Chapter 2Contributing factors and management strategies
Overview
2.1This chapter outlines the potential contributing factors to the 2025 South Australian (SA) harmful algal bloom (HAB) and discusses management strategies for current and future HABs.
2.2Potential contributing factors raised by inquiry participants include a marine heatwave, elevated nutrient levels in the affected waters, and climate change. However, the committee heard that it is still too early to conclusively determine the causes of the HAB.
2.3While the committee also heard that there are currently no viable options to limit the spread of the current HAB, inquiry participants suggested a range of long-term strategies to manage future HABs, including:
HAB research and capacity building;
monitoring and early detection of HABs;
reduction of nutrient inflows; and
climate change mitigation.
2.4This chapter will also outline international experiences with Karenia species of algae, including management and mitigation strategies used in areas that have frequently dealt with HABs.
Contributing factors to the 2025 South Australian harmful algal bloom
2.5Inquiry participants suggested that a number of factors, including climate and environmental factors and land and water management factors, could have contributed to the development of the 2025 SA HAB. For example, the Murray-Darling Basin Authority (MDBA)suggested that:
… multiple factors occurring concurrently in the marine waters of South Australia have created favourable conditions for K. mikimotoi [Kareniamikimotoi]to establish and proliferate, rather than one causal factor.
2.6The SA Government identified three potential drivers:
a marine heatwave (MHW) which started in September 2024 and saw sea temperatures about 2.5°C warmer than usual, combined with calm conditions, light winds and small swells;
the 2022–23 River Murray flood, which washed extra nutrients into the sea; and
a cold-water upwelling in summer 2023–24 that brought nutrient-rich water to the surface.
2.7Other potential contributing factors raised in evidence to the inquiry include climate change and nutrient pollution from land and water management practices.
2.8However, the committee heard that the exact causes of the HAB are unknown due to a paucity of data. Dr Alec Rolston, Director of the Goyder Institute for Water Research, noted that 'there are some conflicting opinions around the causative or contributory aspects to the current algal bloom' and that 'further investigations … are required'.
2.9The Australian and New Zealand Marine Harmful Algal Bloom Network (ANZMHAB Network) submitted that 'it is not possible to determine with certainty the factors that led to [the] growth and proliferation [of the HAB]' because the precise species of algae comprising the HAB have yet to be identified. Professor Shauna Murray, an ANZMHAB Network committee member, stated at a public hearing in late September 2025:
I don't believe we're in a position to make inferences about the role of marine heat waves or nutrients since we don't yet know what species we're dealing with.
2.10The committee heard that researchers are hoping to resolve the identity of the organisms comprising the HAB by mid-October.
2.11Commonwealth Scientific and Industrial Research Organisation (CSIRO) confirmed that our understanding of the HAB and its causative factors is complicated by the 'multi-species nature of the algal bloom, and the ecology of each contributing harmful species'.
2.12The following sections set out the evidence the committee received on each of the potential contributing factors mentioned above.
Marine heatwave combined with calm ocean conditions
2.13MHWs are 'prolonged extreme oceanic warm water events'. According to the Bureau of Meteorology (BoM), a MHW is commonly defined as 'temperatures being warmer than 90 per cent of the previous SST [sea surface temperature] observations at the same time of year over a 30-year period, for at least five days in a row'.
2.14There are a range of ocean and atmospheric drivers of MHWs, including 'enhanced solar radiation into the ocean', 'increased horizontal transport (advection) of heat in ocean currents' and 'warm air … warming the ocean surface'. Large-scale climate drivers, such as El Nino-La Nina, can also 'modulate the frequency, intensity and duration of MHWs'.
2.15MHWs 'can have devastating impacts on marine ecosystems' including the 'direct mortality of marine fish and aquaculture species' and 'substantial declines in kelp forests and seagrass meadows'.
2.16The Australian Climate Service (ACS)—a partnership of BoM, CSIRO, the Australian Bureau of Statistics and Geoscience Australia—has projected with high confidence that the frequency and duration of marine heatwaves will increase with global warming (see Figure 2.1).
Figure 2.1Projected change in median ocean warming and acidification metrics
'GWL' stands for 'global warming level'.
Source: Australian Climate Service, Ocean warming and acidification, 2025, p. 1 (tabled 24 September 2025).
2.17Since September/October 2024, an MHW has affected SA waters. In March 2025, where the bloom was first detected, 'sea surface temperatures … were up to 3°C above the mean for that time of the year'. Throughout much of the first half of 2025, SSTs in the Gulf St Vincent were typically 1–3°C warmer than normal (see Figure 2.2 below).
