Phytoplankton succession and resting stage occurrence in three regions in Sechelt Inlet, British Columbia

• Main Author: Sutherland, Terri
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/30379

Phytoplankton were monitored in three regions in Sechelt Inlet, British Columbia between June and September in 1989. The purpose was to compare the phytoplankton community (region I) transported into the inlet via a strong tidal jet to that which exists inside the inlet (region II) and in an inner shallow basin (region III). Core samples were also collected to compare the phytoplankton present at the water-sediment interface. In 1989 between June and September the temperature, salinity, and nutrient profiles show that the hydrographic conditions in region I were well-mixed, while those in region III were well-stratified. The conditions in region II fluctuated between mixed and stratified conditions. The depths of the 1 % light levels were generally deeper in region I. The depth of the 1 % light level fell above the nitricline in region II on September 25 and in region III on June 9 and July 8. In region III nitrogen and ammonium levels fell below 1 μM in the surface waters between June 25 and September 8. The nitrogen to phosphorus ratios in regions I, II, and III were 8.6, 7.5, and 7.2 respectively. Diatoms exhibited the highest relative biomass of the total phytoplankton groups in regions I and II. Fluctuations within each plankton group were more gradual in region III than those in region I. A reciprocal dominance of diatom to dinoflagellate biomass was observed from one sampling trip to another. The vertical distributions of dinoflagellates, photosynthetic flagellates, and diatoms reveal uniform profiles in region I and thin horizontal layers in region II and III. The biomass maxima of these phytoplankton groups in region III generally remain below the nutrient-depleted surface waters. A temporal succession was observed in region I. Small changes in the relative percent of successional phytoplankton stages in region II and III were observed over the sampling period. The distribution of potentially harmful phytoplankton such as Heterosigma akashiwo, Protogonyaulax catenella and P. tamarensis, Prorocentrum minimum, Dinophysis fortii and D. acuminata, Chaetoceros convolutum and Ch. concavicorne, and Nitzschia pungens are discussed in the text. The water-sediment interface samples of region III in contained the highest number of phytoplankton. Chaetoceros spp. resting spores were found only in region III. Auxospores of Skeletonema costatum were formed only in the incubated cores of region I and III. The mean diameter of sedimented S. costatum cells found in the core samples was significantly different than the mean cell diameter of the larger post-auxospore cells. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate