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Modeling studies have shown that mesoscale and submesoscale processes can stimulate phytoplankton productivity and export production. Here, we present observations from an undulating, towed Video Plankton Recorder (VPR-II) in the tropical Atlantic. The VPR-II collected profiles of oxygen, fluorescence, temperature and salinity in the upper 140 m of the water column at a spatial resolution of 1 m in the vertical and <2 km in the horizontal. The data reveal remarkable "hotspots", i.e. locations 5–10 km wide which have elevated fluorescence and decreased oxygen, both of which are likely the result of intense submesoscale upwelling. Based on estimates of source water, estimated from identical temperature and salinity surfaces, hotspots are more often areas of net respiration than areas of net production — although the inferred changes in oxygen are subject to uncertainty in the determination of the source of the upwelled waters since the true source water may not have been sampled. We discuss the spatial distribution of these hotspots and present a conceptual model outlining their possible generation and decline. Simultaneous measurements of O 2 /Ar in the mixed layer from a shipboard mass spectrometer provide estimates of rates of surface net community production. We find that the subsurface biological hotspots are often expressed as an increase in mixed layer rates of net community production. Overall, the large number of these hotspots support the growing evidence that submesoscale processes are important drivers in upper ocean biological production. [ABSTRACT FROM AUTHOR]

Rich in upwelled nutrients, the Southern Benguela is one of the most productive ecosystems in the world ocean. However, despite its ecological significance the role of trace elements influencing phytoplankton population in the Southern Benguela Upwelling System (SBUS) has not been thoroughly investigated. Here, we report pigment composition, macronutrients (nitrate, phosphate and silicate) and concentrations of dissolved Cd, Co, Fe and Zn during late austral summer and winter seasons in 2004 to understand the relationship between the selected trace elements and phytoplankton biomass in St. Helena Bay (SHB), which falls within the southern boundary of the SBUS. Chlorophyll a concentrations indicate higher phytoplankton biomass associated with high primary production during late summer in SHB where high diatom population is inferred from the presence of fucoxanthin. Diminished phytoplankton biomass and a shift from diatoms to dinoflagellates as the dominant phytoplankton taxa are indicated by diagnostic pigments during late winter. Dissolved trace elements (Cd, Co and Zn) and macronutrients play a significant role in phytoplankton biomass, and their distribution is affected by biological uptake and export of trace elements. Continuous uptake of Zn by diatoms may cause an onset of Zn depletion leading to a period of extended diatom proliferation during late summer. Furthermore, the transition from diatom to dinoflagellate dominated phytoplankton population is most likely facilitated by depletion of trace elements (Cd and Co) in the water column. [ABSTRACT FROM AUTHOR]

The ongoing increase in surface seawater CO 2 level could potentially impact phytoplankton primary production in coastal waters; however, CO 2 sensitivity studies on tropical coastal phytoplankton assemblages are rare. The present study investigated the interactive impacts of variable CO 2 level, light and zinc (Zn) addition on the diatom dominated phytoplankton assemblages from the western coastal Bay of Bengal. Increased CO 2 supply enhanced particulate organic matter (POC) production; a concomitant depletion in δ 13 C POM values at elevated CO 2 suggested increased CO 2 diffusive influx inside the cell. Trace amount of Zn added under low CO 2 level accelerated growth probably by accelerating Zn-Carbonic Anhydrase activity which helps in converting bicarbonate ion to CO 2 . Almost identical values of δ 13 C POM in the low CO 2 treated cells grown with and without Zn indicated a low discrimination between 13 C and 12 C probably due to bicarbonate uptake. These evidences collectively indicated the existence of the carbon concentration mechanisms (CCMs) at low CO 2 . A minimum growth rate was observed at low CO 2 and light limited condition indicating light dependence of CCMs activity. Upon the increase of light and CO 2 level, growth response was maximum. The cells grown in the low CO 2 levels showed higher light stress (higher values of both diatoxanthin index and the ratio of photo-protective to light-harvesting pigments) that was alleviated by both increasing CO 2 supply and Zn addition (probably by efficient light energy utilization in presence of adequate CO 2 ). This is likely that the diatom dominated phytoplankton communities benefited from the increasing CO 2 supply and thus may enhance primary production in response to any further increase in coastal water CO 2 levels and can have large biogeochemical consequences in the study area. [ABSTRACT FROM AUTHOR]

The ongoing rise in atmospheric CO concentration is causing rapid increases in seawater pCO levels. However, little is known about the potential impacts of elevated CO availability on the phytoplankton assemblages in the Southern Ocean's oceanic regions. Therefore, we conducted four incubation experiments using surface seawater collected from the subantarctic zone (SAZ) and the subpolar zone (SPZ) in the Australian sector of the Southern Ocean during the austral summer of 2011-2012. For incubations, FeCl solutions were added to reduce iron (Fe) limitation for phytoplankton growth. Ambient and high (~750 µatm) CO treatments were then prepared with and without addition of CO-saturated seawater, respectively. Non-Fe-added (control) treatments were also prepared to assess the effects of Fe enrichment (overall, control, Fe-added, and Fe-and-CO-added treatments). In the initial samples, the dominant phytoplankton taxa shifted with latitude from haptophytes to diatoms, likely reflecting silicate availability in the water. Under Fe-enriched conditions, increased CO level significantly reduced the accumulation of biomarker pigments in haptophytes in the SAZ and AZ, whereas a significant decrease in diatom markers was only detected in the SAZ. The CO-related changes in phytoplankton community composition were greater in the SAZ, most likely due to the decrease in coccolithophore biomass. Our results suggest that an increase in CO, if it coincides with Fe enrichment, could differentially affect the phytoplankton community composition in different geographical regions of the Southern Ocean, depending on the locally dominant taxa and environmental conditions. [ABSTRACT FROM AUTHOR]

The largest estuarine flow restoration project is the Comprehensive Everglades Restoration Plan (CERP). In 2012, one of its first phases, the C-111 Project, was initiated and designed to increase freshwater flow into northern Florida Bay. Effects of changes in flow and associated nutrients on phytoplankton abundance and composition were studied in two sets of interconnected, quasi-enclosed saline lakes at the southern end of the Everglades that discharge into northern Florida Bay. After C-111 implementation, total dissolved nitrogen (TDN) decreased, driven by especially large declines in [ABSTRACT FROM AUTHOR]

The rapid physical changes affecting the Arctic Ocean alter the growth conditions of primary producers. In this context, a crucial question is whether these changes will affect the composition of phytoplankton communities, augment their productivity, and eventually enhance food webs. We combined satellite and model products with in situ datasets collected during fall and provide new insights into the response of phytoplankton biomass and production in the Canadian Arctic by comparing an interior shelf (Beaufort Sea) and an outflow shelf (Baffin Bay). Correlation analysis was used to distinguish between seasonal and interannual variability and revealed that most biological variables are responding to the interannual pressures of climate change. In southeast Beaufort Sea, a change in phytoplankton community composition occurred, with a significant increase in diatoms from 2% (2002) to 37% (2010-2011) of the total protist abundance. In 2011, photosynthetic picoeukaryotes were twice as abundant as in 2002. For these two phytoplankton groups, abundance was correlated with the duration of the open-water period, which also increased and affected vertical stratification and sea-surface temperature. In contrast, there was a sharp decline in centric diatom abundance as well as in phytoplankton biomass and production in northern Baffin Bay over the years considered. These decreases were linked to changes in seasonal progression and sea-ice dynamics through their impacts on vertical stratification and freshwater input. Overall, our results highlight the importance of stratification and the duration of the open-water period in shaping phytoplankton regimes-either oligotrophic or eutrophic-in marine waters of the Canadian Arctic. [ABSTRACT FROM AUTHOR]

