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Dinoflagellates and vitamin B12 in the Strait of Georgia, British Columbia Cattell, Sidney Allen

Abstract

The purpose of this study was to compare the distribution of dinoflagellates in the Strait of Georgia, British Columbia with a number of environmental parameters, and in particular with vitamin B₁₂ concentrations. The latter was determined by a modified bioassay technique, employing the marine dinoflagellate, Amphidinium carterae Hulburt. The conclusions are based on the analysis of 511 samples from 19 cruises. The annual cycle of vitamin B₁₂ found to be characterized by three major peaks of concentration: 1) a peak following the spring 'bloom' of phytoplankton; 2) a summer increase that was closely associated with silt particles contained in river runoff; and 3) a fall maximum that followed the breakdown of density gradients in the water column. Seventy-seven species of dinoflagellates were recorded from the Strait of Georgia. The temporal distribution of dinoflagellates was divided into two distinct periods of abundance: one occurring during the early spring months and another during the summer months. The results of multiple regression analyses between the dinoflagellates and the environmental parameters measured (vitamin B₁₂, nitrogen, phosphorus, zooplankton, temperature, salinity and sunlight) indicated that the size of the dinoflagellate community in the early spring was closely associated with vitamin B₁₂ concentration in the water column. Nitrogen concentration was apparently a significant factor in determining the size of the community during the late summer months. Phosphorus concentration did not appear to be closely related with total dinoflagellate numbers. The composition and seasonal distribution of the dinoflagellates was found to be essentially similar to that of other northern temperate neritic waters. The major exception was the presence of a distinct spring component in the Strait of Georgia, consisting largely of small nonthecate species.

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