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Vagrants who take a southerly sea change


 
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Paloma Matis, PhD research student at the University of Technology Sydney, brings insights into the East Australian Current, on its oceanography and on its role in the tropicalisation of temperate reefs as far south as Sydney. Paloma has previously completed an honours degree looking at the oceanography of the East Australian Current (EAC) and its influences on different fish communities. This research was carried out on the CSIRO research vessel the Southern Surveyor. The EAC separates at certain points along the coast, and can recirculate northwards in a phenomenon known as retroflection. This generates commonly observed circulation features including cyclonic and anticyclonic eddies. 


 
Below: Figure from Matis et al. 2014 showing the EAC separation zone and eddies with overlaid sea surface temperate from http://www.marine.csiro.au/remotesensing/oceancurrents/SE    

 

Anticyclonic eddies have cores of warm down welling water. Cyclonic eddies have cores of cool water and, because they are upwelling are also nutrient rich. Some larval fish were found to be entrained from coastal waters into the cyclonic eddy creating a potential offshore nursery ground, providing good conditions for baby fish to grow and develop.

Paloma is now working with Professor David Booth, looking at how tropical fish interact with habitat along the east coast of Australia, from the Great Barrier Reef down to Sydney. She is specifically looking at how habitat may structure range expansion in vagrant tropical fish coming down from tropical reefs to temperate reefs like Sydney. Climate change means that many species are moving with their preferred environmental conditions, changing their geographic distribution. Many move away from the equator towards the poles as species try to cope with the increase in temperature.  

Below: 
Paloma surveying tropical fish interactions with habitat on the Great Barrier Reef


 
Range shifts have been detected in many animals with the long spine sea urchin a well-known example in the marine environment. It has extended its range from NSW right down to Tasmania due to the poleward strengthening of the East Australian Current. Unfortunately the catastrophic impact of overgrazing by these urchins has turned diverse algal forests into rocky barren habitat. 

 

Range shifts are expected to become more prevalent as the climate continues to change so understanding them is important to inform appropriate management strategies. Each year the EAC transports tropical fish larvae from the Great Barrier Reef down to places like Sydney. Tosa Bay in Japan, which is the same latitude north as Sydney is south, has seen a tropicalisation of its waters. Tropical corals and reef fish have established themselves, a result of the Kuroshio Current (similar to the EAC) increasing its surface temperatures by ~2° over the last 30 years. 


 
Below:Juvenile butterfly fish seen during a research dive in Sydney    

There is evidence of broadening of range expansion of tropical fish. Other areas of the world are also undergoing tropicalisation, including South Africa, South America, the US and now Australia. Climate change is driving the rapid pole-ward expansion of tropical reef fish, surrounding pole-ward flowing ocean currents in other areas of the world, including Japan, South Africa, South America, the US and Australia.  


 
Different tropical fish have different levels of habitat specialisation. Some like coral, some like rock, for instance, so Paloma’s research is looking at a suite of fish with various habitat specialisations, from those with specific habitats such as one type of coral to more generalist species. Her research will look at the understanding the role of habitat in influencing which species of butterflyfishes and damsel fishes will be more likely to establish populations in a temperate reef environment.


Paloma Matis was interviewed for A Question of Balance by Ruby Vincent. Images supplied by Paloma Matis. Summary text by Victor Barry, February 2016.


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