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.