Mixoplankton are protist plankton that are capable of phototrophy and phagotrophy. These organismsare increasingly recognised not just as freaks of nature, but as a substantial part of marineplankton. Most existing plankton models still assume a strict dichotomy between phototrophsand heterotrophs. Few models consider mixoplanktonic activity as a synergism of the two trophicmodes. Many different mixoplankton functional types exist on a gradient between heterotrophy andphototrophy. The cryptophyte (Teleaulax)-Mesodinium-Dinophysis (TMD) complex is a specificpredator-prey interaction of different types of mixoplankton and a good example of the complexityof mixoplankton interaction and trophodynamics. The specialist non-constitutive mixoplankton(SNCM) Mesodinium acquires its chloroplasts strictly from a specific constitutive mixoplankton(CM) cryptophyte, while the harmful algal bloom (HAB) species Dinophysis acquires its third-handchloroplasts exclusively from Mesodinium.The generic NPZ-style protist model developed here shows that mixoplankton displays dynamicsthat are distinctly different from strict heterotrophs and autotrophs in terms of growth and theway they shape their environment. In addition, there is a clear niche separation between differentmixoplankton types (general non-constitutive mixoplankton (GNCM), SNCM and CM) according tonutrient, prey and light resource availabilities indicating a niche separation of each type. Thus,considering the different mixoplankton functional types in specialised multi-organism relationshipsas they are found in the TMD-complex may be important for their understanding and accurateprediction of growth and biomass development. Currently, none of the many models of Dinophysiscapture the biological dependencies. Results from a nitrogen-based TMD model suggest thatthe timing and quantity of prey availability is crucial for the bloom dynamics of Mesodinium andDinophysis. Some CMs may only feed when phosphate is the limiting nutrient. The results ofthe variable stoichiometric “Perfect Beast” model that was configured as Teleaulax amphioxeia incombination with experimental data strongly suggest that the cryptophyte feeds on bacteria tocompensate for phosphate limitation.This work shows the importance of considering mixoplankton in ecosystem models alongsidestrict heterotrophs and autotrophs and that distinction between different mixoplankton functionaltypes matters. Mixoplankton distinctly differ in their nutrient utilisation and growth dynamics.Predator-prey interactions have different implications for mixoplankton than for heterotrophs andtheir inclusion in models could improve our understanding of the formation of harmful mixoplanktonblooms. The unique physiology of mixoplankton and their nutrient utilisation and trophic levelsneed consideration in species specific models. / Le mixoplancton inclut les protistes planctoniques capables de phototrophie et de phagotrophie.Ces organismes sont de plus en plus reconnus comme une partie importante du plancton marin.Toutefois, la plupart des modèles mathématiques planctoniques existants supposent encoreune stricte dichotomie entre les organismes phototrophes et hétérotrophes et peu de modèlesconsidèrent l’activité mixoplanctonique comme une synergie entre les deux modes trophiques.De nombreux types fonctionnels mixoplanctoniques différents existent dans un gradient entrel’hétérotrophie et la phototrophie. Le complexe cryptophyte (Teleaulax)-Mesodinium-Dinophysis(TMD) est une interaction prédateur-proie spécifique entre différents types de mixoplancton et unbon exemple de la complexité des interactions et des relations trophodynamiques du mixoplancton.Mesodinium, mixoplancton spécialiste non constitutif (SNCM), ne peut acquérir ses chloroplastesque de cryptophytes (mixoplancton constitutif (CM)) spécifiques (tel que Teleaulax), tandis quel’espèce Dinophysis, responsable d’efflorescences algales nuisibles, acquiert ses chloroplastesexclusivement de Mesodinium. Le modèle générique de protistes, de type NPZ, développé dansce travail montre que le mixoplancton présente une dynamique nettement différente de celle deshétérotrophes et autotrophes strictes en termes de croissance et de la façon dont ils façonnentleur environnement. En outre, il existe une séparation de niches claire entre les différents typesde mixoplancton (mixoplancton généraliste non-constitutif (GNCM), SNCM et CM) en fonction dela disponibilité en lumière, en nutriments et en proies. En conséquence, la prise en compte desdifférents types fonctionnels du mixoplancton dans des relations multi-organismes spécialisées,telles qu’on les trouve dans le complexe TMD, peut être importante pour leur compréhension et laprédiction précise de leur croissance et biomasse. Actuellement, aucun des modèles existants deDinophysis ne rend compte de ces dépendances biologiques. Les résultats d’un modèle TMD basésur l’azote suggèrent que le moment et la quantité de proies disponibles sont des facteurs cruciauxpour la dynamique de Mesodinium et de Dinophysis. Certains CM peuvent se nourrir uniquementlorsque le phosphate est le nutriment limitant. Les résultats du modèle à stoechiométrie variable"Perfect Beast", qui a été configuré pour représenter Teleaulax amphioxeia sur base de donnéesexpérimentales, suggèrent fortement que le cryptophyte se nourrit de bactéries pour compenserla limitation en phosphate. Ce travail montre l’importance de prendre en compte le mixoplanctondans les modèles d’écosystème en plus des hétérotrophes et des autotrophes stricts et que ladistinction entre les différents types fonctionnels de mixoplancton est importante. Le mixoplanctonse distingue par son utilisation des nutriments et sa dynamique de croissance. Les interactionsprédateur-proie n’ont pas les mêmes implications pour le mixoplancton que pour les hétérotropheset leur prise en compte dans les modèles pourrait améliorer notre compréhension de la formationdes efflorescences nuisibles de mixoplancton. La physiologie unique du mixoplancton, sonutilisation des nutriments et ses niveaux trophiques doivent être pris en compte dans les modèlesspécifiques aux espèces. / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