Figure 2.2Example of SST anomaly in April 2025 in the Gulf St Vincent and the waters around Kangaroo Island
Source: MDBA, Submission 36, Attachment A, p. 3
2.18Many inquiry participants posited that the MHW may have been a contributing factor to the growth of the HAB. Dr Georgina Wood of the Australian Marine Sciences Association (AMSA) (SA Branch) noted that:
… we cannot definitively attribute the cause of this particular algal bloom, but there is a large body of evidence from algal blooms overseas evidencing the association between warming waters, marine heatwaves and harmful algal blooms.
2.19Ms Faith Coleman, an estuarine ecologist, explained that MHWs 'cause ecological distress, releasing the organic nutrients and encouraging bacterial growth', thereby producing the preferred food sources for mixotrophic dinoflagellates (organisms responsible for the formation of HABs) during their growth phase.
2.20Several submitters pointed out that a previous HAB in SA was linked to a MHW in 2013. According to the South Australian Environment Protection Authority (SA EPA):
During a heatwave in 2013, SSTs were recorded at up to 5°C above the historical average, promoting blooms of the harmful diatom Chaetoceros coarctatus. This event led to widespread marine mortalities, including fish and shellfish, leading to both ecological and economic impacts.
2.21The committee heard that the impacts of the MHW were exacerbated by associated weather conditions, 'characterised by unusually calm seas, light winds, and small swells'. Evidence was received that 'rain-bearing winter storms … would normally cool temperatures and stir ocean waters to limit growth of the bloom and break it up'; however, the absence of these storms allowed the bloom to accumulate and intensify.
2.22Despite many inquiry participants arguing that the MHW was likely a contributing factor to the HAB, other submitters argued that further information about the algae species comprising the HAB is needed before any clear link can be drawn. Emeritus Professor Gustaaf Hallegraeff noted that:
Whereas early bloom stages exhibited Karenia mikimotoi as the dominant species … the later bloom stages were dominated by a Karenia selliformis / cristata complex species, both known to have caused similar mass mortalities mostly in cold-water upwelling habitats (Japan, Russia, Chile, South Africa) Resolving the precise identity of the 4-5 Karenia species in the SA HAB is critical before we can make any statements how it relates to the heat wave event.
Elevated nutrient levels
2.23The committee received evidence that excessive nutrients in the affected SA waters may have contributed to the growth of the HAB.
2.24The MDBA's research shows that elevated nutrient levels (often nitrogen and phosphorous) are one of the causes of marine and coastal environmental algal blooms in Australia. Similarly, the Fisheries Research and Development Corporation (FRDC) has conducted research 'highlight[ing] the role of nutrient inputs, land management practices and water quality in shaping bloom risk for other species at the business and catchment scale'.
2.25Inquiry participants pointed to several possible sources of nutrient inflows. The Surfrider Foundation Australia noted that recent extreme weather events may have deposited large amounts of nutrients in the water:
The 2022–2023 floods in the Murray–Darling Basin delivered large inflows of sediment and nutrients into coastal systems, overwhelming natural filtration and triggering algal blooms (MDBA, 2023). … unprecedented summer 2023–24 cold-water upwelling also elevated nutrient levels in coastal waters (Redmap, n.d.).
2.26While acknowledging that the floods and cold-water upwelling may have played a role, the Biodiversity Council suggested that there may nevertheless have been 'adequate background levels of nutrients for a bloom to form without those irregular sources'. Contributing to these background levels are river discharges which can contain fertiliser run off from agriculture and nutrient-rich bushfire ash; stormwater and treated wastewater; and loss of oyster reefs which could filter excess nutrients.
2022–23 River Murray Flood
2.27Significant flooding occurred along the River Murray between November 2022 and February 2023. It was the 'largest flood event since 1956 and third-highest flood ever recorded' in SA.
2.28The CSIRO noted that the River Murray flood:
… discharge[ed] large quantities of dissolved and particulate nutrients into the coastal ocean. The particulate nutrients, due to being heavier than water, sink, and can accumulate in near-shore waters. Subsequent breakdown of organic particulates in the coastal sediments can release bio-available nutrients into the water column.
