Investigation of the Carbohydrates synthesised by the marine green alga Ace tabulara a crenulata. By means of sequential extractions with different solvents the following carbohydrates were isolated and characterised. 1. From an alcoholic extract D-glucose, D-fructose, allulose, myo-inositol and an alcohol tentatively identified as allo-quercitol. This is only the second time allulose has been found in Nature and the first time in any alga. An homologous series of fructose-containing oligosaccharides were also separated and characterised as 2,1 linked units terminated by a molecule of sucrose at the potential reducing end. 2, Aqueous extraction gave a mixture of a fructan (major) and a sulphated heteropolysaccharide. a) These two polysaccharides were separated on a column of DEAE-cellulose. Using the classical techniques the fructan was characterised as an inulin type polysaccharide, b) (i) The sulphated polysaccharide contained D-glucuronic acid, B-galactose, L-rhamnose and small proportions of xylose and 4-0-methylgalactose. Each of the sugars were separated and characterised. The presence of the last sugar has not been reported as a constituent of any green algal polysaccharide before, (ii) By extraction of stalks and caps separately with cold and hot water and elution from the DEAE-cellulose with 0.5 and 1.0 M potassium chloride similar sulphated polysaccharideswith variable proportions of the different sugars and portions of sulphate were separated. (iii) Structural studies by partial desulphation, methylation, periodate oxidation and partial hydrolysis established the essential similarity of these fractions and that the main structural features are: highly branched molecules containing1,3-linked D-galactose 4-sulphate (major) and 6-sulphate, 1,2-linked Larhamnose and glucuronic acid, galactose and rhamnose all present as end groups. Glucuronic acid is linked to both rhamnose and galactose and galactose units are mutually linked in the macromoiecule. 3. linked mannan was extracted with alkali. Methylation,periodate oxidation and gel filtration studies proved this structure and indicated some degree of branching and a higher molecular weight than those of previously reported for mannans from green algae. PART II: Photosynthetic studies on 1. Acetabularia mediterranea, 2. Fucusvesiculosus and 3. Ulva lactuca1. Pulse labelling experiments with C0 on A.mediterraneafollowed by ethanolic extraction led to the separation of labelled sucrose, glucose, fructose and the first three oligosaccharides characterised in Part 1 (l). A possible biosynthetic inter-conversion of these carbohydrates is described from the results of these experiments. 2. a) Pulse labelling experiments with C0 on Fucus vesiculosas a marine bcrown alga, show that of the low molecular weight carbohydrates formed by photosynthesis, mannitol is formed first The possible conversion of mannitol into laminaran via mono-and di- glucosylmannitol is discussed*b) The polysaccharides, laminaran, xylogalactofucoglucuronan (A), xylogluouronogalactofucan (B), fucoidan (C) and alginic acid were extracted and separated by various fractionation techniques. The radioactivity in each was measured as was the radioactivity in the constituent sugars of the fucose-containing polysaccharides (all of which are sulphated). From the changes in the radioactivity of these polysaccharides in different samples it is postulated that (a) is synthesised first and transformed into (C) via (B).Low molecular weight carbohydrates present in the acid extract are suggested as precursors for the acid polysaccharides. The residual material after acid and alkali extraction was hydrolysed and the radioactivity of the sugars in the hydrolysate wasivmeasured. Glucose was the major radioactive sugar.3. Ulva lactuca, a marine green alga. Similar experiments on U.lactuca were carried out.a) Examination of the 80% ethanol extracts showed that sucrose is the first sugar to be synthesised and this is followed by glucose and fructose. Xylose, ribose(?) and myo-inositol also incorporated radioactivity.b) Starch and a sulphated glucuronoxylcrharrman were extractedand their radioactivities were measured. The former appears to be synthesised most rapidly and to be an active metabolite and the sulphated polysaccharide is laid down as a long term storage product or as part of the skeletal structure of the alga.c) The residual material after ethanolic and aqueous extractions was examined in the same way. Glucose is again the major sugar and the results indicate that the carbohydrate is laid down in the cell wall after other constituents.

1.1. The polysaccharides of two Antarctic brown algae have been studied. 2.1. Ascoseira has been chemically investigated for the first time. 2.2. After extraction of traces of mannitol and some monosaccharides, sequential extraction with aqueous Ca Clg, dilute acid and dilute alkali gave mixtures of laminaran, "fucan" and alginate in unusually low total recovery. 2.3. Laminaran fractions from the aqueous and alkali extracts contained different proportions of 3-(l→3)- and 3-(l→6)- linked units, with evidence of branching in both fractions. 2.4. The "fucans" contained varying proportions of fucose, galactose and glucuronic acid, small amounts of xylose, mannose and glucose, and half-ester sulphate and protein. 2.5. The alginate in the aqueous extract contained about 75% mannuronate residues, that of the alkali extract about 80% guluronate residues. Direct alkaline extraction gave a low molecular weight alginate with a mannuronate to guluronate ratio of about 0.45 and only a small proportion of sequences of alternating residues. 3.1 The mucilaginous exudate, and the "fucan" therein, from the kelp Macrocystis pyrifera have been found to be physically and chemically similar to the same materials from a Californian sample of M. pyrifera. 3.2. Sequential extraction of the Antarctic sample gave "fucan", alginate and a trace of laminaran. 3.3. The "fucan" in the aqueous CaCl₂ extract was shownby partial hydrolysis to be composed of subunits containing about 70% fucose, varying small proportions of xylose, mannose, glucose, galactose and glucuronic acid, and half-ester sulphate and protein. Sulphate was linked only to fucose, and predominantly to carbon atom 4. Further partial hydrolysis gave complex fragments with evidence of mutual and various linkages of most of the monosaccharide residues. Tentative evidence of covalent linkage of protein and polysaccharide was found. 3.4. Direct alkaline extraction of Antarctic M. pyrifera gave a high molecular weight alginate with a mannuronate to guluronate ratio of about 0.95 and a relatively high proportion of sequences of alternating residues.

The ecology and taxonomy of dinoflagellates was investigated in 1982 and 1983 in sea-lochs and coastal waters of north-western Scotland, in order to provide a better understanding of conditions leading to blooms harmful to mariculture. Because such blooms are rare the ecology of all common thecate dinoflagellates was studied, particular attention being paid to the cyst stage and its role in bloom initiation. Creran, a fjordic sea-loch near Oban, was the main site of study; water column sampling was carried out regularly in 1982 and 1983 and the sediments were sampled for cysts in 1983. Distribution of motile dinoflagellates and their cysts on the west coast of Scotland was also investigated on cruises of the R.V. Calanus in the summers of 1982 and 1983. Identification of cells was carried out by light microscopy supplemented by studies using scanning electron microscopy. Links between cysts and motile stages were made by hatching experiments, and these and scanning electron microscopy have led to the discovery of some new cyst-theca relationships. In Loch Creran the first peak of dinoflagellate numbers occurred in May or June with warming of the water column and was dominated by Scrippsiella spp., accompanied in 1983 by Gonyaulax tamarensis. During July and August there was a mixed population, including Serippsiella spp., Heterocapsa triquetra, Protoperidinium spp. and Diplopsalis spp. Salinity stratification at the end of August preceded an autumn succession of G. polyedra, Prorocentrum micans and Ceratium species. Observations suggest that G. polyedra cysts sink rapidly and are retained within the loch, seeding blooms in subsequent years. Two other life strategies were hypothesized as the causes for different observed patterns of seasonal distribution. One involves non-cyst-forming species (for example Protoperidiniumbipes and Prorocentrum micans) present in the loch as motile cells in small numbers throughout the year, and occasionally reaching high concentrations. The other involves species (for example Protoperidinium depressum and Ceratium furca) whose motile cells are transported to the loch by tidal exchange or estuarine circulation from the sea outside. Seventy-two species of motile thecate dinoflagellates were found in the distributional study. Dinoflagellate abundance and variety were greatest in well- or partially-stratified water columns. Of potentially toxic species only Gonyaulax tamarensis was found to be widespread in 1983. Cysts varied in their distribution, with numbers higher in sea-lochs than in Firths and Sounds. Considerable sub-surface populations of cysts were noted in the sediments and viable cysts were encountered at 5 cm depth.

