O estudo das florações de cianobactérias potencialmente tóxicas é de fundamental importância, principalmente se tratando de um reservatório de grande valor econômico e social, devido a seus usos múltiplos e localização próxima a grandes centros urbanos como é o reservatório de Salto Grande (Americana - SP). Assim, este trabalho visou fornecer subsídios para formulação de prognóstico da ocorrência de cianobactérias e produção de toxinas em ambientes aquáticos com elevado grau de eutrofização. Para isto, a pesquisa foi desenvolvida em três escalas: em macrocosmo (represa), foi determinada a variação da ocorrência das espécies de cianobactérias e das demais classes fitoplanctônicas, e analisado o potencial tóxico das amostras coletadas nos meses chuvosos (janeiro, fevereiro e março/98) e de estiagem (junho, julho, agosto e setembro/98) em duas estações de coleta no reservatório de Salto Grande; em mesocosmo (tanques), verificou-se, durante o período de seca, as variações na ocorrência das classes fitoplanctônicas e das espécies de cianobatérias e produção de toxinas, em função da manipulação da razão N/P através da dosagem de nitrogênio e fósforo na água; em microcosmo (garrafões de vidro, em laboratório), foi testado o efeito da redução de fósforo e conseqüente aumento da razão N/P sobre o crescimento e produção de toxinas em culturas de cepas de Microcystis aeruginosa (Kützing) Kützing, isoladas a partir de amostras de florações desta espécie no reservatório de Salto Grande, durante os meses chuvosos e os secos. No ambiente foi detectada a presença de microcistinas na água de todos os dias de coleta, exceto em 25/02/99. Em geral, as concentrações estiveram abaixo do limite de aceitabilidade (1 &#956g.L-1), com exceção da estação 2 nos dias 27/01/99 (39,53 &#956g.L-1) e 22/03/99 (3,98 &#956g.L-1). Nos experimentos em mesocosmos notou-se um aumento da densidade fitoplanctônica) nas 3 condições distintas. Na condição controle (sem manipulação), ocorreu um sensível aumento da porcentagem de contribuição das cianobactérias e diminuição dos demais grupos ao longo dos 11 dias. Na condição de razão N/P baixa, houve um pequeno aumento na porcentagem de contribuição das cianobactérias e clorofíceas, uma diminuição das criptofíceas e os demais grupos não apresentaram grandes alterações. Sob razões N/P alta, as cianobactérias tiveram um aumento, as clorofíceas mantiveram-se constantes e as criptofíceas diminuíram em relação às porcentagens iniciais. As condições dos tanques mantidos com razão N/P baixa foram mais favoráveis às clorofíceas. As cianobactérias apresentaram um aumento de biomassa nas condições dos tanques mantidos com razão N/P alta. Em microcosmos, a fase exponencial teve início no oitavo dia de cultivo em todos os testes. Ao completar aproximadamente 18 dias de experimento, notou-se uma diminuição no rendimento das culturas em meio ASM-1 com redução de fósforo. Em todas as escalas estudadas constatou-se que a concentração de microcistina esteve relacionada a fatores favoráveis ao desenvolvimento das espécies tóxicas. Entretanto, os fatores determinantes para o crescimento de cianobactérias tóxicas, apresentaram diferentes papéis em casa escala estudada. No macrocosmo, a estabilidade da coluna d\'água foi fundamental para o estabelecimento de maiores densidades de espécies tóxicas. Nos mesocosmos, o enriquecimento foi responsável pelo aumento da densidade de espécies tóxicas. Nos microcosmos, a disponibilidade de fósforo esteve diretamente relacionada à taxa de crescimento de Microcystis aeruginosa e conseqüentemente, ao aumento da concentração de microcistina. / The study of the bloom of potential toxic cyanobacteria is of paramount significance, mainly when a reservoir endowed with great social and economical values due to both its multiple uses and its nearness to big urban centres - such as the Salto Grande reservoir, located near the city of Americana in the inland of the State of São Paulo, Brazil - is concerned. Based on such actuality, this work was aimed at supplying resources to devise forecasting the occurrence of cyanobacteria as well as the production of toxins in aquatic environments in which high eutrophication levels are observed. Towards this target, the research was carried out in the three steps that follow. In macrocosmic level (reservoir), the variations of the occurrence of both the cyanobacteria species and the remaining phytoplankton classes were found out, and then the toxic potentiality of the samples collected during the rainy season (January, February and March 1998) and the dry season (June, July, August and September 1998) in two sampling stations at the Salto Grande reservoir was analysed. In mesocosrnic scale (tanks), the variations in the occurrences of the classes of phytoplankton and of the cyanobacteria species - as well as the variations in production of toxins as a function