximum wind speeds. Monthly cumulative precipitation was only significantly associated with diatom biomass. Meanwhile, rainfall primarily affected the algal community structure between 2013 and 2017; an increase in the relative biomass of diatoms coincided with increased precipitation. Coordinating nitrogen and phosphorous use within the Taoge water system should improve lake habitat management; a broader perspective in attempts to control global and regional climate change may be needed.

Seasonal changes in phytoplankton assemblages and environmental variables in highly turbid tropical estuaries of the Mekong River, Vietnam.

The distribution of phytoplankton assemblages in response to physicochemical variables was assessed using Spearman's correlation and canonical correspondence analysis in four highly turbid estuaries of the Mekong River (MKR) system in Ben Tre Province, Vietnam. During two surveys (September 2017 and April 2018) at 20 sampling sites, a total of 162 species were recorded, with a dominance of diatoms (> 50%). Phytoplankton abundance varied from 3.01 × 105 to 11.85 × 105 cells/L, with the highest cell densities found at the BL2 station in the rainy season, mainly attributed to cyanobacteria during the rainy period, whereas diatoms were dominant in the dry season. Chlorophyll-a concentration in this area was low and decreased from the mouth stations. Similarity analysis distinguished the freshwater and oligohaline regions (characterized by lower phytoplankton abundance in the oligohaline areas) from the mesohaline and polyhaline zones (characterized by higher phytoplankton density in the polyhaline sections), based on the salinity gradient, which mostly explained the spatio-temporal distribution of phytoplankton. In which, freshwater and oligohaline sites were dominated by the diatom Coscinodiscus, the euglenoids Lepocinclis, and the green alga Scenedesmus in the rainy season, while mesohaline and polyhaline stations were dominated only by diatom species (Thalassionema and Skeletonema) in the dry season. High salinity and total dissolved solutes, and low nutrients are the major factors affecting phytoplankton growth and lead to low density and low primary biomass in turbid estuarine systems like the MKR estuaries. Our results further emphasize the importance of taking into account of salinity in understanding seasonal changes of phytoplankton communities, which can provide a valuable baseline data for ecological management strategies in tropical estuarine ecosystems.

A catastrophic change in a european protected wetland: From harmful phytoplankton blooms to fish and bird kill

Understanding the processes that underlay an ecological disaster represents a major scientific challenge. Here, we investigated phytoplankton and zooplankton community changes before and during a fauna mass kill in a European protected wetland. Evidence on gradual development and collapse of harmful phytoplankton blooms, allowed us to delineate the biotic and abiotic interactions that led to this ecological disaster. Before the mass fauna kill, mixed blooms of known harmful cyanobacteria and the killer alga Prymnesium parvum altered biomass flow and minimized zooplankton resource use efficiency. These blooms collapsed under high nutrient concentrations and inhibitory ammonia levels, with low phytoplankton biomass leading to a dramatic drop in photosynthetic oxygenation and a shift to a heterotrophic ecosystem phase. Along with the phytoplankton collapse, extremely high numbers of red planktonic crustaceans-Daphnia magna, visible through satellite images, indicated low oxygen conditions as well as a decrease or absence of fish predation pressure. Our findings provide clear evidence that the mass episode of fish and birds kill resulted through severe changes in phytoplankton and zooplankton dynamics, and the alternation on key abiotic conditions. Our study highlights that plankton-related ecosystem functions mirror the accumulated heavy anthropogenic impacts on freshwaters and could reflect a failure in conservation and restoration measures.

Change of the Long-Term Nitrogen and Phosphorus in the Changjiang (Yangtze) River Estuary

The concentration and structure of nutrients play a key role in sustaining marine ecosystems. In recent decades, the change in nutrient input from land has led to significant changes in nutrient concentration and structure in the marginal sea and has had an important impact on the coastal ecosystem. Based on historical data from 1984 to 2016, the long-term variations in nutrients and their potential influencing factors, were analyzed in the Changjiang River Estuary. The concentration of dissolved inorganic nitrogen (DIN) increased gradually from 1984 to 2003, but after 2003 the concentration began to decrease. Compared with DIN, the change in dissolved inorganic phosphate (DIP) had a delayed effect and has exhibited a slow downward trend since 2005. The decreases in DIN and DIP are mainly due to the improvement of wastewater treatment efforts and chemical fertilizer use efficiency in recent years. The retention of nutrients by the Three Gorges Reservoir (TGR) has been another important factor since its completion in 2003, especially because the large amount of particulate phosphorus retained by the TGR has led to a significant decrease in the total phosphorus flux into the sea, which is the main reason for the decrease in DIP. The vatiations of DIP and DIN have been instrumental in causing the observed changes of phytoplankton community in the Changjiang River Estuary.

