Steps to Clean Up the Algal Bloom
Image: Stefan Andrews/Great Southern Reef Foundation
To help us better understand “how could we clean up the algal bloom?”, Environment Institute members, Future Making Fellow Dr Dominic McAfee and Professor Sean Connell have written for The Conversation. Dr McAfee and Professor Connell explain how the distribution of Karenia mikimotoi, the main species of microalgal contributing to the harmful algal bloom (HAB), is much too large for trial solutions of physical, chemical and biological options, which first need to be tested at smaller scales.
As the HAB crisis continues, affecting around 30% of the state’s coastline, the South Australian Government is taking measures to ensure the crisis is addressed at all levels - science and research, communications, community action, and industry support.
The bloom developed due to a mix of events:
- September 2024: a marine heatwave causing water tempreatures to rise about 2.5oC warmer than usual
- 2022-2023: River Murray Flood waters brought a massive dose of nutrients into coastal waters
- 2023-2024: Cold-water upwelling in the summer carried more nutrients to the surface that fed the algae
Experts like Dr McAfee and Professor Connell say “Prevention is the best cure – so we need to tackle these threats”.
Researchers have tried chemical crop-dusting by planes, but chemicals are problematic as they can also kill off “good” algae, leading to further complications.
In China and Japan, clay has been used as a way to combat algal blooms for more than 50 years, as it binds to the algae then causes the cells to sink. While it require copious amounts of clay to work, modified clay technology is a promising, environmentally friendly solution that could be applied on a more limited scale.
Physical methods like mixing surface waters or “bubble curtains” — streams of air that prevent algae from passing through – are useful in aquaculture pens. However, during severe blooms, farmers often must relocate pens entirely, as they’re ineffective against large blooms.
Harnessing “natural microbial warfare” could be another solution, say Dr McAfee and Prof Connell. Microorganisms can naturally regulate algae through predation, for example single-celled organisms like ciliates and flagellates, or by suppressing them through bacteria and viruses.
In the United States scientists are testing natural algicides extracted from algae-killing marine bacteria to help fight Red Tide blooms in Florida. Select bacterial algicides kill specific harmful algae, offering hope for a low-risk application. But again, this approach has only been used at a small experimental scale, not across an entire expanse of coastal waters.
One key potential control mechanisms is a natural solution - oysters – which can filter vast amounts of water each day and remove excess nutrients and algae. Over time oyster reefs have been destroyed in South Australia due to over harvesting, but restoration projects such as at Glenelg Beach have proven that these shellfish ecosystems can easily be restored. Two acres of shellfish have been brought back with oysters filtering over 12 million litres of water a day within a year and a half of the reefs construction.
If the original extent of this natural system was still intact, it could have potentially removed the nutrients that were swept into coastal waters before they could feed the bloom. Native oysters are holding up in affected areas, and feeding on the Karenia algae. In contrast, razorfish and cockles have been impacted by the bloom.
Federal Environment Minister Murray Watt has expedited an expert assessment of the algal bloom to understand if any local flora or fauna may need to be added to the threatened species list. A similar approach that was taken during the 2019-2022 Black Summer Bushfires to assess potentially impacted species.
There is hope that large scale oyster restoration could be the answer to future proofing South Australia against any further HABs. This comes as South Australian Premier Peter Malinauskas announced plans to restore 15 hectares of shellfish reef.
Premier Malinauskas in a recent press conference announced that the HAB is being monitored across 17 key sites, and the good news is that the oysters level of brevetoxin have decreased across Cowell, American River, Stansbury, Port Vincent, and Coobowie. Mussels have also been fully cleared of contamination, and ongoing monitoring of pippis and cuttlefish remain in ongoing consultation with impacted fisheries.
So, what’s next? Dr McAfee and Professor Connell say that in time, the bloom will dissipate as water temperatures drop, and nature will eventually rebuild. As the wind and waves increase, this can also break up the algae, and reduce nutrient levels in the water. However with the looming pressures of global warming and an increase in heavy rainfalls, future blooms are likely to return and we must be prepared to explore methods of recovery while creating a natural resilience.
They recommend investing in conservation and restoration of filter-feeding shellfish reefs. “If we continue with a reactive, fragmented approach to climate, nutrient pollution, and biodiversity loss, we’re guaranteed to face more costly catastrophes. We need to act to build long-term ecological and socio-economic resilience.”
Harmful Algal Bloom Capability Statement
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