Carrying capacity estimations for any population of organisms is made in order to determine the maximum population densities that could result under set environmental conditions. Carrying capacity ( K ) is often used in terrestrial ecosystems to estimate potential plant densities (yields) related to the availability of resources. Here we wanted to see whether a similar concept could be applied to the plants of the ocean: Phytoplankton. Using the Helgoland Roads Time Series data sets, the main focus was on those which control phytoplankton growth in the ocean. We aimed to estimate K and determine whether K is static or variable, evaluated the relationship of phytoplankton K with higher trophic levels. We also provided a guideline to use K as ecosystem management tool. Algorithms were developed to estimate the K based on each controlling factor. A pair-wise comparison matrix was used for weighting the controlling factors and then to integrate the estimated K based on controlling factors to obtain an overall K . Long-term intra-annual and inter-annual mean K were estimated 10.13 × 10 7 cells m −3 and 1.30 × 10 8 cells m −3 , respectively. Our analyses suggest that K should not be considered as a static permanent value. This is because it is driven by overall environmental conditions and is subject to change when overall environment change. We linked the estimated K to pelagic fisheries data of the North Sea and found that phytoplankton K is correlated with the pelagic fisheries of this area. Our overall conclusion is that phytoplankton K is a viable concept and could be utilized as a valuable management tool. [ABSTRACT FROM AUTHOR]

Phytoplankton in a complex network of reservoirs for drinking water supply was sampled in the dry and flood seasons to understand the role of dispersal through hydrochory and of environmental filters in determining the phytoplankton abundance and composition. The main assumptions tested in the present study are that (i) phytoplankton structure in these waterbodies is strongly dependent on the transportation with the river waters flowing through them and (ii) the importance of this stochastic transportation is decreasing as the connectivity with the river decreases allowing environmental filters to shape phytoplankton structure. The multivariate analysis showed that although phytoplankton was inoculated largely by Pearl River water inputs and inflow among the system, the hydraulic architecture of the reservoir network shaped and modulated the composition and abundance of phytoplankton. [ABSTRACT FROM AUTHOR]

The chlorophyll-a (Chla) products of seven processors developed for the Medium Resolution Imaging Spectrometer (MERIS) sensor were evaluated. The seven processors, based on a neural network and band height, were assessed over an optically complex water body with Chla concentrations of 8.10–187.40 mg·m-3 using 10-year MERIS archival data. These processors were adopted for the Ocean and Land Color Instrument (OLCI) sensor. Results indicated that the four processors of band height (i.e., the Maximum Chlorophyll Index (MCI_L1); and Fluorescence Line Height (FLH_L1)); neural network (i.e., Eutrophic Lake (EUL); and Case 2 Regional (C2R)) possessed reasonable retrieval accuracy with root mean square error (R2) in the range of 0.42–0.65. However, these processors underestimated the retrieved Chla > 100 mg·m-3, reflecting the limitation of the band height processors to eliminate the influence of non-phytoplankton matter and highlighting the need to train the neural network for highly turbid waters. MCI_L1 outperformed other processors during the calibration and validation stages (R2 = 0.65, Root mean square error (RMSE) = 22.18 mg·m-3, the mean absolute relative error (MARE) = 36.88%). In contrast, the results from the Boreal Lake (BOL) and Free University of Berlin (FUB) processors demonstrated their inadequacy to accurately retrieve Chla concentration > 50 mg·m-3, mainly due to the limitation of the training datasets that resulted in a high MARE for BOL (56.20%) and FUB (57.00%). Mapping the spatial distribution of Chla concentrations across Lake Kasumigaura using the seven processors showed that all processors—except for the BOL and FUB—were able to accurately capture the Chla distribution for moderate and high Chla concentrations. In addition, MCI_L1 and C2R processors were evaluated over 10-years of monthly measured Chla as they demonstrated the best retrieval accuracy from both groups (i.e., band height and neural network, respectively). The retrieved Chla of MCI_L1 was more accurate at tracking seasonal and annual variation in Chla than C2R, with only slight overestimation occurring during the springtime. [ABSTRACT FROM AUTHOR]

Chytridiomycota, often referred to as chytrids, can be virulent parasites with the potential to inflict mass mortalities on hosts, causing e.g. changes in phytoplankton size distributions and succession, and the delay or suppression of bloom events. Molecular environmental surveys have revealed an unexpectedly large diversity of chytrids across a wide range of aquatic ecosystems worldwide. As a result, scientific interest towards fungal parasites of phytoplankton has been gaining momentum in the past few years. Yet, we still know little about the ecology of chytrids, their life cycles, phylogeny, host specificity and range. Information on the contribution of chytrids to trophic interactions, as well as co-evolutionary feedbacks of fungal parasitism on host populations is also limited. This paper synthesizes ideas stressing the multifaceted biological relevance of phytoplankton chytridiomycosis, resulting from discussions among an international team of chytrid researchers. It presents our view on the most pressing research needs for promoting the integration of chytrid fungi into aquatic ecology. [ABSTRACT FROM AUTHOR]

A study on indigenous microalgae from sluggish tidal freshwater/brackish mangrove dominated creeks(lto-lwolo) emptying into Lagos Lagoon was carried out for twelve months (February 2010 - January 2011).Samples were obtained using a 55 jum plankton net towed at low speed for 10 minutes. Various physico-chemical parameters were monitored; surface water temperature, P04-P, transparency, NO3-N, S04 2' and silica concentrations. All measured chemical parameters were lower in the rainy season while surface water pH ranged from slightly acidic to alkaline (6.42-8.70), chlorophyll 'a' showed its highest value 0.013[j.g/l in the dry season. There was a remarkable change in seasonal salinity values (14.90%o and 0.10%o) while conductivity values ranged between 0.01 and 20.00 (mS/cm) in raining and dry seasons, respectively. Microalgal flora was dominated by diatoms, which comprised of 85% of the total phytoplankton population with 75 species from 32 genera. Chlorophyta, recorded 9% and was represented by 31 species from 12 genera, while Cyanobacteria (4%) comprising of 17 species from 8 genera, and Euglenophyta, represented by one genus with 4 species recorded 2% of the total phytoplankton population. [ABSTRACT FROM AUTHOR]

Increased phosphorus (P) export from sediments to the overlying water column is a significant factor driving the variation of phytoplankton in productivity and community structure in lakes. However, the lack of long-term instrumental data often impeded analyses attempting to associate dynamics of phytoplankton with variation of internal P loading. Here, elements and lipid biomarkers were analyzed in a sediment core from Lake Heihai, a small, deep, and ultraoligotrophic alpine lake in Haba Mountain, Yunnan Province, SW China. The data document incredible enrichment of element iron (Fe) in the sediment, whose concentrations are much higher than those of other common major elements including titanium (Ti), aluminum (Al), calcium (Ca), and magnesium (Mg). This finding, together with the abundance correlation between P and Fe ( n = 30, R = 0.783) suggested that P was probably retained in sediments through sorption with micro-layer of FeOOH at the sediment-water interface. The P/Ti ratios, P/Fe ratios, and P/total organic carbon (TOC) ratios all declined in the sediment since 1980, perhaps indicating increased P release from sediments to the overlying water column initiated by hypolimnion anoxia and sulfidic, which is presumably triggered by regional climate warming since the 1980s. The P-rich bottom water can be injected into photic zone during wind-driven mixing and overturn of the water column, although its frequency and intensity might decline due to stronger water column stratification in warming climate. In response, diatoms exhibited a rapid increase of productivity at this time, because diatoms have a storage vacuole and thereby nutrients such as P can be concentrated and used for cell division long after they are depleted in the bulk fluid. Elevated diatom biomass produced shading of light penetration, allowing for a low productivity for dinoflagellates. This study deepens our understanding of the impact of climate warming on lake systems and highlights the element biogeochemical cycle contributing to the variation of nutrients in the lake water column. [ABSTRACT FROM AUTHOR]