Determination of seasonal changes in phytoplankton community of the coastal waters of Burgaz Island (the Sea of Marmara)

AbstractThe aim of this study is to determine the phytoplankton species found on the shores of Burgaz Island and the basic ecological variables that affect their seasonal distribution between May 2013 and February 2014. Water samples were collected from four stations at six different depths and plankton samples were gathered horizontally and vertically. The analysis of phytoplankton community composition revealed 101 phytoplankton taxa belonging to five classes. As a result of the study, two taxa belonging to the Dinophyceae (Corythodinium frenguellii and Gonyaulax scrippsae) were new records for Turkish coastal waters. Additionally, a taxon belonging to Dinophyceae (Pronoctiluca pelagica) and a taxon belonging to Bacillariophyceae (Nitzschia reversa) were new records for the Sea of Marmara. Prorocentrum micans, was the dominant species throughout all sampling periods. During the study, the highest phytoplankton abundance was observed at 0.5 m depth in May 2013 (138,500 cells l−1) and February 2014 (52,620 cells l−1). Primary ecological variables, such as temperature (9.0–21.5 °C), salinity (15.23–37.22‰) and dissolved oxygen (4.89–15.84 mg l−1), were recorded on each sampling occasion. In addition, nitrite + nitrate–N (NO2 + NO3–N) (0.01–7.37 μg-at N l−1), phosphate (PO4–P) (0.05–51.95 μg-at P l−1) and silicate (SiO4–Si) (0.01–0.20 μg-at Si l−1) concentrations were measured. Chlorophyll a and suspended material values ranged between 0.01–3.17 μg l−1 and 10.0–61.5 mg l−1, respectively. Spearman's rank correlation was used to determine the relationship between phytoplankton species and ecological variables, and Bray–Curtis analysis and Euclidean distance were applied to bring out the similarity between stations.

Characteristics of Phytoplankton Community Structure and Indication to Water Quality in the Lake in Agricultural Areas

In recent years, lakes’ water quality and quantity have been affected and damaged by agricultural activities. The sensitivity of phytoplankton to the hydrological environment can effectively indicate the health of the aquatic ecosystem and the change in water quality. Understanding the changes of phytoplankton communities in lakes contaminated by agriculture may contribute to determining the directions of protection of these water bodies and provide reference cases for wider research. It is found that there are 146 species, 63 genera, and 8 phyla of phytoplankton, including 57 species of Bacillariophyta, 46 species of Chlorophyta, 17 species of Cyanobacteria and Euglenophyta. The total abundance was changed successively with Bacillariophyta (75% in June), Cyanobacteria (50% in July–August), and Chlorophyta (75% in September–October). The total biomass decreased continuously over time. The biomass of Chlorophyta is highest in October (67.4%), and diatoms contribute the most biomass in other months (76.5%). The Redundancy analysis indicated that the main environmental factors affecting phytoplankton’s dynamic change are total salt, water temperature, total phosphorus, and 5-day biochemical oxygen demand. The phytoplankton can be divided into 21 functional groups. The MP group has the highest frequency, mainly distributed in the frequently stirred and turbid shallow water. Representative functional groups indicate the high degree of eutrophication and nutrient-rich conditions and the good associated environment for phytoplankton and slow water flow rate. With the seasonal change of agricultural irrigation and drainage, the water quality of Xinmiao Lake began to deteriorate from medium pollution in July and reached serious pollution in October finally. Furthermore, this research discovered that the risk of cyanobacteria bloom is high in summer, primarily when thermal stratification occurs. This study provides necessary information for understanding and predicting the changes of the phytoplankton community caused by the increase of nutrients, human disturbance, and temperature conditions in eutrophic lakes in agricultural areas.