Bibliography: pages 112-138. / The large volume of seawater used for cooling at Koeberg Nuclear Power Station contains many planktonic organisms which are exposed to heat, chlorine and physical stress during their passage through the system. Phytoplankton biomass, measured as chlorophyll a, was reduced by an average of 55.32% due to entrainment, and productivity was decreased by 38.30% on average, mainly due to chlorination. Zooplankton mortality averaged 22.34% for all species and 30.52% for copepods, the dominant group. The copepod Paracartia africana was used in laboratory experiments designed to simulate entrainment. Latent mortality was monitored up to 60 hours after a 30-minute application of stress factors (physical stress was not simulated), and approximately 75% of the total mortality occurred within the 30-minute period. Male Paracartia experienced higher mortalities than females. Extrapolation of these results predicts an overall entrainment mortality (including latent mortality) of 40% for copepods and 29.04% for total zooplankton, although the latter cannot be substantiated. Plankton entrainment at Koeberg was not considered to be overly detrimental to the marine environment because of the very localised area affected, rapid dispersion of heat and chlorine, rapid regeneration times of phytoplankton and some zooplankton, low abundance of commercially important species and potential recruitment from the surrounding productive Benguela upwelling region.

This thesis focuses on the impact of spatially heterogeneous environments on the spatio-temporal behavior of planktonic systems. Specific emphasis placed is on the influence of spatial variations in the strength of random or chaotic movements (diffusion) of the organisms. Interaction between different species is described by ordinary differential equations. In order to describe movements in space, reaction–diffusion or advection–reaction–diffusion systems are studied. Examples are given for different approaches of diffusive motion as well as for the possible effects on the localized biological system. The results are discussed based on their biological and physical meanings. In doing so, different mechanisms are shown which are able to explain events of fast plankton growth near turbulent flows. In general, it is shown that local variation in the strength of vertical mixing can have global effects on the biological system, such as changing the stability of dynamical solutions and generating new spatiotemporal behavior. The thesis consists of five chapters. Three of them have been published in international peer-reviewed scientific journals. Chapter 1. Introduction: This chapter gives a general introduction to the history of plankton modeling and introduces basic ideas and concepts which are used in the following chapters. Chapter 2. Fokker-Planck law of diffusion: The influence of spatially in- homogeneous diffusion on several common ecological problems is analyzed. Dif- fusion is modeled with Fick’s law and the Fokker–Planck law of diffusion. A discussion is given about the differences between the two formalisms and when to use the one or the other. To do this, the discussion starts with a pure diffusion equation, then it turns to a reaction–diffusion system with one logistically growing component which invades the spatial domain. This chapter also provides a look at systems of two reacting components, namely a trimolecular oscillating chemical model system and an excitable predator–prey model. Contrary to Fickian diffusion, spatial inhomogeneities promote spatial and spatiotemporal pattern formation in the case of Fokker–Planck diffusion. A slightly modified version of this chapter has been published in the Journal of Mathematical Biology (Bengfort et al., 2016). Chapter 3. Plankton blooms and patchiness: Microscopic turbulent motions of water have been shown to influence the dynamics of microscopic species. Therefore, the number, stability, and excitability of stationary states in a predator– prey model of plankton species can change when the strength of turbulent motions varies. In a spatial system these microscopic turbulent motions are naturally of different strength and form a heterogeneous physical environment. Spatially neighboring plankton communities with different physical conditions can impact each other due to diffusive coupling. It is shown that local variations in the physical conditions can influence the global system in the form of propagating pulses of high population densities. For this, three local predator–prey models with different local responses to variation in the physical environment are considered. The degree of spatial heterogeneity can, depending on the model, promote or reduce the number of propagating pulses, which can be interpreted as patchy plankton distributions and recurrent blooms. This chapter has been published in the Journal Ecological Complexity (Bengfort et al., 2014). Chapter 4. Advection–reaction–diffusion model: Here, some of the models introduced in chapter 1 and 2 are modified to perform two dimensional spatial simulations including advection, reaction and diffusion. These models include assumptions about turbulent flows introduced in chapter 1. Chapter 5. Competition: Some plankton species, such as cyanobacteria, have an advantage in competition for light compared to other species because of their buoyancy. This advantage can be diminished by vertical mixing in the surround- ing water column. A non–spatial model, based on ordinary differential equations, which accounts for this effect is introduced. The main aim is to show that vertical mixing influences the outcome of competition between different species. Hystersis is possible for a certain range of parameters. Introducing a grazing predator, the system exhibits different dynamics depending on the strength of mixing. In a diffusively coupled horizontal spatial model, local vertical mixing can also have a global effect on the biological system, for instance, destabilization of a locally stable solution, or the generation of new spatiotemporal behavior. This chapter has been published in the Journal Ecological Modelling (Bengfort and Malchow, 2016).

Cellulase-producing microorganisms are considered as a key player in various environments to degrade the plant biomass and were isolated from various environment like soils, mangroves and oceans. The Red Sea has a unique environment in terms of high seawater temperature, high salinity and low nutrients. This study aims of examining if the Red Sea is a potential resource for cellulase-producing microorganisms and cellulase genes. First, I investigated types of microbial cellulase genes in the Red Sea based on public metagenomic datasets. The analysis revealed 3,383 microbial cellulase were more abundant in shallow depth than in deep seawater, and were classified into 16 sub-GH orthologous groups. These results suggest that the Red Sea environment is potentially an excellent gene resource of microbial cellulases due to its high diversity. Next, cellulase-producing microorganisms were isolated and screened from the Red Sea. Three bacterial and one fungal strain were successfully obtained. The MLTS analysis showed that the three bacterial strains belong to Bacillus paralichiniformis. The 18S rRNA of fungal strain showed 99% similarity to Aspergillus ustus and the enzymatic assay of the four strains showed high cellulase activity. These results suggest that these four isolates secreted active cellulases. Next, I tried to identify cellulase genes actually working during their cellulolysis by conducting comparative transcriptome analysis of the candidate genes and identified cellulase genes that are highly expressed during cellulolysis. To my knowledge, it is the first attempt to find out cellulase genes functioning during their cellulolysis among distinct cellulases on genomes of microorganisms. The results showed that although all the candidate genes were upregulated in general, a limited number of cellulase genes were highly expressed, which are highly expected to have a crucial role in cellulolysis. I also identified operon structures composed of genes including cellulases. This will provide us with the information to elucidate the cellular mechanisms occurring along with the cellulolysis in bacterial strains. We can expect that the Red Sea is a potential resource for new cellulase genes applicable for the industry. These information can be significantly useful for the bio-prospecting research of microbial cellulases in the Red Sea.

