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When most people mention reefs, they usually mean coral reefs, without realising that reefs can be extensive in temperate (cooler) waters. There are fundamental differences in the structure and dynamics of tropical and temperate reefs.
Temperate reefs consist of a rocky substrate, which is colonised by a range of algae and attached invertebrates. Coral reefs are built up by small animals that secrete a calcium carbonate skeleton (corals). Temperate waters are cooler and nutrient levels tend to be higher compared to reefs in tropical waters.
In contrast to the domination by corals on tropical reefs, the dominant biota on temperate reefs are generally macroalgae where there is enough light. In temperate systems, the majority of carbon fixed is via these large algae. In tropical systems, the majority of carbon fixed is by the symbiotic relationship of microscopic algae living in the tissue of sponges and corals. Contrary to common belief, corals are common in temperate waters, but they do not build reefs here.
Australia's Unique South
Australia is well known for its spectacular tropical coral reefs, such as Ningaloo Reef in Western Australia and the Great Barrier Reef in Queensland.
The reefs of Victoria's southern temperate waters are also truly unique. Victoria's long south-facing coastline means we have a huge temperate (or cold water) marine environment.
Australia's many millions of years of geographical isolation means our reefs and marine environment have developed in response to an uncommon combination of environmental forces.
Not surprisingly, the marine life of southern Australia contain a multitude of species found nowhere else on earth. While coral reefs support a huge variety of fish species, it is the temperate southern areas that support a greater diversity of marine life (especially flora and invertebrate fauna). Researchers call this region Australia's Unique South.
The Unique flora and fauna of Victoria's marine environment
Consider these facts: 85% of the temperate fish species, 95% of the species of molluscs and 90% of the species of sea stars or sea urchins (echinoderms) are unique to temperate Australia. Huge ranges of sea squirts (ascidians) are also found, with 189 species recorded. Many of these species are reef dwellers at some stage of their life cycle.
As a comparison in the tropics, where many species tend to disperse more widely, only 13% of fish species, 10% of molluscs and 13% of echinoderms are unique to the region.
In Southern waters 1100 species of red algae described so far represent 25% of the world's total, with 75% of them being unique to our region.
Many ships have come to grief in Victoria waters, plus there is an extensive Ships' Graveyard in Bass Strait, not far from the entrance to Port Phillip Bay and the Port of Melbourne. These wrecks have all become exciting artificial reefs and home to thousands of marine creatures.