2.29The committee heard that at the time of the flood, the ocean was 'already in a weakened state from a severe reduction of fresh flows' from the River Murray. The Lifeblood Alliance stated that there had been 'decades of reduced flushing of floodplains in the Murray-Darling Basin', including 'the elimination of small floods which used to occur every two to three years'. This 'may have resulted in excessive nutrient export during the major floods in 2022–23 that then exacerbated the current marine algal bloom'; however, the Alliance called for further scientific investigations to evaluate the role of river outflows in creating and/or sustaining the current HAB.
2.30Along similar lines, numerous inquiry participants questioned whether the 2022–23 River Murray flood was a contributing factor to the current HAB. The MDBA stated that it had commissioned an analysis by Dr Darren Baldwin to understand whether the flood was a contributing factor, but the analysis was 'unable to determine whether there was a causal link'. The analysis found that:
The flood plume undoubtedly delivered sediments and nutrients to the area where the bloom first developed (Eastern Fleurieu Peninsula) … However, there doesn't appear to be a logical pathway to describe how the flood event at the beginning of 2023 is linked to an event that occurred in 2025.
2.31This is because K. mikimotoi is a mixotrophic organism, meaning that it 'doesn't rely on dissolved nutrients but can access nutrients (and energy) from ingestion of particulate matter'. Additionally, the analysis questioned why a similar K. mikimotoi bloom did not form in the summer of either 2023 or 2024. It concluded that the 2022–23 flooding was either inconsequential to the HAB forming in 2025, or, if it did contribute, other factors were required for the HAB to form.
2.32Similarly, Associate Professor Luke Mosley from the University of Adelaide submitted that it was 'highly uncertain what role the River Murray flood played in the 2025 algal bloom development', noting the 'long time period between the flood-related nutrient delivery in 2022–2023 and the bloom development'.
2.33Emeritus Professor Gustaaf Hallegraeff also observed that:
Most Karenia species can thrive under very low nutrient conditions (preferring ammonia over nitrate), and many are mixotrophic (feeding on other algae, and possibly even deriving nutrient from dead fish) … any claims of a relationship with anthropogenic nutrients or River Murray floods therefore is premature.
Cold-water upwelling
2.34Cold-water upwellings are an 'oceanographic phenomena where deep, cold, and nutrient-rich waters rise to the surface, typically driven by wind patterns and coastal geography'. Upwellings can 'fuel the growth of phytoplankton' which provide food for a wide range of marine life.
2.35The Department of Climate Change, Energy, the Environment and Water (DCCEEW) gave evidence that upwellings can:
… contribute to harmful algal blooms when combined with other environmental factors. The sudden availability of nutrients can trigger rapid algal growth, and under certain conditions—such as warm surface temperatures or periods of calm, still water conditions—this can lead to blooms of toxic or nuisance algae.
2.36The southern continental shelf in Australia, which includes the SAgulfs experiencing the algal bloom, hosts the Great Southern Australian Coastal Upwelling System. This seasonal upwelling occurs from November to April and is driven by southwesterly coastal winds. Key upwelling centres are located:
(a)in the eastern Great Australian Bight around the Eyre Pensinula;
(b)along the Bonney Coast; and
(c)along Tasmania's west coast.
2.37The CSIRO noted that the 'shelf upwelling of cold nutrient rich water off the Bonney Coast (near Robe) … was unusually strong in early 2024' and could have been a contributing factor to the 2025 HAB.
2.38Emeritus Professor Gustaaf Hallegraeff surmised that the HAB was 'most likely initiated by an offshore nutrient upwelling event (as we have seen previously in SA in March 1995 and Feb 2014)’.
2.39However, others cast doubt on whether an upwelling event had an influence on the HAB. Dr Anne E Jensen, an environmental consultant, remarked that 'there was a significant time lag' between the 2023–24 annual upwelling off the southern coast from Robe to Portland and the onset of the HAB, 'raising the question of whether this specific food source would have still been available in early 2025'.
2.40Dr Darren Baldwin's analysis that was commissioned by the MDBA stated that 'because upwelling events occur in most years, it is difficult to see how they are specifically linked to the current bloom'.
2.41Further, Associate Professor Jochen Kaempf claimed that 'it is unlikely that river discharges or upwelling events caused [the South Australian HAB]' because blooms of K. mikimotoi 'can grow under very low nitrogen and phosphorus conditions' and 'neither rely on nitrate-rich waters from coastal upwelling, nor on phosphorus-rich discharges from rivers'.
