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Eutrophication, climate change, and river flow fragmentation are the main cause of nuisance algal blooms worldwide. This study evaluated the conditions that trigger the growth and occurrence of nuisance phytoplankton in the Santa Lucía River, a subtropical floodplain lotic system that supplies drinking water to 60% of the population of Uruguay. The main variables that explained phytoplankton biovolume were extracted from generalized linear models (GLM). The potential impact of nuisance organism advection on water utility was estimated by the phytoplankton biovolume transport (BV TR , m 3 day -1 ), an indicator of biomass load. Santa Lucía River had a wide flow range (0.7×10 5 -1438×10 5 m 3 day -1 ) and eutrophic conditions (median, TP: 0.139 mg L -1 ; TN: 0.589 mg L -1 ). GLMs indicated that phytoplankton biomass increased with temperature and soluble reactive phosphorus. Contrary to expectations, the presence of cyanobacteria was positively associated with periods of high flow that result in high cyanobacterial biovolume transport, with a probability of 3.35 times higher when flow increased by one standard deviation. The cyanobacterial biovolume transported (max: 9.5 m 3 day -1 ) suggests that biomass was subsidized by allochthonous inocula. Biovolume from other nuisance groups (diatoms, cryptophytes, and euglenophytes) was positively associated with low-flow conditions and high nutrient concentrations in the main river channel, thereby indicating that these conditions boost eukaryote blooms. The evaluation of BV TR allows a better understanding of the dynamics of fluvial phytoplankton and can help to anticipate scenarios of nuisance species transport., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The mechanisms that drive species coexistence and community dynamics have long puzzled ecologists. Here, we explain species coexistence, size structure and diversity patterns in a phytoplankton community using a combination of four fundamental factors: organism traits, size-based constraints, hydrology and species competition. Using a 'microscopic' Lotka-Volterra competition (MLVC) model (i.e. with explicit recipes to compute its parameters), we provide a mechanistic explanation of species coexistence along a niche axis (i.e. organismic volume). We based our model on empirically measured quantities, minimal ecological assumptions and stochastic processes. In nature, we found aggregated patterns of species biovolume (i.e. clumps) along the volume axis and a peak in species richness. Both patterns were reproduced by the MLVC model. Observed clumps corresponded to niche zones (volumes) where species fitness was highest, or where fitness was equal among competing species. The latter implies the action of equalizing processes, which would suggest emergent neutrality as a plausible mechanism to explain community patterns.

When phytoplankton growth in lakes is limited by the available phosphate, the external phosphate concentration fluctuates around a threshold value at which available energy is insufficient to drive phosphate incorporation into a polyphosphate pool. As a result, occasional increases in the external concentration are experienced by phytoplankton as a series of phosphate pulses. Based on [(32) P] phosphate uptake experiments with lake phytoplankton, we show that a community is able to process information about the experienced pattern of phosphate pulses via a complex regulation of the kinetic and energetic properties of cellular phosphate uptake systems. As a result, physiological adaptation to alterations of ambient phosphate concentration depends on the pattern of phosphate fluctuations to which the community had been exposed during its previous growth. In this process, the entire community exhibits coherent uptake behaviour with respect to a common threshold value. Thereby, different threshold values result from different antecedent pulse patterns, apparently unrestrained by the amount of previously stored phosphate. The coherent behaviour observed contradicts the basic assumptions of the competitive exclusion principle and provides an alternative perspective for explaining the paradoxical coexistence of many phytoplankton species., (© 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.)

Phytoplankton biomass is a variable used in ecological studies and in monitoring potentially toxic cyanobacterial blooms. Biomass indicators of this community range from general and indirect, such as chlorophyll a concentrations, to specific and quasi-direct measures such as biovolume. Based on the results of a survey addressed to Latin American scientists and technicians as well as a bibliographic search, we discuss the relevance of using biovolume as the most appropriate indicator of biomass, the effort of quantifying phytoplankton using different counting units and the implications for interpretation of the results. Individuals, cells and biovolume were the quantitative units used to report phytoplankton. The individual represents the natural biological unit of the organism (cells, coenobia, colonies or filaments) and has a wide size range. We strongly advise that the phytoplankton reported as individuals per unit volume can lead to conceptual misinterpretation, such as the underestimation of the biomass of blooms. As cells have a large variation in their sizes, it poorly correlates with biovolume or chlorophyll a concentration. Considering all these aspects is crucial when selecting quantitative bioindicators to monitor potentially toxic cyanobacteria. We strongly recommend the use of biovolume as a biomass indicator for phytoplankton in general and consider it imperative for monitoring cyanobacteria. [ABSTRACT FROM AUTHOR]

