Phytoplankton Succession Research Articles

Application of Stable Carbon Isotopes in a Subtropical North Atlantic MesocosmStudy: A New Approach to Assess CO2 Effects on the Marine Carbon Cycle

Stable isotope ratio analysis offers a unique opportunity to obtain information on ecosystem processes. The increase in atmospheric CO2 as a consequence of fossil fuel combustion and land-use change is altering the stable carbon isotope composition (δ13C) of the atmosphere and ocean. This work investigates the application of using δ13C measurements of seawater samples to explore the biogeochemical responses of marine ecosystems to anthropogenic CO2 perturbations. The combination of isotopic and non-isotopic measurements from a subtropical North-Atlantic mesocosm experiment provided a holistic view of the biogeochemical mechanisms that affect carbon dynamics under a gradient of pCO2 ranging from ~350 up to ~1,000 μatm during a phytoplankton succession. A clear CO2 response was detected in the isotopic datasets with 13C shifts of up to ~5%0, but increased CO2 levels only had a subtle effect on the concentrations of the dissolved and particulate organic carbon pools. Distinctive δ13C signatures of the particulate organic carbon pools in the water column and sediment traps were detectable for the different CO2 treatments after a nutrient stimulated phytoplankton bloom. These signatures were strongly correlated (p 13C signatures of the inorganic carbon but not with the δ13C of the dissolved organic carbon pools (p > 0.05). Fractionation of carbon isotopes in phytoplankton was positively affected (9.6 2 levels either because of the higher CO2 availability or because of a shift in phytoplankton community composition. Nevertheless, phytoplankton bloom intensity and development was independent of CO2 concentrations, and higher CO2 levels had no significant effect on inorganic nutrient uptake. Results from this mesocosm experiment showed that variations in the carbon isotopic signature of the carbon pools depend on both physical (air-sea exchange) and biological (community composition) drivers opening the door to new approaches for investigations of carbon cycling in marine ecosystems.

Particle-Associated Microbial Community in a Subtropical Lake During Thermal Mixing and Phytoplankton Succession.

Ecosystem dynamics in monomictic lakes are characterized by seasonal thermal mixing and stratification. These physical processes bring about seasonal variations in nutrients and organic matter fluxes, affecting the biogeochemical processes that occur in the water column. Physical and chemical dynamics are generally reflected in seasonal structural changes in the phytoplankton and bacterio-plankton community. In this study, we analyzed, using 16S rRNA amplicon sequencing, the structure of the bacterial community associated with large particles (>20 μm) in Lake Kinneret (Sea of Galilee, Israel), and its associations to phytoplankton populations. The study was carried out during late winter and early spring, a highly dynamic period in terms of thermal mixing, nutrient availability, and shifts in phytoplankton composition. Structural changes in the bacterioplankton population corresponded with limnological variations in the lake. In terms of the entire heterotrophic community, the structural patterns of particle-associated bacteria were mainly correlated with abiotic factors such as pH, ammonia, water temperature and nitrate. However, analysis of microbial taxon-specific correlations with phytoplankton species revealed a strong potential link between specific bacterial populations and the presence of different phytoplankton species, such as the cyanobacterium Microcystis, as well as the dinoflagellates Peridinium and Peridiniopsis. We found that Brevundimonas, a common freshwater genus, and Bdellovibrio, a well-known Gram-negative bacteria predator, were positively associated to Microcystis, suggesting a potentially important role of these three taxa in the microbial ecology of the lake. Our results show that the dynamics of environmental abiotic conditions, rather than specific phytoplankton assemblages, are the main factors positively correlated with changes in the community structure as a whole. Nevertheless, some specific bacteria may interact and be linked with specific phytoplankton, which may potentially control the dynamic patterns of the microbial community.

