Bays and Estuaries

Barwon Bluff estuary and bay

The Barwon Bluff is perched at the mouth of the Barwon River facing the open coast of Bass Strait. It is important in protecting the estuary and works in partnership with the Ocean Grove Spit. The Barwon River meanders through mangroves and mudflats before it reaches the sea at the base of the Bluff.

Estuaries are formed where rivers meet the sea and where fresh water and sea water mix, in an area partly enclosed by land. Most estuaries have been shaped, over time, by the action of tides, waves, and river flows. A critical factor in an estuary is the level of salinity. Because of the variation in the freshwater and seawater mixing, there are many different ecosystems – some marine, some inter-tidal, some partially freshwater/land systems.

Seagrasses are critical to estuary life. Seagrass beds are the most productive areas in the world. Seagrasses generate more food matter per square metre than any other plant system, except for tropical forests.

Mudflats are places without vegetation where low tides leave soft muddy sediments exposed to the air. They are important feeding areas for many birds and fish. They are teeming with worms, small crustaceans such as crabs and burrowing shrimp, and a variety of snails and other molluscs, many of which use broken down organic debris washed into these areas for food.

Mudflats are made up of very fine particles that restrict water movement into the soil and have little oxygen below the surface. This contributes to the black colour and smelly gases produced in these habitats. These characteristics are due to the activities of bacteria that can survive in the thick airless mud.

Most animals that live in the mud have burrows or special features that allow them to get oxygen from the water above. Animals found in mudflats include Soldier Crab (Mictyris platycheles), Flatworm (Platyhelminthes), Moon Snail (Polinices conicus), Sharptailed Sandpiper (Calidris acuminate) and Wavy Volute (Amoria undulate).