Development Of Phytoplankton Blooms Research Articles

Coastal upwelling systems as dynamic mosaics of bacterioplankton functional specialization

Coastal upwelling areas are extraordinarily productive environments where prokaryotic communities, the principal remineralizers of dissolved organic matter (DOM), rapidly respond to phytoplankton bloom and decay dynamics. Nevertheless, the extent of variability of key microbial functions in such dynamic waters remains largely unconstrained. Our metatranscriptomics analyses of 162 marker genes encoding ecologically relevant prokaryotic functions showed distinct spatial-temporal patterns in the NW Iberian Peninsula upwelling area. Short-term (daily) changes in specific bacterial functions associated with changes in biotic and abiotic factors were superimposed on seasonal variability. Taxonomic and functional specialization of prokaryotic communities, based mostly on different resource acquisition strategies, was observed. Our results uncovered the potential influence of prokaryotic functioning on phytoplankton bloom composition and development (e.g., Cellvibrionales and Flavobacteriales increased relative gene expression related to vitamin B12 and siderophore metabolisms during Chaetoceros and Dinophyceae summer blooms). Notably, bacterial adjustments to C- or N-limitation and DMSP availability during summer phytoplankton blooms and different spatial-temporal patterns of variability in the expression of genes with different phosphate affinity indicated a complex role of resource availability in structuring bacterial communities in this upwelling system. Also, a crucial role of Cellvibrionales in the degradation of DOM (carbohydrate metabolism, TCA cycle, proteorhodopsin, ammonium, and phosphate uptake genes) during the summer phytoplankton bloom was found. Overall, this dataset revealed an intertwined mosaic of microbial interactions and nutrient utilization patterns along a spatial-temporal gradient that needs to be considered if we aim to understand the biogeochemical processes in some of the most productive ecosystems in the world´s oceans.

Majority of Southern Ocean Seasonal Sea Ice Zone Bloom Net Community Production Precedes Total Ice Retreat

AbstractThe Southern Ocean seasonal sea ice zone (SIZ) spring is characterized by sea ice retreat and the development of phytoplankton blooms. Until recently, assessing SIZ blooms and associated net community production (bNCP) has been limited by a lack of under‐ice observations. We relate the timing of phytoplankton growth to the drawdown of surface nitrate and sea ice cover and estimate bNCP from biogeochemical profiling float observations. The onset of biological production closely follows initial sea ice breakup and, on average, 64% of bNCP occurs before total sea ice retreat. This indicates that satellite‐derived estimates largely miss under‐ice production and underestimate SIZ bNCP. Float bNCP estimates range from <1 to >4 mol C m−2 bloom−1, with higher bNCP when sea ice breakup occurs early in the year, and the highest bNCP near topographic features that may increase micronutrient supply. Our results suggest changes in Southern Ocean sea ice will influence future bNCP.

Multi-year variability of summer phytoplankton biomass and size structure in the northern Chukchi and East Siberian Seas, Arctic Ocean: role of light and nutrient availability

In the Arctic Ocean, the northern Chukchi and East Siberian Seas (NCESS) are vulnerable to climate change due to warming, sea ice melting, and surface freshening. To investigate how local physical forcing affects phytoplankton biomass and communities in this area, the multi-year (2015-2020) distributions of summer (August) chlorophyll-a concentrations and size structures using data collected by the Korea-Arctic Ocean Observing System (K-AOOS) program were investigated. The environmental characteristics and phytoplankton communities in the study area showed east-west regional differences. It is characterized by warm fresh waters and strong stratification to the east and cold saline waters and relatively high nutrient and sea ice concentrations to the west. Despite the differences between the east and west regions, patterns of the inter-annual variation in phytoplankton biomass and communities were similar across the entire study area, implying environmental controllers regulating phytoplankton in the NCESS. Inter-annually, higher sea surface salinity and weaker water column stratification were observed in 2017-2019 than in 2015 and 2020, implying the possibility of a potential modulation by the Arctic Oscillation. The shallower nitracline depth and higher surface nutrient concentrations since 2017 compared to the period from 2015-2016, indicate improved nutrient availability due to Atlantic water intrusion. However, average insolation has been relatively low since 2017, with the exception of August 2018. August mean phytoplankton biomass was highest in 2018 in the study area (average 83.7 mgm-2) and was dominated by large-sized phytoplankton. The low phytoplankton biomass in 2017 (23.9 mgm-2) and 2019 (62.4 mgm-2), despite similar characteristics of nutrient concentration to 2018, is likely due to lower average daily insolation in both years (206 μEm-2d-1 and 184 μEm-2d-1 in 2017 and 2019, respectively) compared to the 2018 average (271 μEm-2d-1). These results suggest that increased intrusion through upwelling of Atlantic water, along with nutrient loading, could be a pivotal driving factor contributing to this enhanced production in the NCESS, particularly under conditions where light levels are sufficient for phytoplankton growth and bloom development.

First description of in situ chlorophyll fluorescence signal within East Antarctic coastal polynyas during fall and winter

Antarctic coastal polynyas are persistent and recurrent regions of open water located between the coast and the drifting pack-ice. In spring, they are the first polar areas to be exposed to light, leading to the development of phytoplankton blooms, making polynyas potential ecological hotspots in sea-ice regions. Knowledge on polynya oceanography and ecology during winter is limited due to their inaccessibility. This study describes i) the first in situ chlorophyll fluorescence signal (a proxy for chlorophyll-a concentration and thus presence of phytoplankton) in polynyas between the end of summer and winter, ii) assesses whether the signal persists through time and iii) identifies its main oceanographic drivers. The dataset comprises 698 profiles of fluorescence, temperature and salinity recorded by southern elephant seals in 2011, 2019-2021 in the Cape-Darnley (CDP;67˚S-69˚E) and Shackleton (SP;66˚S-95˚E) polynyas between February and September. A significant fluorescence signal was observed until April in both polynyas. An additional signal occurring at 130m depth in August within CDP may result from in situ growth of phytoplankton due to potential adaptation to low irradiance or remnant chlorophyll-a that was advected into the polynya. The decrease and deepening of the fluorescence signal from February to August was accompanied by the deepening of the mixed layer depth and a cooling and salinification of the water column in both polynyas. Using Principal Component Analysis as an exploratory tool, we highlighted previously unsuspected drivers of the fluorescence signal within polynyas. CDP shows clear differences in biological and environmental conditions depending on topographic features with higher fluorescence in warmer and saltier waters on the shelf compared with the continental slope. In SP, near the ice-shelf, a significant fluorescence signal in April below the mixed layer (around 130m depth), was associated with fresher and warmer waters. We hypothesize that this signal could result from potential ice-shelf melting from warm water intrusions onto the shelf leading to iron supply necessary to fuel phytoplankton growth. This study supports that Antarctic coastal polynyas may have a key role for polar ecosystems as biologically active areas throughout the season within the sea-ice region despite inter and intra-polynya differences in environmental conditions.

Temporal variability of particle flux and its components in the Gotland Basin, eastern Baltic Sea

