Researchers from Curtin University believe rising sea temperatures are to blame for the decline in the number of invertebrates like mollusks and sea urchins on Rottnest Island, off Western Australia's coast some species declining by up to 90% between 2007 and 2021.
Adjunct Professor Fred Wells of Curtin's School of Molecular and Life Sciences, the study's lead author, stated that the west end of Rottnest Island has experienced a "catastrophic decline" in biodiversity.
Marine heatwaves decimate sea urchins
IBRAHIM CHALHOUB/AFP via Getty Images
"We have been monitoring the biodiversity of marine molluscs and echinoderms on rocky reefs at Rottnest Island, Cottesloe, Trigg Point, and Waterman since 1982," Professor Wells explained, as per ScienceDaily.
Despite being designated as sanctuary zones with the highest level of protection from human activity, the researchers discovered that Radar Reef and Cape Vlamingh on Rottnest Island experienced a catastrophic decline in biodiversity between 2007 and 2021, most likely due to exposure to the warm Leeuwin Current.
The metropolitan coastline, on the other hand, which is not influenced by the Leeuwin Current, was discovered to have well-preserved biodiversity and species richness.
Overall, the rocky reefs at Rottnest Island's west end have been severely depleted, with biodiversity and mollusc density declining by 90% or more.
Professor Wells stated that a series of marine heatwaves on WA's west coast in recent years that resulted in abnormally high ocean temperatures had a negative impact on the area's marine plant and animal populations.
Radar Reef and Cape Vlamingh had a mix of tropical, temperate, and WA endemic species, according to our surveys in 1982 and 2007.
Wells expected increased sea temperatures to increase the proportion of tropical species, but this did not occur at the West End of Rottnest, where all three groups declined significantly.
Marine heatwaves have doubled in frequency, becoming longer-lasting, more intense, and more widespread.
According to the IPCC, human activity is the primary cause of the observed increase in ocean heat since the 1970s.
Between 2006 and 2015, the majority of heatwaves occurred, resulting in widespread coral bleaching and reef degradation.
Nearly 60% of the world's ocean surface experienced at least one spell of marine heatwaves in 2021.
According to the UN Environment Programme, if the water continues to warm, all of the world's coral reefs will bleach by the end of the century.
Coral bleaching occurs when reefs are stressed and lose their life-sustaining microscopic algae.
The most recent global bleaching event began in 2014 and lasted until 2017, spreading across the Pacific, Indian, and Atlantic oceans.
The risk of irreversible loss of marine and coastal ecosystems increases as temperatures rise.
Today, widespread changes have been observed, including coral reef and mangrove damage and species migration to higher latitudes and altitudes where the water may be cooler.
According to the most recent UN Educational, Scientific, and Cultural Organization estimates, more than half of the world's marine species may be extinct by 2100.
With a 1.1°C increase in temperature today, an estimated 60% of the world's marine ecosystems have already degraded or are being used in an unsustainable manner.
A 1.5°C increase threatens to destroy 70% to 90% of coral reefs, while a 2°C increase means a nearly 100% loss.