An Enhanced System with Macrophytes and Polyurethane Sponge as an Eco-Technology for Restoring Eutrophic Water: A Pilot Test

Water eutrophication is one of the most serious environmental problems in urban lakes and ponds due to the excessive nutrients. To deal with this problem, the development of methods for supporting ecological rehabilitation has been undertaken. Meanwhile, the trophic interactions during rehabilitation also have been analyzed. In this study, a new technique was employed to solve the water eutrophication problems in an urban pond. To evaluate the water eutrophication at a pilot scale, an enhanced artificial floating-type biological treatment system (FBTS) composed of a floating bed, macrophyte, artificial biofilm carrier (polyurethane sponge) and aerator could be used as equipment for urban pond remediation. In addition, FBTS was employed to decrease the total nitrogen (TN), ammonia-nitrogen (NH3-N), total phosphorus (TP) and chemical oxygen demand (COD) in water. Meanwhile, the changes of water qualities were monitored in the remediation process, and differences in phytoplankton functional group diversity were also registered. Cyanobacteria would decrease after the removal of P, and the diatom assemblage composition changed. The dominant species Cyanophyta were transformed to co-existed with Bacillariophyta, Pyrrophyta and Chlorophyta due to the improvement of water quality. Consequently, this new FBTS could be a promising eco-technology for the removal of nitrogen and phosphorus from eutrophic water, and even could promote the phytoplankton succession.

Embedded reservoir and constructed wetland for drinking water source protection: Effects on nutrient removal and phytoplankton succession

An embedded reservoir that provides an efficient nutrient removal system protects drinking water. However, embedded reservoirs are rarely used in eutrophic shallow lakes because of their undetermined nutrient retention efficiency and unknown effects by the phytoplankton community. In this study, we aim to investigate the nutrient retention and algae succession in an embedded reservoir and adjacent wetland from April 2017 to September 2018 in the eastern part of Lake Taihu, China. More than 40% of total phosphorus (TP) and 45% of particulate phosphorous entering the reservoir were retained semi-annually, and the highest TP removal efficiency was achieved in the reservoir during autumn with an average value of 53.3% ± 9.9%. The overall nitrogen retention efficiency (21.7% ± 37.8%) was lower than that of TP (41.8% ± 27.8%). Similar trends were obtained in the wetland area. An important pathway for phosphorus removal is through particulate matter retention. Our study revealed that nutrient retention mechanisms in the reservoir were primarily via macrophyte absorption, particulate substance sedimentation, and prolonged water residence time. Consequently, the phytoplankton biomass (Chl-a) in the reservoir decreased (from 48.0 to 25.2 μg/L) and water transparency improved, due to the decreased P level and transformation of the phytoplankton group into simple structures with good ecological status. Therefore, the combination of embedded reservoir and constructed wetland ecosystem can be used successfully to protect surface water. The results will be advantageous to groups seeking to preserve drinking water sources.

Effects of Environmental Factors on Phytoplankton Succession and Community Structure in Lake Chuncheon, South Korea.

Effects of Environmental Factors on Phytoplankton Succession and Community Structure in Lake Chuncheon, South Korea.

Remote examination of the seasonal succession of phytoplankton assemblages from time-varying trends

The seasonal succession of phytoplankton assemblages is important to ascertain the dynamics of an aquatic ecosystem structure, whereas its occurrence in response to hydrodynamic alterations is not clearly understood. In view of the characteristics of annual water level variation formed by the Three Gorges Dam Project (TGDP), our understanding about how these changes affect phytoplankton structure and dynamics is still very limited due to the shortage of long-term observation data. In this study, we used Huan Jing 1 charge-coupled device images over the past decade to examine the phytoplankton succession dates between cyanobacterial and green algal blooms in the backwater area of the Three Gorges Reservoir (TGR). The results indicated continuous wavelet transform-based peak analysis is an efficiency tool that can illustrate the temporal pattern of phytoplankton succession using satellite-derived chlorophyll ɑ and Cyano-Chlorophyta index thresholds. Water level, air temperature, pH and total nitrogen/total phosphorus ratio were four important factors affecting the decline and rise phase of cyanobacterial blooms in the TGR from 2008 to 2018. Given that the upstream dam operation is likely to alter ecological and environmental conditions in the backwater area, this mechanism, so-called “water-level linkage”, could alleviate the persistent period of cyanobacterial and green algal blooms. Remote sensing together with time series analysis provided a useful method to examine the seasonal succession of phytoplankton assemblages in the TGR, and these findings provided strategic insight for the water-quality management in the post-TGDP period.

