Marine Habitat: Estuaries
Estuaries are where rivers meet the sea – where salt water mixes with fresh as the tide goes in and out.
Because so many rivers and streams flow in the Strait of Georgia and Puget Sound, the whole area is really a huge estuarine system.
Estuaries are the most biologically productive ecosystems on earth, more productive than grasslands, forests, and even areas of intensive agriculture.
Estuaries make up less than 3% of BC's 27,000 km of coastline (DFO, Review of Estuary Management Plans in BC, 2004).
Yet 80% of our wildlife depend on estuaries for survival. For example:
River nutrients are passed up the foodchain to predators such as bald eagles.
Migrating birds need extensive wetlands when winter snow and ice cover nearby fields, ponds and streams.
After hatching upstream, salmon fry depend on estuaries to grow and acclimate to salt water before heading out to sea.
Salmon also depend on estuaries at the end of their life cycle, when they return to the rivers to spawn.
Estuaries and other wetlands are essential to humans as well. Estuary silt is an irreplaceable pollution filter, cleansing inshore waters and removing toxins such as sulphur dioxide from the air.
Snow geese in the Fraser estuary.
The Fraser River delta is our region's largest estuary. It is the only coastal waypoint of its kind between California and Alaska. Birds from 20 countries and 3 continents depend on the estuary for overwintering or for rest and sustenance during their long annual migration along the Pacific Flyway.
BC Nature Trust has identified three other estuaries around the Strait of Georgia which are also of international significance for migratory birds:
- Comox (1300 hectares)
- Denman Island (2500 hectares)
Cowichan-Chemainus (2000 hectares)
Losing any of these intertidal wetlands would have a severe impact on migratory bird populations – and some species are already endangered.
Nevertheless, coastal estuaries are threatened.
Pollution from the forest industry can harm fragile estuary ecologies:
Toxic wood preservatives from sawmills (even after they've ceased operations) can damage salmon habitat.
Bark and sunken wood waste from log booms decay, which removes oxygen from the shallow water. This smothers bottom life and suffocates fish.
Toxic chemicals from pulp mill effluents get into the aquatic food chain, becoming contentrated in larger animals at the top of the chain.
Around the Strait of Georgia, the biggest pressure on estuary habitat is from urban development and sprawl. Over recent decades, Georgia Strait's estuaries have been disappearing under golf courses, condominiums and trailer parks.
Examples of loss of saltmarsh:
|Nanaimo estuary||more than 50%|
|Cowichan estuary||more than 50%|