Land and water management factors
2.42Inquiry participants mentioned a range of land and water management practices that may have increased the nutrient levels in SA waters and created favourable conditions for HAB growth. For instance, the Environment Institute at the University of Adelaide observed that:
Historically, Adelaide's coastal waters have been impacted by high-nutrient discharges from a combination of sources, including wastewater treatment plants (WWTPs), industrial outfalls, and diffuse-source stormwater runoff from both urbanised areas and agricultural land. The state's gulfs are naturally susceptible to the accumulation of pollutants due to their shallow nature and relatively poor water exchange with the open ocean, which limits their flushing capacity.
2.43Urban stormwater and wastewater were identified by some submitters as 'major contributors to pollution' which 'introduce substantial amounts of nitrogen and phosphorus into South Australia’s coastal waters'. The Clean Ocean Foundation, an environmental charity that monitors wastewater outfalls across Australia, submitted that 'outfalls release nutrients and micropollutants that can trigger or intensify ecological damage, including algal blooms'.
2.44Some submitters also remarked that agriculture and aquaculture operations can create nitrogen and phosphorus pollution in waterways, leading to eutrophication (nutrient enrichment)—'a key cause of algal blooms'. The Environment Institute of Australia, New Zealand (SA Division) claimed that 'tuna and kingfish aquaculture … [is] the largest source of nutrients in the Spencer Gulf by an order of magnitude'.
2.45Associate Professor Luke Mosley explained that:
… land use changes and practices associated with agricultural expansion (e.g. increased use of fertilisers) [in the Murray-Darling Basin], can exacerbate nutrient imbalances by increasing sediment and nutrient loads during irregular floods … more irregular delivery of nutrients from the River Murray … may potentially promote algal blooms due to larger but less frequent nutrient pulses …
2.46Dredging and the dumping of quarry sand along the SA coast were raised by Save West Beach Sand, a community group, as potentially 'play[ing] a role in increasing nutrient levels that fuel algal growth':
Dredging has disturbed nutrient-rich sediments and damaged seabeds and seagrasses, releasing hydrogen sulfide into the marine environment.
Contaminated quarry sand, containing clay, has been dumped onto beaches (approx. 450,000m³ since 2021), and subsequently dispersed by tides and storms, to be lost into drift and the sea.
2.47Mr Victor Vorel, a former chemical technical officer, suggested that the use of ammonium phosphate/ammonium sulphate fire retardantsduring bushfires can leach high concentrations of nitrogen and phosphorus into waterways, and is likely to have 'contributed significantly' to the HAB.
2.48A few inquiry participants expressed a view that desalination plants may have contributed to the HAB. However, the SA Environment Protection Authority (SA EPA) noted that while a 2010 report by the South Australian Research and Development Institute (SARDI) theorised that activities associated with the Adelaide Desalination Plant may promote HABs, 'a comprehensive and on-going monitoring program since that report has confirmed there is no evidence to support a causal link between the desalination plant and HABs'.
2.49Doctors for the Environment Australia stated that there had been 'widespread and sometimes bizarre misinformation about algal blooms', and pointed out that:
… links to desalination plants show lack of understanding that the algal bloom thrives in low salinity water. Mapping shows no relationship between desalinisation plants and the bloom.
Climate change
2.50A range of inquiry participants argued that climate change is the underlying driver of the current HAB. The Conservation Council of South Australia (Conservation Council SA) said that the current HAB is a 'direct manifestation of the climate crisis', as each of the major contributing factors to the HAB 'can be directly or indirectly linked to the influence of the human-driven climate crisis'.
2.51The Conservation Council SA underlined that climate change amplifies extreme hydrological events such as the 2022–23 River Murray flood; leads to stronger ocean currents and altered wind patterns which intensify cold-water upwellings; and increases the frequency and severity of marine heatwaves.
2.52A joint submission by Professor Caitlin Byrt (Australian National University) and Dr Ben Long (University of Newcastle) elucidated that climate change can boost HAB growth in various ways:
Climate change is causing greater variability in weather which complicates analysis of the ocean currents and river flows that impact nutrient availability and feed algal blooms. Changes in currents and flows can boost the ingredients required to supply algae with their building blocks for life. Drought events and intense rainfall are both associated with climate change, and they both exacerbate bloom conditions because intense rainfall is associated with increases in nutrient runoff and drought events can cause concentration of nutrients in waterways.
2.53Additionally, the Lifeblood Alliance argued that the current HAB is a 'direct consequence of the escalating climate crisis', as the HAB was precipitated by 'a prolonged marine heatwave and altered rainfall patterns' associated with climate change.