of the ratio N/P that was dealt with by means of dosing nitrogen and phosphorus in the water - were observed during the dry season. In microcosmic level (glass bottles \"in lab\"), the effect of reducing phosphorus (and consequently increasing the ratio N/P) on the growth and the production of toxins in cultures of Microcystis aeruginosa (Kützing) Kützing strains - isolated from bloom samples of this species at the Salto Grande reservoir, during the wet and the dry seasons - was tested. At the environment, the presence of rnicrocystin in the water of all the samples, with the exception of the 25th of February 1999, was detected. Apart from the station 2 during January 2th 1999 (39.53 µg.L-1) and March 2th 1999 (3.98 µg.L-1), the concentrations stayed below the limit of acceptability (1 µg.L-1). At the experiments in mesocosmic scale, in 3 different conditions, increasing in phytoplankton density was observed. At the control condition (without manipulation), both reasonable augmentation of the percentage of the cyanobacteria contribution and diminishment of the other groups during the 11 days were detected. Under the condition of low N/P ratio, a slight rise of the percentage of the cyanobacteria and chlorophycea contribution and a decrease of the cryptophycea were observed; the other groups did not present much change. Under the condition of high N/P ratio, it was seen that the cyanobacteria increased, the chlorophycea remained unaffected and the cryptophycea decreased in comparison to the initial percentages. The conditions ofthe tanks that had been maintained at low N/P ratio favoured more the chlorophycea. The cyanobacteria presented biomass augmentation under the conditions of the tanks that had been maintained with high N/P ratio. For every test at the microcosmic level, the exponential stage had begun at the 8th development day. After being experimented for nearly 18 days, yield decrease of the cultures at the environment ASM-1 with phosphorus reduction was observed. In every scale that had been studied, it was noted that the microcystin concentration is related to unfavourable factors as far as the development of the toxic species is concerned. However, the determining causes for the growth of toxic cyanobacteria played different roles in each scale studied. At the macrocosmic level, enrichment was the responsible for increasing the density of the toxic species. At the microcosmic level, phosphorus availability had been directly related to Microcystis aeruginosa growth rate and, therefore, to the increase of microcystin concentration.

Phytoplankton communities in fifteen lakes in the Mt. St. Helens area were surveyed to assess the abundance and species present. Eleven of the lakes were inside the blast zone of the 1980 eruption and four were located outside the blast zone as a comparison. The hypothesis is that lakes will cluster together based on the algal species present and that some algae will be correlated with certain environmental conditions. A cluster analysis was performed to determine if the lakes would group together based on algal abundance. There did not appear to be any distinct clustering among the study lakes, but this analysis did help to sort out some similarities of algal species present between lakes. It demonstrated that the lakes outside the blast zone were not functional as control lakes because they were very different from the blast-zone lakes. They had different assemblages of algae and their origin was so different from the blast-zone lakes that there was little overlap between them. The factor analysis was applied to determine the relationships between environmental variables and phytoplankton. The hypothesis is that certain algae are associated with each other and with identifiable environmental factors. Factor analysis should detect these patterns. The factors represent some condition in the environment but the analysis would be virtually meaningless unless these conditions can be recognized and the factors named. From the factor analysis alone, I could not name the factors but returned to the task after the canonical correlation analysis was performed. The canonical correlation analysis gave some clues to identify the environmental conditions that exert control on these algae. The most useful statistical technique used in this study was the canonical correlation analysis. This analysis is a useful tool in community ecology studies where species-environment relationships can be inferred from community composition and environmental data. The environmental data used was nutrient and light attenuation present at the time the phytoplankton samples were taken. From this analysis I summarized a list of algae and with what environmental conditions that they are associated. Trophic state categories were assigned to the lakes from a trophic state index based on phytoplankton biovolume.