Eutrophication, climate change, and river flow fragmentation are the main cause of nuisance algal blooms worldwide. This study evaluated the conditions that trigger the growth and occurrence of nuisance phytoplankton in the Santa Lucía River, a subtropical floodplain lotic system that supplies drinking water to 60% of the population of Uruguay. The main variables that explained phytoplankton biovolume were extracted from generalized linear models (GLM). The potential impact of nuisance organism advection on water utility was estimated by the phytoplankton biovolume transport (BVTR, m3 day−1), an indicator of biomass load. Santa Lucía River had a wide flow range (0.7×105–1438×105 m3 day−1) and eutrophic conditions (median, TP: 0.139 mg L−1; TN: 0.589 mg L−1). GLMs indicated that phytoplankton biomass increased with temperature and soluble reactive phosphorus. Contrary to expectations, the presence of cyanobacteria was positively associated with periods of high flow that result in high cyanobacterial biovolume transport, with a probability of 3.35 times higher when flow increased by one standard deviation. The cyanobacterial biovolume transported (max: 9.5 m3 day−1) suggests that biomass was subsidized by allochthonous inocula. Biovolume from other nuisance groups (diatoms, cryptophytes, and euglenophytes) was positively associated with low-flow conditions and high nutrient concentrations in the main river channel, thereby indicating that these conditions boost eukaryote blooms. The evaluation of BVTR allows a better understanding of the dynamics of fluvial phytoplankton and can help to anticipate scenarios of nuisance species transport. [ABSTRACT FROM AUTHOR]

Copyright of Innotec is the property of Laboratorio Tecnologico del Uruguay and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In vivo pigment fluorescence methods allow simple real‐time detection and quantification of freshwater algae and cyanobacteria. Available models are still limited to high‐cost fluorometers, validated for single instruments or individual water bodies, preventing data comparison between multiple instruments, and thus, restricting their use in large‐scale monitoring programs. Moreover, few models include corrections for optical interference (water turbidity and colored dissolved organic matter, CDOM). In this study, we developed simple models to predict phytoplankton and cyanobacterial chlorophyll a (Chl a) concentrations based on Chl a and C‐phycocyanin in vivo fluorescence, using multiple low‐cost handheld fluorometers. We aimed to: (1) fit models to mixed cyanobacterial and microalgal cultures; (2) cross‐calibrate nine fluorometers of the same brand and series; (3) correct the CDOM and turbidity effects; and (4) test the algorithms' performance with natural samples. We achieved comparable results between nine instruments after the cross‐calibration, allowing their simultaneous use. We obtained algorithms for total and cyanobacterial Chl a estimation. We developed parametric corrections to remove CDOM and turbidity interferences in the algorithms. Five sampling sites (from a lake, a stream, and an estuary) were used to test the algorithms using eight cross‐calibrated fluorometers. The models showed their best performance after CDOM and turbidity corrections (total Chl a: R2 = 0.99, RMSE = 7.8 μg Chl a L−1; cyanobacterial Chl a: R2 = 0.98, RMSE = 9.8 μg Chl a L−1). In summary, our models can quantify total phytoplankton and cyanobacterial Chl a in real time with multiple low‐cost fluorometers, allowing its implementation in large‐scale monitoring programs. [ABSTRACT FROM AUTHOR]

Abstract: The resilience of cyanobacterial blooms challenges lake restoration programmes based on nutrient load reduction. The survival of organisms may depend on episodic short‐term fluctuations of nitrogen (N) and phosphorus (P). Insight into physiological responses to shifts in nutrient limitation will improve our understanding of cyanobacterial bloom resilience. This study investigated the resilience and collapse of a long‐term cyanobacterial bloom dominated by Planktothrix agardhii and Raphidiopsis mediterranea, subjected to different periods of dissolved inorganic nitrogen (DIN) and phosphorus (SRP) inputs in Lago Rodó, a polymictic, hypereutrophic (6.0 ± 1.6 μmol total P/L) and turbid lake (attenuation coefficient: 4.7 ± 1.7 m−1). Phytoplankton composition, nutrient dynamics and physiological monitoring of [32P] phosphate uptake kinetics were studied over four summers. The influence of environmental nutrient supply on phytoplankton net phosphate uptake kinetics was analysed with a flow–force model that gives the threshold value of phosphate uptake ([Pe]A), a limiting concentration below which incorporation is not energetically possible by organisms, and the membrane conductivity coefficient (LP). The [Pe]A reflects the affinity and LP the activity of the cellular uptake systems. Nutrient supply into the lake sustained high DIN:SRP ratios and high cyanobacterial biomass that showed P‐deficiency features characterised by low [Pe]A (5.4 ± 0.5 n m [32P] phosphate) and high LP. High cyanobacterial biomass persisted after external nutrient inflows were interrupted for 14 months, which resulted in low dissolved DIN:SRP ratios; however, N2‐fixers did not develop. The collapse of cyanobacterial populations occurred under the lowest N:P ratios, low affinity and activity of phosphate uptake systems and strong water outflows. Our study suggests that the alleviation of N‐deficiency under high N:P ratios enhances the activation of phosphate uptake systems by cyanobacteria. The flexible physiological response results in more efficient exploitation of limiting nutrients favouring cyanobacterial resilience under suboptimal conditions. [ABSTRACT FROM AUTHOR]