2.54Along similar lines, the Surfrider Foundation Australia asserted that HAB events are 'warning signals of systemic stress in our marine and coastal environments', and noted that:
… climate change itself remains the underlying driver of increasingly frequent, severe, and prolonged environmental events and degradation, including floods, marine heatwaves, and widespread habitat loss.
2.55On the other hand, the committee received evidence that the relationship between climate change and HABs is complex, with the FRDC saying that the link 'has not been fully investigated in Australia and will vary depending on the [algal] species responsible'. The FRDC noted that 'most Karenia species are temperate, meaning heat waves and nutrient fluxes may not promote their growth'.
2.56Likewise, the ANZMHAB Network submitted that:
While climate change may be increasing the frequency of HABs worldwide, it has not led to uniform increases in HABs in Australia or any other country (Hallegraeff et al. 2010). Many HAB species preferentially grow in cold water or low nutrient conditions.
… Some species of harmful algae may become more abundant … while others may diminish as conditions no longer suit them.
2.57Associate Professor Jochen Kaempf indicated that K. mikimotoi growth is 'relative[ly] insensitive to temperature variations of 17.5–22.5°C' and therefore questioned whether climate change effects were relevant to the development of the current HAB.
Management strategies for the current bloom
2.58There was widespread consensus among inquiry participants that by the time the current HAB was detected, there was no way to effectively reduce its size or prevent it from spreading further.
2.59The SA Government stated that, as the algal bloom is naturally occurring, there is 'no way to "kill" or treat the bloom directly' and that blooms tend to break down naturally when conditions change. These changes include:
a decrease in water temperatures;
an increase in wind and wave action which breaks up the algae; and
a reduction in the nutrient levels in the water.
2.60Dr Mark Doubell, a research scientist and Oceanography Subprogram Leader at SARDI, gave evidence that the HAB was already at a vast scale and in the open coastal ocean by the time it was detected, and that he was 'not aware of any effective mitigation measures that would work at that scale and in those environments'.
2.61Further, Dr Donald Anderson, Senior Scientist at the Woods Hole Oceanographic Institution and Director of the United States (US) National Office for Harmful Algal Blooms, testified that with a bloom of this size, the focus is on managing the issue rather than controlling it. He observed that the current HAB is 'far too extensive—too big—to consider controlling using some of the methods that we have been using in the US and in Asia', adding:
The largest area that's been treated anywhere in the world is roughly a hundred square kilometres. Your bloom is many times bigger than that already, so, if you tried to do something, you would be doing something that no-one else in the world has ever done.
2.62Government strategies to manage the economic, public health and environmental aspects of the current HAB are discussed elsewhere in this report.
Management strategies for future blooms
2.63The committee heard a range of strategies that could be implemented to better manage future HABs and mitigate their impacts. This section sets out the key management strategies discussed throughout the inquiry.
Monitoring and early detection of harmful algal blooms
2.64A large number of inquiry participants called for investment in long-term monitoring and early detection systems for HABs, expressing concern at the adequacy of existing systems. Dr Christopher Keneally, a microbial ecologist based at the University of Adelaide, espoused the benefits of long-term monitoring and forecasting of HABs in his submission:
HABs are episodic, but our capability to address them must be continuous. Sustained observations and data infrastructure are prerequisites for credible forecasts and prevention.
2.65The FRDC's submission similarly underlined the value of early detection systems:
Studies indicate forecasting HABs can protect human health, the environment, and economies, with early warnings allowing for timely interventions to mitigate negative impacts, such as shellfish/fish harvesting restrictions.
2.66Numerous inquiry participants supported the development of a national early-warning system for HABs. Professor Craig Simmons, the Chief Scientist for SA, told the committee:
I think it's abundantly clear that we need to work towards not just a state based but a national early-warning system for harmful algal blooms. We need to be looking at funding and supporting real-time toxin detection. … the early-warning and predictive capacity is key here. That all needs to link with predictive modelling and ecological monitoring.
2.67The committee received evidence on various types of monitoring, ranging from large-scale oceanographic monitoring to algal bloom-specific monitoring techniques. CSIRO indicated that HAB forecasting in other countries involves a combination of monitoring tools such as 'field sampling, modelling, and satellite observations'. The Great Southern Reef Foundation noted that each different type of monitoring is important and should be used in conjunction with others:
Physical environmental monitoring and forecasting (e.g. temperature, waves, currents, nutrients etc.) are critical to providing real time or advanced warnings of marine heatwaves, or conditions that could trigger HABs. Similarly early detection of the onset of HABs and monitoring the taxonomy, extent and intensity of HABs specifically, is critical to diagnosing the nature of the event unfolding and the types of impacts to be expected.
