More than 500 species of fish, algae, coral and invertebrates that live on Australia’s reefs have declined in the past decade, according to research published in the journal Nature.
The researchers assessed population trends of 1,057 shallow reef common species, at 1,636 sites around Australia over the past decade.
After their analysis, they were able to determine that 57% of the species had declined, and almost 300 were declining, such that they could be classified as threatened species.
Reef species declined
About 28% of the species analyzed had suffered falls of 30% of their population, or more just in a decade, while species that live in colder waters were the most affected.
In these groups are much tropical fish, invertebrates from temperate zones, particularly echinoderms, marine animals distinguished by having their bodies divided into five equal parts, and macroalgae from southwestern Australia. Coral populations, meanwhile, remained relatively stable.
Another of the results of the research indicates that the largest fish were declining faster than the smaller ones, probably due to fishing pressure that aggravates the increase in temperatures.
And it is precisely global warming that is the main reason for the decline of species in this country, according to the study. Rising temperatures would likely have been the main driver of cataracts with marine heat waves and an increase in ocean temperatures affecting species living on rocky and coral reefs.
“Population declines generally occurred in heat wave years, when local water temperatures exceeded 2008 temperatures by more than 0.5°C. After heat waves, species abundances generally trended to decrease near the warm limits and to increase near the cold ones”, the researchers explained.
For Graham Edgar, a marine ecologist at the University of Tasmania and lead author of the study, the declines were most marked on rocky, kelp-dominated reefs in the colder waters off southern Australia, known as the Great Southern Reef.
Endemic species will be ‘gone from Earth’
According to a recent study, over 30 percent of invertebrates inhabiting the shallow and cool waters of southern Australia are considered to be highly endangered. Dr. Asta Audzijonyte, a researcher at the University of Tasmania’s Institute for Marine and Antarctic Studies, explained that unlike tropical waters, the majority of marine flora and fauna in Australia’s southern region are unique to the area.
She stated that around 70 percent of cold water species found in southern Australia and Tasmania are only found in Australia, whereas only three percent of tropical species have this level of endemism.
Although Dr. Audzijonyte was not involved in the study, her expertise provided additional context to the findings.
The study also revealed evidence of extreme marine heatwaves, as stated by Professor Edgar. He explained that the most significant event recorded was the 2011 heatwave off the coast of south-western Australia, where the Leeuwin current’s temperature increased by approximately 4 degrees Celsius.
This caused a substantial influx of tropical species to move towards the south-western area, and the data indicated that the cold-water species have not yet recovered from this event.
Additionally, after the 2016 eastern Australia marine heatwave, only 25 percent of the 24 warm-temperate species that were previously spotted at subtropical sites on the southern Great Barrier Reef and Coral Sea were observed again at those sites.
How do we know when marine species go extinct?
According to Professor Edgar, although biodiversity plays a crucial role in our lives, no country worldwide is systematically monitoring the changes occurring in marine environments.
Therefore, if a marine species becomes extinct within the last five years, it will likely go unnoticed since there is no standardized assessment of the biology of the marine system.
The smooth handfish is an example of a species that Professor Edgar believes has likely been extinct for some time.
Although it was briefly listed as extinct on the IUCN Red List, it was later removed because targeted studies had not been conducted to confirm its disappearance, which is a challenging task.
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