High-resolution sediment trap study of organic-walled dinoflagellate cyst production and biogenic silica flux in Saanich Inlet (BC, Canada)

Dinoflagellate cyst fluxes and assemblage composition were investigated from November 2007 to February 2010 in Patricia Bay, Saanich Inlet (BC, Canada). Samples were collected using a sediment trap deployed at ~97m water depth. The sampling interval ranged from 0.5 to 19.5days, allowing for a high-resolution study of dinoflagellate cyst production in relation to measured environmental parameters. Ninety-six samples were collected and a total of 42 dinoflagellate cyst taxa were identified. The dinoflagellate cyst flux was very high and ranged from ~149,000 to ~2,400,000cystsm^-2day^-1, with an average of ~777,000cystsm^-2day^-1.Seasonal and interannual variation in cyst assemblage was recorded. It reflects changes in environmental parameters such as sea-surface temperature, sea-surface salinity, solar insolation, river discharge, and biogenic silica flux. Fluxes of cysts produced by autotrophic dinoflagellates, particularly Spiniferites spp. and Spiniferites bentorii, were greatest during winter. Spring dinoflagellate cyst assemblages were dominated by Brigantedinium spp. and Quinquecuspis concreta. In summer the assemblages were characterized by an increase of cysts produced by heterotrophic dinoflagellates, in particular by Echinidinium delicatum, E. cf. delicatum, Votadinium spinosum and cysts of Protoperidinium minutum. Multivariate statistical analysis performed on the data supports the observed seasonal trends, where winter taxa are associated with low sea-surface temperatures, low salinity, and high Cowichan River discharge, whereas summer taxa are associated with warmer sea-surface temperatures, higher solar insolation and increased biogenic silica flux. The cyst assemblage from nearby surface sediment was shown to be very similar to an annual average sediment trap assemblage.