Sinking particles were studied by analyzing samples collected in a sediment trap at 180 m depth in the Gotland Basin, eastern Baltic Sea between 1999 and 2020. The aim of this study was to determine the temporal variability of the particle flux and its components and how their changes are linked to phytoplankton blooms. The variables studied included total particle flux, particulate organic carbon and nitrogen, biogenic silica, C:N ratio and the isotopic composition of organic carbon and nitrogen. The total particle flux and its components reached maximum values in 2003, 2012 and 2015. Long-term means over the 22-year period of the total particle flux and its components particulate organic carbon and nitrogen, biogenic silica were estimated at around 152, 22, 3 and 8 mg m−2 d−1, respectively. The C:N ratio and the isotopic composition of organic carbon and nitrogen showed high variability around their long-term means of 9, -25‰ and 4‰, respectively. The annual variability of the components of the flux particulate organic carbon (3–65 mg m−2 d−1), particulate organic nitrogen (0.4–9 mg m−2 d−1) and biogenic silica (1–24 mg m−2 d−1) exhibited the same general pattern as the total particle flux (11–450 mg m−2 d−1) over the study period. On the seasonal scale, sinking material in summer contributed roughly one-third (31%) to the total particle flux, followed by winter (27%), spring (24%) and autumn (19%). The highest particle flux occurred mostly in April, July and November, during and after the appearance of phytoplankton blooms in the Gotland Basin. The phytoplankton community changed from silicon-rich species to nitrogen-fixing cyanobacteria, indicating a shift in nitrogen sources from nitrate-based to N2-based over the year. The spring bloom, dominated by diatoms, was characterized by a lighter carbon and heavier nitrogen isotopic composition, while the summer bloom, mainly of diazotrophic cyanobacteria, was characterized in contrary by heavier carbon and lighter nitrogen isotopes. Although no trend was found in the data, the variability observed in the sinking material was related to the changes over time in the phytoplankton community in the Gotland Basin. The findings of this study provide new and valuable information for our understanding of the temporal variability of sinking material linked to the development of phytoplankton blooms and nutrient sources in the Gotland Basin, and underscore the importance of continued monitoring to understand the potential impacts of environmental changes on this fragile ecosystem.

A solution for autonomous, adaptive monitoring of coastal ocean ecosystems: Integrating ocean robots and operational forecasts

This study presents a proof-of-concept for a fully automated and adaptive observing system for coastal ocean ecosystems. Such systems present a viable future observational framework for oceanography, reducing the cost and carbon footprint of marine research. An autonomous ocean robot (an ocean glider) was deployed for 11 weeks in the western English Channel and navigated by exchanging information with operational forecasting models. It aimed to track the onset and development of the spring phytoplankton bloom in 2021. A stochastic prediction model combined the real-time glider data with forecasts from an operational numerical model, which in turn assimilated the glider observations and other environmental data, to create high-resolution probabilistic predictions of phytoplankton and its chlorophyll signature. A series of waypoints were calculated at regular time intervals, to navigate the glider to where the phytoplankton bloom was most likely to be found. The glider successfully tracked the spring bloom at unprecedented temporal resolution, and the adaptive sampling strategy was shown to be feasible in an operational context. Assimilating the real-time glider data clearly improved operational biogeochemical forecasts when validated against independent observations at a nearby time series station, with a smaller impact at a more distant neighboring station. Remaining issues to be addressed were identified, for instance relating to quality control of near-real time data, accounting for differences between remote sensing and in situ observations, and extension to larger geographic domains. Based on these, recommendations are made for the development of future smart observing systems.

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.

Interannual variability in particulate organic matter distribution and its carbon stable isotope signatures from the western Indian shelf waters

Particulate organic carbon and nitrogen (POC, PN, collectively particulate organic matter, POM) and the stable isotopic signature of POC (δ13CPOC) are important to delineate its sources and recycling in shelf water. The present study provides insights into the factors responsible for spatial and interannual variability in POM and δ13CPOC values along the western Indian shelf waters (8° N –21° N) during the southwest (SW) monsoon (August) 2017 and 2018. The dominance of phytoplankton-derived POM with a negligible terrestrial influence was evident from the positive correlation between POC and TChla contents, ratios of C: N, and δ13CPOC signatures. Prominent upwelling signatures [cold nutrient-rich water, higher POM, total Chlorophylla (TChla), and δ13CPOC values] were noted in the south (8–12° N), whereas low nutrient warm waters (lower values of POM, TChla, and δ13CPOC) were prevalent in the north (13–21° N). Phytoplankton biomass was significantly higher and matured in 2017 due to an early and stronger upwelling in the south. In 2018, delayed and weak upwelling (evident from Ekman offshore transport and pumping velocity) resulted in the late development of phytoplankton bloom and lower POM. Furthermore, considerably lower nutrient supply within the mixed layers in 2018 compared to 2017 was partially attributed to the enhanced spatial expansion of low salinity waters closer to the surface. In the north, in 2018, higher wind speeds enhanced vertical mixing resulting in increased nutrient supply and TChla compared to 2017. We conclude that monsoon wind speed in the northern shelf and strength as well as the timing of the upwelling, including freshwater flux in the south, can be the key factors in modulating the interannual variability in POM distribution and δ13CPOC signature in the western Indian Shelf waters.