Climate change is rapidly reducing the Arctic Ocean summer sea ice cover, consequently altering the patterns of primary production, with reducing ice algal-, but increasing phytoplankton primary production. As benthic consumers rely on the sinking phytodetritus for food, changes to food availability could render the benthos vulnerable if they prefer ice algae as a food source. The aim this thesis was to investigate the benthic macroinfaunal dietary reliance on ice algae and phytoplankton in North Water Polynya (NOW) and Lancaster Sound (LS) in Canadian Arctic Archipelago, and how a shift from one food source to another impacts the benthic community resource utilisation and nutrient cycling processes. I hypothesised that ice algae would be preferentially consumed and respired by the benthos. Natural abundance stable isotope analysis showed that phytoplankton is the main food source for macroinfauna in NOW and LS. 13C-15N isotope tracer experiments showed that while in NOW the accumulative macroinfaunal uptake of ice algal C was higher than uptake of ice algae, in LS more ice algal C and N was consumed. None of the major taxonomic groups exclusively preferred ice algae. No difference in bacterial uptake of the two algal types was observed at either site, but the respiration of phytoplankton C was significantly higher than respiration of ice algal C. The processing rates of phytoplankton-derived C were 39–46% higher than processing rates of ice algal C. Therefore, the hypothesis of ice algal preference by benthos must be rejected. I conclude that benthic macroinfauna exhibit great dietary flexibility, making them resilient against climate mediated changes in food sources, and that increasing availability of phytoplankton food can benefit the benthos in the future. Additionally, the transition from ice algae to phytoplankton dominated food can significantly enhance benthic organic matter processing, and especially respiration, rates in the future.

Biofouling, through undesirable colonisation of surfaces by marine organisms, is responsible for significant economic and environmental impacts that justify the use of antifouling (AF) coatings. Extracts from cultivable microalgae were investigated as a sustainable and eco-friendly source of AF compounds. A multi-functional bioassay was developed to test microalgal extracts against biofilm-forming bacteria and diatoms (behaviour, growth, adhesion, toxicity, species interactions). The AF activity of extracts from seven microalgae was investigated against microfoulers, macroalgae and barnacles, and, the impact of stresses was assessed. Inhibitory activities were recorded against a wide spectrum of organisms between 0.01 and 100 μg.mL-1, and complex doseresponses with stimulatory effects were highlighted. The AF activity was improved using competition and dark stress on marine microalgae, and was repressed using predation on freshwater species. Replicate experiments conducted using dark stress demonstrated the stability of stress responses, when comparing AF activity and metabolic profiles, for Cylindrotheca closterium and Thalassiosira pseudonana. These strains, which showed high biomass and extract yields (5%-10%), were further studied for fractionation and field-tests. Fractions of intermediate polarity from C. closterium demonstrated the most potential in the laboratory. In the field tests, Cc5 still showed moderate activity against early formation of algal slime in Portsmouth, and Cc6 reduced invertebrates’ settlement in Toulon. The microalgal culture-associated bacteria studied showed high diversity, microalgal proximity, and multifaceted chemical interactions. A comparative study showed that microalgal and bacterial extracts exhibited different patterns of AF activity and distinct chemical signatures, confirming the microalgal origin of extracts studied throughout. This work proposed a multi-functional AF screening of microalgal compounds for a better understanding of the mode of action, it demonstrated the tangible potential of microalgal extracts for AF applications, and it addressed the limits of an AF strategy based solely on chemical interactions - encouraging future use of combinatory approaches.

For the first time, presented within this thesis, is an investigation into the species richness and community composition of a group of beautiful but taxonomically challenging green algae - the desmids. This thesis represents the first account of a systematic sampling approach for desmid species and community assemblages in relation to national and local environmental variation. Sampling was focused on intact blanket mire with the aim of capturing a rich baseline dataset of desmid diversity. Previous works had highlighted desmids as being especially species rich in these acidic, nutrient-poor peatland habitats. A nested sampling approach was used to collect desmids from blanket mire microhabitats along the hummock-pool microtopographic gradient, from sites nationally within Scotland. This approach revealed remarkable species richness with 202 taxa sampled, including one new species. Distinct desmid communities were found to be strongly associated with the hummock-lawn-pool microhabitats within patterned blanket mire. This topographic aspect of peatland structure and its associated co-variables (such as pH and water table depth) also have a strong link to desmid diversity with the richest communities being found in association with a consistent supply of water close to the water table. Generally, ‘unstable' habitats supported lower desmid diversity. A field experiment was established to investigate the effects of drainage and drain restoration on desmid communities. This highlighted the loss of desmid diversity in drained peatlands and a successful but slow recovery of diversity upon restoration through drain blocking. The findings of this PhD project provide an understanding of the spatial scale of desmid community structure and the factors which are important for informing future conservation strategies for peatland habitats to maintain the diversity of this fascinating microbial group.

