Sea Phytoplankton Research Articles

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

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

Seasonal and Inter-Annual Variability of the Phytoplankton Dynamics in the Black Sea Inner Basin

We explore the patterns of Black Sea phytoplankton growth as driven by the thermohaline structure and circulation system and the freshwater nutrient loads. Seasonal and inter-annual variability of the phytoplankton blooms is examined using hydrodynamic simulations that resolve mesoscale eddies and online coupled bio-geochemical model. This study suggests that the bloom seasonality is homogeneous across geographic locations of the Black Sea inner basin, with the strongest bloom occurring in winter (February–March), followed by weaker bloom in spring (April–May), summer deep biomass maximum (DBM) (June–September) and a final bloom in autumn (October–November). The winter phytoplankton bloom relies on vertical mixing of nitrate from the intermediate layers, where nitrate is abundant. The winter bloom is highly dependent on the strength of the cold intermediate layers (CIL), while spring/summer blooms take advantage of the CIL weakness. The maximum phytoplankton transport across the North Western Shelf (NWS) break occurs in September, prior to the basin interior autumn bloom. Bloom initiation in early autumn is associated with the spreading of NWS waters, which in turn is caused by an increase in mesoscale eddy activity in late summer months. In summary, the intrusion of low salinity and nitrate-rich water into the basin interior triggers erosion of the thermocline, resulting in vertical nitrate uplifting. The seasonal phytoplankton succession is strongly influenced by the recent CIL disintegration and amplification of the Black Sea circulation, which may alter the natural Black Sea nitrate dynamics, with subsequent effects on phytoplankton and in turn on all marine life.

Floristic Findings in the Barents Sea: Climatic Trend as a Florogenesis Factor

The results of floristic studies on plankton in the Barents Sea performed from 2007 to 2018 are discussed in the paper. The findings of 16 species new to the indigenous flora were documented and their distribution in the Barents Sea and adjacent waters was analyzed. We also calculated statistical indicators (indices) that characterize the regularity and quantitative expression of their presence in certain sectors of the sea. The data obtained demonstrate the intensity and direction of invasion of Atlantic algal flora. The most intense and regular invasion is directed eastward from the southwestern border of the Barents Sea to its central part. No less stable, but a less intense vector of influence of Atlantic flora was found in the northwestern Barents Sea directed southward to the central and eastern parts of the sea. These processes are characterized from the historical aspect as the activation of florogenesis coincident in time and, most likely, caused by the current climatic situation in the region, mainly by the increased advection of Atlantic water. At least one adventive species has been discovered to be currently integrated into the succession system of the Barents Sea phytoplankton in the position of seasonal dominant.

Seasonal Variability and Estimation of Annual East Siberian Sea Phytoplankton Primary Production and Comparison with the Other Siberian Seas

Studies of seasonal variability of the East Siberian Sea (ESS) water column primary production (IPP) and evaluation of its total annual value (PPtot) were performed using MODIS-Aqua data (2002–2018). Region-specific primary production and chlorophyll algorithms were used for the first time to achieve that result. Northeastern and Southwestern regions were distinguished in ESS based on multiyear average daily primary production. Seasonal variations in IPP in the Northeastern region were characterized by the maximum in June (273 mgC m–2 d–1). The maximum of water column primary production value in the Southwestern region was recorded in May (311 mgC m–2 d–1). The maximum of IPP for the entire ESS was registered in June (273 mgC m–2 d–1). Values of daily primary production and PPtot in the Southwestern region were, respectively, 1.8 and 2 fold higher than in the Northeastern region. The multiyear averaged value of ESS IPP was equal to 91 mgC m–2 d–1 and PPtot value was equal to 9 TgC. Productivity of the Siberian seas decreased eastward.

