Marine Life on Australia’s Southern Reefs in Decline: Study

  • Majority (57%) of reef species have declined in the past 10 years
  • Southern Australian reef species squeezed from habitat by climate change
  • Fish numbers plummeting from climate change and overfishing

Australia needs to better manage its southern waters and marine life, the Australian Marine Conservation Society said after a new report showed that reef marine life in our temperate waters is being squeezed out of its habitat by climate change and collapsing.

The report, Continent-wide declines in shallow reef life over a decade of ocean warming, published in Nature today, shows that the majority (57%) of Australian shallow-reef species experienced population declines between 2008 and 2021, based on observations of 1,057 species of fish, mobile invertebrates, coral and seaweeds, collected from 1,636 sites around Australia. Nearly 30% of all observed species declined by more than 30%, which could qualify them as threatened for the IUCN Red List. As many as 138 more shallow-water reef species could now qualify for Endangered and Critically Endangered listing after suffering huge population declines in the past decade, while 158 more species could qualify as Vulnerable.

AMCS Sustainable Seafood Program Manager Adrian Meder said: “This report is truly alarming and a wake-up call for the Australian Government if it’s aiming for no further extinctions. Southern Australia’s reef marine life is getting hit by a double whammy of climate change and overfishing.

“The report shows that northern marine life is moving south because of climate change and the marine heatwaves it causes. Increasing numbers of warm water species in the south are squeezing out cold water species, which are hemmed in a ‘climate trap’ by the Southern Ocean and have nowhere else to go. This is deeply concerning as 70% of the marine life in our southern waters are found nowhere else on the planet, while only 3% of our tropical marine life is endemic to Australia. Once the endemic marine life goes extinct, they go extinct globally. A notable example is the iconic weedy seadragon, whose numbers have dropped 59% in the past 10 years.

“South-eastern Australia is the most populated part of the coast, supports our biggest fisheries and suffers the biggest impacts from development and pollution. On top of that, our southern marine life is facing waters warming 3-4 times the global average.

“Species inhabiting the Great Southern Reef – the kelp-covered rocky reefs that run from NSW to Western Australia – are generally declining in numbers more rapidly, and are more threatened with extinction than tropical species. A strong heatwave off southwestern Australia in 2011 also caused seaweed populations to drop rapidly, and most affected seaweeds remain at greatly reduced levels.

“Of further concern is how little of our southern waters are protected from fishing. The paper notes that 14% of Queensland waters are protected in no-fishing zones but only 1% of Tasmanian waters are protected. We know that marine sanctuaries are one of the best tools we have to build resilience into ocean ecosystems and can help support fish populations to recover in the face of these increasing threats.

“The report also showed that fish numbers are collapsing more in species targeted by fisheries. Exploited fish species had declined 29% on average compared with a 12% average decline in unexploited fishes. The loss of large exploited species can profoundly influence population numbers of other species and can impact the whole food chain.

“We need better protection for our unique southern waters and we need better management of our fisheries.”

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