The biomass and productivity of primary producers in the surf zone of the ocean beach at Wrightsville Beach, North Carolina, USA, were measured during all seasons, along with environmental parameters and nutrient levels. Variation in biomass (chlorophyll a ) was associated with temperature. Primary production (PP), measured by in situ 14-C incubations, was a function of chlorophyll a , tide height at the start of incubations, and rainfall in the preceding 24-hr period. Biomass-normalized production (P B ) was also a function of tide height and rainfall in the preceding 24-hr period. We interpreted these results as evidence of surf production 1) as combined contributions of phytoplankton and suspended benthic microalgae, which may confound application of simple P-E models to surf zone production, and 2) being regulated by nutrient source/supply fluctuations independently from other factors. Surf zone biomass and production levels are intermediate between relatively high estuarine values and much lower coastal ocean values. Surf zone production may represent an important trophic connection between these two important ecosystems. [ABSTRACT FROM AUTHOR]

Although both local processes (photosynthesis, respiration, grazing, and settling), and transport processes (advective transport and diffusive transport) significantly affect local phytoplankton dynamics, it is difficult to separate their contributions and to investigate the relative importance of each process to the local variability of phytoplankton biomass over different timescales. A method of using the transport rate is introduced to quantify the contribution of transport processes. By combining the time-varying transport rate and high-frequency observed chlorophyll a data, we can explicitly examine the impact of local and transport processes on phytoplankton biomass over a range of timescales from hourly to annually. For the Upper James River, results show that the relative importance of local and transport processes differs on different timescales. Local processes dominate phytoplankton variability on daily to weekly timescales, whereas the contribution of transport processes increases on seasonal to annual timescales and reaches equilibrium with local processes. With the use of the transport rate and high-frequency chlorophyll a data, a method similar to the open water oxygen method for metabolism is also presented to estimate phytoplankton primary production. [ABSTRACT FROM AUTHOR]

The Atlantic sector of the Southern Ocean is characterized by markedly different frontal zones with specific seasonal and sub-seasonal dynamics. Demonstrated here is the effect of iron on the potential maximum productivity rates of the phytoplankton community. A series of iron addition productivity versus irradiance (PE) experiments utilizing a unique experimental design that allowed for 24 h incubations were performed within the austral summer of 2015/16 to determine the photosynthetic parameters αB, PBmax and Ek. Mean values for each photosynthetic parameter under iron-replete conditions were 1.46±0.55 (μg (μg Chl a)-1 h-1 (μM photonsm-2 s-1/-1) for αB, 72.55±27.97 (μg (μg Chl a)-1 h-1) for PBmax and 50.84±11.89 (μM photons m-2 s-1) for Ek, whereas mean values under the control conditions were 1.25±0.92 (μg (μg Chl a)-1 h-1 (μM photonsm-2 s-1/-1) for αB, 62.44±36.96 (μg (μg Chl a)-1 h-1) for PB max and 55.81±19.60 (μM photonsm-2 s-1) for Ek. There were no clear spatial patterns in either the absolute values or the absolute differences between the treatments at the experimental locations. When these parameters are integrated into a standard depth-integrated primary production model across a latitudinal transect, the effect of iron addition shows higher levels of primary production south of 50° S, with very little difference observed in the subantarctic and polar frontal zone. These results emphasize the need for better parameterization of photosynthetic parameters in biogeochemical models around sensitivities in their response to iron supply. Future biogeochemical models will need to consider the combined and individual effects of iron and light to better resolve the natural background in primary production and predict its response under a changing climate. [ABSTRACT FROM AUTHOR]

This study is the first in situ work comparing rapid light curves (RLC) and non-sequential steady-state light curves (N-SSLC) in their efficiency to characterize phytoplankton photosynthetic activity and acclimation status. Measurements were carried out at two time scales (daily and annual) using the Pulse Amplitude Modulated fluorometry on samples taken in the coastal waters of a macrotidal ecosystem (the Strait of Dover, eastern English Channel). RLC and N-SSLC were compared under a wide range of environmental conditions and phytoplankton composition in order to define the best methodology to accurately capture short and long-term adjustments in the functioning of the photosynthetic apparatus. The relationships between the photosynthetic parameters extracted from RLC and N-SSLC were also studied to evaluate the possibility to use RLC to predict N-SSLC photosynthetic parameters and thus obtaining the acclimation status at steady state. At daily scale, the maximum electron transport rate and light saturation coefficient resulting from RLC (respectively, ETR and E ) were found to follow more closely short-term environmental light variations than ETR and E resulting from N-SSLC (ETR and E ) did. RLC were thus able to detect rapid changes in photosynthetic activity that would have been overlooked with N-SSLC measurements. At annual scale, few differences were found between RLC and N-SSLC. Variations of ETR and α derived from RLC and N-SSLC were very similar but absolute values were lower for RLC measurements. Because, at daily scale, RLC better capture the short-term changes in photosynthetic activity than N-SSLC do, using RLC to predict N-SSLC photosynthetic parameters and getting information about steady-state acclimation status is not possible at this time scale. However, this can be done at seasonal scale. [ABSTRACT FROM AUTHOR]

The distribution variation in chromophoric dissolved organic matter (CDOM) content in mid-latitude subtropical drinking water source reservoirs (MDWSRs) has great significance in the security of aquatic environments and human health. CDOM distribution is heavily influenced by biogeochemical processes and anthropogenic activity. However, little is known regarding the impact of component variation and phytoplankton growth on CDOM distribution variation in MDWSR. Therefore, samples were collected from a representative MDWSR (the Shanzai Reservoir) for analysis. CDOM absorption and fluorescence coupling with parallel factor analysis were measured and calculated. The results indicated that only two CDOM components were found in the surface water of Shanzai Reservoir, fulvic acid, and high-excitation tryptophan, originating from terrestrial and autochthonous sources, respectively. The types of components did not change with the season. The average molecular weight of CDOM increased in proportion to its fulvic acid content. The distribution variation in CDOM content mainly resulted from the variation in two CDOM components in summer and from high-excitation tryptophan in winter. Phytoplankton growth strongly influenced the distribution variation of CDOM content in summer; the metabolic processes of Cyanobacteria and Bacillariophyta consumed fulvic acid, while that of Cryptophyta produced high-excitation tryptophan. [ABSTRACT FROM AUTHOR]

The reproductive strategy of diatoms includes asexual and sexual phases, but in many species, including the model centric diatom Thalassiosira pseudonana, sexual reproduction has never been observed. Furthermore, the environmental factors that trigger sexual reproduction in diatoms are not understood. Although genome sequences of a few diatoms are available, little is known about the molecular basis for sexual reproduction. Here we show that ammonium reliably induces the key sexual morphologies, including oogonia, auxospores, and spermatogonia, in two strains of T. pseudonana, T. weissflogii, and Cyclotella cryptica. RNA sequencing revealed 1,274 genes whose expression patterns changed when T. pseudonana was induced into sexual reproduction by ammonium. Some of the induced genes are linked to meiosis or encode flagellar structures of heterokont and cryptophyte algae. The identification of ammonium as an environmental trigger suggests an unexpected link between diatom bloom dynamics and strategies for enhancing population genetic diversity. [ABSTRACT FROM AUTHOR]

Maputo Bay is highly affected by large tidal changes and riverine freshwater input with a phytoplankton biomass peak during March each year. Microscopy analysis was used to describe how the phytoplankton community composition was affected by tidal changes, during four in situ incubation experiments. Using stable isotope tracers, new and total primary production, based on nitrate ( 15 NO 3 − )- and carbon ( 13 C–bicarbonate)-assimilation were estimated. The highest biovolume of phytoplankton (> 2 μm) and also the highest C– and NO 3 − -assimilation rates (nM h −1 ) were found at spring-high tide. The C:N (mol:mol) ratio of particulate organic matter (POM) varied between 6.0 and 8.2. The proportion of diatoms in the phytoplankton community was higher at spring-high tide as compared to neap-low tide, whereas dinoflagellates were found in a reverse pattern. New production ranged between 6.3% and 10.4% of total primary production and was thus within the range previously reported for tropical regions. The largest proportion of NO 3 − -based new production relative to total production was estimated during calm conditions and spring-high tide. Concordantly, a large fraction of the microplanktonic community covered their N-demand by other sources of N than NO 3 − . [ABSTRACT FROM AUTHOR]

A variety of biomarkers were examined from Ocean Drilling Program Core 1202B to reconstruct temperature and phytoplankton community structures in the southern Okinawa Trough since 20 ka. Two molecular temperature proxies (U37K' and TEX86) show 5°C to ~6°C warming during the glacial-interglacial transition. Prior to the Holocene, The U37K' -derived temperature was generally 1°C to 4°C higher than TEX86-derived temperature. This difference, however, was reduced to <1°C in the Holocene. Correspondingly, the phytoplankton biomarkers (e.g., C37:2 alkenone, brassicasterol, C30 1,15 diol, and dinosterol) indicate a shift of planktonic community structures, with coccolithophorids becoming more abundant in the Holocene at the expense of diatoms/dinoflagellates. This shift is related to the variability of nutrients, temperature, and salinity in the Okinawa Trough, likely controlled by the sea level and the intensity of the Kuroshio Current. The phytoplankton community change may have had profound implications for atmospheric CO2 fluctuations during glacial-interglacial cycles since diatoms and dinoflagellates have a higher efficiency of the biological pump than coccolithophorids. [ABSTRACT FROM AUTHOR]

Predicting how freshwater biota respond to multiple stressors is currently a major challenge facing aquatic ecologists and environmental managers. Lake Simcoe is an ideal location to test the impact of multiple stressors on aquatic biota over time, as changes in climate warming, species invasions, nutrient loading, and human population growth have occurred throughout the last three decades., In this study, we used a suite of multivariate analyses to quantify the unique and interactive effects of physico-climatic, water quality, and biological variables in explaining phytoplankton community composition from 1986 to 2012., Changes in water quality, zooplankton abundance and community composition (following the invasion of Bythotrephes longimanus), euphotic zone temperature and thermal stability, and the invasion of zebra mussels ( Dreissena polymorpha) acting at different times throughout the period of record, were associated with major shifts in the phytoplankton community of Lake Simcoe: dominance of eutrophic diatoms and cyanobacteria from 1986 to 1997 shifted to chlorophytes after 1998, then again to a diverse mix of taxa represented by all major categories of algae after 2004., Contrary to expectation, we found little evidence that interactions between multiple stressors are taking place in Lake Simcoe. Instead, our results demonstrated the sequential nature of multiple stressors in influencing interannual variation in phytoplankton community structure. By occurring consecutively over time, we propose a 'sequence of stressors' has influenced the ecological health of the lake over the preceding three decades., Considered by category, biological stressors, followed by water quality, then temperature and climate, explained the largest amount of total variance in the phytoplankton data. The prominence of zooplankton community changes as significant predictors of phytoplankton community change throughout the period of record suggests the top-down effect of these herbivores are also very important., Our results highlight the importance of extensive ecosystem monitoring in determining ecosystem health. Our approach may assist in the management of other aquatic systems, where identifying when multiple stressors are not operating may simplify the management process, allowing remediation efforts to focus on the most impactful stressors as primary targets for ecosystem restoration. [ABSTRACT FROM AUTHOR]

Lake Baikal, Siberia, is the most biodiverse freshwater lake on Earth. However, despite decades of painstaking limnological research on Baikal, broad spatial data on nutrient (nitrogen (N), phosphorus (P), silica (Si)) concentrations and temperature are sparse, as is our understanding of the bottom-up factors that limit phytoplankton in the lake. Earlier studies have suggested both N and P as limiting nutrients in Baikal, but the evidence, mostly based on elemental ratios, is limited and somewhat conflicting. We present experimental evidence that N and P co-limit phytoplankton productivity in some areas of Baikal during summer, along with the results of a comprehensive spatial survey of surface temperature, nutrients and chlorophyll a (Chl a) in Lake Baikal that support the experimental finding of colimitation. Surface water incubations from two trophically contrasting locations revealed co-limitation by N and P, as well as a positive effect of temperature (fluorescence after 5 d was ∼10% higher at 15°C than at 10°C). In a linear model of the survey data (26 sampling locations), N, P, and their interaction (N × P) were all significant predictors of Chl a concentration, indicating that either N or P (or both) may limit summer phytoplankton, depending on location. In contrast to the incubation experiments, temperature was not a significant predictor of Chl a concentration across the 26 sites we sampled. Lake Baikal is undergoing rapid warming and increased nutrient loading, which may boost phytoplankton productivity in the lake; however, the magnitude of this response will depend on ratios of soluble N and P inputs. [ABSTRACT FROM AUTHOR]

Quantifying how environmental factors control the growth of phytoplankton communities is essential for building a mechanistic understanding of global biogeochemical cycles and aquatic food web dynamics. The strong effects of temperature on population growth rate have inspired two frameworks-the Eppley curve and the metabolic theory of ecology-that produce different quantitative relationships and employ distinct statistical approaches. Reconciling these relationships is necessary to ensure the accuracy of ecosystem models. In this paper, we develop ways to compare these frameworks, overcoming their methodological differences. Then, analyzing an extensive dataset (> 4200 growth rate measurements), we find that increases in population growth rate with temperature are consistent with metabolic theory, and weaker than previous estimates of the Eppley curve. A 10°C temperature increase will increase growth rates by a factor of 1.53, rather than 1.88 as in previous studies of the Eppley curve. Size and functional group membership are also critical. Population growth rates decrease with size, but much less strongly that metabolic theory predicts. The growth rates of different functional groups scale similarly with temperature, but some groups grow faster than others, independent of temperature. Our results reconcile the analytical methods of the Eppley curve and metabolic theory, demonstrate that metabolic theory's temperature-scaling predictions are more accurate, and provide new insights into the factors controlling phytoplankton growth. To avoid over-estimating the effects of temperature on primary productivity, the parameterization of ecosystem models should be revised. [ABSTRACT FROM AUTHOR]

There is general concern about the rapid decline in biodiversity. The consequences of biodiversity declines are expected to impact ecosystem functioning. Primary production is one of the ecosystem-functions where existing data already support such expectations. However, for a mechanistic understanding of these processes more experimental investigations are needed. In terrestrial primary producer communities a directed removal of species is one important tool in the experimental portfolio to study the consequences of a decline in biodiversity. However, this is notoriously difficult in suspended aquatic primary producer communities consisting of mostly unicellular phytoplankton. As phytoplankton are responsible for about 50% of global primary production, detailed knowledge of whether and how diversity declines will impact the functioning of natural phytoplankton communities is of crucial importance. Here, we tested two different methods, dilution and disturbance-to manipulate diversity of natural freshwater plankton communities along an experimental gradient in a directed way. Dilution will alter community composition by affecting mainly rare species whereas disturbance will affect mainly stress sensitive species. Both methods resulted in distinct and replicable species richness gradients. Such gradients enable the mechanistic study of general responses to biodiversity loss in natural phytoplankton communities with shared evolutionary history in an ecological meaningful way. [ABSTRACT FROM AUTHOR]

We established a new indoor mesocosm facility, 12 fully controlled 'Planktotrons', designed to conduct marine and freshwater experiments for biodiversity and food web approaches using natural or artificial, benthic or planktonic communities. The Planktotrons are a unique and custom-tailored facility allowing long-term experiments. Wall growth can be inhibited by a rotating gate paddle with silicone lips. Additionally, temperature and light intensity are individually controllable for each Planktotron and the large volume (600 L) enables high-frequency or volume-intense measurements. In a pilot freshwater experiment various trophic levels of a pelagic food web were maintained for up to 90 d. First, an artificially assembled phytoplankton community of 11 species was inoculated in all Planktotrons. After 22 d, two ciliates were added to all, and three Daphnia species were added to six Planktotrons. After 72 d, dissolved organic matter (DOM, an alkaline soil extract) was added as an external disturbance to six of the 12 Planktotrons, involving three Planktotrons stocked with Daphnia and three without, respectively. We demonstrate the suitability of the Planktotrons for food web and biodiversity research. Variation among replicated Planktotrons ( n = 3 minimum) did not differ from other laboratory systems and field experiments. We investigated population dynamics and interactions among the different trophic levels, and found them affected by the sequence of ciliate and Daphnia addition and the disturbance caused by addition of DOM. [ABSTRACT FROM AUTHOR]