Seasonal changes in phytoplankton community related with environmental factors in the Busan coastal region in 2014

Seasonal changes in phytoplankton community related with environmental factors in the Busan coastal region in 2014

Adaptive carbon export response to warming in the Sargasso Sea

Ocean ecosystem models predict that warming and increased surface ocean stratification will trigger a series of ecosystem events, reducing the biological export of particulate carbon to the ocean interior. We present a nearly three-decade time series from the open ocean that documents a biological response to ocean warming and nutrient reductions wherein particulate carbon export is maintained, counter to expectations. Carbon export is maintained through a combination of phytoplankton community change to favor cyanobacteria with high cellular carbon-to-phosphorus ratios and enhanced shallow phosphorus recycling leading to increased nutrient use efficiency. These results suggest that surface ocean ecosystems may be more responsive and adapt more rapidly to changes in the hydrographic system than is currently envisioned in earth ecosystem models, with positive consequences for ocean carbon uptake.

Uncoupled changes in phytoplankton biomass and size structure in the western tropical Atlantic

Structural changes in phytoplankton communities have large influence on marine elemental cycling, food web dynamics and carbon export. Here we used data from two field expeditions, performed in spring and fall, over a coast-offshore gradient to investigate phytoplankton structure and dynamics in the Southwestern Tropical Atlantic (SWTA). Results revealed a predominant role of the thermohaline structure as the main driver of phytoplankton dynamics regardless the season. In fall, the thermocline and nutricline shallowing promoted a biomass increase, which was 3-fold higher around the oceanic islands. The structure of phytoplankton community mainly varied vertically, with Prochlorococcus pigments contributing greatly to the higher nutrient Deep Chlorophyll Maximum, whereas other Cyanophyceae predominated in nutrient poor surface layers during the two seasons. In addition, a clear coast-offshore variability in the new production ( Fp ) was observed, with the shelf region displaying higher values (up to 0.21), promoted by larger Bacillariophyceae pigments concentration, thus suggesting a coastal influence on shelf production. Although the phytoplankton biomass increased seasonally, our results highlighted a predominance of recycled production ( Fp ) and uncoupled dynamics between biomass and size of phytoplankton structure, with pico- and nanophytoplankton dominating the relative biomass, i.e., ca. 80% of the community in both seasons. We hypothesize that these patterns may result from a strong nitrogen limitation (N:P of around 3:1), which likely constrain a pronounced growth of the microphytoplankton. • Uncoupled dynamics between phytoplankton size structure and biomass were revealed. • A decreasing gradient of biomass and new production from shelf to offshore was pointed out. • Seasonal changes in thermocline shape the phytoplankton dynamics and size structure. • Phytoplankton diversity increased with depth, but was mainly dominated by small cells.

Response of Phytoplankton Community Structure to Vegetation Restoration after Removal of Purse Seine in Shengjin Lake

Aquatic vegetation has been restored since the removal of seine nets from the lake surface of Shengjin Lake in 2018. Through four seasons of phytoplankton sampling surveys from 2019–2020, we analyzed spatial and temporal changes in phytoplankton communities, water quality, and aquatic plant recovery in conjunction with previous research literature to reveal the response mechanisms of phytoplankton community structure to rapidly recovering aquatic vegetation. The results showed that the Secchi depth increased (0.4 m to 0.7 m), the concentration of total phosphorus decreased (0.053 mg/L to 0.41 mg/L), the species of aquatic plants (5 species to 16 species), phytoplankton species (210 species to 254 species) and cell density increased after the removal of the seine. Since the removal of the seine of Shengjin Lake, the aquatic vegetation cover has exceeded 80%, the phytoplankton biodiversity has increased, and the water quality has recovered to II-III water status. Our results show that aquatic plants improve water quality through direct and indirect effects and influence phytoplankton community structure together with the water environment, which can provide guidance for the restoration situation of the middle and lower reaches of the Yangtze River through-river lake ecosystems.

Effects of Early Sea-Ice Reduction on Zooplankton and Copepod Population Structure in the Northern Bering Sea During the Summers of 2017 and 2018

A remarkable early sea-ice reduction event was observed in the northern Bering Sea during 2018. In turn, this unusual hydrographic phenomenon affected several marine trophic levels, resulting in delayed phytoplankton blooms, phytoplankton community changes, and a northward shift of fish stocks. However, the response of the zooplankton community remains uncharacterized. Therefore, our study sought to investigate the zooplankton community shifts in the northern Bering Sea during the summers of 2017 and 2018 and evaluate the effects of early sea-ice melt events on the zooplankton community, population structure of large copepods, and copepod production. Five zooplankton communities were identified based on cluster analysis. Further, annual changes in the zooplankton community were identified in the Chirikov Basin. In 2017, the zooplankton community included abundant Pacific copepods transported by the Anadyr water. In 2018, however, the zooplankton community was dominated by small copepods and younger stages of large copepods (Calanus glacialis/marshallaeandMetridia pacifica), which was likely caused by reproduction delays resulting from the early sea-ice reduction event. These environmental abnormalities increased copepod production; however, this higher zooplankton productivity did not efficiently reach the higher trophic levels. Taken together, our findings demonstrated that zooplankton community structure and production are highly sensitive to the environmental changes associated with early sea-ice reduction (e.g., warm temperatures and food availability).

Environmental Impact on Harmful Species Pseudo-nitzschia spp. and Phaeocystis globosa Phenology and Niche

Global environmental change modifies the phytoplankton community, which leads to variations in their phenology and potentially causes a temporal mismatch between primary producers and consumers. In parallel, phytoplankton community change can favor the appearance of harmful species, which makes the understanding of the mechanisms involved in structuring phytoplankton ecological niches paramount for preventing future risk. In this study, we aimed to assess for the first time the relationship between environmental conditions, phenology and niche ecology of harmful species Phaeocystis globosa and the complex Pseudo-nitzschia along the French coast of the eastern English Channel. A new method of bloom detection within a time-series was developed, which allowed the characterization of 363 blooms by 22 phenological variables over 11 stations from 1998 to 2019. The pairwise quantification of asymmetric dependencies between the phenological variables revealed the implication of different mechanisms, common and distinct between the taxa studied. A PERMANOVA helped to reveal the importance of seasonal change in the environmental and community variables. The Outlying Mean and the Within Outlying Mean indexes allowed us to position the harmful taxa niche among the rest of community and quantify how their respective phenology impacted the dynamic of their subniches. We also discussed the possible hypothesis involved and the perspective of predictive models.

Short-term changes in algal blooms and phytoplankton community after the passage of Super Typhoon Lekima in a temperate and inner sea (Bohai Sea) in China

Extensive multi-species harmful algal blooms (HABs) were triggered by Super Typhoon Lekima in Laizhou Bay (Bohai Sea) in August 2019. After conducting two field cruises before and after the typhoon passage, we employed both high-performance liquid chromatography (HPLC)-pigment and microscopic methods to study the changes in the phytoplankton community and biomass. Following the passage of Lekima, the average surface salinity decreased, while dissolved inorganic nitrogen and dissolved silicate concentrations increased in the study area. The phytoplankton abundance and Chl a significantly increased after the typhoon event. Post-typhoon, the highest abundance values of Pseudo-nitzschia spp., Noctiluca scintillans, and Coscinodiscus spp. reached 106 cells/L and those of Bacillaria paxillifera, Ceratium spp., and Gymnodinium catenatum were in the order of 105 cells/L. HPLC-pigment CHEMTAX analysis showed that the biomass (Chl a) of dinoflagellates, diatoms, cryptophytes, chlorophytes, and haptophytes increased significantly after the typhoon. The increase in Chl a concentration was mainly attributable to large-sized phytoplankton, which are mostly diatoms and dinoflagellates. This study highlights that typhoons may cause HABs by introducing large amounts of freshwater and nutrients and change the phytoplankton community in a temperate and inner bay.

Phytoplankton community and driving environmental factors in Lake Dongping after 3 years implementation of the east route of South-to-North Water Diversion Project

为掌握东平湖浮游植物在南水北调东线工程运行后的群落结构变化特征及探究其环境驱动因子，于通水运行3周年后的2017年分4个季节对东平湖的18个样点进行采样调查，同步开展水环境调查.结果显示：共检出浮游植物191种属（包括变种），其中硅藻门、绿藻门、裸藻门、蓝藻门、金藻门、黄藻门、甲藻门和隐藻门分别为64、57、28、22、8、5、4和3种属；优势种属包括蓝藻门的漂浮泽丝藻（Limnothrix planctonica）和色球藻（Chroococcus sp.），绿藻门的小球藻（Chlorella vulgaris）以及硅藻门的小环藻（Cyclotella sp.）、舟形藻（Nauicula sp.）和针杆藻（Synedra sp.）等（优势度Y>0.02）；全年密度和生物量分别为6.74×10⁶ cells/L和5.71 mg/L，并呈现显著季节与空间差异.浮游植物密度季节变化为夏季 > 秋季 > 冬季 > 春季，生物量季节变化为夏季 > 冬季> > 秋季 > 春季；春、夏、秋、冬季物种数分别为71、78、53和125种，Shannon-Wiener多样性指数（H'）均值分别为1.90、1.84、1.76和2.52，Margalef丰富度指数（D）均值为3.07、3.98、2.79和4.75；冗余分析与Pearson相关性分析结果显示，水体综合营养状态指数、高锰酸盐指数、氨氮和水温是影响东平湖浮游植物群落结构的关键驱动因子.对比南水北调东线工程实施之前及通水初期的结果，东平湖浮游植物优势种群无明显变化，密度则较通水初期稍有升高.本研究分析了东平湖浮游植物群落的时空分布特征，发现调水工程可能通过物质带入影响水质，进而引起浮游植物量增加，湖区养殖的退出及增殖放流的实施降低了富营养化风险，但仍存在浮游植物生物量特别是蓝藻生物量升高的风险，建议在调水管理中加强水域生态监测及生境调控技术研究，保障调水水质安全.;In order to investigate the community characteristics of phytoplankton and the determining factors in Lake Dongping after implementation of the east route of South-to-North Water Diversion Project, seasonal samples of phytoplankton and aquatic environment from 18 sampling sites were collected in 2017. A total of 191 taxa of phytoplankton (genera or species) were identified with 64 taxa of Bacillariophyta, 57 taxa of Chlorophyta, 28 taxa of Euglenophyta, 22 taxa of Cyanophyta, 8 taxa of Chrysophyta, 5 taxa of Xanthophyta, 4 taxa of Pyrrophyta and 3 taxa of Cryptophyta. The dominant taxa were Limnothrix planctonica and Chroococcus sp. of Cyanophyta, Chlorella vulgaris of Chlorophyta and Cyclotella sp., Nauicula sp. and Synedra sp. of Bacillariophyta, etc (Y>0.02). The phytoplankton density and biomass were 6.74×10⁶ cells/L and 5.71 mg/L with the seasonal variation of density being summer > autumn > winter > spring and that of biomass being summer > winter > autumn > spring, respectively. About the phytoplankton diversity in four quarters, the number of species was 71, 78, 53 and 125, while the averages of the Shannon-Wiener index were 1.90, 1.84, 1.76 and 2.52 and Margalef diversity index were 3.07, 3.98, 2.79 and 4.75, respectively. Meanwhile, the results of redundancy analysis and Pearson analysis for the relationship between phytoplankton and aquatic environment showed that the factors such as comprehensive nutrition state index, permanganate index, ammonia nitrogen concentration, and water temperature played a key role in affecting the structure and dynamics of the phytoplankton community in Lake Dongping. Compared with before implementation of the east route of South-to-North Water Diversion Project and the initial stage of it, although the density of phytoplankton showed a rise, there was no obvious response in their dominant genera. This study preliminarily verified the spatiotemporal distribution characteristics of the phytoplankton community in Lake Dongping. Total phytoplankton density was found to have increased with the change of water quality caused by the east route of South-to-North Water Diversion Project. The withdrawal of aquaculture and implementation of fishery enhancement and releasing had reduced the risk of eutrophication, but the proliferation of phytoplankton probably increased the risk of algal-bloom in Lake Dongping. Given the changes of phytoplankton community and water quality after water diversion, it is necessary to strengthen the ecological monitoring and controlling in the management of water quality safety and stability.

Seasonality of phytoplankton community and dynamics of autotrophic carbon in a cold temperate port (Argentina)