2.68The committee heard that properly analysing and communicating the results of monitoring is also important. The Conservation Council SA stated that there should be a dedicated scientific body who can interpret the data, analyse risks and issue early warnings. Divers for Climate called for monitoring data to be available on a 'centralised, publicly accessible online platform that consolidates algal bloom forecasts, monitoring updates, and risk alerts' and in a format that is understandable for non-scientific audiences.
Algal bloom-specific monitoring
2.69The committee received evidence that oceanographic data alone is not sufficient to monitor HABs, and that more specific testing and equipment are also required.
2.70The FRDC noted that 'currently, there is a disconnect between broad-scale oceanographic monitoring programs' and 'small-scale, species-specific algal bloom monitoring'. It said that, at present, 'IMOS [Integrated Marine Observing System] microbiome metabarcoding is not sensitive enough to discriminate between the different HAB species' which is needed for detailed HAB tracking.
2.71Likewise, the ANZMHAB claimed that the IMOS network of buoys and water sampling is not designed for HABs, and that more fine-grained testing capable of identifying individual HAB species is required:
Both the microscopy and molecular genetic methods employed in these programs (e.g. IMOS/BPA Marine Microbiome project; SSU V4 based amplicon sequencing) are not suitable for marine HAB detection because they cannot discriminate different HAB species, and sampling frequencies in most cases are too sparse (e.g monthly) necessary to detect/track often rapid (<weekly) changes on concentration and distribution of HABs. Oceanographic detection methods that detect pigments such as chlorophyll a or other algal pigments, including methods that detect haptophyte-specific pigments like fucoxanthins, are not able to detect Karenia at the species level.
2.72Various inquiry participants pointed out the limitations of satellite monitoring to track HABs and suggested that monitoring should be expanded to include microscopic, molecular and biotoxin detection methods. The ANZMHAB Network called for in-situ water sampling in addition to satellite monitoring:
Water sampling should occur at least fortnightly. Key environmental factors to measure include macronutrients (phosphates, nitrates, silicates), micronutrients (trace metals), water properties (temperature, salinity, dissolved oxygen, pH, carbon levels). Satellite remote sensing can help in some cases, but it has many limitations: it will likely miss low-biomass blooms, it cannot distinguish between harmful and harmless species, it only detects surface blooms (~5 metres deep), and is less reliable in shallow water due to bottom reflectance.
2.73A number of inquiry participants mentioned that the extent of current HAB testing is very limited, and mainly occurs through the South Australian Shellfish Quality Assurance Program (SASQAP). Professor Steer from SARDI stated that prior to 18 March 2025, there was no 'routine surveillance of microalgae species outside of our SASQAP … sites that are linked with our industry'.
2.74Dr Alison Turnbull indicated that a characteristic of marine aquaculture programs which hold the best long-term monitoring data for phytoplankton is that 'data is siloed, often confidential, and is restricted in geographical coverage'. The FRDC recommended research be undertaken 'to inform broadening/coordinating coastal and marine monitoring including biotoxins beyond fishing and aquaculture programs'.
Reducing nutrient inflows
2.75Inquiry participants put forward suggestions for reducing nutrient inflows to waterways, with the aim of reducing the likelihood of future HABs.
2.76Dr Dominic McAfee, a marine ecologist, called for 'a land-to-sea continuum of restoration and nutrient management … to not only stop [nutrients] at the source but also manage [them] as [they] move down through the system'. The Environment Institute at the University of Adelaide proposed an 'integrated catchment-based approach to restoring landscapes and reducing nutrient and sediment run-off', involving strategies such as riparian revegetation and wetland restoration.
2.77The Biodiversity Council highlighted the need to 'address major sources of … human-influenced nutrient and dissolved carbon'. Academics from the Australian National University and University of Newcastle pointed out that:
Reducing nutrient pollution will require actions from many sectors and across agricultural, industrial and urban areas: Actions such as improved organic and nutrient-rich waste management and chemical use practices, land use planning changes and community engagement.
2.78Some argued that agricultural land management could be improved to reduce nutrient runoff, such as by minimising fertiliser inputs.
