Responses of subtidal benthos of the Strait of Georgia, British Columbia, Canada to ambient sediment conditions and natural and anthropogenic depositions.

Patterns in infaunal biota in the Strait of Georgia are explored relative to water depth, substrate type, organic content of sediments and sedimentation characteristics. The analyses are based on geographically-diverse grab and core data collected over a 19-year period. Infaunal abundance and biomass were not predictable by sediment particle size, organic content or water depth. While organic flux was a reasonable predictor of biotic factors, quality of organic material, relative proportions of organic and inorganic input and source of inputs were also important in this regard. Areas with high accumulation of sediment and high organic flux rates from terrestrial (riverine) sources supported the highest macro-infaunal abundance and biomass found to date in the Strait of Georgia, and were dominated by bivalves. Polychaetes dominated in low organic deposition conditions, and where anthropogenic organic deposition was high. However, biota were severely impoverished in sediments with high organic content from marine deposition, due to low fluxes and poor quality of organic material. Taxa number was related to percent total nitrogen and to the ratio of organic/inorganic flux, both in background conditions and where there was labile organic enrichment. Faunal communities from the Fraser River delta, which experiences considerable bottom-transported riverine material, were very different in composition from those that proliferate in habitats with high deposition and organic flux from the water column.