No description available.

No description available.

A study was made of the terrestrial and freshwater algae of Aldabra Atoll, Indian Ocean. Field work was carried out between September 1972 and June 1973. Wide ranging excursions were made to various areas of the atoll in order to collect information on the species present together with physico-chemical and descriptive data from representative habitats. Data were collected in a standard manner and stored in a computable form using a modified version of a stream recording system devised in Durham, 1053 samples were collected during the field study, of which 521 were complete with detailed taxonomic and environmental data. The latter are stored on computer file at Durham. The 521 samples constituted an Aldabran data bank and a range of computer programmes facilitated the rapid retrieval of information and the performing of statistical analyses. An example of one such statistical analysis is included in the present study. A taxonomic checklist is given of the 291 species together with descriptions of these species, comparisons with the descriptions given by other authors, the areas of Aldabra from which they were recorded, notes on distribution on Aldabra, habitats, abundance and comparisons with records of other workers. Blue-green algae are the most abundant species present, predominating in both terrestrial and freshwater habitats. In terrestrial habitats they are often present almost to the exclusion of other species, though in freshwater habitats this predominance is less well-marked. It is probable that some species are restricted to certain regions or habitats: the reasons for such restriction are discussed. A study of one physiological process in blue-green algae is presented. The nitrogen-fixing potential of Tolypothrix byssoidea and several Nostoc species was investigated using the acetylene reduction assay technique. The study includes rates measured between 0930 and 1200 h, a 24 h time course study for Nostoc Commune and laboratory studies on the onset of acetylene reduction after rewetting.

This thesis reports a study of the dominant communities of photosynthetic prokaryotes, growing in the intertidal zone of the lagoon of Aldabra Atoll, Indian Ocean. The work was carried out from November 197A- to June 1975. Physico-chemical and descriptive data collected from standard transects of the intertidal zone are presented, together with the Eh-pH ranges of various communities associated with lagoon sediments. A taxonomic checklist is given of species from marine and brackish habitats, with descriptions and notes on distribution and abundance. More detailed studies were made on various communities of blue-green algae and photosynthetic bacteria. These included estimations of standing crop, the monitoring of physico-chemical parameters over 24 hour periods, and studies on the ability to fix nitrogen in situ as indicated by the acetylene reduction assay technique.

In the last decade diatoms have been shown to release. a wide range of secondary metabolites, such as polyunsaturated aldehydes (PUAs), produced by a wound-activated mechanism. PUAs are highly reactive molecules that in most cases induce a drastic reduction in the reproductive response of predators, such as copepods. The variable toxicity of diatoms observed in nature suggests a modulation of PUA production by environmental factors. My results indicate a strong dependence ofPUA production on culture age, nutrient limitation and other stress factors, such as UV exposure and low light conditions, in cultures of Skeletonema marinoi, suggesting a direct link between toxin production and cell physiological state. Since it has been hypothesized that PUAs may be released in seawater also as a I result of cell mortality, phytoplankton lysis rates were estimated during four oceanographic cruises conducted during periods of diatom blooms in the Northern Adriatic Sea. High lysis rates were observed and preliminary results indicated substantial amounts ofPUAs released in seawater. The effects of dissolved PUAs were therefore investigated on organisms other than predators, such as cooccurring bacteria and phytoplankton in culture. PUAs are toxic for several phytoplankton species at concentrations well within the range potentially produced by diatoms. Diatoms can be immunized by sub-lethal concentrations of PUAs. In this case, PUAs may act as signal molecules for bloom termination. PUAs induce also different effects on bacterial growth; some strains are inhibited while others show remarkable resistance to these compounds, and a few of them were even stimulated. Therefore, PUAs appear to have multiple functions in diatoms, namely as chemical defense against grazers, allelochemicals against phytoplankton and bacteria, and signal molecules within their populations.

Small scale patchiness of phytoplankton biomass was the area around a single sampling station on a freshwater lake (Charnwood Water, Loughborough) between October l978 and October 1981. Patchiness in zooplankton and nutrients was also investigated. Data were initially examined by one-way analysis of variance in order to separate actual variation from measurement error. Nested analysis of variance models were used to examine the relative contributions of horizontal. vertical and diurnal variation and two-way analysis of variance was used to examine the importance of horizontal variation on the resolution of seasonal changes in phytoplankton biomass.