In situ oxygen tracers (triple oxygen isotope and oxygen/argon ratios) were used to evaluate meridional trends in surface biological production and export efficiency across ~8000 km of the tropical and subtropical South Atlantic in March-May 2013. We used observations of picophytoplankton, nanophytoplankton, and microphytoplankton to evaluate community structure and diversity and assessed the relationships of these characteristics with production, export efficiency, and particulate organic carbon (POC) fluxes. Rates of productivity were relatively uniform along most of the transect with net community production (NCP) between 0 and 10 mmol O2 m−2 d−1, gross primary production (GPP) between 40 and 100 mmol O2 m−2 d−1, and NCP/GPP, a measure of export efficiency, ranging from 0.1 to 0.2 (0.05-0.1 in carbon units). However, notable exceptions to this basin-scale homogeneity included two locations with highly enhanced NCP and export efficiency compared to surrounding regions. Export of POC and particulate nitrogen, derived from sediment traps, correlated with GPP across the transect, over which the surface community was dominated numerically by picophytoplankton. NCP, however, did not correlate with POC flux; the mean difference between NCP and POC flux was similar to published estimates of dissolved organic carbon export from the surface ocean. The interrelated rates of production presented in this work contribute to the understanding, building on the framework of better-studied ocean basins, of how carbon is biologically transported between the atmosphere and the deep ocean. [ABSTRACT FROM AUTHOR]

Changes in the abundance of a taxon can have large effects on communities, particularly if that taxon is a strong interactor. These changes may arise as a consequence of environmental change, recruitment from dormant stages, or quirks of population dynamics, and have effects that ripple through a community interaction network. We hypothesized that cyanobacteria, which are increasing in many freshwater lakes globally, may be strong interactors because they can exert large and persistent effects on the biomass and composition of other phytoplankton. To test this hypothesis, we evaluated how the phytoplankton community responded to different densities of Gloeotrichia echinulata, a large colonial cyanobacterium increasingly observed in low-nutrient lakes in northeastern North America, in an in situ mesocosm experiment. We observed that many phytoplankton taxa, especially diatoms and green algae, responded primarily to increased nutrient availability (a result of Gloeotrichia's nitrogen fixation and translocation of phosphorus from the sediments), while a few taxa (two euglenophytes, one dinoflagellate, and one cyanobacterium) responded to both the direct and indirect effects of Gloeotrichia. Surprisingly, Gloeotrichia reduced the compositional variability of the phytoplankton community relative to the non-Gloeotrichia control treatment; there was no effect on the aggregate temporal variability of total non-Gloeotrichia biovolume. Moreover, experimentally increased densities of Gloeotrichia coincided with increasing complexity of the phytoplankton community in network analyses of taxon co-occurrences, as indicated by significantly greater network density and transitivity and shorter path lengths. Taken together, these findings suggest that Gloeotrichia may be a strongly interacting species in low-nutrient lakes, with the potential to increase the resilience of phytoplankton communities to future disturbance by increasing compositional stability and network complexity. [ABSTRACT FROM AUTHOR]

The spring phytoplankton bloom is a major, extensively studied phenomenon in temperate oceans. Much less is known about blooms in subtropical seas. Yet, even in temperate seas the processes determining the initiation of the bloom and the phytoplankton dynamics during the preceding mixed-layer deepening are still debated. Here we assess the validity of two bloom-initiation mechanisms, previously proposed for temperate oceans, for the case of the subtropical oligotrophic Gulf of Aqaba (northern Red Sea): the Critical Depth Hypothesis and the Dilution-Recoupling Hypothesis. The Gulf is a unique water body, where convective mixing during winter reaches hundreds of meters in depth, entraining nutrients that support conspicuous spring blooms. Our study is based on a long time series of oceanographic and meteorological parameters complemented with experimental measurements of grazing rates. We show that neither the Critical Depth nor the Dilution-Recoupling hypotheses explain the phytoplankton dynamics during the winter and spring in the Gulf. Instead, we suggest that the phytoplankton dynamics is governed by a “Dispersion-Confinement Mechanism”. During winter, phytoplankton cells that photosynthesize and grow in the upper (illuminated) layer are homogeneously dispersed by vertical mixing. Thereby the deepening of the mixed layer leads to the dilution of the cells with plankton-free water from below, which together with grazing, maintain their relatively low concentration. Once mixing stops, the cells are no longer vertically dispersed, allowing their accumulation in the upper layer and, in turn, the development of the spring bloom. High specific growth rates, necessary to maintain the increase of the entire (integrated) phytoplankton biomass during the deepening of the mixed layer (the “Dispersion Phase”) as well as supporting their rapid growth during the bloom (the “Confinement Phase”) are possible due to the entrainment of nutrients by deep vertical mixing. Although this mechanism is proposed here for the case of a nutrient-limited oligotrophic sea, its relevance for temperate oceans deserves further consideration. [ABSTRACT FROM AUTHOR]

Human impacts on carbon, nitrogen and phosphorus cycles have differentially increased the flux of C, N and P to the coastal zone creating an altered environment with respect to nutrient stoichiometry for production and transfer of organic matter. Such changes can be more pronounced in closed and semi-enclosed ecosystems. The spatio-temporal variability in chl a, phytoplankton C, N and P content and stoichiometry were measured along with nutrients to reveal relations between them in a coastal lagoon. High nitrate concentrations and low availability of phosphate produced skewed nutrient stoichiometry that reflected itself in the large deviations of PC:PN and PN:PP from their corresponding Redfield ratios while the dynamic nature of fluctuations in nutrient concentrations led to wide variations in phytoplankton C, N and P content and in their ratios. The findings of the study provide insights into the possible alterations in phytoplankton stoichiometry in similar ecosystems receiving high inputs which is not balanced with phosphorus and/or where P-reduction is the mode of eutrophication control as both can produce skewed nutrient stoichiometry. [ABSTRACT FROM PUBLISHER]

Evaluation of hydrological data obtained between 2000 and 2013 from a time series station in Kuwait Bay (station K6) and an offshore southern location (station 18) off Kuwait showed drastic increase in salinity by 6 units. We tested the hypothesis that increased salinity impacted phytoplankton community characteristics in these semiarid waters. The Arabian Gulf receives seasonal freshwater discharge in the north via Shatt Al-Arab estuary with a peak during March-July. A north to south gradient in the proportion of the freshwater exists between station A in the vicinity of Shatt Al-Arab estuary and station 18 in the southern offshore area. At station A, the proportion of freshwater was the highest (25.6-42.5%) in 1997 but decreased to 0.8-4.6% by 2012-2013. The prevailing hyperhaline conditions off Kuwait are attributed to decrease in the river flow. Phytoplankton data showed a decrease in the number of constituent taxa in the last one decade from 353 to 159 in the Kuwait Bay and from 164 to 156 in the offshore area. A shift in their biomass was caused by a decrease in diatom species from 243 to 92 in the coastal waters and from 108 to 83 in the offshore areas with a concomitant increase of smaller algae. Mutivariate agglomerative hierarchical cluster analysis, non-metric multi-dimensional scaling, and one-way analysis of similarity analyses on phytoplankton data at different taxonomic levels confirmed significant changes in their community organization on a decadal scale. These evidences support our hypothesis that the salinity-related environmental changes have resulted in a coincidental decrease in species diversity and significant changes in phytoplankton community between the years 2000-2002 and 2012-2013, off Kuwait. This in turn would affect the pelagic trophodynamics as evident from a drastic decrease in the catch landings of Tenulosa ilisha (Suboor), Carangoides sp. (Hamam), Otolithes ruber (Nowaiby), Parastromateus niger (Halwaya), and Epinephelus coioides (Hamoor) in Kuwait. [ABSTRACT FROM AUTHOR]