2.79Submitters also raised urban water and stormwater management as an area where improvements could be made. The Surfrider Foundation Australia asserted that:
This algal bloom event is an opportunity to identify areas for improved stormwater infrastructure and strengthen public education efforts to reduce pollutants entering the system from urbanisation.
Limiting nutrient flow into sensitive coastal waters may be possible by tightening rules for wastewater treatment facilities, including improved waste management and monitoring procedures (CSIRO, 2020).
2.80Additionally, there were proposals for lifting water quality standards, such as through 'legally binding numeric criteria for water quality' in South Australian legislation, or requiring appropriate nutrient management strategies to be incorporated into Murray-Darling Basin water quality management plans.
Climate change mitigation
2.81A range of inquiry participants spoke about the importance of taking urgent action on climate change to address the possible root cause of the HAB. Many submitters and witnesses called for rapid emissions reduction and transitioning away from fossil fuels to renewable energy. For instance, the Victorian National Parks Association supported the Biodiversity Council's recommendation to 'accelerate Australia's decarbonisation efforts', saying that 'minimising ocean warming is the most important step in preventing harmful algal blooms not just in SA but also along other Australian coastlines'.
2.82The Australian Marine Conservation Society stressed that the current HAB is a stark warning of the consequences of climate change:
Australia must face the reality. Climate change is already reshaping our oceans with devastating consequences. We need urgent, scaled-up action to cut climate pollution.
International experiences with Karenia species of algae
2.83Mixed blooms of Karenia species have been detected worldwide, with HABs dominated Karenia mikimotoi (K. mikimotoi) being some of the most documented.
2.84K. mikimotoi, the species which dominated early stages of the current SA HAB,has also been identified in areas such as:
the Asia-Pacific (New Zealand, Singapore, China, Japan, Korea, and India);
Europe (France, Ireland, United Kingdom, Scotland, Wales, Spain and Portugal); and
the Americas (United States and Chile).
2.85Additionally, Karenia selliformis/cristata, the species which dominated later stages of the SA HAB, is 'known to have caused similar mass mortalities mostly in cold-water upwelling habitats (Japan, Russia, Chile, [and] South Africa)'.
2.86Various submitters and witnesses encouraged Australia to learn from, and work with, other countries that have experienced similar HAB events.
2.87The ANZMHAB Network pointed out that there are international HAB research and management networks that Australia should draw on, including the International Society for the Study of Harmful Algae and the HAB Programme led by the United Nations Educational, Scientific and Cultural Organization's (UNESCO) International Oceanographic Commission (IOC).
East Asia
2.88The committee heard that countries in East Asia—particularly China, Japan and Korea—have long-standing research and management programs for dealing with HABs.Professor Shauna Murray noted that:
The most impactful of K. mikimotoi blooms have occurred in China over the past two decades. In 2012, more than 300 square kilometres of abalone farms were affected, causing about A$525 million in lost production (Cen et al 2024).
2.89CSIRO's submission outlined the monitoring and forecasting systems that are in place in Japan and China:
Japan operates regionally focused water quality and HAB prediction services, which combine field sampling, modelling, and satellite observations to provide alerts to fishery cooperatives. China has developed an extensive national HAB early-warning system led by the State Oceanic Administration, which integrates satellite monitoring, modelling, and field surveillance to provide forecasts and risk assessments for coastal waters.
2.90Some inquiry participants mentioned that bloom control and mitigation techniques have been used for many years in China and Korea, including the use of modified clay (known as 'clay flocculation') to minimise HAB impacts on aquaculture. This method involves:
… the spraying of a solution of clay. We call them 'modified clays' now because we sometimes add constituents that make them more effective. … It's a very natural mineral, but, if used the right way, it can actually control these types of blooms.
2.91The ANZMHAB Network cautioned that 'selecting the right type of clay' is important as Karenia species have been observed to release intracellular toxins when they have come into contact with certain clay flocculants in South Korea, resulting in 'amplif[ied] fish-killing effects'.
2.92Although clay flocculation is not suitable for controlling large-scale HABs such as the one currently occurring in SA, it was suggested by Dr Donald Anderson that it would nonetheless be valuable to 'conduct some very small-scale studies over a few thousand square metres, perhaps, to test methodologies and develop capabilities'.
