Toxic algal bloom threatens South Australian marine life and coastlines
A toxic algal bloom has wreaked havoc along South Australia's coastlines, prompting health warnings and raising concerns among residents and marine professionals.
South Australian coastlines have been choked by a violent algal bloom. Picture: Patrick Stock
South Australian coastlines have been choked by a violent algal bloom that has killed marine life and impacted nearby residents and beachgoers.
The harmful algal bloom (HAB) was first detected off the Fleurieu Peninsula in March, and has since expanded to more than 4,400 sq km impacting metropolitan beaches Port River, West Lakes, Fleurieu Peninsula, Kangaroo Island, Yorke Peninsula, Eyre Peninsula and the Coorong.
The HAB is comprised of multiple algae species, including the harmful dinoflagellate Karenia mikimotoi, which is particularly menacing due to its large spatial extent and long lifespan.
The HAB caused discoloured water and foam along parts of the coastline with individuals having reported experiencing respiratory issues and pets having fallen violently ill.
The harmful algal bloom (HAB) was first detected off the Fleurieu Peninsula. Picture: Caroline Horn
The South Australian government released warnings against entering the water and remaining on the beach for prolonged periods of time.
Most microalgal (phytoplankton) blooms are natural phenomena, and occur in coastal waters when triggered by long hot periods, low winds, and low tidal ranges. However, marine heatwaves and nutrient pollution can exacerbate these blooms, potentially leading to HABs that result in severe ecological and economic impacts.
Algal blooms impact marine ecosystems by depleting oxygen in the water, blocking sunlight, and producing toxins. Additionally, as the bloom begins to die, it further reduces oxygen levels, which can drop below the threshold needed for marine life to survive, resulting in mass deaths.
Citizen scientists in South Australia have submitted over 1400 reports to non-profit OzFish, which revealed that more than 200 marine species, including approximately 100 fish and shark species, have been killed by the algae.
Additionally, the algal bloom has negatively impacted around 400 species of fish, invertebrates and associated marine and coastal biodiversity.
More than 200 marine species, including approximately 100 fish and shark species, have been killed by the algae. Picture: Lochie Cameron
Why has it appeared in South Australia?
South Australian experts have identified three potential contributing factors to the severe HAB:
A marine heatwave that began in September 2024 - which sent sea temperatures soaring to 2.5°C above average - in combination with calm, small swell conditions and light winds.
An unexpected cold-water upwelling in the summer of 2023-2024 which pushed nutrient-dense water to the surface of the ocean.
A nutrient influx from the 2022-2023 flooding of the River Murray.
South Australian experts have identified three potential contributing factors to the severe HAB. Picture: Great Southern Reef Foundation
What government action has been taken in response?
Nationally, the federal Environment Minister addressed the issue and announced a $14m assistance package on July 22, but is yet to declare the algal bloom a national disaster.
Locally, the state government established a taskforce and reference group, ‘The Harmful Algal Bloom Reference Group,’ comprised of representatives from Seafood Industry South Australia, RecFish SA, Conservation Council, Tourism Industry Council, and First Nations groups, to address the algal bloom repercussions with stakeholders, and support scientific monitoring.
On 4 July, agencies including DEW, PIRSA, EPA, and SA Health met with commercial fishers, tourism operators, and local councils to provide updates on public health and environmental effects of the algal bloom, and discuss research priorities to mitigate outbreaks.
The state government has also been conducting weekly water samples at 17 sites across West Lakes, the Port River, the Patawalonga River, and jetties at Largs Bay, Grange, Glenelg, and Port Noarlunga.
This article will be updated as more information arises.