Bio-optical evidence for increasing Phaeocystis dominance in the Barents Sea

Increasing contributions of prymnesiophytes such as Phaeocystis pouchetii and Emiliania huxleyi to Barents Sea (BS) phytoplankton production have been suggested based on in situ observations of phytoplankton community composition, but the scattered and discontinuous nature of these records confounds simple inference of community change or its relationship to salient environmental variables. However, provided that meaningful assessments of phytoplankton community composition can be inferred based on their optical characteristics, ocean-colour records offer a potential means to develop a synthesis between sporadic in situ observations. Existing remote-sensing algorithms to retrieve phytoplankton functional types based on chlorophyll-a (chl-a) concentration or indices of pigment packaging may, however, fail to distinguish Phaeocystis from other blooms of phytoplankton with high pigment packaging, such as diatoms. We develop a novel algorithm to distinguish major phytoplankton functional types in the BS and apply it to the MODIS-Aqua ocean-colour record, to study changes in the composition of BS phytoplankton blooms in July, between 2002 and 2018, creating time series of the spatial distribution and intensity of coccolithophore, diatom and Phaeocystis blooms. We confirm a north-eastward expansion in coccolithophore bloom distribution, identified in previous studies, and suggest an inferred increase in chl-a concentrations, reported by previous researchers, may be partly explained by increasing frequencies of Phaeocystis blooms. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Weddell Sea Phytoplankton Blooms Modulated by Sea Ice Variability and Polynya Formation

AbstractSeasonal sea ice retreat is known to stimulate Southern Ocean phytoplankton blooms, but depth‐resolved observations of their evolution are scarce. Autonomous float measurements collected from 2015–2019 in the eastern Weddell Sea show that spring bloom initiation is closely linked to sea ice retreat timing. The appearance and persistence of a rare open‐ocean polynya over the Maud Rise seamount in 2017 led to an early bloom and high annual net community production. Widespread early ice retreat north of Maud Rise in 2017, however, had a similar effect, suggesting that the polynya most impacted the timing of bloom initiation. Still, higher productivity rates at Maud Rise relative to the surrounding region are observed in all years, likely supported by flow‐topography interactions. The longer growing season in 2017–2018 also allowed for separation of distinct spring and fall bloom signals, the latter of which was primarily subsurface and associated with mixed‐layer deepening.

The impact of physical processes on taxonomic composition, distribution and growth of phytoplankton in the open Black Sea

In autumn 2017, the influence of strong storms and mesoscale physical processes on phytoplankton has been studied in the Black Sea. Data on the taxonomic composition and biomass of phytoplankton, the concentration of chlorophyll-a (Chl), particulate organic carbon, primary production, chemical and physical properties of the environment were obtained using field observations, satellite scanners and two Bio-Argo floats. Different species predominated in cold-water and warm-water areas. In the vast cold-water area formed in the central part of the sea due to strong wind exposure for a month, two diatoms prevailed in the phytoplankton biomass: Pseudosollenia calcar-avis and Hemiaulus hauckii . Three-month observations using satellites and Bio-Argo floats showed that in the upper mixed layer (UML) an increase in Chl during the autumn occurred in a pulse mode in response to severe storms which caused the deepening of the UML. In the warm-water area with depleted inorganic nitrogen, located in the north-eastern part of the sea, coccolithophore Emiliania huxleyi prevailed. Periods with high precipitation were often followed by an increase in the abundance of coccolithophores, which indicates an important role of terrestrial runoff as a source of nutrients. Two different mechanisms increased the phytoplankton biomass and Chl in young (two-week-old) mesoscale cyclonic eddies located within the cold-water area. The rise of the nutricline and wind-induced mixing resulted in pulsed nutrient inputs into the upper layers which stimulated the growth of diatoms and dinoflagellates. At the same time, the uplift of nutricline to a depth of 25–30 m with the daily integrated irradiance of 0.2–1.0 mol photons m −2 day −1 was sufficient to form a strong deep Chl maximum consisting of small flagellates and unicellular cyanobacteria. • Cold-water and warm-water areas determine different prevailing species • A growth of phytoplankton occurs in a pulse mode • Cyclonic eddies stimulate the growth of diatoms and dinoflagellates in the upper layer • Uplift of nutricline to thermocline in cyclonic eddies forms a strong deep chlorophyll maximum • Deep chlorophyll maximum consist of small flagellates and unicellular cyanobacteria

Climate effects on temporal and spatial dynamics of phytoplankton and zooplankton in the Barents Sea