A importância de estudos sobre a produção primária (PP) marinha é consenso devido ao seu papel no ciclo do carbono global. Técnicas rápidas e não invasivas para medição de taxas de PP foram desenvolvidas nas últimas décadas para melhorar a resolução espacial e temporal das aquisições de dados, além de suprir as desvantagens e lacunas deixadas pelos métodos clássicos que envolvem a incubação de amostras. Os objetivos deste trabalho são: (1) comparar duas técnicas mais novas, a Bio-óptica (PPabs) e a Fluorescência Ativa Variável (PPFire), com o método clássico de evolução de oxigênio pelo metabolismo da comunidade planctônica que estima a PP bruta (PPB), (2) e determinar a influência de variáveis oceanográficas e como elas podem predizer a PP no canal de São Sebastião ao longo de diferentes períodos amostrais (verões de 2014, 2016 e 2018, inverno de 2014 e primavera de 2015). A PPB variou entre 47,55 e 341,94 mg C m-3 d-1, a PPabs entre 73,7 &#177; 6,9 e 454,9 &#177; 25,8 mg C m-3 d-1 e a PPFire entre 9,0 e 57,8 mg C m-3 d-1 no verão de 2018. As relações entre os métodos foram significativas (PPB vs PPabs, p = 0,007, PPB vs PPFire, p = 0,01 e PPabs vs PPFire, p = 0,01). A partir de uma regressão linear múltipla, vimos que a PPB (p = 0,003) e PPFire (p < 0,001) foram previstas pela temperatura e pela concentração da clorofila-a, já a PPabs (p = 0,007) pelas duas variáveis adicionadas a salinidade. Esses resultados indicam que apesar dos métodos apresentarem magnitudes diferentes, informações adicionais sobre o ambiente são incorporadas por cada técnica. A PPB acrescenta informações quanto a comunidade planctônica como um todo, a PPabs sobre a composição pigmentar e de tamanhos de espécies e a PPFire sobre a fotofisiologia das células fitoplanctônicas. Quanto às condições oceanográficas, as relações com a temperatura e a salinidade indicam que os métodos são sensíveis a alteração de massas d\'água, como a Água Central do Atlântico Sul (ACAS), bem como a entrada de aporte continental por plumas de rios, que são responsáveis pela disponibilidade de luz e nutrientes que afetam a PP no canal. Concluindo, os métodos são complementares e podem variar de diferentes formas conforme a dinâmica local, no entanto, são significativamente proporcionais uns aos outros, o que indica a robustez entre as medidas das duas técnicas mais novas aqui comparadas. / There is a consensus of the importance of primary production (PP) studies due to its role on the global carbon cycle. Fast and non-invasive techniques to measure rates of PP were developed in the last few decades to improve temporal and spatial data acquisition, and to overcome disadvantages and gaps associated with classical methods using incubation of samples. The aim of this work are: (1) compare two newer techniques, Bio-optical (PPabs) and Active Variable Fluorescence (PPFire), to the classical method involving oxygen evolution by the planktonic community metabolism (PPB), and (2) determine the influence of oceanographic variables and investigate how they could predict PP in the São Sebastião channel. PPB varied between 47.55 and 341.94 mg C m-3 d-1, PPabs between 73.7 &#177; 6.9 and 454.9 &#177; 25.8 mg C m-3 d-1 and PPFire between 9.0 and 57.8 mg C m-3 d-1 in the summer of 2018. The relationships between methods were significant (PPB vs PPabs, p = 0.007, PPB vs PPFire, p = 0.01 and PPabs vs PPFire, p = 0.01). After a multiple linear regression test, we found that PPB (p = 0.003) and PPFire (p < 0.001) were predicted by temperature and chlorophyll-a concentration, however, PPabs (p = 0.007) was also predicted by salinity. These results indicate that despite the methods show different magnitudes, each one includes different information about the environment. The PPB adds overall information about the planktonic community, while the PPabs adds pigment composition and species size and the PPFire adds phytoplankton cell photophysiology. We found correlations with the different PPs and temperature and salinity indicating that the three methods are sensitive to water mass changes, as the South Atlantic Central Water (SACW) and the intrusion of river plumes in the channel, both responsible for light and nutrients availability. In conclusion, the three methods are complementary and could vary in different ways due to local dynamics. However, they are proportional to each other, showing strength to the use of the two newest techniques (PPabs and PPFire).