Discontinuity Analysis Reveals Alternative Community Regimes During Phytoplankton Succession

Phytoplankton develops recurring spring and summer blooms, a well-recognized model in plankton succession theory. We used a 5-year (2007-2011) plankton data set and utilized discontinuity analysis to assess the cross-scale biomass (carbon content) structure in the sampled plankton data, a surrogate of ecological resilience and regime shifts. We hypothesized that spring and summer blooms comprise alternative community regimes, manifested in distinct cross-scale structure between these blooms. We also hypothesized that cross-scale structure within blooms is stable, indicating resilient regimes of individual blooms. Both hypotheses were supported by our analyses. Results show that discontinuity analysis provides complementary information about phytoplankton community succession compared to traditional taxonomic studies. This highlights that traditional phytoplankton successional models and ecological resilience concepts are not mutually exclusive. Combined they offer a broader view of ecological dynamics that may help refine theoretical ecology which in turn can inform management.

Phytoplankton functional composition shows higher seasonal variability in a large shallow lake after a eutrophic past

AbstractEutrophication is a well‐known problem of global proportions with some easily recognizable and potentially harmful effects on aquatic habitats, but our knowledge on the underlying associated changes in ecosystem functioning is rather limited. Relevant studies suggest that seasonal variability in the functional composition of phytoplankton shows an increase as eutrophication progresses. The aim of the present study was to test this hypothesis through the assessment of long‐term changes in the functional diversity and composition of phytoplankton in a large shallow lake situated in Central Europe with a history of dramatic changes in trophic state. Contrary to our expectations, results have shown that the maximum range of compositional variability had a significant negative correlation with the summer biomass maxima. On the other hand, average seasonal variability measured as annual beta diversity exhibited an increasing trend throughout the years from the period of early eutrophication to the recent period of reoligotrophication, seemingly following a decline in functional richness and a long‐term rise in annual mean water temperature. The enhanced variability in phytoplankton succession implies that all the ecosystem processes connected to the phytoplankton follow more complex seasonal dynamics. Besides changing community structure, trophic state also seems to be an important factor in setting the limits to compositional changes during the annual cycle, whereas long‐term warming is likely to enhance instability in the phytoplankton. The trajectories of these two factors and the changes in seasonal succession indicate a lake in transition, urging more in‐depth research efforts to understand the impact of climate change on this specific ecosystem, and raise the question of whether the observed changes can also occur in other similar aquatic systems.

Chytrid infecting the bloom-forming marine diatom Skeletonema sp.: Morphology, phylogeny and distribution of a novel species within the Rhizophydiales

Chytrids have long been recognised as important parasites of microalgae in freshwater systems, able to shape the dynamics of blooms, the gene pool of their host and phytoplankton succession. In the sea however, where the presence of these organisms is erratic and ephemeral, studies concerning chytrids are sparse and confined to metabarcoding surveys or microscopy observations. Despite the scarcity of data, chytrid epidemics are supposed to play an important role in marine biogeochemical cycles, being one of the drivers of phytoplankton dynamics. Here we combine microscopy observations and in silico mining of a single-cell whole genome to molecularly and morphologically characterise a novel chytrid parasite of the dominant diatom genus Skeletonema. Morphological observations highlight features of the thallus and ascertain the parasitic nature of the interaction whilst the genetic markers obtained allows for a phylogenetic reconstruction, placing the new species in the order Rhizophydiales. Thanks to the molecular data obtained we are also able to provide a first investigation of the global distribution of this organism by screening the Ocean Sampling Day (OSD) dataset, highlighting a northern transatlantic dissemination.

Temporal succession, spatial dynamics and diversity of phytoplankton in the meromictic Laguna de la Cruz: the role of stratification patterns

espanolLa Laguna de La Cruz es un pequeno lago cartisco meromictico situado en Cuenca (Centro de Espana), cuyos patrones de estratificacion y mezcla termica determinan en gran medida la estructura y composicion de sus poblaciones de fitoplancton. En este lago la sucesion en la zona oxica de la columna de agua se inicia con la mezcla otonal, tomando protagonismo las diatomeas, con algunas especies como Cyclotella delicatula, del tipo funcional (codon) B, dominando la comunidad en toda la columna oxica de agua durante el invierno. Esta especie persiste en primavera, pero ligada entonces a capas mas profundas. En primavera, al principio de la estratificacion termica, se produce el desarrollo en las capas superiores de picocianobacterias, criptoficeas, y dinoflagelados, correspondientes a los grupos funcionales Z, Y, y Lo, quedando las dos primeras progresivamente recluidas en la oxiclina a medida que la estratificacion avanza. Con el avance del periodo de estratificacion se desarrollan densas poblaciones de cloroficeas de los grupos funcionales F, X, y J en el epilimnion y el metalimnion, mientras que hacia final del verano se seleccionan especies de Cosmarium, pertenecientes al grupo funcional NA, que pasan a ser dominantes hasta que la mezcla otonal vuelve a dar paso a las diatomeas. En su conjunto, la fuerte estratificacion de la columna de agua permite crear diferentes nichos con una distribucion vertical diferencial del fitoplancton durante los periodos de estratificacion, lo que favorece su diversidad en el conjunto de la columna de agua. Sin embargo, diversos tipos de perturbaciones, tales como episodios de fuertes lluvias, movimientos horizontales de masas de agua y, en especial, el fenomeno de blanqueamiento que ocurre todos los anos hacia mitad del verano, alteran en cierta medida el patron sucesional. EnglishLaguna de La Cruz is a small meromictic karstic lake located in Cuenca (Central Spain), whose stratification and thermal mixing patterns largely determine the structure and composition of its phytoplankton populations. In this lake, the succession in the oxic zone of the water column starts, with the autumnal mixing, with some diatom species, such as Cyclotella delicatula, of the functional codon B, dominating the community throughout the oxic water column during the winter. This species persists in spring, but then linked to deeper layers. In spring, at the beginning of the thermal stratification, picocyanobacteria, cryptophytes, and dinoflagellates develop in upper layers, corresponding, respectively, to the functional coda Z, Y, and Lo, with the first two being progressively restricted to the oxycline as the stratification advances. As stratification advances, dense populations of chlorophytes belonging to the functional groups F, X, and J develop in the epilimnion and the metalimnion, while towards the end of the summer Cosmarium species, belonging to the functional group NA, are selected and become dominant until the autumnal mixing favors again the diatoms. As a whole, the strong stratification of the water column allows for the appearance of different niches with a differential vertical distribution of the phytoplankton during the stratification periods, which favors its diversity within the whole water column. However, several types of disturbances, such as episodes of heavy rainfall, horizontal movements of water bodies and, in particular, the whitening that occurs every year towards the middle of summer, alter the successional pattern to some extent.

Quantifying the role of organic phosphorus mineralisation on phytoplankton communities in a warm-monomictic lake

ABSTRACTPhosphorus (P) is a key driver of phytoplankton growth in lentic systems. During summer-stratified periods when dissolved inorganic P (DIP) is low, the phytoplankton assemblage often has elevated P uptake rates. Under these conditions, dissolved organic P (DOP) can become an important source of P for phytoplankton and a driver of phytoplankton succession. We examined how DOP mineralisation by alkaline phosphatase (AP) activity (APA), relative to phytoplankton P release (i.e., from exudation and lysis), meets phytoplankton P uptake and how it is associated with phytoplankton community composition changes under thermally stratified DIP-depauperate conditions in a large warm-monomictic lake. We found that when phytoplankton internal P stores were low (<0.65 µg P µg−1 Chl-a), APA increased, resulting in potential DOP mineralisation rates of 88 µg L−1 h−1 P, which is at the upper end of rates in the literature. APA represented up to 89% of the total phytoplankton P uptake and was much higher than the rate of phytoplankton P release. We found that elevated APA coincided with peak phytoplankton biovolume and dominance of the phytoplankton assemblage by cyanobacteria. Further, APA was strongly positively associated with the majority of the 10 most dominant cyanobacteria, including the key toxin-producer Raphidiopsis raciborskii (previously Cylindrospermopsis raciborskii). Our results indicate that under DIP-depauperate conditions, DOP mineralised by APA may be a major source of P for phytoplankton, and the ability to produce AP may be a key factor in the occurrence of bloom-forming cyanobacteria.