The changes within and between seasons in phytoplankton composition and abundance determine the carbon biomass available for upper levels of the food web. Temporal changes in phytoplankton community and environmental parameters in a port in Puerto Madryn, Southwest Atlantic were analysed. During an annual period (2011–2012), samples of surface seawater were collected approximately monthly. We determined phytoplankton community structure (species composition and abundance) and biomass (determined by carbon content and chlorophyll a (Chl a)). Water temperature, salinity and transparency were measured when sampling the surface water and local meteorological data were considered. The main groups observed were diatoms (Bacillariophyta; the most abundant during the concentration peaks of Chl a), dinoflagellates (Dinophyta) and flagellates, which mainly included species of Cryptophyta and Chlorophyta. Diatoms exhibited blooms in March (summer–autumn) and September (spring), represented by Skeletonema costatum and Pseudo-nitzschia spp. respectively. Dinoflagellates contributed to the highest carbon biomass, with peaks in January (summer) and April (autumn), exemplified by Prorocentrum micans and Scrippsiella acuminata, respectively. Temporal differences in community composition were related to the seasonal changes in temperature, solar irradiance, precipitation, salinity and wind velocity. The environmental conditions seem not only to determine the species composition but also cell size distribution: nanoplanktonic (≤ 20 µm) species dominated mainly during late spring, summer and early winter while microplanktonic species (> 20 µm) during late winter and early spring. Our results showed within-season changes and show that not only Chl a, but also carbon content can be considered, as the former is a biased estimator of phytoplankton biomass. This study provides the first seasonally resolved estimation in the area of the carbon biomass available for upper levels of the food web and a necessary information for future scenarios prediction. HIGHLIGHTS• Two diatom blooms were followed by an increase in dinoflagellate abundance.• Annual environmental conditions drive the phytoplankton community structure.• First seasonally estimation of autotrophic biomass availability for Patagonian trophic web.

Sinking Rate and Community Structures of Autumn Phytoplankton Responses to Mesoscale Physical Processes in the Western South China Sea.

To examine the influence of mesoscale eddy on the natural phytoplankton community and its sinking rate changes, a comprehensive investigation cruise was carried out in the western South China Sea in autumn 2016. A total of 108 phytoplankton species were found, which belong to 54 phytoplankton genera; most of them were dominated by Dinophyta (54 genera), followed by Bacillariophyta (50 genera), Cyanophyta (3 genera), and Chrysophyta (1 genus). Bacillariophyta and Dinophyta were the main phytoplankton communities in the investigated sea area. The sinking rate of phytoplankton ranged from 0.12 to 3.17 m day–1, determined by the SETCOL method. The highest phytoplankton sinking rate was found in the 200-m water layer, followed by the DCM layer. No significant correlation was found between phytoplankton sinking rates and most of the environmental parameters during this cruise. At a similar time, we have carried out the estimation of carbon flux in the investigated sea area by using the sinking rate of phytoplankton, which showed that the carbon flux ranged from 2.41 × 10–6 to 0.006 mg C m–2 day–1; in addition, the maximum was at the 200-m layer. Phytoplankton community and sinking rate were significantly affected by the mesoscale eddy processes. The cold eddy could affect the community distribution of diatom and dinoflagellate, and the upwelling mainly affects the community of dinoflagellate. Both of them could contribute to a higher sedimentation rate of phytoplankton in the surface and DCM layers. Warm eddy could reduce the abundance of phytoplankton in the surface layer; simultaneously, the sinking rate of phytoplankton in the shallow water layer above 100 m is also reduced. These results can fill in the knowledge gap of mesoscale eddy processes in the study of phytoplankton community change and sinking rate; furthermore, it can provide insights into phytoplankton carbon and its implementation in further carbon sink.

Phytoplankton settling quality has a subtle but significant effect on sediment microeukaryotic and bacterial communities

In coastal aphotic sediments, organic matter (OM) input from phytoplankton is the primary food resource for benthic organisms. Current observations from temperate ecosystems like the Baltic Sea report a decline in spring bloom diatoms, while summer cyanobacteria blooms are becoming more frequent and intense. These climate-driven changes in phytoplankton communities may in turn have important consequences for benthic biodiversity and ecosystem functions, but such questions are not yet sufficiently explored experimentally. Here, in a 4-week experiment, we investigated the response of microeukaryotic and bacterial communities to different types of OM inputs comprising five ratios of two common phytoplankton species in the Baltic Sea, the diatom Skeletonema marinoi and filamentous cyanobacterium Nodularia spumigena. Metabarcoding analyses on 16S and 18S ribosomal RNA (rRNA) at the experiment termination revealed subtle but significant changes in diversity and community composition of microeukaryotes in response to settling OM quality. Sediment bacteria were less affected, although we observed a clear effect on denitrification gene expression (nirS and nosZ), which was positively correlated with increasing proportions of cyanobacteria. Altogether, these results suggest that future changes in OM input to the seafloor may have important effects on both the composition and function of microbenthic communities.