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 193-220). / Southern Ocean net community productivity plays an out sized role in regulating global biogeochemical cycling and climate dynamics. The structure of spatial-temporal variability in phytoplankton ecosystem dynamics is largely governed by physical processes but a variety of competing pathways complicate our understanding of how exactly they drive net population growth. Here, I leverage two coupled, 3-dimensional, global, numerical simulations in conjunction with remote sensing data and past observations, to improve our mechanistic understanding of how physical processes drive biology in the Southern Ocean. In Chapter 2, I show how different mechanistic pathways can control population dynamics from the bottom-up (via light, nutrients), as well as the top-down (via grazing pressure). In Chapters 3 and 4, I employ a higher resolution, eddy resolving, integration to explicitly track and examine closed eddy structures and address how they modify biomass at the mesoscale. / Chapter 3 considers how simulated eddies drive bottom-up controls on phytoplankton growth and finds that division rates are, on average, amplified in anticyclones and suppressed in cyclones. Anomalous division rates are predominately fueled by an anomalous vertical iron flux driven by eddy-induced Ekman Pumping. Chapter 4 goes on to describe how anomalous division rates combine with anomalous loss rates to drive anomalous net population growth. Biological rate-based mechanisms are then compared to the potential for anomalies to evolve strictly via physical transport (i.e. dilution, stirring, advection). All together, I identify and describe dramatic regional and seasonal variability in when, where, and how different mechanisms drive phytoplankton growth throughout the Southern Ocean. Better understanding this variability has broad implications to our understanding of how oceanic biogeochemisty will respond to, and likely feedback into, a changing climate. / Specifically, the uncertainty associated with this variability should temper recent proposals to artificially stimulate net primary production and the biological pump via iron fertilization. In Chapter 5 I argue that Southern Ocean Iron Fertilization fails to meet the basic tenets required for adoption into any regulatory market based framework. / by Tyler W. Rohr. / Ph. D. / Ph.D. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Marine microbes are an essential component of global biogeochemical cycles. In oligotrophic marine surface waters, the phytoplankton, phototrophic, single-celled (on occasion, colonial) organisms, is often dominated by the picoplankton (cells <2 micrometers in size), which constitute the base of the marine food chain. The picophytoplankton is composed of three main groups of organisms: two genera of cyanobacteria, Prochlorococcus and Synechococcus, and a third group, the picoeukaryotes. Even though numerically less abundant than cyanobacteria, picoeukaryotes can contribute significantly to biomass and primary production in this size fraction. Furthermore, picoeukaryotes are a diverse group but this diversity is still underexplored and their ecological roles and physiology is poorly understood. Here uncultured protists are investigated using 18S rRNA gene clone libraries, phylogenetic analyses, specific fluorescence in situ hybridization (FISH) probes and other methods in tropical and subtropical waters. Gene sequences comprising a unique eukaryotic lineage, biliphytes, were identified in most samples, whether from high (30 degrees Celsius) or low (5 degrees Celsius) temperature waters. Sequences within this uncultured group have previously been retrieved from mid and high latitudes. Phycobilin-like fluorescence associated with biliphyte-specific FISH probed cells indicated they may be photosynthetic. Furthermore, the data indicated biliphytes are nanoplanktonic in size, averaging between 3.0 and 4.1 micrometers. Using the 18S rRNA gene, sequences belonging to a broadly distributed but uncultivated pico-prymnesiophytes were retrieved. We investigated the ecological importance of these natural pico-prymnesiophyte populations and field experiments showed that they could grow rapidly and contributed measurably to primary production. They also appear to form a large portion of global picophytoplankton biomass, with differing contributions in five biogeographical provinces, from tropical to high latitudes. Finally, the physiology of the picoeukaryote Micromonas was studied under a shift from medium to high light and UV radiation. Results showed that the growth of these photosynthetic cells was synchronized with the light: dark period. Forward angle side scatter and red autofluorescence from chlorophyll increased throughout the light period and decreased during the dark period. This is consistent with cell division occurring at the beginning of the dark period. Additionally, genes proposed to have roles in photoprotection were up-regulated under high light and UV, but not in controls.