Based on the investigation in waters around Nanri Island in spring and autumn of 2011, we analyzed spatial and temporal changes in species, abundance and diversity index of phytoplankton, and explored the relation between phytoplankton community structure and environment. The result showed that 106 species of phytoplankton, in 48 genera were identified, wherein diatom was the dominant species in abundance. Abundance in spring was significantly higher than that in autumn, ecological groups feature eurythermal and warm water species. Investigation showed that the heterogeneity of the marine environment of was high, and phytoplankton species diversity was low. Salinity and nutrients, as two major factors that influenced temporal and spatial variation of phytoplankton distribution abundance, were significantly correlated with phytoplankton abundance in spring. Compared to islands survey data during 1990-1991, dominant species were mainly few species, which succeed from domination of both dinoflagellate and diatom to domination of diatom. [ABSTRACT FROM AUTHOR]

High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO2 levels ranging from ambient (343 μatm) to 1641 μatm in six 650 l minicosms. Productivity assays were performed to identify whether a CO2 threshold existed that led to a decline in primary productivity, bacterial productivity, and the accumulation of Chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140 μatm. CO2 levels ≥ 1140 μatm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csPP14C), causing significant reductions in gross primary production (GPP14C), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO2 on C : N ratios. Over time, the phytoplankton community acclimated to high CO2 conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO2 treatments ≥ 953 μatm (days 3-5), yet gross bacterial production (GBP14C) remained unchanged and cell-specific bacterial productivity (csBP14C) was reduced. Towards the end of experiment, GBP14C and csBP14C markedly increased across all treatments regardless of CO2 availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Such changes in phytoplankton community production could have negative effects on the Antarctic food web and the biological pump, resulting in negative feedbacks on anthropogenic CO2 uptake. Increases in bacterial abundance under high CO2 conditions may also increase the efficiency of the microbial loop, resulting in increased organic matter remineralisation and further declines in carbon sequestration. [ABSTRACT FROM AUTHOR]

The effects of ongoing changes in ocean carbonate chemistry on plankton ecology have important implications for food webs and biogeochemical cycling. However, conflicting results have emerged regarding species-specific responses to p CO2 enrichment and thus community responses have been difficult to predict. To assess community level effects (e.g., production) of altered carbonate chemistry, studies are needed that capitalize on the benefits of controlled experiments but also retain features of intact ecosystems that may exacerbate or ameliorate the effects observed in single-species or single cohort experiments. We performed incubations of natural plankton communities from Narragansett Bay, RI, USA in winter at ambient bay temperatures (5–13 °C), light and nutrient concentrations. Three levels of controlled and constant CO 2 concentrations were imposed, simulating past, present and future conditions at mean p CO 2 levels of 224, 361, and 724 μatm respectively. Samples for carbonate analysis, chlorophyll a , plankton size-abundance, and plankton species composition were collected daily and phytoplankton growth rates in three different size fractions (<5, 5–20, and >20 μm) were measured at the end of the 7-day incubation period. Community composition changed during the incubation period with major increases in relative diatom abundance, which were similar across p CO 2 treatments. At the end of the experiment, 24-hr growth responses to p CO 2 levels varied as a function of cell size. The smallest size fraction (<5 μm) grew faster at the elevated p CO 2 level. In contrast, the 5–20 μm size fraction grew fastest in the Present treatment and there were no significant differences in growth rate among treatments in the >20 μm size fraction. Cell size distribution shifted toward smaller cells in both the Past and Future treatments but remained unchanged in the Present treatment. Similarity in Past and Future treatments for cell size distribution and growth rate (5–20 μm size fraction) illustrate non-monotonic effects of altered p CO 2 on ecological indicators and may be related to opposing physiological effects of high CO 2 and low pH both within and among species. Interaction of these effects with other factors (e.g., nutrients, light, temperature, grazing, initial species composition) may explain variability among published studies. The absence of clear treatment-specific effects at the community level suggests that extrapolation of species-specific responses or experiments with only present day and future p CO 2 treatments levels could produce misleading predictions of ocean acidification impacts on plankton production. [ABSTRACT FROM AUTHOR]

Starting in September 2010, a monitoring program was developed for evaluating the water quality in six artificial lakes (reservoirs) of the Apulia Region (Southern Italy). Lake ecological status was evaluated according to the requirements of the 2000/60/EC Water Framework Directive. Phytoplankton taxonomic composition, biovolume and chlorophyll a data were used in an application of the Italian methods (Italian Phytoplankton Assessment Method or New Italian Method) for water quality assessment of artificial lakes. Even though all the reservoirs were classified as being in good ecological status, the phytoplankton communities of the six reservoirs were different and characterized by highly site-specific components and by distinctive dominant taxa. The influences of environmental variables on the phytoplankton communities were analyzed. Results of Constrained Coordinate Analysis (CCA) indicated strong influences of the trophic gradient and water depth on the phytoplankton assemblages, but significant factors are also the surrounding landscape and the origin and the history of the lakes. A functional traits-based analysis was carried out to support the water quality assessment tools. Twenty-one morpho-functional groups were identified. Most of them were common in all six lakes, so functional properties clearly recur among different phytoplankton species. [ABSTRACT FROM AUTHOR]

Environmental mechanisms that drive changes in phytoplankton community structure remain a remarkably understudied topic in phytoplankton ecology. For this study, two seasons and four sampling sites in the Florida Keys (FK) were selected for phytoplankton analyses to test if environmental constraints select for driving taxonomic diversity. One hundred and twenty-six taxa belonging to 10 classes and 6 phyla were identified, where significant differences in taxonomic composition and biovolume characterized the FK on spatial and temporal scales, with Bacillariophyta being the most representative phylum. A small number of taxa were limited to specific sites or seasons, whereas the majority were present at all sites and in both seasons, albeit in different densities. Canonical correspondence analysis results demonstrated that taxa are distributed along seasonal and spatial gradients defined by temperature, light and waves. The resultant variability in species composition indicates that the phytoplankton community structure is related to changing hydrodynamic conditions, temperature and light availability, which define the temporal and spatial filters for the most important phytoplankton functional groups observed in this study. [ABSTRACT FROM AUTHOR]

In the context of maintenance of biodiversity and ecological functions, microbial ecologists face the challenge of linking individual level variability in functional traits to larger scale ecosystem processes. Phytoplankton cell size and shape are key traits under selection by environmental filters and species interactions. Spatial differences in resource availability shape species diversity according to their use efficiency. Niche partitioning promotes plankton diversity. Here, we explore how size and shape enter the diversity game. How does taxonomic and morpho-functional community structure vary at different spatial scales? What are the potential drivers shaping the structure of phytoplankton communities? We explore these questions by looking at the individual level variability in taxonomic and morphological traits in a biogeographical snapshot of natural phytoplankton communities in coastal ecosystems around the globe. We found that taxonomic variability is mainly concentrated at local and regional levels, whereas shape and size variability are mainly concentrated at a local level, despite the environmental heterogeneity of ecosystems. Species diversity was more variable than trait diversity from local to global spatial scales. We suggest that structural organization of phytoplankton communities in coastal ecosystems may follow a hierarchical pattern of trait organization, where a different combination of multiple functional traits may represent effective strategies and promote success under given environmental conditions as a resolution of Hutchinson's paradox. [ABSTRACT FROM AUTHOR]

The fluxes of energy, matter, and organisms are important structuring forces of metaecosystems. Such ecosystem fluxes likely interact with environmental heterogeneity and differentially affect the diversity of multiple communities. In an aquatic mesocosm experiment, we tested how ecosystem flux and patch heterogeneity affected the diversity of bacteria, phytoplankton, and zooplankton metacommunities, and the structure and functioning of metaecosystems. We built metaecosystems consisting of three mesocosms that were either connected by flux of living organisms, organic material, and nutrients (alive ecosystem flux) or only by flux of organic material and nutrients (dead ecosystem flux). The three patches of each metaecosystem were either homogeneous or heterogeneous in nutrient loading. We found that the three groups of organisms responded differently to our treatments: flux of living organisms increased bacterial diversity irrespective of nutrient heterogeneity, while flux effects on phytoplankton diversity depended on nutrient heterogeneity, potentially indicating source-sink effects. Although zooplankton diversity was largely unaffected by our manipulations, subtle changes of community composition in response to ecosystem flux had strong effects on lower trophic levels, highlighting the importance of indirect flux effects via alterations in trophic interactions. Furthermore, differential effects of communities on the mean and spatial variability of local abiotic environments influenced the development of metaecosystem heterogeneity through time. Despite identical nutrient loading at the scale of the metaecosystem, abiotic conditions diverged between homogeneous and heterogeneous metaecosystems. For example, concentrations in dissolved organic carbon ( DOC) were higher in homogeneous than heterogeneous metaecosystems, possibly because of differential responses of the algal community to local environmental conditions. Similarly, we found that flux effects on organisms translated into effects on DOC concentrations at the patch level, suggesting that flux-mediated changes in abundances of species can alter abiotic conditions. Our study shows that the dynamics of biotic and abiotic compartments of spatially structured ecosystems are intricately linked, highlighting the importance of integrating metacommunity and metaecosystem perspectives. [ABSTRACT FROM AUTHOR]

Diversity plays critical roles in ecosystem functioning, but it remains unclear how best to model phytoplankton diversity in order to better understand those roles and reproduce consistently observed patterns in the ocean. In contrast to the typical approach of resolving distinct species or functional groups, we present a ContInuous TRAiT-basEd phytoplankton model (CITRATE) that focuses on macroscopic properties such as total biomass, mean trait values, and trait variance. This phytoplankton component is embedded within a Nitrogen-Phytoplankton-Zooplankton-Detritus-Iron model that itself is coupled with a simplified one-dimensional ocean model. Size is used as the master trait for phytoplankton. CITRATE also incorporates "trait diffusion" for sustaining diversity, as well as simple representations of physiological acclimation, i.e. flexible chlorophyll-to-carbon and nitrogen-to-carbon ratios. We implemented CITRATE 1.0 at two contrasting stations in the Northwest Pacific where several years of observational data are available. The model is driven by physics forcing including vertical eddy diffusivity imported from three-dimensional ocean circulation models. One common set of model parameters for the two stations was optimized using the Delayed Rejection Adaptive Metropolis-Hasting Monte Carlo (DRAM) algorithm. The model faithfully reproduced most of the observational patterns and gave robust predictions on phytoplankton mean size and size diversity. With proper physical forcing, CITRATE 1.0 can be applied to any oceanic station where either nitrogen or iron limits phytoplankton growth. [ABSTRACT FROM AUTHOR]

Phytoplankton community structure and their physiological response in the vicinity of the Antarctic Polar Front (APF; 44°S to 53°S, centred at 10°E) were investigated as part of the ANT-XXVIII/3 Eddy-Pump cruise conducted in austral summer 2012. Our results show that under iron-limited ( < 0.3 μ mol m − 3 ) conditions, high total chlorophyll-a (TChl-a) concentrations ( > 0.6 mg m − 3 ) can be observed at stations with deep mixed layer ( > 60 m ) across the APF. In contrast, light was excessive at stations with shallower mixed layer and phytoplankton were producing higher amounts of photoprotective pigments, diadinoxanthin (DD) and diatoxanthin (DT), at the expense of TChl-a, resulting in higher ratios of (DD+DT)/TChl-a. North of the APF, significantly lower silicic acid (Si(OH) 4 ) concentrations ( < 2 mmol m − 3 ) lead to the domination of nanophytoplankton consisting mostly of haptophytes, which produced higher ratios of (DD+DT)/TChl-a under relatively low irradiance conditions. The Si(OH) 4 replete ( > 5 mmol m − 3 ) region south of the APF, on the contrary, was dominated by microphytoplankton (diatoms and dinoflagellates) with lower ratios of (DD+DT)/TChl-a, despite having been exposed to higher levels of irradiance. The significant correlation between nanophytoplankton and (DD+DT)/TChl-a indicates that differences in taxon-specific response to light are also influencing TChl-a concentration in the APF during summer. Our results reveal that provided mixing is deep and Si(OH) 4 is replete, TChl-a concentrations higher than 0.6 mg m − 3 are achievable in the iron-limited APF waters during summer. [ABSTRACT FROM AUTHOR]

The biochemical composition of particulate organic matter (POM) produced through phytoplankton photosynthesis is important in determining food quality for planktonic consumers as well as the physiological conditions of phytoplankton. Major environmental factors controlling the biochemical composition were seasonally investigated in Gwangyang Bay, South Korea, which has only natural conditions (e.g., no artificial dams). Water samples for the biochemical compositions were obtained from three different light depths (100, 30, and 1 %) mainly at three sites in Gwangyang Bay from April 2012 to April 2013. Different biochemical classes (carbohydrates, CHO; proteins, PRT; and lipids, LIP) were extracted, and then the concentrations were determined by the optical density measured with a spectrophotometer. The highest and lowest PRT compositions among the three biochemical classes were found in April 2012 (58.0 %) and August 2012 (21.2 %), whereas the highest and lowest LIP compositions were found in August 2012 (49.0 %) and April 2012 (24.8 %), respectively. The CHO composition was recorded as high in January 2013 and remained above 25% during the study period. The calorific contents of the food material (FM) ranged from 1.0 to 6.1 Kcalm-3 (annual average ±SD = ±1.1 Kcal m-3). Based on a Pearson's correlation coefficient analysis, a major governing factor in the biochemical composition of POM was dissolved inorganic nitrogen loading from the river input in Gwangyang Bay. In conclusion, a relatively larger amount of FM and the higher calorific contents of POM found in this study compared to other regions reflected good nutritive conditions for sustaining productive shellfish and fish populations in Gwangyang Bay. Continuous observations are needed to monitor the marine ecosystem response to potential environmental perturbations in Gwangyang Bay. [ABSTRACT FROM AUTHOR]

Anthropogenic activities resulted in major shifts in nutrient inputs to coastal seas, which may have altered the biomolecule composition of phytoplankton because of different C : N : P requirements for biosynthesis. In order to understand the effects of N- and P-limitation on the allocation of photosynthetically fixed C, we directly measured seasonal and spatial dynamics of amino acid, fatty acid and carbohydrate concentrations and biosynthesis rates in the phytoplankton of the North Sea using a novel 13C-tracer approach. Nutrient limitation and season had large effects on composition and biosynthesis rates of all biochemical classes, for instance the contribution of protein derived amino acids varied up to fourfold in concentration and up to eightfold in biosynthesis rates. Nutrient specific effects and the prevailing nutrient limitations were identified by short-term (24-72 h) nutrient addition experiments. Addition of the growth-limiting nutrient increased amino acid synthesis while storage compound synthesis decreased concurrently. The strongest effect was detected in N-limited flagellates, where amino acid synthesis increased up to fivefold within 24 h upon relief of nutrient limitation. P-limitation was only detected in diatom-dominated near-coast stations, and amino acid synthesis responded much slower, likely because of the necessary preceding synthesis of ribosomes. This metabolic elasticity of phytoplankton in response to nutrient availability will have major consequences for their nutritional value within the food web and subsequently the carrying capacity of coastal ecosystems. [ABSTRACT FROM AUTHOR]

The fine vertical distribution of phytoplankton groups within the deep chlorophyll maximum (DCM) was studied in the NE Atlantic during summer stratification. A simple but unconventional sampling strategy allowed examining the vertical structure with ca. 2 m resolution. The distribution of Prochlorococcus, Synechococcus, chlorophytes, pelagophytes, small prymnesiophytes, coccolithophores, diatoms, and dinoflagellates was investigated with a combination of pigment-markers, flow cytometry and optical and FISH microscopy. All groups presented minimum abundances at the surface and a maximum in the DCM layer. The cell distribution was not vertically symmetrical around the DCM peak and cells tended to accumulate in the upper part of the DCM layer. The more symmetrical distribution of chlorophyll than cells around the DCM peak was due to the increase of pigment per cell with depth. We found a vertical alignment of phytoplankton groups within the DCM layer indicating preferences for different ecological niches in a layer with strong gradients of light and nutrients. Prochlorococcus occupied the shallowest and diatoms the deepest layers. Dinoflagellates, Synechococcus and small prymnesiophytes preferred shallow DCM layers, and coccolithophores, chlorophytes and pelagophytes showed a preference for deep layers. Cell size within groups changed with depth in a pattern related to their mean size: the cell volume of the smallest group increased the most with depth while the cell volume of the largest group decreased the most. The vertical alignment of phytoplankton groups confirms that the DCM is not a homogeneous entity and indicates groups' preferences for different ecological niches within this layer. [ABSTRACT FROM AUTHOR]