These studies on the plankton of Tomales Bay were designed to determine the effects of such physical factors as tides, temperatures, salinities and sunshine on the quantities of various types of organisms, and to obtain a more comprehensive picture of estuarine life at the Pacific Marine Station. The studies were begun in the summer of 1948 and continued through the summer of 1953. Although various studies have been conducted on different aspects of marine plankton, the only general treatments of the subject of which the writer is aware are those of Johnstone (1924), Ricketts and Calvin (1951), Sproaton (1949) and Sverdup (19461). It is hoped that these additional studies will be of general interest to biologists and that they may form the basis for the solution of some of the many intriguing problems which have been encountered and are here presented in graphic form.

Thesis (M.Sc. (Aquaculture)) -- University of Limpopo, 2022 / The aim of this study was to provide baseline limnology data that can be used in the management of small dams, Molepo Dam and Hout River Dam. Physico-chemical parameters were assessed to determine the water quality and the effect of water level fluctuations on water quality. Water temperature, pH, dissolved oxygen, turbidity, electrical conductivity, nitrate, total phosphorus, total nitrogen and chlorophyll-a were assessed during the dry season (May-Oct) and wet season (Nov-Apr). Physico chemical parameters showed seasonal variations with the exception of pH. The mean total phosphorus (1.06 and 0.98 mg/L), total nitrogen (1.27 and 1.56 mg/L) and chlorophyll-a (2.97 and 3.32 µg/L) were higher in the dry season than wet season in Molepo Dam and Hout River Dam respectively. Water level fluctuations had a significant effect on total nitrogen, total phosphorus and turbidity in Molepo Dam and total nitrogen in Hout River Dam. Plankton were used as indicators of water quality. Phytoplankton and zooplankton were sampled using nets of 71 µm and 132 µm mesh respectively and identified to genus and species at both Molepo Dam and Hout River Dam. Individual species, number per litre for phytoplankton groups that contributed significantly in terms of abundance were Microcystis aeruginosa and Oscillatoria sp. in both Molepo Dam and Hout River Dam during the dry season months. The Shannon-Wiener diversity index was high during the wet season in these small dams. The abundance of Cyanophyta was greatest during the dry season followed by Desmids in Molepo Dam and Hout River Dam. During the wet season, Bacillariophyta were not recorded for Hout River Dam. The highest composition for Chlorophyta (15.4%) in Molepo Dam was recorded during the wet season months. Phytoplankton abundance was highest in Molepo Dam as compared to Hout River Dam throughout the sampling period. Zooplankton was dominated by Cladocerans (Bosmina longirostris) in both small dams. This study showed that plankton can be used as indicators of water quality. Zooplankton communities were dominated by Bosmina longirostris which was present throughout the sampling period possibly indicating clear water in Molepo Dam and Hout River Dam. Copepoda were sub-dominant phyla mainly represented by Cycloid sp. which are also indicators of clean water. The study determined the abundance and composition of fish species and growth parameters of the most abundant fish species (Oreochromis mossambicus) in the two small dams. Scales were successfully used for the age determination of O. mossambicus. The rings on the scales were validated as being true annuli by marginal increment analysis which indicated that the distance between the last annuli and the scale edge was shortest in the wet season months in Molepo Dam and Hout River Dam. This is the time in which annulus formed. Annulus formation of O. mossambicus at these small dams coincided with the onset of increased water temperature and rainfall (increased water levels and increased water inflow into the dams) in this region. Furthermore, the growth performance index (ϕ) of male O. mossambicus was higher than that of female O. mossambicus in both Molepo Dam and Hout River Dam. The study provides the first record of limnology baseline data of Molepo Dam and Hout River Dam / National Research Foundation (NRF) and Department of Agriculture, Forestry and Fisheries (DAFF)

