Temporal variations among planktonic diatom asseblages in a turbulent environment of the southern Strait of Georgia, British Columbia, Canada

Abstract

We examined the species composition and concentration of planktonic algae as well as irradiance and near-surface temperature and salinity 3 times per week for 1 yr in a turbulent marine environment with continously high nutrient concentrations. Seasonal variations in temperature and salinity were small, and diatoms composed the largest percentage of phytoplankton (≤5 μ) cell numbers throughout the year. We observed at last 96 diatom species, of which some present throughout mot of the year while others were observed for periods as short as 1 to 2 wk. Diatom species diveristy reached minimum and maximum values during winter and summer months, respectively, and was positively correlated to temperature and daylength correlated to salinity. Winter and spring blooms occured and were numerically dominated by small and large cells of Skeletonema costatum, respectively, and Pseudo-nitzschia delicatissima, resulting in minimum seasonal values of species, which peaked during summer months. The first 4 axes of a canonical correspondence analysis (CCA) explained 76% of the variance in the variance in the diatom data; the measured environmental variables explained 90% of this variation, of which temperature had a dominant role. We discuss possible environmental optima of 44 diatom species based on results of CCA and make suggestions regarding altered measures of diversity.