Фитопланктон в различных экотопах озера Отстойник (Самарская область)

This article presents the results of the study of the species composition and main indicators of the quantitative development of phytoplankton in various ecotopes (pelagic zone, phytal zone) of Lake Otstoynik. It is a small pond belonging to the system of Vasilievsky lakes of Togliatti, Samara Oblast. Initially it served as a receiver of nitrogen fertilizer production waste. In the 90s of XX century, the technological use of this lake was terminated but the rehabilitation works to restore the ecosystem of the reservoir was not carried out. Modern condition of the ecosystem is entirely the result of self-purification and self-healing. Therefore, the materials presented in this article may be of interest to experts on environment, especially those who work in the field of cost-benefit analysis in predicting the development of a "zero" scenario, i.e. without interference through recreational activities in the recovery processes of disturbed aquatic ecosystems. The study deals with the species composition of the plankton algoflora in various ecotopes of the reservoir (open pelagic zone and phytal zone formed by reed), its floral and еcological/geographical analysis. In addition, it considers seasonal succession of phytoplankton in different ecotopes in the period from 2014 to 2016, analyzes quantitative indicators of development (abundance, biomass) of phytoplankton, the role of the major divisions of algae in their formation. We estimated the level of species diversity in different ecotopes of the reservoir with the use of the Shannon-Weaver index. In terms of quantitative development of phytoplankton, the level of water trophies was estimated. Based on the data of sapro/biological analysis, the pollution level has been established and the class of water quality in the investigated water body has been determined.

Structural Characteristics and Associated Factors Influencing Phytoplankton Abundance and Species Composition in Huangmaohai Bay, Pearl River Estuary

Jia, H.; Chen, M.; Su, W.; Zhang, S., and Zhao, K., 2019. Structural characteristics and associated factors influencing phytoplankton abundance and species composition in Huangmaohai Bay, Pearl River Estuary. Journal of Coastal Research, 35(1), 72–81. Coconut Creek (Florida), ISSN 0749-0208.Temporal–spatial variations of phytoplankton abundance and species composition, as well as associated environmental factors, were investigated to understand phytoplankton succession at Huangmaohai Bay in December 2010 and August 2011. Concentrations of both chlorophyll-a and nutrient showed apparent spatial variability with significantly higher levels in the upstream area of the estuary than in the offshore area. Temporal variation of the chlorophyll-a concentration showed that the concentration in the summer was 1.25 times higher than that in the winter. Significantly higher abundances of cyanobacteria and chlorophytes were found at the upstream sites where the system was influenced by freshwater input. In contrast, diatoms and dinoflagellates primarily dominated at the downstream sites. Phytoplankton abundance was higher in the summer (629.66 × 104 cells/m3) than in the winter (466.75 × 104 cells/m3). A canonical correspondence analysis of phytoplankton community and environmental factors indicated that dissolved inorganic phosphorus, nitrogen, and salinity were the key environmental factors influencing the spatial variation of phytoplankton. Dinoflagellates, cyanobacteria, and chlorophytes were generally sensitive to salinity, whereas diatoms were generally sensitive to nutrients. Because Huangmaohai Bay is part of the Pearl River Estuary, this study not only fills a gap toward understanding this region but also aids marine protection department personnel in making effective management plans that can be put into action.

