Life is declining on the reefs around Australia with more than half of the most common species in population decline, a new analysis shows.
Scientists have collected data from three Australian reef monitoring programs that are among the oldest in the world.
The result is a sobering national picture of dwindling volumes of shallow reef species under increasing pressures, including heat waves brought on by climate change.
The study found that 57 percent of the 1,057 common species examined suffered population declines between 2008 and 2021.
They included many species of tropical fish, as well as invertebrates found in the reefs that encircle the southern half of the country.
Population declines often followed years of heat waves, when local water temperatures rose by more than half a degree.
The South Australian weedy sea dragon, for example, experienced an alarming population decline of 59 percent between 2011 and 2021.
Scientists say 28 species, many unique to Australia, potentially qualify as critically endangered, having suffered declines of more than 80 percent.
Another 110 could be considered endangered, with declines of more than 50 percent. And 158 species could qualify as vulnerable, having lost 30 percent of their populations.
Interestingly, 55 coral species that were investigated did not change significantly as a group over the past decade.
Despite cases of extensive coral mortality and bleaching due to heat on the Great Barrier Reef and Coral Sea, tropical coral populations have been trending upwards in north-eastern Australia since 2008, but at low in the northwest.
However, the scientists caution that those findings must be seen in the context of the overall decline of the past 45 years.
Study author Graham Edgar of the University of Tasmania says there have been catastrophic declines in some species, but the real story is in the consistency of the big picture.
The data collected shows that species are under pressure across the country, from those at the very top to the tropical barrier reef and the colder Great Southern Reef.
Professor Edgar says that there is no systematic monitoring of most of the species included in the analysis and that means that losses are not controlled.
“We are having catastrophic losses, particularly some of the colder water species off Tasmania, that are (basically) not recognized and not managed.
“Colder-water species in Tasmania, and off Victoria and southern New South Wales … are at a tipping point for climate change. The water temperature in this region has risen, on average, 1.5°C since the 1940s.
“As temperatures rise, the warmer water NSW species move south and basically crowd the species here.”
And they have nowhere to go, south of Tasmania.
The species that exist in the busy southeast corner of the nation are also feeling the heat that comes with human pressures.
All of these things have serious implications for many species found nowhere else on Earth.
“Most scientific and public attention and management attention is focused on the Great Barrier Reef, for obvious reasons,” says Professor Edgar.
“But the species that live around the Great Southern Reef are uniquely Australian. About 70 percent of the species are not found in any other country, while for tropical species in the analysis it was only three percent.
If there is one big takeaway from the analysis, it is the pressing need to correct the lack of monitoring of Australia’s marine biodiversity.
And while that happens, work must intensify to protect what is uniquely Australian and prevent silent disappearances.
The study has been published in the journal Nature.
—PAA
