PHYTOPLANKTON ECOLOGY OF SECHELT INLET, A FJORD SYSTEM ON THE BRITISH-COLUMBIA COAST .1. GENERAL FEATURES OF THE NANOPLANKTON AND MICROPLANKTON

The Sechelt Inlet complex (British Columbia, Canada), including Narrows and Salmon Inlets, was sampled from May 1988 to September 1990 in order to describe the nutrient and plankton regimes. Species succession within the inlet was typical for temperate unpolluted waters despite aquaculture activity and nutrient-loading from the town of Sechelt at the southern end. The N : P ratio in the upper 21 m of 8.3, which is well below the Redfield ratio of 16, suggests an N-limited system. The ratio is also lower than those found in adjacent systems, and supports the assumption that Sechelt Inlet is the least influenced by oceanic waters. The N:P ratio also coincides with the optimum ratio for Skeletonema costatum of 8.1 which suggests that either the system provided an optimal nutrient regime for this diatom or the dominance of S. costatum determined ambient N: P ratios. The spring bloom, dominated by S. costatum and Thalassiosira nordenskioeldii, occurred early (in March) due to the combined influence of stratification, created by runoff from Salmon Inlet, and shelter from wind exposure. By summer the waters became depleted of nitrate down to 5 m, and nanoplankton, composed chiefly of cryptomonads and Chrysochromulina spp., prevailed. Bimodal peaks in nanoflagellate biomass occurred each summer, with the cryptomonads remaining regular components. Under normal meteorological conditions Chrysochromulina spp. would codominate but during 1989, storm activity in May somehow caused the replacement of the prymnesiomonads by the silicoflagellate Dictyocha speculum. The latter occurred in its askeletal form during the late summer nanoflagellate peak. The water injected through the mouth of Sechelt Inlet by a tidal jet combined with water overlying the anoxic bottom of inner Narrows Inlet and caused stimulation of plankton growth at the confluence of these 2 inlets. There was also high biomass at the shallow southern end possibly due to increased mixing over a sill and mild eutrophication.