Resource Sheet 2 - Oceans Day 2006

Water — From the Mountains to the Seas 2

Estuaries — Where Waters Meet and Mingle

Estuaries are found at river mouths and are where fresh river waters blend with salty ocean waters to form an array of productive habitats. In fact, marshes, beaches, dunes, rocky shores and deep-water marine habitats can all be found in estuaries.

There are thousands of estuaries along Canada’s three coastlines. Some, such as the Mackenzie estuary in the Northwest Territories and the St. Lawrence estuary in Quebec, are huge and offer important habitat to belugas and other whales. Others are small but no less important. In the Courtenay River estuary on Vancouver Island, for example, trumpeter swans spend the winter.

A large variety of plants and animals call estuaries home and many more spend at least part of their lives there. Plants, from tall grasses to tiny algae, thrive on the generous buffet of minerals and nutrients that wash down the watershed and settle onto the ocean bed as the currents slow. They, in turn, support a flourishing food chain of crabs, clams, oysters, snails and other shellfish. Seals, whales and fish, including sharks, likewise come to dine … just as you might visit your favourite restaurant!

The bounty of a rich habitat comes with a price, so not all kinds of plants and animals can survive here. Estuaries have constantly changing salt concentrations, water levels and temperatures. For example, the salt content in the water can vary from ocean strength (3.5 per cent) to almost none (fresh water actually has a concentration of about 0.5 per cent). Water that is a mix of fresh and salt is called brackish.

But that’s not the only challenge for estuarine life. Water temperatures and levels can also vary. Depending on the time of the year, the fresh water coming from a watershed can be considerably warmer or colder than the ocean water it meets. Many fish and invertebrate species like lobsters use temperature to tell them when to breed, and sudden changes of even a few degrees can affect their success. Daily tides and seasonal changes in river levels add an additional challenge. Many plants and animals that live here have adapted to spending part of their lives submerged in water and part of their lives high and dry.

Because of their biological richness, estuaries have always been very important to humans:

Historically, estuaries drew Aboriginal Peoples to all three coasts. The abundance of food and availability of fresh water made them ideal locations to live.
Today, the diverse and productive habitats of estuaries support many forms of commercial fishing, bringing salmon, lobster, crab, shrimp, mussels and oysters to your plate.
Estuaries are perfect places for recreation. Boating, swimming, fishing, birdwatching and hunting are among the many activities you can enjoy.
Aquaculture, the farming of marine animals, such as salmon, trout, mussels and oysters, is common in or near estuaries.
Estuaries continue to be important navigation routes for ships.

The Seacoast

The coast is considered to be the part of the ocean shore that excludes the river estuaries. Like estuaries, Canada’s coasts support a variety of habitats, including salt marshes, rocky shores, beaches, dunes and tidal flats. Peatlands, sometimes called muskegs, are special coastal wetlands that are very common in the north.

Coastal habitats are more exposed to the open ocean than estuaries, so they receive more of their nutrients and materials from waves and tides. But they are also affected by watersheds. Fresh and brackish water from estuaries can be carried along the coast by ocean currents and dilute the salt concentration of seawater. Nutrients, sand and silt can likewise make their way along the coast.

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