Nature changes continuously and is only seemingly at equilibrium. Environmental parameters like temperature, humidity or insolation may strongly fluctuate on scales ranging from seconds to millions of years. Being part of an ecosystem, species have to cope with these environmental changes. For ecologists, it is of special interest how individual responses to environmental changes affect the dynamics of an entire population – and, if this behavior is predictable. In this context, the demographic structure of a population plays a decisive role since it originates from processes of growth and mortality. These processes are fundamentally influenced by the environment. But, how exactly does the environment influence the behavior of populations? And what does the transient behavior look like? As a result from environmental influences on demography, so called cohorts form. They are age or size classes that are disproportionally represented in the demographic distribution of a population. For instance, if most old and young individuals die due to a cold spell, the population finally consists of mainly middle-aged individuals. Hence, the population got synchronized. Such a population tends to show regular fluctuations in numbers (denoted as oscillations) since the alternating phases of individual growth and population growth (due to reproduction) are now performed synchronously by the majority of the population.That is, one time the population growths, and the other time it declines due to mortality. Synchronous behavior is one of the most pervasive phenomena in nature. Gravitational synchrony in the solar system; fireflies flashing in unison; coordinate firing of pacemaker cells in the heart; electrons in a superconductor marching in lockstep. Whatever scale one looks at, in animate as well as inanimate systems, one is likely to encounter synchrony. In experiments with phytoplankton populations, I could show that this principle of synchrony (as used by physicists) could well-explain the oscillations observed in the experiments, too. The size of the fluctuations depended on the strength by which environmental parameters changed as well as on the demographic state of a population prior to this change. That is, two population living in different habitats can be equally influenced by an environmental change, however, the resulting population dynamics may be significantly different when both populations differed in their demographic state before. Moreover, specific mechanisms relevant for the dynamic behavior of populations, appear only when the environmental conditions change. In my experiments, the population density declined by 50% after ressource supply was doubled. This counter-intuitive behavior can be explained by increasing ressource consumption. The phytoplankton cells grew larger and enhanced their individual constitution. But at the same time, reproduction was delayed and the population density declined due to the losses by mortality. Environmental influences can also synchronize two or more populations over large distances, which is denoted as Moran effect. Assume two populations living on two distant islands. Although there is no exchange of individuals between them, both populations show a high similarity when comparing their time series. This is because the globally acting climate synchronizes the regionally acting weather on both island. Since the weather fluctuations influence the population dynamics, the Moran effect states that the synchrony between the environment equals the one between the populations. My experiments support this theory and also explain deviations arising when accounting for differences in the populations and the habitats they are living in. Moreover, model simulations and experiments astonishingly show that the synchrony between the populations can be higher than between the environment, when accounting for differences in the environmental fluctuations (“noise color”). / Die Natur unterliegt ständigen Veränderungen und befindet sich nur vermeintlich in einem Gleichgewicht. Umweltparameter wie Temperatur, Luftfeuchtigkeit oder Sonneneinstrahlung schwanken auf einer Zeitskala von Sekunden bis Jahrmillionen und beinhalten teils beträchtliche Unterschiede. Mit diesen Umweltveränderungen müssen sich Arten als Teil eines Ökosystems auseinandersetzen. Für Ökologen ist interessant, wie sich individuelle Reaktionen auf die Umweltveränderungen im dynamischen Verhalten einer ganzen Population bemerkbar machen und ob deren Verhalten vorhersagbar ist. Der Demografie einer Population kommt hierbei eine entscheidende Rolle zu, da sie das Resultat von Wachstums- und Sterbeprozessen darstellt. Eben jene Prozesse werden von der Umwelt maßgeblich beeinflusst. Doch wie genau beeinflussen Umweltveränderungen das Verhalten ganzer Populationen? Wie sieht das vorübergehende, transiente Verhalten aus? Als Resultat von Umwelteinflüssen bilden sich in Populationen sogenannte Kohorten, hinsichtlich der Zahl an Individuen überproportional stark vertretene Alters- oder Größenklassen. Sterben z.B. aufgrund eines außergewöhnlich harten Winters, die alten und jungen Individuen einer Population, so besteht diese anschließend hauptsächlich aus Individuen mittleren Alters. Sie wurde sozusagen synchronisiert. Eine solche Populationen neigt zu regelmäßigen Schwankungen (Oszillationen) in ihrer Dichte, da die sich abwechselnden Phasen der individuellen Entwicklung und der Reproduktion nun von einem Großteil der Individuen synchron durchschritten werden. D.h., mal wächst die Population und mal nimmt sie entsprechend der Sterblichkeit ab. In Experimenten mit Phytoplankton-Populationen konnte ich zeigen, dass dieses oszillierende Verhalten mit dem in der Physik gebräuchlichen Konzept der Synchronisation beschrieben werden kann. Synchrones Verhalten ist eines der verbreitetsten