The nature and extent of microbial biodiversity remain controversial with persistent debates over patterns of distributions (i.e. cosmopolitanism vs. endemism) and the processes that structure these patterns (neutrality vs. selection). We used culture-independent approaches to address these issues focusing on two groups of ciliates, the Oligotrichia (Spirotrichea) and Choreotrichea (Spirotrichea). To assess the diversity of these ciliates, we designed primers specific to SSU rDNA of ciliates within these clades, and investigated (1) geographic and temporal distributions along three coastal sites in the Northwest Atlantic; (2) the relationship between ciliate communities in the benthos and the plankton along the New England coast; and (3) diversity in ciliate communities across an environmental gradient at six stations in Long Island Sound spanning the frontal region that separates the fresher Connecticut River outflow plume from the open Sound. Each collection had its own distinct assemblage of rare and abundant ciliate haplotypes, and genealogical analyses of our samples combined with published sequences from identified morphospecies reveal that haplotype diversity at these sites is greatest within the genus Strombidium, in the Oligotrichia. Clustering of phylogenetic types indicates that benthic assemblages of oligotrichs and choreotrichs appear to be more like those from spatially distinct benthic communities than the ciliate communities sampled in the water above them. Neither ciliate diversity nor species composition showed any clear relationship to measured environmental parameters (temperature, salinity, accessory pigment composition, and chorophyll), although we observed that diversity decreased moving from nearshore to offshore. We find no strong fit of our communities to log series, geometric, or log normal distributions, though one of the 3 clusters is most consistent with a log series distribution. These analyses suggest that Oligotrich and Choreotrich communities in coastal environments may be distributed in a neutral manner. We investigated the effectiveness of molecular approaches in characterizing ciliate diversity in our samples. Estimates of diversity based on molecular markers are similar to estimates from morphological observations for Choreotrich ciliates, but much greater for Oligotrich ciliates. Sediment and plankton subsamples differed in their robustness to repeated subsampling. Sediment gave variable estimates of diversity while plankton subsamples produced consistent results.

No description available.

No description available.

This study documents the occurrence of dinoflagellate, chlorophyte, and acritarch cysts from the Upper Cretaceous upper Cusseta, Ripley, and lower Providence Formations in the USGS Fort Gaines core, drilled in Clay County, Georgia. A total of 75 taxa were identified, consisting of 36 genera, 61 species, and 5 subspecies of dinoflagellates, 3 genera and 4 species of chlorophytes, 3 genera and 4 species of acritarchs, and 1 problematical protozoan. 15 of these taxa are unpublished. The study's cyst assemblage was statistically analyzed to ascertain paleoecologic patterns. The results from cluster analysis and detrended correspondence analysis indicate the presence of four cyst associations. The <i>Deflandrea pannucea</i> association is interpreted as indicative of low salinity related to nearby river discharge. The <i>Deflandrea</i> sp. A association is confined to the inner shelf. The <i>Exochosphaeridium bifidum</i> and <i>Glaphyrocysta reticulosa</i> associations alternate under normal marine conditions. The associations correlate well with observed lithologies and lithologic change. Comparison of this study's assemblage with other Late Cretaceous assemblages provides limited information, since many biostratigraphically-important species are not present in this study. However, comparisons with Wilson's (1974), Benson's (1976), and Firth's (1984) zonations suggest a Lower Maastrichtian age for all strata in this study. / M.S.