By Yvette Barry
Coastal waters in many locations around Australia are warming up, according to the CSIRO Marine and Atmospheric Research.
Water temperature monitoring around Australia has revealed a trend of ocean warming.
CSIRO marine scientist Dr Alistair Hobday said most seas have increased in temperature since the 1880s, with some regions changing more than others.
Queensland coastal waters have already warmed about 0.6°C above average since the 1960s; while waters off South Australia have warmed less than 0.5 degrees.
The average sea surface temperature has risen by about 0.8°C on the east coast of Tasmania, southern NSW and eastern Victorian seas compared to the 1960s. These regions are part of the “Tasman Sea hotspot” for ocean warming.
Dr Hobday said the warmer waters along Australia’s east coast were caused by the extension and increased strength of the East Australian Current (EAC) bringing warmer water from the north.
“The East Australian Current is likely to strengthen in the future with a changing climate,” said Dr Hobday. “This will extend warm waters further south and change the tropical and subtropical extents of coastal environments and marine habitats.”
A few degrees rise in water temperature over time doesn’t sound like much. But even small changes impact the distribution and physiology of fish and marine life. Marine species have their own set of conditions they prefer to live in, like temperature and pH. Some biota will move (if they can), also known as shifting their range, in search of these conditions if things get too hot at home. Others may adapt well to warming seas; while some will not survive in the changing conditions.
On the other side of the country, Western Australia has experienced variable coastal warming over the past 20 years. But this is linked to natural variability rather than long-term change. Yet Western Australia’s unusual “marine heatwave” in 2011 saw central and southern coastal temperatures rise more than 3 degrees above average during the March-April period (see satellite image below).
An example of a marine 'heat wave': comparing sea surface temperatures off the coast of Western Australia in the summer of 2005 (left) compared to summer 2011 (right) (CSIRO).
This heatwave was associated with the death of algae and seagrasses, fish and crays, and some coral bleaching. And WA fisheries received more reports of subtropical species like whale sharks, Spanish mackerel, emperor species and damsel fish species that were seen further south than they’re usually found.
“Even though WA’s south-flowing Leeuwin Current is likely to weaken over the coming century, we still expect ocean warming to drive southward range shifts in marine biota and there may be more frequent extreme temperature events,” said Dr Hobday.
Warmer waters lead to changes in biodiversity, population connectivity, ocean productivity and changes in the distribution of pelagic species (those living in the open sea), in particular. This is linked to the southward shift of some marine biota on Australia’s east and west coasts.
Another scenario is playing out in South Australia, which has experienced a relatively weak ocean warming of less than 0.5°C over the last few decades.
“South Australia’s strong coastal upwelling brings cool water to the surface and buffers the impact of sea surface warming even if atmospheric temperatures have risen,” said Dr Hobday.
As such, marine range shifts have not been as clear-cut in SA waters. SA fisheries have had more recent reports of the blue swimmer crab (Portunus pelagicus) further from the gulf areas than it is usually found. And there has been a change in the numbers of some species such as the Sea Lion (Neophoca cinerea) and different kelp species.
But ocean warming is not the only reason why marine life move away from their usual homes. Other factors like pH (e.g. ocean acidification), competition for food or habitat, salinity, currents, fishing activity, storms and pollution – to name just a few – will also influence species distribution.
Given these factors, and the general trend of warming seas, it’s no wonder some marine life are being spotted further away from their usual range along Australia’s coastlines. Possibly looking for cooler waters and their preferred marine conditions?
What about warming in the seas near you? Click on your region below for sea temperature monitoring by the CSIRO, images and potential impacts on marine life:
Acknowledgement: Data shown in these images represent the temperature of water at the surface and are collected by satellite, and processed at CSIRO by Chris Rathbone and colleagues. Further information is available at http://oceancurrent.imos.org.au/. Images prepared by Alistair Hobday and Jason Hartog (CSIRO).
Thermometer drawing: Elsa Gartner, IMAS.