How the bays were made

Port Phillip Bay and Western Port

At the edge of the Gondwana supercontinent millions of years ago, molten rock accumulated and formed around what is now the Mornington Peninsula. Gradually a mountain range began to erode on a fringe of Gondwana which would eventually become Port Phillip Bay.

Today, Port Phillip Bay comprises an area of 1,930 km² with a 333 km coastline and over 1,000 species of marine plants and animals.

Western Port was formerly a major river drainage system.

Western Port has an area of 656 km² with two large islands, French Island and Phillip Island.

Climate change

An historical approach ...

Pleistocene epoch

Global climate transformed during the Pleistocene epoch, which started about 2.6 million years ago. Chilling temperatures and expansive glaciers has now come to define the Ice Age. At the peak of this era, 30% of Earth’s surface was covered in ice and sea levels were approximately 120 m lower than today.

Holocene epoch

The Holocene epoch started approximately 11.5 thousand years ago, and reaches to the present day. It is marked by the retreat of the glaciers in an ongoing thawing of the previous Ice Age. The period is defined by a climate which is recognisably warmer and similar to that of today.

Around south-eastern mainland Australia, scientists believe a high level of vegetation replaced the Pleistocene grasslands and herb-fields. Woody plants such as southern beeches began to spread, encouraged by rising precipitation, temperature and rainfall levels, which peaked between 7,000 and 4,000 years ago.

The last 10,000 years

Water filled both bays about 10,000 years ago as a result of the ice sheets melting. Research has been conducted into the rise and fall of sea levels in the bay by using seismic and core dating of the basin’s surface.

Scientists know that the basin dried out during a time of between 2,800 and 1,000 years ago, presumably caused by a sand blockage at The Heads, coupled with high evaporation rates.

The Bunjil Dreaming Story (see animation) recalls a time when Port Phillip Bay was a dry basin, which was used for hunting local fauna.

Flora and fauna

Plant life

Indigenous Australians occupied the land surrounding the bays from about 30,000-40,000 years ago and survived on local food sources unrecognisable today. There was little precipitation, strong winds and low temperatures, so Victoria’s flora was sparse and low-lying. Through the ebb and flow of climate there were periods of lush forests and woodlands, but at this point in time, the vast majority of Australia was treeless and even the iconic Casuarina and Eucalyptus plants were rare, found only in sheltered, wetter micro-habitats’.

Prehistoric animals

Beaumaris Bay is world famous amongst palaeontologists because of its diversity of marine and terrestrial fossils and is home to Australia’s richest marine fossil site.

A list of fossils found around the bays include; extinct marine mammals, molluscs, brachiopods, echinoderms, corals, crustaceans. Beaumaris Bay is the only place in Australia that’s hosted a fossil belonging to Megascyliorhinus, an extinct shark.

In the Black Rock Sandstone at Beaumaris a leg bone of a ‘thunder bird’ Dromornithidae dating as far back as 23 million years ago. Prior to the Pleistocene epoch when the bays were dry, the aquatic basins hosted marine mammal fossils dating back to the early Oligocene, which ended 23.8 million years ago.

Ostrea angasi: mud oyster. Image credit - Julian Finn, Museums Victoria

Where did Port Phillip Bay's shellfish reefs go?

Shellfish reefs, made up of oysters, mussels and other shellfish, were a feature of Port Phillip Bay, providing a rich source of food for the bay’s traditional owners.

The last 100 years

Many marine animals that once inhabited the bays are now extinct. Grey nurse sharks were plentiful in the bay in the 19^th Century, before being exploited by trophy hunters.

According to Parks Victoria, harlequin fish have not been spotted in Port Phillip Bay for over 100 years, though specimens exist of their once living in the bay.

Citizen science

Whales were once frequent visitors to the bays. You can join a campaign to spot, photograph and log a whale sighting in a new program run by the Dolphin Research Institute.

The Two Bays Whale Project is aiming to increase the scientific data and photographic catalogue of siting of whales in the bays. The key species for this citizen science project will be humpback and southern right whales but may also include other species such as killer, minke and blue whales (also occasionally seen in nearby waters).

Contact the Two Bays Whale Project