A 14‐ka Record of Dust Input and Phytoplankton Regime Changes in the Subtropical NE Pacific: Oceanic and Terrestrial Processes Linked by Teleconnections at Suborbital Scales

AbstractWe study shifts in phytoplankton proxies linked to terrigenous inputs and teleconnections in a core from Soledad Basin, Gulf of Ulloa, NW Mexico, spanning the end of the deglaciation and the Holocene. We used biogenic opal (% opal), organic carbon (% total organic carbon [TOC]), and inorganic carbon (% CaCO3) as proxies of productivity and opal/TOC and CaCO3/TOC ratios as proxies of nutrient uptake and C‐export by siliceous and carbonate organisms. We reconstructed terrestrial inputs and identified authigenic gypsum. Based on opal/TOC and CaCO3/TOC ratios, we found periodic changes of ~0.5, 1.1–1.8 ka cycle in phytoplankton proxies exporting siliceous and carbonate skeletal debris to the sediments. An increase in carbonate organisms occurred during 14–8.7 ka, corresponding to reduced El Niño–Southern Oscillation (ENSO)‐like variability, in parallel to the northward displacement of the Intertropical Convergence Zone (ITCZ) and an overall negative phase of the Pacific Decadal Oscillation (PDO). An increase in siliceous organisms occurred between 6 and 3 ka, coincident with strong ENSO‐like conditions, southern migration of ITCZ, and less intense but more frequent positive PDO‐hydrological variability. Grain size analyses show significant amounts of fine fraction (dust &lt;6.6 μm) present during the early‐ to mid‐Holocene in agreement to extreme weather on land, with episodes of eolian and fluvial transport to the sea. The ENSO‐like variations influenced biological C‐export producers on a scale of 1.1–1.8 ka, but PDO‐related variability is uncertain. We suggest that Holocene drivers for phytoplankton successions are changes in insolation, ITCZ migration, California Current upwelling, nutrient inputs by advection, and terrestrial sources.

Drivers of phytoplankton blooms in the northeastern Black Sea

In order to understand of the processes controlling phytoplankton successions in the NE Black Sea, long-term data series are needed. We compiled 15 years (2002–2017) of measurements from which the existence emerges of a tight link between phytoplankton species dominance and nutrients concentrations. The latter is strongly influenced by wind direction. The link between algal dominance and nutrients is mediated by the growth strategy adopted by algal species. In spring, when nutrients are abundant, small diatoms such as Pseudo-nitzschia pseudodelicatissima, with a “rapid growth strategy”, prevail. In late spring and early summer, when N is low and P and Si are high, coccolithophorids such as Emiliania huxhleyi dominate, thanks to an “affinity growth strategy”. Large diatoms, especially Pseudosolenia calcar-avis, dominate in summer and autumn, when their “storage growth strategy” allows the exploitation of discontinuous upwelling of nutrients. These seasonal changes of dominant species influence the structure of the food web.

High photosynthetic rates associated with pico and nanophytoplankton communities and high stratification index in the North West Atlantic

The biological dynamics of pelagic marine ecosystems are strongly influenced by the size structure and ecological succession of phytoplankton, which in turn modifies photosynthetic efficiency. Variability in photosynthetic rates is closely coupled with changes in community structure, but it is difficult to obtain coincident data at high enough resolution to characterise these changes. In this study, we employ hierarchical cluster analysis on chlorophyll-normalised high performance liquid chromatography (HPLC) pigment concentrations from the North West Atlantic, to identify seasonal successional trends amongst phytoplankton populations. Changes in phytoplankton community were also analysed as a function of mean equivalent spherical diameter (MESD) derived from absorption measurements, photosynthetic rates, water-column stratification and temperature. Well-mixed conditions in spring to early summer were associated with populations of large cells containing high concentrations of fucoxanthin, chlorophyll-c1 and chlorophyll-c2 relative to chlorophyll-a (Chl a). As stratification increased over the course of the summer, these cells were replaced by populations dominated by chlorophyll-b, 19'-hexanoyloxyfucoxanthin, 19'-butanoyloxyfucoxanthin and divinyl chlorophyll-a, indicative of small picophytoplankton. As stratification decreased in autumn, MESD and alloxanthin increased, suggesting the presence of cryptophytes. Positive relationships were found between MESD and the quantum yield of photosynthesis (φm) for 7 out of the 8 phytoplankton clusters identified, while negative relationships between mean mixed layer photosynthetically active radiation and φm and the light limited slope of photosynthesis (αB) were observed for 4 clusters, as a result of nutrient limitation and photo-protection. The highest photosynthetic rates were associated with a pico & nanophytoplankton communities, which increased from spring to late summer as stratification intensified. By contrast, diatom communities had the lowest photosynthetic rates throughout the year. These successional patterns in the dominant phytoplankton size-class and phenology support Margalef's mandala in terms of the relationship between turbulence and community structure. The study sheds new light on assemblages dominated by smaller cells, under warm, stratified conditions, having higher photosynthetic efficiencies, which has implications for the carbon flux in the NW Atlantic.