This study examines the influence of intertidal macroalgae on sediment accumulation, and the effect of sediment cover on intertidal community structure. Three shores on the North Yorkshire coast, England, were used to investigate differences in the quantity of sediment trapped by ten morphologically different algal species, and the relationship between morphology and the quantity of sediment trapped. The quantity of sediment accumulated in quadrats of four different macroalgal communities (canopy, turf, canopy/turf and bare rock) was also examined. Differences in sediment cover and community structure were investigated on the intertidal rocky shore at Holbeck, North Yorkshire. The distribution and position of both were described using transects across three sites, whilst relationships were examined using 54 fixed quadrats in the mid shore. Across three different shores the mass of dried sediment g⁻¹ macroalgal dry mass was found to differ between macroalgal species. All measured aspects of macroalgal morphology correlated with the quantity of sediment trapped. Macroalgae with different morphologies trapped different gram size compositions but no differences were found hi the quantity of sediment accumulated by turf, canopy, bare rock or unmanipulated algal communities. At three different sites at Holbeck, the site with the greatest sediment cover had lower macroalgal species diversity, richness and total abundance, patellid and littorinid abundance. Although differences were found in sediment cover between sites in the mid shore, no differences were found hi community structure. Sediment cover had negative correlations with macroalgal richness and diversity in algal quadrats, but positive correlations with macroalgal abundance and diversity in bare rock quadrats. Within individual macroalgae morphology was found to affect the quantity of sediment trapped, however at quadrat level macroalgal morphology had no effect. At both the level of the quadrat and the whole shore sediment cover influenced community structure, whilst within the mid shore alone sediment cover did not affect community structure. This work suggests that relationships/interactions between sedimentation and intertidal community structure are scale dependent.

This thesis concerns two aspects of microorganism behaviour. Firstly, the phenomenon of bioconvection is explored, where suspensions of motile microorganisms that are denser than the fluid in which they swim spontaneously form concentrated aggregations of cells that drive fluid motion, forming intricate patterns. The cells considered herein orientate by gyrotaxis, a balance between a gravitational torque due to uneven starch deposits causing cells to be bottom heavy and a viscous torque due to fluid flow gradients, and phototaxis, biased movement towards or away from a light source. In Chapters 2 and 3, a stochastic continuum model for gyrotaxis is extended to include phototaxis using three physically diverse and novel methods. A linear stability analysis is performed for each model and the most unstable wavenumber for a range of parameter values is predicted. For two of the models, sufficiently strong illumination is found to stabilize all wavenumbers compared to the gyrotaxis only case. Phototaxis is also found to yield non-zero critical wavenumbers under such strong illumination. Two mechanisms that lead to oscillatory solutions are presented. Dramatically different results are found for the third model, where instabilities arise even in the absence of fluid flow. In Chapter 4, an experimental study of pattern formation by the photo-gyrotactic unicellular green alga species Chlamydomonas nivalis is presented. Fourier analysis is used to extract the wavelength of the initial dominant mode. Variations in red light illumination are found to have no significant effect on the initial pattern wavelength. However, fascinating trends for the effects of cell concentration and white light intensity on cells illuminated either from above or below are described. This work concludes with comparisons between theoretical predictions and experimental results, between which good agreement is found. Secondly, we investigate the intracellular pathways and processes that lead to hydrogen production upon implementation of a two-stage sulphur deprivation method in the green alga C. reinhardtii. In Chapter 5, a novel model of this system is constructed from a consideration of the main cellular processes. Model results for a range of initial conditions are found to be consistent with published experimental results. In Chapter 6, a parameter sensitivity of the model is performed and a study in which different sulphur input functions are used to optimize the yield of hydrogen gas over a set time is presented, with the aim of improving the commercial and economic viability of algal hydrogen production. One such continuous sulphur input function is found to significantly increase the yield of hydrogen gas compared to using the discontinuous two-stage cycling of Ghirardi et al. (2000).

