This thesis examines the phytoplankton diversity in the Oslo Fjord and the seasonality of the size, shape and abundance of the genus Dinophysis Ehrenberg. The genus, which contains several toxin-producing species, has previously been shown to at times be highly form variable, and delimitation of some of the species has been the subject of much discussion.
Samples were gathered from station Missingene (OF2) in the outer Oslo Fjord. Net hauls and natural water samples were collected for cell quantification and size measurements nearly once per month between the late summer of 2009 and the early summer of 2011.
Cell counts were performed in an inverted microscope and used to examine seasonality of diatoms and dinoflagellates, as well as to calculate the biodiversity through Shannon's diversity index and species richness. Photographs of Dinophysis cells in net haul samples were used to measure length and width of individuals.
Shannon's diversity index showed between 1.13 and 3.53 bits, with no clear correlation to neither temperature nor salinity, and no significant variation between the seasons. Between 16 and 53 total species were found in cell counts for any given month from this study, with an average of approximately 28 total species per month. Species richness did not correlate with salinity nor temperature, and did not appear to vary with the seasons. 90 separate species were registered between 2009 and 2010, and 82 species were found between 2010 and 2011.
Diatoms and dinoflagellates followed a previously reported pattern in which diatom abundance was higher than that of dinoflagellates throughout the sampling period, with the exceptions of late spring/early summer in 2010 and 2011. Vernal blooms of particularly Skeletonema spp. and Pseudo-nitzschia spp. were detected in January 2010 and February 2011.
Dinophysis acuminata and D. norvegica were found to be the two most abundant species of their genus, and made up most of the Dinophysis species detected during cell counts. Dinophysis acuminata and D. norvegica both showed a short-lived abundance increase in the late spring/early summer of 2010, showing cell numbers of up to 1000 cells L-1 and 1600 cells L-1, respectively.
Dinophysis acuminata and D. norvegica both had highly variable cell sizes, whereas D. rotundata did not show the same morphological variation. Most cell sizes did not conform to previously reported size ranges.
Hydrographical data showed a correlation with the sizes of D. acuminata, D. norvegica and D. rotundata, though high significance (p <0.0005) was only shown with temperature against the length and salinity against the length-width ratio of D. acuminata cells. Dinophysis acuta did not have a sufficient sample size to provide any statistical significance.