Sensitivity of Bacterioplankton to Environmental Disturbance: A Review of Baltic Sea Field Studies and Experiments

Bacterioplankton communities regulate energy and matter fluxes fundamental to all aquatic life. The Baltic Sea offers an outstanding ecosystem for interpreting causes and consequences of bacterioplankton community composition shifts resulting from environmental disturbance. Yet, a systematic synthesis of the composition of Baltic Sea bacterioplankton and their responses to natural or human-induced environmental perturbations is lacking. We review current research on Baltic Sea bacterioplankton dynamics in situ (48 articles) and in laboratory experiments (38 articles) carried out at a variety of spatiotemporal scales. In situ studies indicate that the salinity gradient sets the boundaries for bacterioplankton composition, whereas regional environmental conditions at a within-basin scale, including the level of hypoxia and phytoplankton succession stages, may significantly tune the composition of bacterial communities. Also the experiments show that Baltic Sea bacteria are highly responsive to environmental conditions, with general influences of e.g. salinity, temperature and nutrients. Importantly, nine out of ten experiments that measured both bacterial community composition and some metabolic activities showed empirical support for the sensitivity scenario of bacteria – i.e. that environmental disturbance caused concomitant changes in both community composition and community functioning. The lack of studies empirically testing the resilience scenario, i.e. experimental studies that incorporate the long-term temporal dimension, precludes conclusions about the potential prevalence of resilience of Baltic Sea bacterioplankton. We also outline outstanding questions emphasizing promising applications in incorporating bacterioplankton community dynamics into biogeochemical and food-web models and the lack of knowledge for deep-sea assemblages, particularly bacterioplankton structure-function relationships. This review emphasizes that bacterioplankton communities rapidly respond to natural and predicted human-induced environmental disturbance by altering their composition and metabolic activity. Unless bacterioplankton are resilient, such changes could have severe consequences for the regulation of microbial ecosystem services.

Regional climate and patterns of phytoplankton annual succession in the open waters of the Black Sea

The annual succession of phytoplankton of the open waters of the Black Sea was investigated on the basis of a database covering the 30-year period from 1985 to 2014. Seasonal variations of the taxonomic composition were analysed with regard to weather conditions and the physical and chemical properties of the environment. Two different patterns of annual phytoplankton succession were revealed for the post-winter period from March to November. After cold winters a classical annual succession of diatoms → dinoflagellates → coccolithophores → dinoflagellates → diatoms was observed, whereas after regular winters another type of succession; dinoflagellates → dinoflagellates → coccolithophores → diatoms → diatoms, took place. These two successions corresponded to seasonal dynamics of nitrate concentration and its share in the total inorganic nitrogen. During cold years these parameters decreased from spring to summer with a subsequent increase in autumn, whereas in regular years they were unusually high in summer. The enigma of this summer nitrate enrichment is well explained by the hypothesis of increasing cross-shelf nutrient transport. During regular years, weak hydrodynamic forcing occurs throughout the year, resulting in a large number of mesoscale eddies along the shelf in summer–autumn that in turn cause the intense transport of coastal waters rich in nitrate to the Sea interior. Development of the large-celled diatom Pseudosolenia calcar-avis in the sea basin observed in summer is in line with this hypothesis. This mechanism was also confirmed by positive relationships between the high sea-surface temperature, and the low Ekman pumping velocity and mean kinetic energy of currents in winter on the one hand, and the contribution of diatoms to the total phytoplankton biomass in summer–autumn, on the other. A case study of mesoscale eddies in the open waters in summer–autumn demonstrated a shift in species composition to large-celled diatoms inside these structures. Climate warming observed during the last 25 years resulted in a decrease in the frequency of cold winters from 30% to 15%, which has led to a decline in the annual phytoplankton standing stock. Thus, in the Black Sea, climate warming affects phytoplankton not directly by an increase in temperature, but by a decrease in the frequency of cold winters.