'Boom-and-busted' dynamics of phytoplankton-virus interactions explain the paradox of the plankton.

Summary Rapid virus proliferation can exert a powerful control on phytoplankton host populations, playing a significant role in marine biogeochemistry and ecology. We explore how marine lytic viruses impact phytoplankton succession, affecting host and nonhost populations.Using an in silico food web we conducted simulation experiments under a range of different abiotic and biotic conditions, exploring virus–host–grazer interactions and manipulating competition, allometry, motility and cyst cycles.Virus‐host and predator–prey interactions, and interactions with competitors, generate bloom dynamics with a pronounced ‘boom‐and‐busted’ dynamic (BBeD) which leads to the suppression of otherwise potentially successful phytoplankton species. The BBeD is less pronounced at low nutrient loading through distancing of phytoplankton hosts, while high sediment loading and high nonhost biomass decrease the abundance of viruses through adsorption. Larger hosts are inherently more distanced, but motility increases virus attack, while cyst cycles promote spatial and temporal distancing.Virus control of phytoplankton bloom development appears more important than virus‐induced termination of those blooms. This affects plankton succession – not only the growth of species infected by the virus, but also those that compete for the same resources and are collectively subjected to common grazer control. The role of viruses in structuring plankton communities via BBeDs can thus provide an explanation for the paradox of the plankton.

Variability in spring phytoplankton blooms associated with ice retreat timing in the Pacific Arctic from 2003-2019.

The Arctic is experiencing rapid changes in sea-ice seasonality and extent, with significant consequences for primary production. With the importance of accurate monitoring of spring phytoplankton dynamics in a changing Arctic, this study further examines the previously established critical relationship between spring phytoplankton bloom types and timing of the sea-ice retreat for broader temporal and spatial coverages, with a particular focus on the Pacific Arctic for 2003–2019. To this end, time-series of satellite-retrieved phytoplankton biomass were modeled using a parametric Gaussian function, as an effective approach to capture the development and decay of phytoplankton blooms. Our sensitivity analysis demonstrated accurate estimates of timing and presence/absence of peaks in phytoplankton biomass even with some missing values, suggesting the parametric Gaussian function is a powerful tool for capturing the development and decay of phytoplankton blooms. Based on the timing and presence/absence of a peak in phytoplankton biomass and following the classification developed by the previous exploratory work, spring bloom types are classified into three groups (under-ice blooms, probable under-ice blooms, and marginal ice zone blooms). Our results showed that the proportion of under-ice blooms was higher in the Chukchi Sea than in the Bering Sea. The probable under-ice blooms registered as the dominant bloom types in a wide area of the Pacific Arctic, whereas the marginal ice zone bloom was a relatively minor bloom type across the Pacific Arctic. Associated with a shift of sea-ice retreat timing toward earlier dates, we confirmed previous findings from the Chukchi Sea of recent shifts in phytoplankton bloom types from under-ice blooms to marginal ice zone blooms and demonstrated that this pattern holds for the broader Pacific Arctic sector for the time period 2003–2019. Overall, the present study provided additional evidence of the changing sea-ice retreat timing that can drive variations in phytoplankton bloom dynamics, which contributes to addressing the detection and consistent monitoring of the biophysical responses to the changing environments in the Pacific Arctic.

