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Since many approaches to dealing with algal blooms are inefficient, expensive, or harmful, it was concluded that a biologically-synthesized chemical agent, specifically inhibitory to pre-bloom algal cells, might prove helpful in controlling algal blooms. Fungi were chosen as the biological entities to investigate for such a chemical.

A culture collection of clonal, axenic cultures of 35 Arthrospira strains and five strains, which were duplicate subcultures of the original isolates, was established. In addition, eight morphological mutants were isolated from cultures of these strains. All strains are different from those belonging to the genus Spirulina as concluded from TEM and PyMS studies. All Arthrospira strains, duplicates and different morphotypes were screened for variation in morphological, ultrastructural, physiological and biochemical characters for taxonomic purposes. Special emphasis was put on the analysis of factors which influence the morphology of the trichome helix, as this is the feature most characteristic forArthrospira strains. For example, the orientation of coiling was found to be influenced by genetic drift or the growth temperature, but can also be reversed by mechanical impact. Studies were also made on the ability to utilize sugars for growth. None of the strains grew on sucrose, but many grew on glucose and/or fructose. Growth in the presence of sucrose under photoheterotrophic conditions required an adaptation process, though sucrose is not being utilized for growth. Analysis of fatty acid composition of all strains revealed quantitative differences between strains, most markedly in the unsaturated fatty acid fraction. Repeat experiments showed the same results each time, indicating the value of this approach for identification purposes. Similarly, lectin-binding to cell surface structures proved to be a useful approach for differentiation between strains. Analysis of the whole cell composition by pyrolysis mass spectrometry (PyMS) did not confirm the clusters based on other phenotypic characters, but showed that there is a high similarity between duplicate strains or different morphotypes derived from the same stock. Numerical analysis of the data for 28 characters resolved the helical strains in two phenotypic clusters which show a high correlation to the two molecular clusters based on ARDRA of the ITS of the same set of strains. The helical trichome morphology of the strains showed the highest correlation to either of the clusters. Comparison of species descriptions and morphological characters of the strains, as determined in the presented work, indicate, that phenotypic cluster I is composed of Arthrospira maxima, A. fusiformis and A. indica, while A. platensis forms phenotypic cluster II

The use of algae as heavy metal bioindicators in aquatic environments has received much attention. In this study, the performance of a common freshwater living green alga, Cladophora sp. as a mercury bioindicator and its potential for phytoremediation applications was assessed by various parameters which included the influence of contact time, pH, initial mercury concentration and the presence of competing metal cations. A rapid uptake of mercury by Cladophora sp. was displayed. More than 99% of mercury in solution was removed within the first 5 min of contact and equilibrium was attained after 10 min. High adsorption capacities of 800 mg kg-1, 530 mg kg-1 and 590 mg kg-1 at pH 3, 6.5 and 8.5 respectively were obtained at the optimum mercury concentration of 1.0 mg l-1. Competitive adsorption studies showed that the selectivity of heavy metal cations by Cladophora sp. was in the following order: Hg2+ ˃Fe2+˃Cu2+˃ Zn2+ ˃ Co2+. These results indicate that living Cladophora sp. algae are suitable for use as mercury bioindicators in AMD waters and are also suitable for the removal of mercury in AMD conditions.

Algal/invertebratee ndosymbioseas re common in the marinee nvironmenta nd appeart o be nutritional in nature. The giant Tridacnid clams form a mutualistic extracellular endosymbiosis with dinoflagellate algae (zooxanthellae) of the species Symbiodiniunt microadriaticum. The large size of the Tridacnids is generally attributed to the nutritional role of their endosymbionts. This thesis examines the nature and mechanisms by which important biochemicals, such as lipids, are translocated from the symbionts to the host. Methodologies have been developed to enable the determination of the carbon isotope composition of individual saturated and polyunsaturated fatty acids to enable natural abundance isotopic variations in these compounds to be investigated in the Tridacnid-algal symbiosis. Compound specific isotope analysis of fatty acids in different species of Tridacnids, their zooxanthellae and non-symbiotic species reveal that several fatty acids are apparently directly translocated from algae to host. Evidence is presented for the synthesis of fatty acids from acetate by the clam. Carbon isotopic data also reveal that carbon limitation may play a role in lipid metabolsim in giant clams. Compound specific isotope analysis has also been used to investigate the contribution of translocated compounds during a diel cycle in clam haemolymph and reveals that concentrations of key metabolites vary over the diel cycle as a function of irradiance. The cyclic sugar alcohol scyllo-inositol was detected in clam haemolymph, which may be related to osmoregulation in the clam or to a signalling role in cell proliferation. Oxygen and carbon stable isotope compositions and strontium abundances of shell carbonate are examined in several clams subjected to varying degrees of phosphate and ammonium nutrient supplementation to investigate the relationship between growth rate and stable isotope compositions and strontium contents.