Temporal and spatial dynamics of phytoplankton and zooplankton in the Barents Sea have been investigated during the last three decades using remote sensing and in situ observations. Satellite-derived sea surface temperatures increased in the period 1998–2017 by 1.0 °C as an average for the Barents Sea. We found significant positive relationships between ice-free conditions (open water area and duration) and satellite-based net primary production (NPP). The estimated annual NPP for the Barents Sea more than doubled over the 1998–2017 period, from around 40 to over 100 Tg C. The strong increase in NPP is the result of reduction of sea ice, extending both the area and period available for phytoplankton production. In areas where ice extent has decreased, satellite-derived chlorophyll a shows that the timing of the peak spring phytoplankton bloom has advanced by over a month. Our results reveal that phytoplankton dynamics in the ecosystem have been changing rapidly and that this change is driven mainly by bottom-up climatic processes. Autumn mesozooplankton biomass showed strong interannual variability in the 1990s, displaying an inverse relationship with capelin biomass, the most abundant planktivorous fish. In some regions, e.g. Central Bank, capelin biomass explained up to 50% of the mesozooplankton variability during 1989–2017. Though capelin biomass has varied considerably, mesozooplankton biomass has remained rather stable since the mid-2000s (6–8 g dry wt. m−2), resulting in a weakening of the negative relationship between capelin and mesozooplankton biomass in recent years. The stable zooplankton biomass indicates favorable conditions (prolonged/increased NPP) for mesozooplankton production, partly counteracting high predation levels. Overall, we observed trends in phytoplankton phenology that were strongly associated with changes in sea ice cover driven by fluctuations in temperature regime, a trend that may intensify should the ecosystem become even warmer due to climate change. Further reductions of sea ice and associated ice algae is expected to have adverse effects on sympagic fauna and ice dependent species in the Arctic food web. The ice-free conditions may promote further Atlantification (or borealization) of plankton and fish communities in the Barents Sea.

Методология комплексного мониторинга современного состояния фитопланктонного сообщества прибрежных вод Черного моря

Методология комплексного мониторинга современного состояния фитопланктонного сообщества прибрежных вод Черного моря

A SPATIO-TEMPORAL ANALYSIS ON THE COMPOSITION AND ABUNDANCE OF PHYTOPLANKTON IN SEGARA ANAKAN LAGOON AREA

SegaraAnakan Lagoon (LSA) is a dynamic estuary with humid tropical climate, of which water fluctuates as the result of water hydrodynamics and changes in monsoon. The LSA area is influenced by natural factors (estuary of freshwater flow of Citanduy Watershed and high sedimentation) and various anthropogenic factors. Such conditions may influence the water’s ecological conditions. This research aims at examining such ecological changes as phytoplankton’s biological indicators (composition and abundance), since phytoplankton is able to naturally respond to environmental changes. The method is conducted with spatially in-situ measurement on phytoplankton abundance in the seven areas of SegaraAnakan Lagoon with different characteristics: (1) TPI and Port of Majingklak; (2) Pelawangan Barat LSA bordering the Indian Ocean; (3) Locks of Cikonde and Cimeneng Rivers; (4) Mangrove Forest; (5) KampungLaut Community Settlement; (6) Conservation Area “Mina Wisata” Ujung Alang; (7) Floating Net Culture. A temporal approach (time series) is then conducted for 1 year based on the representativeness of monsoon: West, Transition I, East and Transition II. Phytoplankton abundance is quantitatively analyzed using Lackey Drop Microtransect Counting method, and for ease of spatio-temporal interpretation, the results are displayed in the form of thematic map using Arc Gis 10.2 software. The analysis results show that spatially, the phytoplankton abundance in the seven areas ranges from 4474.80 ± 3408.25-8712.00 ± 6444.89 indv/L. Meanwhile, with the temporal analysis, the highest abundance takes place in the Transition I season of 9956.57 ± 5300.23 indv/L, and the lowest is in West season of 4129.71 ± 3139.88 indv/L. In the whole spatio-temporal period, the phytoplankton composition is dominated by Division Chrysophyta, and then respectively by Divisions Chlorophyta, Cyanophyta, Pyrophyta and Euglenophyta. The composition and abundance of freshwater, estuary and sea phytoplankton are spatio-temporally, evenly distributed in the seven areas, which is expectedly resulted from the Flushing Time mechanism from freshwater flow of Citanduy Watershed and the influence of water hydrodynamics of Indian Ocean at Pelawangan Barat entering the lagoon area.