Phytoplankton response to climate changes and anthropogenic activities recorded by sedimentary pigments in a shallow eutrophied lake

Studies that address the potential effects of climate and anthropogenic activities on lacustrine phytoplankton succession are scarce in the shallow lakes. In the present work, the succession of phytoplankton community inferred from sedimentary pigments has been investigated; the impacts of climate and anthropogenic activities on the succession have been evaluated by the generalized additive models (GAMs) in a shallow eutrophied lake, Lake Chaohu, located eastern China. The results show that phytoplankton succession can be divided into two periods: pre-1960s and post 1960s. The mean values of ββ‑Car and Chl a increased after the 1960s at both sites sampled, from 0.013 to 0.359, and 0.013 to 1.382 μg g−1, respectively (site C4), and from 0.015 to 0.530, and 0.010 to 0.921 μg g−1, respectively (site C14), reflecting significant increases of primary productivity since the 1960s. The percentage of diatoms and dinoflagellates preserved in sediments decreased from ~90% to ~15% since the 1960s, while cyanobacteria and green algae increased from ~5% to ~35%, respectively, reflecting the shift of the lake phytoplankton community. This succession was related to construction of the Chaohu Dam in 1963, increasing discharges of anthropogenic N and P into the Lake, and a generally warming environment as reflected by increasing average air temperatures. The results of GAMs showed aquatic total phosphorus (TP) concentration is the dominant contributor to phytoplankton community change, explaining 42.74%, 40.27%, 40.77% and 72.28% of the variance of total algae, cyanobacteria, green algae, and diatoms and dinoflagellates, respectively. The positive impacts of increasing TP concentrations on abundances of total algae, cyanobacteria, and green algae were observed during periods of relatively high TP concentrations since the mid-1970s. The positive responses of total algae, cyanobacteria, green algae and diatoms and dinoflagellates to increasing average air temperatures were observed since the mid-1990s, showing that a generally warmer environment facilitated algae proliferation.

Photophysiology of nitrate limited phytoplankton communities in Kongsfjorden, Spitsbergen

AbstractIn Arctic coastal regions, the phytoplankton bloom is often initiated by meltwater induced stratification in spring, while subsequent nutrient depletion is believed to drive phytoplankton succession in summer. The associated changes in photophysiology are difficult to identify, because these can be governed by acclimation to light and nutrient availability as well as variations in phytoplankton biomass and taxonomic composition. In the present study, the consequences of nutrient limitation for photophysiology and growth were assessed in natural phytoplankton communities from Kongsfjorden, Spitsbergen. A series of nutrient addition experiments demonstrated N‐limitation from mid‐June onwards and possible co‐limitation with P later in summer. The onset of N‐limitation was associated with a pronounced change in taxonomic composition from a dictyochophytes to a haptophytes dominated community. Fast Repetition Rate fluorometry measurements of photosystem II (PSII) photophysiology showed that the dictyochophytes dominated community was characterized by high PSII efficiency and electron transport rates which were efficiently used for growth. Marked changes in PSII photophysiology were observed later in summer, with decreasing efficiencies, lower connectivity between reaction centers, and slower turnover rates. Simultaneously, alternative electron requirements downstream of PSII became more important and energy was likely allocated to the uptake of nutrients rather than carbon fixation and growth. Relief of nutrient limitation during the nutrient addition experiments did not lead to pronounced changes in PSII photophysiology. It is, therefore, concluded that PSII photophysiology of the phytoplankton community in Kongsfjorden is associated with changes in species composition rather than a direct effect of nutrient availability or nutrient limitation.