Phänomene in der Natur und kann z.B. in synchron schwingenden Brücken, als auch bei der Erzeugung von Lasern oder in Form von rhythmischem Applaus auf einem Konzert beobachtet werden. Wie stark die Schwankungen sind, hängt dabei sowohl von der Stärke der Umweltveränderung als auch vom demografischen Zustand der Population vor der Veränderung ab. Zwei Populationen, die sich in verschiedenen Habitaten aufhalten, können zwar gleich stark von einer Umweltveränderung beeinflusst werden. Die Reaktionen im anschließenden Verhalten können jedoch äußerst unterschiedlich ausfallen, wenn sich die Populationen zuvor in stark unterschiedlichen demografischen Zuständen befanden. Darüber hinaus treten bestimmte, für das Verhalten einer Population relevante Mechanismen überhaupt erst in Erscheinung, wenn sich die Umweltbedingungen ändern. So fiel in Experimenten beispielsweise die Populationsdichte um rund 50 Prozent ab nachdem sich die Ressourcenverfügbarkeit verdoppelte. Der Grund für dieses gegenintuitive Verhalten konnte mit der erhöhten Aufnahme von Ressourcen erklärt werden. Damit verbessert eine Algenzelle zwar die eigene Konstitution, jedoch verzögert sich dadurch die auch die Reproduktion und die Populationsdichte nimmt gemäß ihrer Verluste bzw. Sterblichkeit ab. Zwei oder mehr räumlich getrennte Populationen können darüber hinaus durch Umwelteinflüsse synchronisiert werden. Dies wird als Moran-Effekt bezeichnet. Angenommen auf zwei weit voneinander entfernten Inseln lebt jeweils eine Population. Zwischen beiden findet kein Austausch statt – und doch zeigt sich beim Vergleich ihrer Zeitreihen eine große Ähnlichkeit. Das überregionale Klima synchronisiert hierbei die lokalen Umwelteinflüsse. Diese wiederum bestimmen das Verhalten der jeweiligen Population. Der Moran-Effekt besagt nun, dass die Ähnlichkeit zwischen den Populationen jener zwischen den Umwelteinflüssen entspricht, oder geringer ist. Meine Ergebnisse bestätigen dies und zeigen darüber hinaus, dass sich die Populationen sogar ähnlicher sein können als die Umwelteinflüsse, wenn man von unterschiedlich stark schwankenden Einflüssen ausgeht.

Lakes are important global ecosystems and many of them are nutrient-poor (unproductive). Especially in northern boreal latitudes, lakes may be heavily subsidized by terrestrial organic material (t-OM) from peat layers in the catchment. Thus, in addition to heterotrophic bacteria and phytoplankton, zooplankton may also use the particulate fraction of peat layer t-OM (t-POM) as a potential food source in those systems. Inputs of t-OM in northern latitudes are anticipated to increase in the future due to increasing precipitation and temperature. As t-OM is a good substrate for bacterial growth and as bacteria can often outcompete phytoplankton for inorganic nutrients, the proportions of heterotrophic bacteria and phytoplankton are expected to change in unproductive lakes. This may have pronounced impacts on zooplankton population dynamics. The aim of my thesis was to investigate how changes in food quality and quantity will affect metazoan zooplankton performance in unproductive lakes. Three laboratory studies assessed the quality of specific food components (phytoplankton, bacteria and peat layer t-POM) and their effects on Daphnia survival, growth and reproduction. Further, a mesocosm study with a full natural plankton community tested the predictions of the Light:Nutrient-Hypothesis in an unproductive clear water lake in situ by adding carbon and inorganic nutrients and changing light availability. I found that pure bacterial (Pseudomonas sp.) or t-POM diets could not sustain Daphnia populations, even though both were readily ingested. Daphnids needed at least 10-20% phytoplankton (Rhodomonas) in the diet to survive and even higher proportions (≥ 50%) were necessary for the production of viable offspring. Further, I showed that the dilution of non-limiting concentrations of Rhodomonas with increasing proportions of Pseudomonas or t-POM led to decreased Daphnia performance. Both Pseudomonas and t-POM lack essential biochemicals (fatty acids and sterols). In contrast, mineral nutrient limitation only occurred on t-POM-dominated diets as evidenced by a labeling experiment that showed Daphnia can incorporate carbon and phosphorus from Rhodomonas and Pseudomonas with similar efficiencies. Thus, peat layer t-POM was a lower quality food than Pseudomonas. This was corroborated by the finding that intermediate additions of Pseudomonas to limiting amounts of Rhodomonas supported increased Daphnia survival, growth and reproduction while t-POM additions had no beneficial effect. My results suggest that high terrestrial stable isotope signals in metazoan zooplankton are most likely derived from t-OM that is channeled tohigher trophic levels via the microbial loop (i.e. heterotrophic bacteria and/or bacterivorous protozoa) but not from direct metazoan feeding on t-POM. Furthermore, bacteria may serve as an important supplement to zooplankton diets when phytoplankton abundance is low. However, a sufficient proportion of high quality phytoplankton is always necessary to fulfil mineral and especially biochemical requirements of zooplankton in unproductive aquatic systems. The results of the mesocosm study showed that the Light:Nutrient-Hypothesis is not applicable to unproductive clear water systems in which the phytoplankton community is dominated by mixotrophs. In the face of the theoretical predictions, low light levels led to decreased zooplankton biomass. This was most likely caused by a shift in the algal community composition towards less edible taxa. Another reason may have been a weakening of the microbial loop. This is in line with the results of the laboratory studies that point out the importance of the microbial food web for zooplankton nutrition in unproductive lakes.