New Zealand
2.93The committee received evidence that New Zealand (NZ) 'experiences blooms of many of the same HAB species as Australia', and has invested in HAB monitoring and testing following a 'pinnacle HAB event in the early 1990s'. According to Dr Kirsty Smith from NZ's Cawthron Institute, that HAB event 'closed down … commercial and wild shellfish harbours for over six months' and was a turning point for NZ to introduce a monitoring program that is still in place today.
2.94Since then, 'weekly monitoring of phytoplankton and biotoxins in shellfish from commercial and also non-commercial (i.e., recreational shellfish harvesting) sites has occurred', using light microscopy—and in some cases, molecular genetic methods—to analyse water samples. The ANZMHAB Network explained that:
In New Zealand, monitoring of HABs in commercial bivalve shellfish aquaculture areas is funded by the shellfish industry. At select locations in New Zealand, where recreational collection of wild shellfish for personal consumption is popular, the Ministry for Primary Industries [MPI] is responsible for the collection and analysis of routine water and shellfish samples to inform risk management … MPI issue warnings to the public about the risks of consuming non-commercial shellfish when toxicity in shellfish (from commercial and non-commercial sites) exceeds pre-determined limits. Monitoring for HABs that cause shellfish toxicity is well established in New Zealand but if there is a bloom of a HAB species associated with a dermal or respiratory illness or other health issue, ad hoc sampling is done by regional councils or public health officials. If there is a risk MPI will work with the National Public Health Service to issue a public health warning.
United States
2.95Throughout the inquiry, submitters and witnesses frequently pointed to the US nationally coordinated HAB program and work underway in the state of Florida as good examples of strong HAB management. The SA Government repeatedly remarked that it was learning from the US experience with HABs and communicating with relevant state and federal government officials about their approach to HAB management and mitigation.
2.96Dr Donald Anderson, Director of the US National Office for Harmful Algal Blooms, gave evidence that the US national program on HABs 'involves research, monitoring and management at the national level that then filters down to many of the regions'. Federal legislation—the Harmful Algal Bloom and Hypoxia Research and Control Act (US) (US HABHRC Act)—was originally enacted in 1998 and is reauthorised approximately every four years, in recognition of the threats posed by HABs. The US HABHRC Act:
… authorizes and coordinates research, monitoring, forecasting, and mitigation efforts among various federal agencies—primarily led by NOAA (National Oceanic and Atmospheric Administration)—in collaboration with states, tribes, academic institutions, and local stakeholders. The Act provides a framework for understanding the causes and impacts of HABs and hypoxia, improving early warning systems, and developing effective control and response strategies.
2.97Three national entities have oversight for the national HAB program:
The Interagency Working Group on Harmful Algal Blooms and Hypoxia: a body that coordinates the federal government's work on researching, forecasting, controlling and mitigating HAB and hypoxia events across the US. The Working Group comprises representatives from various 'federal agencies involved in oceanic, freshwater, environmental, public health, and agricultural research or management';
The National Harmful Algal Bloom Committee: a coordinating body for the US HAB community, including 'academic researchers, resource managers, state and federal agencies, and other stakeholders'; and
The US National Office for Harmful Algal Blooms: a body that works to coordinate and unify HAB efforts among federal, state and local institutions and the wider scientific and management communities, and to act as a focal point for HAB-related data.
2.98The NOAA, the lead coordinating federal agency for HABs, provides forecasts for regions prone to bloom events, using:
… [a combination of] satellite ocean colour data, in situ measurements, and hydrodynamic models to provide near real-time assessments and short-term forecasts of bloom extent, intensity, and movement, supporting early warnings for fisheries and coastal communities.
2.99At the state level, Florida has developed extensive experience in dealing with Karenia brevis blooms, which have occurred almost annually since the late 1940s. Dr Cynthia Heil, Director of the Red Tide Institute in Florida, told the committee that the approach to managing HABs in Florida involves three key aspects:
We have, firstly, an emphasis on research to better understand the blooms and the physiology of the organism so we can better predict the blooms when they occur each year. Secondly, by monitoring blooms, and not just taking a water sample and counting the cells but providing the fiscal support and recruiting the expertise so you have them in place to monitor blooms from year to year, we're seeking to provide up-to-date monitoring information to the public and to industry stakeholders so they can make better informed decisions based on accurate information. Thirdly, and this is more recently in the last six or seven years, we've had a focus on developing a toolbox of potential methods, compounds and technologies to mitigate Karenia blooms and their impacts so we can better manage them.
Next chapter
2.100The next chapter outlines the response from the SA and Commonwealth governments, including support and recovery arrangements.