Heterocapsa rotundata is a mixotrophic dinoflagellate that can ingest picoplankton, including bacteria, and is known to form large blooms in temperate estuaries during wet winters, particularly when grazing pressure on phytoplankton is low. We hypothesized that phagotrophy gives H. rotundata an advantage over other phytoplankton species during low light conditions. We used laboratory and field experiments to investigate changes in phagotrophy by H. rotundata in response to changes in light availability. Prey removal experiments with a non-axenic culture of H. rotundata were used to determine changes in H. rotundata's ingestion rates in response to changes in irradiance. Fluorescent microspheres were used to measure in situ ingestion rates of H. rotundata collected on 20 different occasions from the Choptank River during the winter of 2016. In situ H. rotundata ingestion rates were tested for correlation with inorganic nutrient concentrations and irradiance levels. Ingestion rates measured with cultured and in situ H. rotundata followed similar patterns and ingestion rates increased as irradiance decreased. H. rotundata has the potential to obtain nutrients from multiple nutrient sources, switching from phototrophy to partial heterotrophy as irradiance decreases. This response may allow H. rotundata to survive and to potentially form blooms when growth rates of most other estuarine phytoplankton species is low. [ABSTRACT FROM AUTHOR]

As part of the ANACONDAS program, we investigated the role of the Amazon plume in stimulating offshore nitrogen fixation and export production during the river's high-discharge period (May-June 2010). Using the shipboard underway system, we performed high-resolution sampling of over 450,000 km2 of surface waters, characterizing the distribution of nutrients, phytoplankton, particulate organic matter (POM), and stable carbon and nitrogen isotopes of POM in the offshore plume. We found distinct regional variations in diazotroph communities, with the Diatom-Diazotroph Associations (DDA) Hemiaulus hauckii - Richelia intracellularis dominating the low N : P mesohaline waters to the northwest of the plume axis and Trichodesmium spp. primarily occupying oceanic waters to the east. Nutrient availability broadly shaped diazotroph distributions along the salinity gradient, but habitat longevity may also play a role in the finer-scale distributions of communities, particularly of DDAs. H. hauckii and Trichodesmium spp. affected the nitrogen and carbon budgets in fundamentally different ways within the plume-influenced regions, with H. hauckii making much greater contributions to the particulate nitrogen pool and to CO2 drawdown than Trichodesmium spp., leading to much higher export fluxes. Our findings provide an important constraint on the role of the Amazon plume in creating distinct niches and roles for diazotrophs in the nutrient and carbon budgets of the western tropical North Atlantic. [ABSTRACT FROM AUTHOR]

The dissolved nitrogen (DN) regime in Jiaozhou Bay (JB) has shifted recently, and the phytoplankton community structure showed decreased diatom and increased dinoflagellate concentrations. This study combined field microcosm experiments, the Nutrients–bi-Phytoplankton–Detritus (NbPD) biogeochemical model, and statistical analysis, and obtained some results. The growth/death of dominant phytoplankton populations were comprehensively determined by the processes of nutrient uptake, excretion and decomposition of phytoplankton in JB. Kinetic parameters indicated that Skeletonema costatum preferentially absorbed NH 4 -N and NO 3 -N, while Protoperidinium pellucidum preferentially absorbed domestic-derived dissolved organic nitrogen. Moreover, S. costatum , as R-strategists, needed a faster uptake rate and slower excretion rate to achieve high growth efficiency but with faster decomposition, while P. pellucidum , as K-strategists, could maintain stability with a more active metabolism. Overall, this study discussed the key factors modulating the diatom dinoflagellate community structure changes in JB, providing a scientific basis for ecosystem-based management. • Impact of dissolved nitrogen on dominant algal species structure in Jiaozhou Bay. • Algal regime shift mechanism with dissolved nitrogen structure in coastal waters. • Skeletonema costatum efficiently absorbed NH 4 -N and NO 3 -N. • Peridinium pellucidum preferentially absorbed domestic-derived dissolved organic nitrogen. • Shift from water quality-based to ecosystem-based environmental management. [ABSTRACT FROM AUTHOR]

• Eukaryotic algae sharply increased when the water discharge increased. • Synechococcus and Cyanobium dominated in phytoplankton communities. • Phytoplankton dynamics influence the natural abundance of H 2 O 2. • A H 2 O 2 peak was found when Dolichospermum dominance was ended, and Microcystis increased. • A high correlation was found between H 2 O 2 and microcystin (r = 0.83, p < 0.01). Phytoplankton communities are major primary producers in the aquatic realm and are responsible for shaping aquatic ecosystems. The dynamics of algal blooms could be determined by a succession of variable taxonomic groups, which are altered based on complex environmental factors such as nutrient availability and hydraulic factors. In-river structures potentially increase the occurrence of harmful algal blooms (HABs) by increasing water residence time and deteriorating water quality. How flowing water stimulates cell growth and affects the population dynamics of phytoplankton communities is a prioritized question that needs to be addressed for water management tactics. The goal of this study was to determine if an interaction between water flow and water chemistry is present, furthermore, to determine the relationship among phytoplankton community successions in the Caloosahatchee River, a subtropical river strongly influenced by human-controlled water discharge patterns from Lake Okeechobee. Particularly we focused on how phytoplankton community shifts influence the natural abundance of hydrogen peroxide, the most stable reactive oxygen species and a byproduct of oxidative photosynthesis. High-throughput amplicon sequencing using universal primers amplify 23S rRNA gene in cyanobacteria and eukaryotic algal plastids revealed that Synechococcus and Cyanobium were the dominant cyanobacterial genera and their relative abundance ranged between 19.5 and 95.3% of the whole community throughout the monitoring period. Their relative abundance declined when the water discharge increased. On the contrary, the relative abundance of eukaryotic algae sharply increased after water discharge increased. As water temperature increased in May, initially dominant Dolichospermum decreased as Microcystis increased. When Microcystis declined other filamentous cyanobacteria such as Geitlerinema, Pseudanabaena , and Prochlorothreix increased in their relative abundances. Interestingly, a peak of extracellular hydrogen peroxide was observed when Dolichospermum dominance was ended, and M. aeruginosa numbers increased. Overall, phytoplankton communities were strongly impacted by human-induced water discharge patterns. [ABSTRACT FROM AUTHOR]

The viability of algal cells is one of the most fundamental issues in marine ecological research. In this work, a method was designed to identify algal cell viability based on digital holography and deep learning, which divided algal cells into three categories: active, weak, and dead cells. This method was applied to measure algal cells in surface waters of the East China Sea in spring, revealing about 4.34 %–23.29 % weak cells and 3.98 %–19.47 % dead cells. Levels of nitrate and chlorophyll a were the main factors affecting the viability of algal cells. Furthermore, algal viability changes during the heating and cooling were observed in laboratory experiments: high temperatures led to an increase in weak algal cells. This may provide an explanation for why most harmful algal blooms occur in warming months. This study provided a novel insight into how to identify the viability of algal cells and understand their significance in the ocean. [Display omitted] • Based on viability, we divided algal cells into active, weak, and dead cells. • We found 4.34 %–23.29 % weak and 3.98 %–19.47 % dead cells in the East China Sea. • The nitrate level had the greatest effect on the viability of algal cells. • The warming process was more conducive to the occurrence of harmful algal blooms. [ABSTRACT FROM AUTHOR]