Phytoplankton ecology of Sechelt Inlet, a fjord system on the British Columbia coast. I. General features of the nano- and microplankton

Abstract

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 21m of 8.3, well below the Redfield ratio of 16, suggests an N-limited system. 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 nordenskioldii, occurred early (in March) due to the combined influence of stratification, created by runoff from Salmon Inlet, 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 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 inlets. There was also high biomass at the shallow southern end possibly due to increased mixing over a sill and mild eutrophication. -from Authors