Blooms of Nostocales (Cyanobacteria) are thought to be invading subtropical and temperate water bodies. According to nutrient stoichiometry and physiological differences between cyanobacterial groups, the replacement of non-heterocystous species by Nostocales is favored when dissolved inorganic nitrogen decreases. However, some studies have shown different trends. We used laboratory bioassays to evaluate the concomitant effects of light and nutrient enrichment on phytoplankton assemblages dominated by non-heterocystous filamentous cyanobacteria. Three nutrient conditions (no addition, addition of phosphate, and addition of nitrate and phosphate) and two light intensities (40 and 80 µmol photon m s) were assayed. Nostocales replaced or co-dominated with non-heterocystous species in all treatments by the end of the study. The shift in community composition towards Nostocales dominance led to an increase in species richness, which suggests that species with different eco-physiological traits may have differential impacts on diversity. The highest saxitoxin concentrations were measured in no addition treatments, which could link production to nutritional stress. Nostocales featured high phenotypic plasticity in terms of changes in average trichome volume and growth rates. These results help to have a better understanding of the conditions under which Nostocales predominance can occur. [ABSTRACT FROM AUTHOR]

Copyright of Innotec is the property of Laboratorio Tecnologico del Uruguay and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The cyanobacteria P lanktothrix agardhii and C ylindrospermopsis raciborskii are bloom-forming species common in eutrophic freshwaters. These filamentous species share certain physiological traits which imply that they might flourish under similar environmental conditions. We compared the distribution of the two species in a large database (940 samples) covering different climatic regions and the Northern and Southern hemispheres, and carried out laboratory experiments to compare their morphological and physiological responses. The environmental ranges of the two species overlapped with respect to temperature, light and total phosphorus ( TP); however, they responded differently to environmental gradients; C . raciborskii biovolume changed gradually while P . agardhii shifted sharply from being highly dominated to a rare component of the phytoplankton. As expected, P . agardhii dominates the phytoplankton with high TP and low light availability conditions. Contrary to predictions, C . raciborskii succeeded in all climates and at temperatures as low as 11 °C. C ylindrospermopsis raciborskii had higher phenotypic plasticity than P . agardhii in terms of pigments, individual size and growth rates. We conclude that the phenotypic plasticity of C . raciborskii could explain its ongoing expansion to temperate latitudes and suggest its future predominance under predicted climate-change scenarios. [ABSTRACT FROM AUTHOR]

The mechanisms that drive species coexistence and community dynamics have long puzzled ecologists. Here, we explain species coexistence, size structure and diversity patterns in a phytoplankton community using a combination of four fundamental factors: organism traits, size-based constraints, hydrology and species competition. Using a 'microscopic' Lotka-Volterra competition (MLVC) model (i.e. with explicit recipes to compute its parameters), we provide a mechanistic explanation of species coexistence along a niche axis (i.e. organismic volume). We based our model on empirically measured quantities, minimal ecological assumptions and stochastic processes. In nature, we found aggregated patterns of species biovolume (i.e. clumps) along the volume axis and a peak in species richness. Both patterns were reproduced by the MLVC model. Observed clumps corresponded to niche zones (volumes) where species fitness was highest, or where fitness was equal among competing species. The latter implies the action of equalizing processes, which would suggest emergent neutrality as a plausible mechanism to explain community patterns. [ABSTRACT FROM AUTHOR]

1. A logical way of distinguishing functional groups of phytoplankton is to cluster species according to their functional traits, such as growth rate and nutrient assimilation constants. However, data for such an approach are lacking for the vast majority of the species. 2. In this study, we show that a classification based on simple morphological traits may capture much of the variability in functional properties among the phytoplankton. We used information on more than 700 freshwater species, from more than 200 lakes situated in climate zones ranging from subpolar to tropical. 3. Morphological characteristics correlated well with functional properties, such as growth rate and sinking rate, and also with the population size and biomass attained in the field. This suggests that morphology is a good predictor of the functional characteristics of species. 4. Cluster analysis was used to define seven species groups based on morphology. Although some of the clusters are taxonomically homogeneous, others include species of several separate divisions. Functional traits (not used for the classification) differed significantly among the clusters, suggesting that the clusters may indeed represent meaningful functional groups. 5. Advantages of our morphological approach to classification include its objectivity, its independence from taxonomic affiliations, and the relative ease of its application to the majority of species for which physiological traits are unknown and are not readily determined. [ABSTRACT FROM AUTHOR]