Algal blooms are a major worldwide water treatment concern due to their potentially harmful effects on humans and livestock. The main cause of algal bloom proliferation is eutrophication of water sources. Anthropogenic effects contribute significantly to the increased levels of nutrients within source waters. With the world‘s population continuing to grow the likelihood is that algal blooms will worsen in the future. Algal blooms can cause release of toxins which in high concentrations are a serious health hazard for humans and animals. Blooms ability to grow rapidly consuming nutrients and oxygen, at such an elevated rate that anoxia can occur increasing the incidences of fish kills and rates of bacterial growth, consequently recreational use of water sources may be suspended. From a water treatment perspective algal cells can block filters for example diatoms, green species increase turbidity and chlorophyll a, and cyanobacteria produce taste and odour issues related usually to toxin release among other problems increasing the chemical demand necessary to treat the water supply. Algal bloom control measures that are presently employed range from nutrient limitation to aeration and destratification. Phosphorus and nitrogen are the two main nutrients which enhance bloom growth, so if prevention of nutrient accumulation could be implemented this would be considered the best solution for bloom prevention, yet this has proved to be difficult. To find bloom control methods which are green that is to consume little energy, reduce water treatment costs and chemical use in water treatment, is a challenge. However recent investigations into the use of ultrasound have confirmed it as being one such method. Successful use of ultrasound in numerous other applications including wastewater treatment made it an ideal candidate to test as a green solution to algal bloom control. Cont/d.

No description available.

Emiliania huxleyi is an ecologically important marine phytoplankton and it is regularly forms large blooms. Viruses are an important agent of mortality in blooms, however, little is known about the host: virus interactions in this system. This project investigated how infection at different stages of the host cell cycle influenced: virus adsorption, infection and production and host lysis and cell cycle. Cultures were infected during the G l , S or G2 + M phase and monitored for 2 hours for adsorption and infection or monitored for 48 hours for virus production, host lysis and host cell cycle. A three fold increase in infection during the G2 + M phase was recorded, however there was no significant difference in virus adsorption or virus production between phases. Cultures infected in the G2 + M phase lysed faster than cultures infected Gl or S phase and there was a three fold increase in infection success if infected during the G2 + M phase. This may be due to changes in the host at the point of cell division. All cultures showed a deviation from the normal cell cycle activity after 24 hours of infection and remained in a stable, compromised state after this point. Virus production was independent of infection phase, this result may have been an artefact of the virulent nature of the system as the infected hosts began to lyse 4 hours after infection enabling a constant supply of viruses and repeated infections outside the initial phase of infection. The ecological significance of these findings is believed to maintain a variation in virus production and host loss which allows both components of the systems to perpetuate.

For the conservation and management of natural resources, a detailed knowledge of the ecology and genetics of individual species is essential. Red seaweeds are an important component of marine ecosystems but few species have been the focus of research. Gracilariopsis longissima is a poorly studied member of a family of agarophytes of commercial importance, although it is thought to occur commonly around the coast of Britain. This report provides new information about the ecology and population genetics of the species with the identification of 11 populations around the coasts of Devon and Cornwall, seven of which were in the Fal Estuary and Helford River complex. Site characteristics are described, in particular with regard to substrata which were found to be significantly different between sites. New ecological data about algal assemblages in which Gs. longissima occurs is reported for spring (four sites) and summer (five sites), with significant differences seen for all except two sites. Anecdotal reports that Gs. longissima grows mainly on smaller substrata were investigated but were unsupported by the evidence, although a non-random distribution with respect to substrate size was found, which needs further investigation. Microsatellites were newly developed for the species but were thought to be monomorphic and were not pursued. Cross-genera amplification with Gracilaria gracilis microsatellites did not provide sufficiently reliable data. A number of molecular methods were optimised and used to identify populations and investigate the genetics of three populations. These results are the first report of population genetics in the species. Intra-population genetic variation was seen to be high when estimated using RAPD primers and was accompanied by significant differentiation between the populations investigated. Biofilms occur on almost all submerged aquatic surfaces, including living organisms. Gs. longissima is no exception: epiphytes and biofilms were investigated and found to be highly diverse and well-attached, with some thalli in some populations completely obscured by overgrowth. Cleaning methods were tested, with mechanical removal proving to be the most successful. Biofilms were also found to affect RAPD profiles, confirming that cleaning of wild collected specimens was essential for reliable RAPD data to be obtained.