The development of modern glacial climates occurred during the Eocene-Oligocene transition (34 to 35.5 Ma) when a decrease of atmospheric CO2 led to a global temperature fall. The ocean was deeply affected, both in the surface and the deep-sea, suffering a strong reorganization including currents and phytoplankton distribution. Spanning that time, 35 samples from the North Atlantic Ocean Drilling Program Site 612 have been analyzed by counting coccoliths abundance in different size groups (&lt; 4 µm, 4 to 8 µm and &gt; 8 µm) and silica fragments abundance. Absolute coccoliths abundance were estimated with two different methods, the “drop” technique and microbeads calibration. In addition, a fragmentation index was calculated to assess the preservational state of the samples. The results obtained fit in the global picture of a decrease in phytoplankton abundance across theEocene-Oligocene boundary, although coccolith and silica fragments abundances show slight different patterns. Absolute abundances estimates showed a large difference between the “drop” and the microbeads methods. The temperature at which samples are dried seems to affect microbeads distribution, leading to an underestimation at temperatures higher than 60º C. In future work the current dataset will be updated with additional calibration and replicate counts to confirm that the “drop” estimates are the more valid results. As the fragmentation index was fairly constant in all samples, no major differences in nannofossil preservation were inferred. Coccoliths abundance drops are thought to be triggered by global temperature fall, general decrease of atmospheric CO2, changes in oceanic circulation, pulses of nutrients or a combination of those. / Under tidsspannet som täcker övergången mellan eocen och oligocen, för ungefär 35.5 till 34 miljoner år sedan, genomgick jordens klimat en stor förändring. Under eocen hade vår planet ett varmare klimat och var i ett så kallat ”greenhouse state”. Mot slutet av denna period och i början av oligocen skiftade emellertid klimatet till en kallare regim, ett så kallat ”icehouse state”. Under detta tillstånd minskade andelen koldioxid i atmosfären vilket medförde att den globala temperaturen minskade. Vidare påverkades också havet och speciellt de fytoplankton som levde där, då de påverkas av temperatur och inflödet av näringsämnen. Fytoplankton står för en betydande del av jordens pågående fotosyntes samt är basen av den organiska matkedjan. Syftet med denna undersökning är att studera förekomsten av coccoliter, små kalcitplattor som produceras av en typ av nannoplankton som kallas coccolitoforider. Coccoliter från en djuphavskärna härstammande från norra Atlanten har därför samlats in och för-ändringen av mängden fytoplankton över nämnda tidsspann mätts. Vidare har också bitar av kisel från andra växtplankton räknats. Resultatet av denna studie var att båda grupperna var rikligare under den sista delen av eocen men mängden sjönk snabbt i början av oligocen. Det finns inte tillräckligt med information för att reda ut orsakerna av detta, men det är troligt att minskningen i temperatur och CO2-tillgängligheten för fotosyntesen är viktiga faktorer.

