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Phytoplankton ecology of Gwaii Haanas, Queen Charlotte Islands, British Columbia Toews, Heather Naomi Juliet

Abstract

A National Marine Conservation Area (NMCA) has been proposed for the waters around Gwaii Haanas National Park Reserve/Haida Heritage Site and Parks Canada is interested in obtaining information on the marine resources in the surrounding waters in order to monitor and manage this marine area. Samples were taken from the waters of the fjords and island passages of the proposed NMCA in order to study the relationships between physical and chemical parameters and abundance and diversity of the phytoplankton in these nearshore areas of Gwaii Haanas. This thesis reports nutrient concentrations, phytoplankton biomass (chlorophyll), and physical parameters during the summers (July and August) of 2001 and 2002 for these waters. Samples were collected using the PV Gwaii Haanas II as a ship-of-opportunity. A total often cruises were conducted and samples were taken for salinity, temperature, density, total suspended solids, Secchi disk depth, nitrate, phosphate, and silicic acid concentrations, chlorophyll a concentrations in two size fractions, and samples for phytoplankton identification. These data were compared for spatial and interannual differences by comparing coasts (east vs. west) and by comparing years (2001 vs. 2002). Variability was very high and few comparisons were significant. Mixed layers were shallow or non-existent on both coasts and in both years. Nutrient concentrations were significantly higher in 2002 than in 2001 as there was a greater intensity of upwelling in 2002 as compared with 2001. Nitrate was observed to be a factor limiting phytoplankton growth in a large proportion of stations, and consequently N:P and N:Si ratios were lower than that required for phytoplankton growth. Surface chlorophyll a concentrations showed no differences, but integrated chlorophyll a concentrations showed significantly higher concentrations in 2002 than in 2001. There was more sunlight and less precipitation in 2002 compared to 2001 and there was more phytoplankton at depth as the light penetrated deeper. The most abundant phytoplankton species were Leptocylindrus danicus, Chaetoceros spp., Thalassiosira spp., Skeletonema costatum, and a group of Pseudonitzschia species referred to as "A". Canonical correspondence analysis (CCA) was performed on these data to determine the relationships between environmental variables and phytoplankton community composition. Most of the phytoplankton species and groups were observed where nutrient concentrations were high and the depth of light penetration was greater than average. Dinoflagellates were more often found in warmer water while diatoms were more often found where the water was colder. The depth of the mixed layer had the least influence on phytoplankton distribution while the silicic acid concentration had the greatest influence. This contradicts the real data which found silicic acid to be not a limiting factor at any of the stations. There was little spatial variability found in nutrient and chlorophyll a concentrations, only silicic acid had a significant difference between coasts with higher concentrations on the west coast than the east and the large size fraction (> 5 μm) of chlorophyll a was higher on the east coast than the west coast. Temporal variability was observed with higher nutrient and integrated chlorophyll a concentrations in 2002 compared to 2001. This study has provided the first extensive near-shore physical, chemical, and biological data in the waters surrounding Gwaii Haanas National Park Reserve/Haida Heritage Site, documenting nutrient and chlorophyll concentrations as well as providing a phytoplankton species list. These data will be useful as a baseline for continuing studies throughout Gwaii Haanas as it becomes an NMCA.

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