Size-fractionated biomass and primary productivity of Sargasso Sea phytoplankton

The size structure of phytoplankton communities greatly influences the function of pelagic food webs and, ultimately, the flux of material from the surface ocean to the deep sea. While the biomass and taxonomic composition of organisms in a specific size class are important characteristics of a food web, the activity of that size fraction is more directly relevant to trophic dynamics and biogeochemical cycling. Even if a size class dominates cell abundance or biomass, does it necessarily contribute the most to total primary productivity (PP)? We asked this question for phytoplankton communities from the Sargasso Sea. The picophytoplankton (0.7–2 μm) accounted for 53–85% of the total integrated chl-a and 46–99% or more of the total integrated PP. The microphytoplankton (20–200 μm) were responsible for up to 38% of the total PP, but accounted for no more than 22% of total chl-a. Variations in the picophytoplankton size-class explained 84% of the variance in total integrated chl-a and 87% of the variance in total PP. Size-dependent relative contributions to chl-a versus PP varied with depth, with differences generally driven by vertical variations in C:chl-a ratios and chl-specific rates of PP. Use of the relative contributions of picophytoplankton to biomass as a predictor of their contributions to total primary productivity resulted in an average underestimate of ~7%.

Adaptation of Red Sea Phytoplankton to Experimental Warming Increases Their Tolerance to Toxic Metal Exposure

Our recent study has demonstrated the rapid adaptation of the Red Sea phytoplankton to ocean warming, with associated constraints of physiological performance. However, the possible tradeoff between thermal adaptation and the organism’s tolerance to other environmental drivers in a warmer future scenario remains understudied. Here, we designed an evolutionary selection environment where the Red Sea diatom Chaetoceros tenuissimus was adapted to ambient (26 oC) and warming (30 oC) temperature scenarios for over 2000 generations. These strains were subsequently exposed to a range of copper (Cu) dose over three assay temperatures (26 oC, 30 oC, and 35 oC), to assess whether the adaptation to experimental warming is accompanied by a reformed tolerance to toxic pollutants. Most previous studies on Cu toxicity in marine phytoplankton were conducted within a small range of temperature (20−25 oC), indicating the need for further assessments to reveal the potential complex interactive effects between pollutants and more significant warming in the future. The acute Cu toxicity was estimated in terms of reduction in cell abundance (cells mL−1), growth rate (μ) and PSII photosynthetic efficiency (Fv/Fm), with 48 h median effective concentration values (EC50) varying from 2.22−20.19 μg L−1. We found a statistically significant interaction between assay temperature, selection temperature, and Cu doses in all the criteria tested. However, under extreme warming scenario (35 oC), the Cu sensitivity was significantly reduced, indicating cumulative antagonistic effects between these factors. Adaptation of phytoplankton to higher temperatures may help maintain their heavy metal tolerance, although a shift in temperature during the tests clearly altered their sensitivities. We conclude that selection for warming having made cells more resistant to Cu at the selection temperature in comparison to ambient-adapted population tested at 26 oC. However, in warming-adapted cells, this was traded off against cupper resistance at 26 oC.

Climate Driven Changes in Timing, Composition and Magnitude of the Baltic Sea Phytoplankton Spring Bloom

Spring phytoplankton blooms contribute a substantial part to annual production, support pelagic and benthic secondary production and influence biogeochemical cycles in many temperate aquatic systems. Understanding environmental effects on spring bloom dynamics is important for predicting future climate responses and for managing aquatic systems. We analyzed long-term phytoplankton data from one coastal and one offshore station in the Baltic Sea to uncover trends in timing, composition and size of the spring bloom and its correlations to environmental variables. There was a general trend of earlier phytoplankton blooms by 1–2 weeks over the last 20 years, associated with more sunshine and less windy conditions. High water temperatures were associated with earlier blooms of diatoms and dinoflagellates that dominate the spring bloom, and decreased diatom bloom magnitude. Overall bloom timing, however, was buffered by a temperature and ice related shift in composition from early blooming diatoms to later blooming dinoflagellates and the autotrophic ciliateMesodinium rubrum.Such counteracting responses to climate change highlight the importance of both general and taxon-specific investigations. We hypothesize that the predicted earlier blooms of diatoms and dinoflagellates as a response to the expected temperature increase in the Baltic Sea might also be counteracted by more clouds and stronger winds. A shift from early blooming and fast sedimenting diatoms to later blooming groups of dinoflagellates andM. rubrumat higher temperatures during the spring period is expected to increase energy transfers to pelagic secondary production and decrease spring bloom inputs to the benthic system, resulting in lower benthic production and reduced oxygen consumption.

Short term primary production in western Mediterranean Sea phytoplankton communities subjected to the combined stress of high irradiance and low nutrients during summer stratification

Thermal stratification of the water column promotes contrasting conditions with respect to irradiance level and nutrient concentration for phytoplankton growth, demanding more research on which environmental factor has more importance in determining the photosynthetic performance of the communities. For this purpose, two research surveys were performed in several coastal stations located in the Alboran Sea (Western Mediterranean Sea) at the end of 2008 and 2009 summers. Primary productivity was estimated by determining photosynthetic electron transport rates (ETRB) and inorganic carbon assimilation rates (PPCB) at two different depths within the water column, surface and chlorophyll a vertical maximum depth (CM). At the surface, communities presented similar photo-acclimation features during the two surveys, which were different from those obtained for the CM samples that grew at more favorable nutrient and light conditions. The acclimation response to surface conditions consisted in the reduction in the chlorophyll a (Chl a) cell content, and the increase in the Chl a specific light absorption coefficient [a*(λ)], initial slope of ETRB vs. Irradiance curves (αB) and light saturation parameter (Ek), indicating that the communities were acclimated to stress conditions (i.e. high PAR and UVR dose and low nutrient availability). However, the in situ primary productivity was unaffected; on the contrary, both PPCB and ETRBin situ increased with respect to the values obtained for communities growing at CM depth. Furthermore, ΦETR,C (i.e. the molar ratio of transported e− to assimilated carbon) in surface samples was similar to CM samples (8.0 ± 3.5 compared with 7.5 ± 5.3 mol e− [mol−1 C], respectively). The analysed phytoplankton communities were mainly dominated by diatom. This corroborates that diatoms possess a greater capacity to cope with high irradiance levels, even at low nutrient concentrations registered during this study at surface waters.

Estimation of seasonal and inter-annual variations of phytoplankton in the Black Sea on the base of remote sensed data procession and chlorophyll a in situ measurements

The patterns of the seasonal and inter annual variability in the development of phytoplankton, including coc- colithophores, were studied in the northeastern part of the Black Sea in various seasons. The research was carried out on the base of remote sensed data provided by the Modis Aqua ocean color scanner and long-term ship observations. The results indicate that, in the coastal and open waters of the Black Sea, the development of phytoplankton reaches the highest level in the fall-winter and winter-spring seasons, i.e., in the periods of active winter convection. It was noted that there is a relationship between the level of coccolithophore development in the summer period and the minimal temperature of the sea surface layer in the preceding winter. The most active coccolithophore blooms, were observed after the coldest winters. Unusual winter and early spring coccolithophore blooms taking place in mild hydro meteorological conditions were registered in the Black Sea, on the base of satellite data and were confirmed by in situ measurements.

Vertical average irradiance shapes the spatial pattern of winter chlorophyll-a in the Yellow Sea

Strong turbulence in temperate shelves during winter months enhances the vertical mixing of the water column, consequently pumps up nutrients and induces high turbidity in the upper ocean. Thus, light availability often becomes an important factor to impact phytoplankton biomasses and their spatial patterns in winter. To quantitatively assess the effect of light availability on the spatial pattern of phytoplankton in the Yellow Sea in winter, we used vertical average irradiance (Im) as a light index which denotes the average irradiance received by phytoplankton during their vertical motion, and then analyzed the spatial correlation between winter climatological Im and chlorophyll-a (Chl-a). The result from a set of high-resolution satellite-derived climatological data (2003–2016) demonstrated that there is a significantly positive correlation (R = 0.71, p < 0.0001) between Chl-a and Im in space. The observational data of 2016 winter further showed that Im is much more important in determining the spatial pattern of Chl-a concentrations than nutrients, due to the availability of sufficient nutrients but very limited light availability for almost the entire sea area. Relatively high Chl-a regions (>1 mg/m3) are in response to an environmental condition of Im > 50 μmol photons/m2/s, total suspended matter concentration (TSM) < 10 mg/L, and mixed layer depth (MLD) < 40 m. In coastal waters, TSM is the key factor to cause low Im; while MLD is more important in deep offshore waters to determine the Im values.