Photosynthetic picoeukaryotes (PPEs) are single celled algae of <3μm diameter, present in both marine and freshwater environments. Marine PPEs have begun to gain increasing recognition as important, ubiquitous primary producers, after largely being overlooked in favour of the more numerous picocyanobacteria for many years. Molecular studies have shown the group to be extremely diverse. However, most molecular studies have used PCR with general primers targeting the nuclear 18S rRNA gene to construct clone libraries and have been dominated by heterotrophic picoeukaryotes. To overcome this problem, more recent molecular studies have targeted the 16S rRNA gene of marine algal plastids, an approach which essentially excludes heterotrophic organisms. In this PhD thesis, the molecular diversity of the PPE community was analysed over broad spatial scales using both 16S and 18S rRNA gene markers to begin to draw global conclusions on the phylogenetic composition of this group and identify the major players in marine CO2 fixation. Moreover, distributions of various PPE classes were also analysed along a range of cruise transects with dot blot hybridisation of PCR amplified DNA using class-specific plastid 16S rRNA gene targeted oligonucleotide probes. All major ocean basins were analysed, encompassing a range of nutrient regimes and latitudes. The dot blot hybridisation approach revealed that the classes Prymnesiophyceae and Chrysophyceae appeared to be ubiquitous and dominated the PPE community throughout large expanses of the global ocean. Furthermore, these classes showed strongly complementary distributions along some of the transects analysed. Clone library construction demonstrated that both classes are comprised of an array of genetic lineages, many with no close cultured counterpart. For one cruise transect, the extended Ellett Line in the North Atlantic Ocean, a fluorescent in situ hybridisation approach was used as a PCR-independent assessment of the PPE community. This approach largely supported the dot blot hybridisation data. Other classes, Cryptophyceae, Pinguiophyceae, Pelagophyceae, Eustigmatophyceae, Pavlovophyceae, Trebouxiouphyceae, Chlorarachniophyceae and Prasinophyceae clade VI, were detected at lower abundances by dot blot hybridisation, with some classes restricted to specific sites. Multivariate statistics indicated that the distribution patterns of PPE classes were influenced by both temperature and nutrient concentrations. However, at the global scale, a large proportion of the variation in dot blot hybridisation data could not be explained by the environmental parameters measured. It is likely that the classes harbour different ecotypes which are individually influenced by environmental factors. Furthermore, biotic parameters not measured in this work e.g. viral lysis, predation or parasitic infection may have been important in controlling the PPE community.

The determination of calcareous chlorophyte distributional limits is via temperatures---namely isocrymal limits, because the green algae are very susceptible to cold temperatures. The calcereous green algae are today and were in the past, one of the most sensitive and useful environmental indicators. As well as being useful in distribution analysis, they are a useful part of biotic analysis in general. Calcareous green algae are mostly, but not wholly tropical in nature---they are found in shallow marine environments up to their range extent of just into temperate water masses (12&deg;C isocrymal). The Dasycladales were dominated form of calcareous alga in the Jurassic (today their role has been largely taken over by the Halimidaceae). It can be seen that in the Upper Jurassic (where there are enough datapoints to form a reasonable limit, as opposed to the Lower or Mid Jurassic) that the Halimedaceae appeared to terminate at a line slightly southwards of the Dasycladales (this compares with the modern situation of a shared termination limit). Modern calcareous Chlorophyta distributions can delimit in the 12&deg;C isocrymal water temperature boundary, and this limit can be imposed on the Jurassic Chlorophyta distribution dataset for palaeothermometry purposes. Together with selected isotope values, it is possible to estimate Jurassic isocrymes across Western Europe. This suggests the possibility of creatures such as belemnites (which are used for isotopically derived palaeotemperatures) having recorded summer temperatures in their isotopes rather than annual average. Modern algal temperature value differences (isocrymal versus summer maximum) is by &sim;10&deg;C and this change in values for the Jurassic Chlorophyta produces temperature figures equivalent to a majority of the isotopically derived temperature values.