Study charts decade of loss on Australian reefs

Life is dwindling on the reefs that ring Australia with more than half of the most common species in population decline, new analysis shows.

Scientists have collated data from three Australian reef monitoring programs that are among the longest-running in the world.

The result is a sobering national picture of shrinking volumes of shallow-reef species under mounting pressures, including heatwaves driven by climate change.

The study found 57 per cent of the 1057 common species examined suffered population declines between 2008 and 2021.

They included many species of tropical fish, as well as invertebrates on reefs that wrap around the southern half of the country.

Population declines often followed heatwave years, when local water temperatures were up by more than half a degree.

Southern Australia's weedy sea dragon, for example, saw an alarming population decline of 59 per cent from 2011 to 2021.

Scientists say 28 species - many unique to Australia - potentially qualify as critically endangered, having suffered declines of more than 80 per cent.

Another 110 could be considered endangered, with declines of more than 50 per cent. And 158 species could qualify as vulnerable, having lost 30 per cent of their populations.

Interestingly, 55 coral species that were investigated did not change significantly as a group over the past decade.

Despite instances of extensive coral mortality and bleaching due to heat on the Great Barrier Reef and in the Coral Sea, tropical coral populations have trended upwards in Australia's north east since 2008 but down in the northwest.

However, scientists warn those findings must be considered in the context of general decline over the past 45 years.

Study author Graham Edgar, from the University of Tasmania, says there are have been catastrophic declines in some species but the real story is in the consistency of the bigger picture.

Collated data shows species are under pressure nationwide, from those off the Top End to the tropical Barrier Reef, and the cooler Great Southern Reef.

Professor Edgar says there is no systematic monitoring of most species included in the analysis and that means losses are going unchecked.

"We're having catastrophic kind of losses of particularly some of the cooler water species off Tasmania, that are (basically) going unrecognised and unmanaged.

"The colder water species in Tasmania, and off Victoria and southern NSW ... are in a climate change hot-spot. Water temperatures across this region have gone up, on average, 1.5C since the 1940s.

"As the temperatures rise, you are getting warmer water species from NSW moving south and basically crowding the species here."

And there's nowhere for them to go, south of Tasmania.

Species that exist off the nation's crowded southeast corner are also feeling the heat that comes with human pressures. 

All these things have serious implications for many species found nowhere else on Earth.

"Most scientists and public attention and management attention is focused on the Great Barrier Reef, for obvious reasons," Prof Edgar says.

"But the species living around the Great Southern Reef are uniquely Australian. About 70 per cent of the species occur in no other country, whereas for the tropical species in the analysis it was only three per cent."

If there's one big takeaway from the analysis, it is the pressing need to fix the lack of monitoring of Australia's marine biodiversity.

And while that's happening, work must ramp up to protect what is uniquely Australian and ward off silent vanishings.

The study has been published in the journal Nature.