A perfect storm: An anomalous offshore phytoplankton bloom event in the NE Atlantic (March 2009)

While primary productivity is more stable in oceanic regions, it may vary to a great extent with the proximity to coasts, where mesoscale processes may intertwine and shape phytoplankton community composition and biomass. Sometimes, this may lead to the development of anomalous phytoplankton blooms (i.e., episodic blooms that exceed several times the average phytoplankton biomass). A massive bloom observed off the Western Iberian Coast (SW Europe) during March 2009 prompted a full investigation on its spatial and temporal extent, its causes, and its potential impact on the ecosystem. Results revealed that the March 2009 bloom was both novel in terms of biomass in a regional context and one of the largest anomalous blooms until now described in terms of relative magnitude. Its causes were due to a concurrence of long-term (deep winter MLD) and short-term factors (coastal upwelling, sudden changes in the water column, consistent offshore water transport). Its impact on the regional ecosystem is difficult to gauge, although the high concentrations of particulate organic carbon at surface during the bloom period suggests that it may have had a significant local impact. Since climate change is expected to increase the frequency and intensity of extreme weather events, it is possible that anomalous blooms will also become more frequent, expanding their role in shaping carbon export and food webs. These results are crucial for the monitoring of the Western Iberian Coast and are applicable to other complex coastal upwelling regions where phytoplankton biomass and variability have a crucial link to fisheries.

Fe-binding organic ligands in coastal and frontal regions of the western Antarctic Peninsula

Abstract. Organic ligands are a key factor determining the availability of dissolved iron (DFe) in the high-nutrient low-chlorophyll (HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe is investigated along a natural gradient of the western Antarctic Peninsula, from an ice-covered shelf to the open ocean. An electrochemical approach, competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV), was applied. Our results indicated that organic ligands in the surface water on the shelf are associated with ice-algal exudates, possibly combined with melting of sea ice. Organic ligands in the deeper shelf water are supplied via the resuspension of slope or shelf sediments. Further offshore, organic ligands are most likely related to the development of phytoplankton blooms in open ocean waters. On the shelf, total ligand concentrations ([Lt]) were between 1.2 and 6.4 nM eq. Fe. The organic ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands on the shelf from bloom-associated ligands offshore. Overall, organic ligand concentrations always exceeded DFe concentrations (excess ligand concentration, [L′] = 0.8–5.0 nM eq. Fe). The [L′] made up to 80 % of [Lt], suggesting that any additional Fe input can be stabilized in the dissolved form via organic complexation. The denser modified Circumpolar Deep Water (mCDW) on the shelf showed the highest complexation capacity of Fe (αFe'L; the product of [L′] and conditional binding strength of ligands, KFe'Lcond). Since Fe is also supplied by shelf sediments and glacial discharge, the high complexation capacity over the shelf can keep Fe dissolved and available for local primary productivity later in the season upon sea-ice melting.

Spatiotemporal dynamics of marine microbial communities following a Phaeocystis bloom: biogeography and co-occurrence patterns.

Marine microbes play important roles in the development of phytoplankton blooms. The diversity and composition of free living (FL) and particle attached (PA) microbial communities have been well studied, while little is known about their geographic and co-occurrence patterns, especially during the subsiding process of Phaeocystis globosa blooms. Herein, the beta-diversity of FL and PA microbial communities in both the surface and bottom layers of different habitats were comprehensively examined during succession of a P. globosa bloom event. The results showed that microbial communities from bloom and non-bloom sites exhibited distinct community compositions. Among the different sampling sites, the community similarities decreased with spatial distance, in which the FL communities' similarity in bottom waters was more influenced by spatial variation. The variation of microbial communities was mostly attributed to environmental selection, spatial distance, and the abundance of P. globosa successively. The co-occurrence networks of microbial communities in bloom and non-bloom waters differed in terms of structure and composition, and the bloom network had more links and closer relationships between genera than the non-bloom network. The correlation among genera and modules suggested that the bloom microbes were likely driven by high environmental selection and low competitive effect between each other.

Carbon Export in the Seasonal Sea Ice Zone North of Svalbard From Winter to Late Summer

Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlier and occur further north with retreating and thinning sea ice cover. The current study is the first compilation of phytoplankton bloom development and fate in the seasonally variable sea ice zone north of Svalbard from winter to late summer, using short-term sediment trap deployments. Clear seasonal patterns were discovered, with low winter and pre-bloom phytoplankton standing stocks and export fluxes, a short and intense productive season in May and June, and low Chl a standing stocks but moderate carbon export fluxes in the autumn post-bloom conditions. We observed intense phytoplankton blooms with Chl a standing stocks of >350 mg m−2 below consolidated sea ice cover, dominated by the prymnesiophyte Phaeocystis pouchetii. The largest vertical organic carbon export fluxes to 100 m, of up to 513 mg C m−2 day−1, were recorded at stations dominated by diatoms, while those dominated by P. pouchetii recorded carbon export fluxes up to 310 mg C m−2 day−1. Fecal pellets from krill and copepods contributed a substantial fraction to carbon export in certain areas, especially where blooms of P. pouchetii dominated and Atlantic water advection was prominent. The interplay between the taxonomic composition of protist assemblages, large grazers, distance to open water, and Atlantic water advection was found to be crucial in determining the fate of the blooms and the magnitude of organic carbon exported out of the surface water column. Previously, the marginal ice zone was considered the most productive region in the area, but our study reveals intense blooms and high export events in ice-covered waters. This is the first comprehensive study on carbon export fluxes for under-ice phytoplankton blooms, a phenomenon suggested to have increased in importance under the new Arctic sea ice regime.

Riverine and Oceanic Nutrients Govern Different Algal Bloom Domain Near the Changjiang Estuary in Summer

AbstractThe Changjiang Estuary and adjacent sea area in the East China Sea suffer from frequent harmful algal blooms. However, the relative importance of riverine nutrient input from the Changjiang River and oceanic nutrient input from the Taiwan Warm Current and Kuroshio Current to the development and distribution of summer phytoplankton blooms in this area remains unclear. To address this problem, we deployed a coupled physical‐biological model. The coupled model successfully reproduces the main hydrographic and biogeochemical features in this domain. Both satellite observations and model results show two regions of elevated chlorophyll concentrated in this site. Simulated results show that harmful algal blooms in the region north of the Zhoushan Islands are mainly driven by riverine nutrients from the Changjiang River, while algal blooms in the region south of the Zhoushan Islands are mainly controlled by nutrients from the open ocean. Nutrient input, particularly phosphate, from the Kuroshio subsurface water contributes most to the accumulation of dinoflagellate biomass and chlorophyll in the southern region, while the Taiwan Warm Current has less influence. This has implications for nutrient control and land management practices: Although reducing riverine nutrient loads may significantly reduce phytoplankton growth north of the Zhoushan Islands, it will have little effect in the area to the south.

Interplay of regional oceanography and biogeochemistry on phytoplankton bloom development in an Arctic fjord

Ongoing sea-ice melting and associated environmental changes influence the bloom phenology and biogeochemistry of the Arctic Ocean. Kongsfjorden, a fjord in Svalbard, has already undergone the transition of being sea-ice covered in winter to sea-ice free, and now stands vulnerable to Atlantic water intrusion and glacier melting. We monitored physical and biogeochemical variables in the fjord between July 2015 and July 2016 using Indian Arctic subsurface mooring in Kongsfjorden. The year-round records of nitrate represent the first reported sensor-based observation in the region. Here, we used the high-resolution time-series of chlorophyll a, nitrate, dissolved oxygen, photosynthetically active radiation, turbidity, temperature, and salinity to study their interactions and assess how do they relate to the development of phytoplankton bloom. Results indicated a high nitrate concentration (up to 13.3 μM) and near-zero chlorophyll a in winter. The spring bloom was spotted from mid-April to the first week of June (up to 7.2 μg/L chlorophyll a at 25 m), however, with discontinuities due to high winds events. The chlorophyll a was negatively correlated with nitrate (r = −0.7, p < 0.001). Further, we observed temperature, salinity, and density characteristic of Atlantic water at 25 m and 35 m in autumn and early-winter, which coincided with nitrate peaks. This indicated nitrate supply by Atlantic inflow during the non-bloom period. We say that the features of the bloom start evolving from rather quiescent autumn and winter before it reaches an active state in spring-summer. Year-round high-resolution observations are crucial to study phytoplankton bloom phenology as any shift or change in the phenology will affect higher trophic levels and biogeochemical cycles.

High throughput sequencing of 18S rRNA and its gene to characterize a Prorocentrum shikokuense (Dinophyceae) bloom

Comparing phytoplankton non-bloom and bloom communities using rRNA and its coding gene can help understand the shift of dominant species and its driving processes (e.g., intrinsic growth or grazing). Here we conducted high-throughput sequencing of 18S rRNA and its coding gene for studying non-bloom and bloom plankton communities in East China Sea. The non-bloom community was dominated by diatoms whereas during the bloom it was dominated by the dinoflagellate Prorocentrum shikokuense (formerly P. donghaiense). P. shikokuense rRNA abundance and rRNA:rRNA gene ratio both increased markedly in the bloom, indicating that the bloom arose from active growth. In contrast, some non-bloom species showed low DNA abundances during the bloom albeit high rRNA:rRNA gene ratios, suggesting that cell loss processes such as grazing might have prevented these species from blooming or that these species might be at an early stage of bloom development. Furthermore, Pearson's correlation analysis showed that dinoflagellate abundance was positively correlated with temperature and negatively related to dissolved inorganic phosphate (DIP) concentrations, suggesting warm and DIP-poor environment as a niche space for P. shikokuense. Our results demonstrate the usefulness of combined analysis of rRNA and its gene in characterizing phytoplankton bloom development to shed light on the complex phytoplankton dynamics and regulating mechanisms in the course of bloom development.

Phytoplankton blooms in front of cape Galata (Black Sea) during the period 2008-2017

Abstract. The aim of the study was to identify the peculiarities of the development of phytoplankton blooms (annual and seasonal dynamics) in front of cape Galata, Bulgarian Black Sea coast in the period 2008-2017. In that area up to 30 nautical miles (nm), from 6 stations (G-1, G-3, G-5, G-10, G-20 and G-30, respectively at 1, 3, 5, 10, 20 and 30 nm from the coast), 187 phytoplankton samples were collected. A total of six phytoplankton species were recorded, developing with the following blooming concentrations: Emiliania huxleyi, Oscillatoria sp., Merismopedia sp., small Flagellates (Cryptophyceae), Prorocentrum cordatum (minimum) and Pseudo-nitzschia delicatissima. It was found that the reported in previous periods trend of increasing phytoplankton biomass in front of cape Galata had already changed. Compared to the observed quantities in the period 1993-2007, the current phytoplankton values in the surface layer (up to 30 nm in front of cape Galata) were 1.63 times lower in abundance and 5.60 times lower in biomass.

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.

Testing the Canyon Hypothesis: Evaluating light and nutrient controls of phytoplankton growth in penguin foraging hotspots along the West Antarctic Peninsula

AbstractBiological hotspots along the West Antarctic Peninsula (WAP) are characterized by high phytoplankton productivity and biomass as well as spatially focused penguin foraging activity. While unique physical concentrating processes were identified in one of these hotspots, understanding the mechanisms driving the blooms at these locations is of high importance. Factors posited to explain the blooms include the upwelling of macronutrient‐ and micronutrient‐enriched modified Upper Circumpolar Deep Water (mUCDW) and the depth of the mixed layer influencing overall light availability for phytoplankton. Using shipboard trace‐metal clean incubation experiments in three different coastal biological hotspots spanning a north‐south gradient along the WAP, we tested the Canyon Hypothesis (upwelling) for enhanced phytoplankton growth. Diatoms dominated the Southern region, while the Northern region was characterized by a combination of diatoms and cryptophytes. There was ample concentration of macronutrients at the surface and no phytoplankton growth response was detected with the addition of nutrient‐enriched mUCDW water or iron solution to surface waters. For all treatments, addition of mUCDW showed no enhancement in phytoplankton growth, suggesting that local upwelling of nutrient‐enriched deep water in these hotspots was not the main driver of high phytoplankton biomass. Furthermore, the dynamics in the photoprotective pigments were consistent with the light levels used during these incubations showing that phytoplankton are able to photoacclimate rapidly to higher irradiances and that in situ cells are low light adapted. Light availability appears to be the critical variable for the development of hotspot phytoplankton blooms, which in turn supports the highly productive regional food web.