Millions of years of Victorian marine and coastal environments

Victoria’s marine and coastal environments formed millions of years ago at the edge of the Gondwana supercontinent.

Isolated for around 65 million years, the high species richness and diversity of Australia’s southern coast is influenced by the resulting enclosed element as well as temperate, tropical and cold-water elements.

Scientists estimate humans have occupied Victoria’s south east for at least the past 30,000 years, with recent archaeology investigations suggesting 120,000 years ago for the site of Moyjil in Warrnambool, Victoria, and offers intriguing possibilities of much earlier occupation (Proceedings of the Royal Society of Victoria, 2018). The site contains remains of shellfish, crabs and fish in what may be a ‘midden’, but definitive proof of human occupation is lacking and investigations are ongoing (reference Australia Museum). The archaeology of sites in Victoria illustrates Traditional Owners’ cultural connection with the land.

Molten rock accumulated and formed around what is now the Mornington Peninsula and gradually a mountain range began to erode on a fringe of Gondwana which would eventually become Port Phillip Bay.

Victoria’s coastal geology is a broad representation of the rest of the state, hosting rocks from Cambrian (580 million years ago) to the earlier Quaternary dune systems and sedimentary lagoons (10,000 years ago).

The Victorian coastline has been influenced by tectonic activity and earth movements as well as sea level changes, faulting, uplift and subsidence. Coastal landforms evolved due to interactions between geological factors and coastal processes like ocean swell, storm surge, wind, current, changing sea levels and tidal activity.

Victoria’s coast continues to be influenced by relatively shallow waters of Bass Strait that drive the degree and direction of wave and storms.

Indigenous Australians occupied the land surrounding the bays, and survived on local food sources. Aboriginal peoples of the coastal and marine areas of Victoria (“Saltwater People”) identify today as Monero/Ngarigo, Bidwell, Yuin, Gunaikurnai, Boon Wurrung, Bunurong, Wurundjeri, Wathaurung/Wadawurrung, Eastern Maar and Gunditjmara.

Cultural, social and spiritual meaning of Sea Country to Aboriginal Victorians is demonstrated in historical and contemporary accounts of Aboriginal dreaming stories. Dating back thousands of years, these stories are vital to understanding the importance of the ecological and social contexts and informing the development of systems that facilitate the cultural application of Sea Country management and care in the contemporary Victorian land and seascape.

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

Learn more about “Saltwater People” and Cultural Landscape Health and Management

 

History specific to Port Phillip Bay and Western Port

Climate change

Pleistocene epoch

Global climate transformed during the Pleistocene epoch, which started about 2.6 million years ago. Chilling temperatures and expansive glaciers have now come to be defined as 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 like 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 Port Phillip Bay and Western Port about 10,000 years ago due to 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.

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 known to host 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 was found. 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.

Many marine animals that once inhabited the bays are now extinct. Grey nurse sharks were plentiful in the bay in the 19th 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 time in the bay.

Links

Learn more about “Saltwater People” and Cultural Landscape Health and Management

Seagrass (Zostera nigricaulis)
Image credit - Julian Finn, Museums Victoria