Review of the Benthos of the Strait of Georgia and Contiguous Fjords

Abstract

The distribution of benthic communities in the Strait of Georgia is partially determined by the relative areas of various sediment types, their depths, and characteristics of overlying water. Rocky shores, which account for 88% of the shoreline length, have been fairly closely examined and communities have been described in the context of worldwide zonation patterns. The ecology of macrofauna and meiofauna of unconsolidated sediments at several estuaries (Nanaimo, Fraser, Squamish) has been documented. In eelgrass beds, very diverse invertebrate communities are found, whereas in brackish marshes closer to river mouths the ecosystem is characterized by a few very abundant species. To date, between 325 and 350 macroalgae species have been recorded from the shallow subtidal habitats of the Strait. In an intensive study at Bath Island, 10 algal communities were defined, each with an associated faunal group. The deep subtidal habitats are extensive: 71% of the surface area of the bottom of the Strait is between 50 and 300 m. These habitats are dominated by burrowing macrofauna such as holothurians, bivalves, and the heart urchin, Brisaster latifrons. The fauna of the rocky walls of fjords connecting with the Strait are characterized by cup corals, brachiopods, and sponges. Even though subject to low and fluctuating dissolved oxygen levels, a diverse fauna of epilithic organisms has been found in Saanich Inlet. Agglomeration, flocculation, and zooplankton pelletization are important mechanisms for transport of phytodetrital food for deep subtidal benthos. Provision of organic material from nearshore and riverine production sites is very important because of the extensive shoreline around the Strait. Juvenile salmonids, especially chinook (Oncorhynchus tshawytscha) and chum (O. keta), are strongly shoreline oriented and feed on epibenthic crustaceans and insects on foreshores. The deeper subtidal habitats in the Strait apparently do not support productive bottom fish communities. Although the major benthic assemblages have been described and standing crops have been estimated, there are very few data on the dynamics of benthic communities, secondary production of zoobenthos, benthic–pelagic coupling, or the quantitative relationships between oceanographic variables and benthic production.