We compared phytoplankton and phytobenthos pigment strategies in 17 shallow lakes and ponds from northern Canada and Alaska, sampled during mid to late summer. Benthic chlorophyll a concentrations (8–261 mg m−2) greatly exceeded those of the phytoplankton (0.008–1.4 mg m−2) in all sites. Cyanobacteria dominated the phytobenthos, while green algae and fucoxanthin-groups characterized the plankton. Both communities had higher photoprotection in cold, UV-transparent, high latitude waters. Phytoplankton had higher concentrations of photoprotective carotenoids per unit chlorophyll a than the phytobenthos. The planktonic photoprotective pigments were positively correlated with UV-penetration, and inversely correlated with temperature and coloured dissolved organic matter. A partial redundancy analysis showed that the benthic pigments were related to latitude, area and temperature. The UV-screening compound scytonemin occurred in high concentrations in the phytobenthos and was inversely related to temperature, while benthic carotenoids per unit chlorophyll a showed much lower variability among sites. These differing pigment strategies imply divergent responses to environmental change between the phytobenthos and phytoplankton in high latitude lakes. [ABSTRACT FROM AUTHOR]

Our pigment analyses from a year-long study in the coastal Beaufort Sea in the western Canadian Arctic showed the continuous prevalence of eukaryotic picoplankton in the green algal class Prasinophyceae. Microscopic analyses revealed that the most abundant photosynthetic cell types were Micromonas-like picoprasinophytes that persisted throughout winter darkness and then maintained steady exponential growth from late winter to early summer. A Micromonas (CCMP2099) isolated from an Arctic polynya (North Water Polynya between Ellesmere Island and Greenland), an ice-free section, grew optimally at 6°C–8°C, with light saturation at or below 10 μmol photons·m−2·s−1 at 0°C. The 18S rDNA analyses of this isolate and environmental DNA clone libraries from diverse sites across the Arctic Basin indicate that this single psychrophilic Micromonas ecotype has a pan-Arctic distribution. The 18S rDNA from two other picoprasinophyte genera was also found in our pan-Arctic clone libraries: Bathycoccus and Mantoniella. The Arctic Micromonas differed from genotypes elsewhere in the World Ocean, implying that the Arctic Basin is a marine microbial province containing endemic species, consistent with the biogeography of its macroorganisms. The prevalence of obligate low-temperature, shade-adapted species in the phytoplankton indicates that the lower food web of the Arctic Ocean is vulnerable to ongoing climate change in the region. [ABSTRACT FROM AUTHOR]

We investigated the fine pigment structure and composition of phytoplankton and benthic cyanobacterial mats in Ward Hunt Lake at the northern limit of High Arctic Canada and the responses of these two communities to in situ nutrient enrichment. The HPLC analyses showed that more than 98% of the total pigment stocks occurred in the benthos. The phytoplankton contained Chrysophyceae, low concentrations of other protists and Cyanobacteria (notably picocyanobacteria), and the accessory pigments chl c2, fucoxanthin, diadinoxanthin, violaxanthin, and zeaxanthin. The benthic community contained the accessory pigments chl b, chl c2, and a set of carotenoids dominated by glycosidic xanthophylls, characteristic of filamentous cyanobacteria. The black surface layer of the mats was rich in the UV-screening compounds scytonemin, red scytonemin-like, and mycosporine-like amino acids, and the blue-green basal stratum contained high concentrations of light-harvesting pigments. In a first bioassay of the benthic mats, there was no significant photosynthetic or growth response to inorganic carbon or full nutrient enrichment over 15 days. This bioassay was repeated with increased replication and HPLC analysis in a subsequent season, and the results confirmed the lack of significant response to added nutrients. In contrast, the phytoplankton in samples from the overlying water column responded strongly to enrichment, and chl a biomass increased by a factor of 19.2 over 2 weeks. These results underscore the divergent ecophysiology of benthic versus planktonic communities in extreme latitudes and show that cold lake ecosystems can be dominated by benthic phototrophs that are nutrient sufficient despite their ultraoligotrophic overlying waters. [ABSTRACT FROM AUTHOR]