Diversity, ecology and domoic acid production of <i>Pseudo-nitzschia</i> spp. in Scottish waters

Some diatoms of the genus Pseudo-nitzschia produce the toxin domoic acid (DA). Accumulation of DA in shellfish has led to harvesting closures in western Scottish waters since 1999. This thesis investigated the diversity, ecology and distribution of toxic and non-toxic Pseudo-nitzschia species in western Scottish waters and physiological aspects of growth and toxin production dynamics of P. seriata. The temporal and spatial distribution of phytoplankton was analysed in two separate field studies. 1) Temporal changes were followed by sampling a site in coastal Scottish waters weekly to fortnightly over a period of three years. 2) The spatial distribution of the phytoplankton community was investigated by sampling a transect across the shelf. Within both studies, physical, biological and chemical parameters were measured and correlated to temporal and spatial distribution patterns in the phytoplankton community, indicating seasonality, and differences in the distribution of toxic and non-toxic Pseudo-nitzschia species between coastal and offshore waters. From those samplings 59 clonal cultures of Pseudo-nitzschia, comprising 7 species (2 of them toxic), were established. Strains were identified via classic morphological and genetic techniques. Phylogenetic relationships were established between Scottish Pseudo-nitzschia strains. P. seriata was identified for the first time in Scottish waters as a DA producer. Laboratory experiments with cultured strains showed a) enhanced toxin production by P. seriata under silicate (Si) and phosphate (P) limitation, with higher DA production under Si than under P limitation b) similar cell yields of P. seriata, when grown in nitrate or ammonia based media c) a preference for spring light conditions (short day length) in a non-toxic P. delicatissima strain and summer light conditions (long day length) for a toxic P. seriata strain, expressed by enhanced biomass yield under the respective light condition. It was also shown that the presence of bacteria enhanced the growth of single P. seriata cells

The Relationship between Phytoplankton Distribution and Water Column Characteristics in North West European Shelf Sea Waters

Phytoplankton underpin the marine food web in shelf seas, with some species having properties that are harmful to human health and coastal aquaculture. Pressures such as climate change and anthropogenic nutrient input are hypothesized to influence phytoplankton community composition and distribution. Yet the primary environmental drivers in shelf seas are poorly understood. To begin to address this in North Western European waters, the phytoplankton community composition was assessed in light of measured physical and chemical drivers during the “Ellett Line” cruise of autumn 2001 across the Scottish Continental shelf and into adjacent open Atlantic waters. Spatial variability existed in both phytoplankton and environmental conditions, with clear differences not only between on and off shelf stations but also between different on shelf locations. Temperature/salinity plots demonstrated different water masses existed in the region. In turn, principal component analysis (PCA), of the measured environmental conditions (temperature, salinity, water density and inorganic nutrient concentrations) clearly discriminated between shelf and oceanic stations on the basis of DIN∶DSi ratio that was correlated with both salinity and temperature. Discrimination between shelf stations was also related to this ratio, but also the concentration of DIN and DSi. The phytoplankton community was diatom dominated, with multidimensional scaling (MDS) demonstrating spatial variability in its composition. Redundancy analysis (RDA) was used to investigate the link between environment and the phytoplankton community. This demonstrated a significant relationship between community composition and water mass as indexed by salinity (whole community), and both salinity and DIN∶DSi (diatoms alone). Diatoms of the Pseudo-nitzschia seriata group occurred at densities potentially harmful to shellfish aquaculture, with the potential for toxicity being elevated by the likelihood of DSi limitation of growth at most stations and depths

Diversity, ecology and domoic acid production of Pseudo-nitzschia spp. in Scottish waters

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Depth profiles and contour plots of nutrients at stations M and F.

<p>Depth profiles of: (a) dissolved inorganic phosphate (DIN), (b) silicate (DSi) and (c) nitrate (DIN) concentrations in µM within the top 250 m at stations M and F. Contour plots of (d) dissolved inorganic phosphate, (e) dissolved inorganic silicate, (f) dissolved inorganic nitrate, for shelf stations 1G to 10G.</p

PCA eigenvalues.

<p>Eigenvalues of the environmental variables: coefficients in the linear combinations of variables making up principal components of PCA.</p

Temperature, salinity and density depth profiles and contour plots.

<p>Depth profiles of: (a) Temperature, (b) salinity and (c) density profiles within the top 250 m of at Open Atlantic stations M and F. Contour plots of (d) water temperature [°C], (e) salinity and (f) density, for shelf stations 1G to 10G.</p

MDS ordinations of environmental variables.

<p>MDS ordination of stations along the Ellett Line transect, sampled during D257. Samples above 100 m depth were included, data were fourth root transformed. (a) all stations, (b) expanded view of stations 1G, 2G, 4G, 6G, 7G, 10G.</p