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

Abstract

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.

Date of Award	6 Jul 2004
Original language	English
Awarding Institution	The Open University
Sponsors	UHI Studentship
Supervisor	Keith Davidson (Supervisor), Paul Tett (Supervisor) & Chris J S Bolch (Supervisor)