Madden\u2013Julian Oscillation Enhances Phytoplankton Biomass in the Maritime Continent

In addition to monsoon-driven rainfall, the Maritime Continent (MC) is subject to heavy precipitation caused by the Madden–Julian Oscillation (MJO), a tropical convection-coupled circulation that propagates eastward from the Indian to the Pacific Ocean. This study shows that riverine runoff from MJO-driven rainfall in the western MC significantly enhances phytoplankton biomass not only in the coastal regions but as far as the nutrient-poor Banda Sea, located 1,000 km downstream of the riverine source. We present observational estimates of the chlorophyll-a concentration in the Banda Sea increasing by 20% over the winter average within an MJO life cycle. The enhancement of phytoplankton in the central Banda Sea is attributed to two coinciding MJO-triggered mechanisms: enhanced sediment loading and eastward advection of waters with high sediment and chlorophyll concentrations. Our results highlight an unexpected effect of MJO-driven rainfall on the downstream oceanic region. This finding has significant implications for the marine food chain and biogeochemical processes in the MC, given the increasing deforestation rate and projections that global warming will intensify both the frequency and strength of MJO-driven rainfall in the MC.

Synchrony is more than its top-down and climatic parts: interacting Moran effects on phytoplankton in British seas.

Large-scale spatial synchrony is ubiquitous in ecology. We examined 56 years of data representing chlorophyll density in 26 areas in British seas monitored by the Continuous Plankton Recorder survey. We used wavelet methods to disaggregate synchronous fluctuations by timescale and determine that drivers of synchrony include both biotic and abiotic variables. We tested these drivers for statistical significance by comparison with spatially synchronous surrogate data. Identification of causes of synchrony is distinct from, and goes beyond, determining drivers of local population dynamics. We generated timescale-specific models, accounting for 61% of long-timescale (> 4yrs) synchrony in a chlorophyll density index, but only 3% of observed short-timescale (< 4yrs) synchrony. Thus synchrony and its causes are timescale-specific. The dominant source of long-timescale chlorophyll synchrony was closely related to sea surface temperature, through a climatic Moran effect, though likely via complex oceanographic mechanisms. The top-down action of Calanus finmarchicus predation enhances this environmental synchronising mechanism and interacts with it non-additively to produce more long-timescale synchrony than top-down and climatic drivers would produce independently. Our principal result is therefore a demonstration of interaction effects between Moran drivers of synchrony, a new mechanism for synchrony that may influence many ecosystems at large spatial scales.

Variability of organic nitrogen and its role in regulating phytoplankton in the eastern Arabian Sea

The relative importance of organic nitrogen (ON) and inorganic nitrogen (IN) as nitrogen sources for the phytoplankton communities were studied through a seasonal time series of nitrogen species in the eastern Arabian Sea. Seasonal data on nitrogen species showed that ON dominates the system throughout the year and account for >90% of the total nitrogen (TN) during north east monsoon (NEM). The average ON concentration in the study region was 11.5 μM during NEM as compared to 7.2 μM during south west monsoon (SWM). The contribution of picoplankton to the total phytoplankton pool (fpico) increased from 19% during SWM to 36% in NEM. Along with cyanobacteria, the diatoms Thalassionema nitzchoides and Thalassiosira sp. and among the dinoflagellates Pronoctiluca sp. were found to proliferate in ON rich waters. We suggest atmospheric deposition, riverine-input, resuspension of bottom sediment and ground water intrusion as the possible sources of ON in the study region.

Seasonal and Interannual Variability of Phytoplankton in the Black Sea on the Basis of Remote Sensing Data and In Situ Measurements of Chlorophyll-a

The patterns of the seasonal and interannual variability in the development of phytoplankton, including coccolithophores, were studied in the northeastern part of the Black Sea in various seasons. The research was carried out on the basis of long-term observations and data provided by the Modis Aqua ocean color scanner. This paper reports that, in the coastal and open waters of the Black Sea, the development of phytoplankton reaches the highest level in the fall–winter and winter–spring seasons, i.e., in the periods of active winter convection. Coastal waters are also characterized by expressed spring peak of chlorophyll “a” concentrations associated with phytoplankton bloom in March. Winter and spring coccolithophore blooms, which are unusual for the Black Sea, were registered on the basis of satellite data. It was noted that there is a relationship between the level of coccolithophore development in the summer period and the minimal temperature of the sea surface layer in the preceding winter. The most active coccolithophore blooms, which were registered in 2006 and 2012, were observed after the coldest winters.