Despite the critical role algae serve as primary producers, increases or accumulation of certain algae may result in Harmful Algal Blooms (HABs). Algal toxins from these blooms contribute significantly to incidences of food borne illness, and evidence suggests HABs are expanding in frequency and distribution. Mitigation of these HABs without knowledge of the ecological purpose and biochemical regulation of their toxins is highly unlikely. The production, function, and potential of secondary metabolites produced by the dinoflagellates Karenia brevis and Pyrodinium bahamense, were investigated. Brevetoxins were demonstrated by two different methods to localize within the cytosol of Karenia brevis. Differential and density-dependent centrifugation followed by Enzyme Linked Immunosorbant Assays (ELISAs) indicated that brevetoxin was not contained by any cellular organelles. Light microscopy of brevetoxin immunolabeled preserved cells visually confirmed these results, showing stain to be distributed throughout the cytosol and notably absent from the nucleus. These results have implications for brevetoxin synthesis and function. The complex cyclization process of brevetoxin therefore likely occurs in the cytosol after export of a polyketide precursor from the chloroplast. Functionally, this cellular location suggests use of brevetoxin in cytosolic functions such as signaling and chelation. Culture experiments of Pyrodinium. bahamense var. bahamense were undertaken to determine the effects of nutrients and environmental conditions on growth requirements and toxin production. HPLC analysis was employed to separate and quantify the saxitoxins. As eutrophication is a concern where this species is most problematic, in the Indian River Lagoon area of Florida, utilization of urea and ammonium were explored and compared to nitrate. While all nitrogen conditions yielded similar growth curves in P. bahamense, the cultures using urea contained a substantially lesser amount of the potent STX congener. This difference implies the urease enzyme utilized by P. bahamense is inefficient and urea based fertilizers are unlikely to create blooms with greater toxicity. Cyst production in P. bahamense was found to depend on nutrient limitation. Cultures utilizing ammonium displayed a smaller proportion of cysts, presumably attributable to the bioavailablility of ammonium. The total toxin content of P. bahamense was found to vary inversely with growth rate, although mole percents of the saxitoxins were largely unchanged over a suite of environmental parameters including temperature, salinity, and pH. Possible reasons for the reported increase in HABs include global warming, dumping of ballast water, and nutrient influx. These studies outline controls on toxin synthesis and production and conditions needed for growth and will aid in predicting environmental and human health effects pending these global changes. Extracts of K. brevis and P. bahamense cultures were assayed against various pathogenic agents. Growth of K. pneumoniae was inhibited by extracts of both K. brevis and P. bahamense. An extract of K. brevis additionally inhibited MRSA, while a P. bahamense extract additionally inhibited both S. aureus and MRSA as well as the most common protozoan vector of malaria, P. falciparum. The activity of a dinoflagellate against an Apicomplexan (P. falciparum) found in this study is especially interesting as the phyla are closely phylogenetically related. Differences in activity of extracts against P. falciparum between a clonal culture on P. bahamense from the Indian River Lagoon and a 2011 bloom sampled from Tampa Bay were observed. Drugs are losing their effectiveness against these infectious agents, making pursuit of new drugs an important field. These results suggest that HAB dinoflagellates hold promise in drug discovery similar to other phytoplankton.

Algae provide an important role in aquatic food web and biochemical cycles in aquatic systems. They are affected by different environmental factors, such as pH, light, temperature and nutrients. This study aimed to describe the composition abundance and density of phytoplankton in the Hoa Binh reservoir during period from March to December 2011. Phytoplankton samples were collected monthly at four sampling stations. Result obtained showed that 6 phytoplankton classes were recorded: Cyanobacteria, Chlorophyceae, Bacillariophyceae, Euglenophyceae, Dinophyceae and Cryptophyceae. Bacillariophyceae and Cyanobacteria were the most abundant phytoplankton families constituting 61% and 32% respectively of total phytoplankton community. Colony-forming and solitary filamentous-forming of Cyanobacteria group (e.g. Microcystis aeruginosa, M. wesenbergi and Oscillatoria sp. respectively) were a common component of phytoplankton community in the early summer and autumn periods (April and September). The total cell densities of phytoplankton varied seasonally from 84210 to 100x106 cell/L. Phytoplankton density varied with season with high values in early summer and winter (April and December) and low values in summer – autumn periods (from June to October). / Tảo đóng vai trò quan trọng trong mạng lưới thức ăn và chu trình sinh địa hóa của thủy vực và chúng chịu sự chi phối của nhiều yếu tố môi trường như ánh sáng, pH, nhiệt độ và dinh dưỡng. Nghiên cứu này trình bày đa dạng thành phần loài và biến động sinh khối thực vật phù du tại hồ chứa Hòa Bình từ tháng 3 đến tháng 12 năm 2011. Các mẫu thực vật nổi được thu thập hàng tháng tại 4 điểm. Kết quả đã xác định được 6 lớp tảo chính bao gồm: Vi khuẩn lam, tảo lục, tảo silic, tảo mắt, tảo giáp và tảo lông roi hai rãnh. Nhóm tảo silic và Vi khuẩn lam chiếm ưu thế với độ phong phú tương đối là 61% và 32% tương ứng trong quần xã thực vật nổi. Vi khuẩn lam dạng tập đoàn và dạng sợi (Microcystis aeruginosa, M. wesenberg, Oscillatoria sp. tương ứng) chiếm ưu thế trong quần xã thực vật nổi vào các thời điểm đầu hè và mùa thu (tháng 4 và tháng 9). Tổng mật độ tế bào thực vật nổi dao động từ 84210 đến 100 x106 cell/L. Mật độ thực vật nổi biển động theo mùa với sinh khối tê bào cao vào đầu hè và mùa đông (tháng 4 và tháng 12) và sinh khối tế bào thấp vào các mùa hè và thu (tháng 6 đến tháng 10).