Northeastern view from Bicheno, Tasmania
Northeastern view from Bicheno, Tasmania Image: Don Colgan
© Australian Museum

Conserving the structures established by long-term evolutionary processes is critical for long-term biodiversity sustainability.

In my most recent research, I confirmed eight main genetic boundaries along the coasts of southeastern Australia by examining the interaction of evolution and geography in developing contemporary biodiversity patterns. The breakdown of any one of these boundaries through human activities would cause significant non-natural biodiversity changes but we need to know more about the origins of the boundaries and the threats they face before being able to draw conclusions.

This research results from a review of work by myself and many others who have studied numerous plants and vertebrate and invertebrate animals using mitochondrial DNA sequencing and other genetic techniques. I examined whether the geographic patterns of genetic variation could be explained by factors such as areas of unsuitable habitat, physical geography, ocean currents and sea surface temperatures or their interaction.

The boundaries between the three major biogreographical provinces of southern Australia are also genetic boundaries. These are the junctions between the Peronian and Maugean provinces in southern New South Wales and the Maugean and Flindersian provinces in South Australia. Three main boundaries are associated with unsuitable habitat. Long sandy stretches on the Ninety Mile Beach in Victoria and the Younghusband Peninsula/Coorong in South Australia affect species from the rocky intertidal, and Bass Strait acts as a barrier for coastal species with short larval lives.

Looking south from Green Cape, NSW
Looking south from Green Cape in the overlap of the Peronian and Maugean biogeographic provinces. Image: Don Colgan
© Australian Museum

Blue Mussel, Genus Mytilus, on a rock
Blue Mussel, Genus Mytilus Image: Dr Isobel Bennett
© Australian Museum

The three most important genetic boundaries are associated with the Bassian Isthmus which is the landbridge formed between Wilsons Promontory in Victoria and northeastern Tasmania when sea levels fall during periods of maximum glaciation (the growing of glaciers and lowering of sea levels). Species can be divided into separate populations by the bridge of land that is formed when sea levels fall. The evolutionary divergence between the separated populations may continue when they meet after sea levels rise as glacial ice melts. Many organisms continue to show geographic separation on either side of the Wilsons Promontory, northeastern Tasmania and southeastern Tasmania.

Genetic structure in the coastal fauna of southeastern Australia is predominantly associated with a small number of areas. We need to know more about the origins and maintenance of this structure before we can conserve the structure effectively for the long-term. But we do know that it is important to prevent species being transported across genetic boundaries by ballast water discharge, hull biofouling or the provision of artificial substrate. Such transport would cause erosion of structure within species thereby reducing their capacity to adapt to local conditions (including by the evolution of new species). We can also predict that climate change will continue to play a part in determining genetic boundaries, with increasing sea surface temperatures and changes to the currents in the region posing challenges for maintaining the capacity of the southeastern Australian system to evolve naturally.

Don Colgan, Principal Research Scientist

More Information: