Navigating South Australia’s Toxic Algal Bloom: A Guide for Seafood Consumers
South Australia’s coastline is currently grappling with a severe environmental crisis: a harmful algal bloom (HAB) caused by the toxic dinoflagellate Karenia mikimotoi. This bloom has led to extensive marine life fatalities, impacting over 200 species across more than 4,500 square kms, from Adelaide’s southern beaches to Kangaroo Island and the Yorke Peninsula .
Understanding the Impact on Seafood
The bloom’s effects on marine ecosystems are profound. Mass die-offs of fish, shellfish, and other marine organisms have been reported, raising concerns about the safety and sustainability of seafood from affected areas. While SA Health advises that live-caught fish are safe to eat, they strongly recommend against consuming dead fish or shellfish found on beaches due to potential spoilage and the risk of toxin exposure .
Health Advisories and Safety Measures
SA Health has issued warnings to avoid swimming, diving, or engaging in activities that may lead to water ingestion in affected areas. Check your local authority before doing any of these activities. These advisories aim to protect public health from potential exposure to harmful algal toxins. The authorities will take precautionary measures as they want you to be safe.
Economic and Environmental Consequences
The algal bloom has not only disrupted marine life but also significantly impacted local industries. Fisheries and aquaculture sectors are facing substantial losses, with oyster farmers reporting estimated damages between $40,000 to $50,000 due to lease shutdowns. Oysters are filter feeders (known as the canary of the estuaries) so will always be a gateway to such HAB’s. Tourism is also affected, as beach closures and health advisories deter visitors, leading to economic downturns in coastal communities.
Environmental Factors and Climate Change
Experts attribute the bloom to a combination of factors, including a marine heatwave with sea temperatures approximately 2.5°C above average, calm weather conditions, and nutrient-rich waters . These conditions create an ideal environment for Karenia mikimotoi to proliferate, highlighting the broader implications of climate change on marine ecosystems.
Has this occurred elsewhere?
Japan - Karenia mikimotoi blooms have been documented in Japan since the 1930s, particularly in the Seto Inland Sea and Kyushu regions. These events have caused mass mortalities of fish and shellfish, with economic losses estimated at approximately ¥9 billion over a 30-year period. Trends indicate an increase in bloom frequency and duration, attributed to factors like rising sea temperatures and nutrient enrichment.
Ireland - In the summer of 2005, Ireland’s Atlantic coast experienced a significant K. mikimotoi bloom, resulting in extensive fish kills and disruptions to aquaculture operations. The bloom’s persistence and toxicity led to substantial economic losses and highlighted the need for improved monitoring and response strategies.
China - Coastal regions of China, especially Fujian Province, have faced frequent K. mikimotoi blooms. A notable event in 2012 led to financial losses exceeding 2 billion yuan due to widespread fish and shellfish deaths. These blooms are often linked to eutrophication and changing oceanographic conditions.
Norway and New Zealand - Both countries have reported K. mikimotoi blooms causing fish mortalities and impacting aquaculture. In Norway, blooms have affected salmon farms, while New Zealand has seen impacts on various marine species. These events underscore the global reach of K. mikimotoi and its potential to disrupt marine ecosystems. The largest documented outbreak (>180 people) occurred in New Zealand 1992, associated with consumption of cockles and green shell mussels. This was followed by smaller outbreaks 1994-1996, but no illnesses have been reported since.
USA (Gulf of America/Mexico) where Karenia brevis blooms recurrently and were reported by Spanish explorers as early as the 1500s. The USA has implemented a egulatory level at 20 mouse units/100g of shellfish, equivalent to 0.8 mg brevetoxin per kg shellfish, which has proven effective to prevent illness. This level is listed in the Codex Standard for live and raw bivalves CXS 292-2008, and the Codex Standard for Abalone CXS 312-2013.
Australia has implemented the same regulatory level. Until further information on the oral toxicities of individual BTX analogues becomes available, current best practice is to consider the cumulative sum of brevetoxins (including metabolite toxins) for regulatory purposes.
Outcomes and Lessons Learned
- Ecological Impact: K. mikimotoi blooms lead to hypoxic conditions and release toxins that damage gill tissues, causing mass die-offs of marine life. The loss of biodiversity can have long-term effects on ecosystem stability.
- Economic Consequences: Fisheries and aquaculture industries suffer significant losses due to fish kills and harvest closures. Tourism can also be affected by beach closures and negative perceptions.
- Public Health: While K. mikimotoi is primarily harmful to marine life, exposure can cause skin irritation and respiratory issues in humans, leading to health advisories and beach closures.
- Management Strategies: Affected regions have emphasized the importance of early detection, monitoring programs, and public awareness campaigns. Research into bloom dynamics and mitigation techniques continues to be a priority. Outbreaks (where two or more people get sick) occasionally occur in these areas; the rarity of outbreak notifications is attributed to successful regulation and monitoring.
Understanding past K. mikimotoi bloom events provides valuable insights into managing current and future occurrences. Continued research, monitoring, and international collaboration are essential to mitigate the impacts of these harmful algal blooms.
What is Neurotoxic Shellfish Poisoning (NSP)?
NSP is a foodborne intoxication caused by consumption of brevetoxins and brevetoxin metabolites: a group of stable, fat-soluble chemical toxins. The parent brevetoxins BTX-1 and BTX-2 are produced by the marine dinoflagellate Karenia brevis and potentially other Karenia species such as K. papilionacea. The parent toxins are metabolised by marine organisms to form multiple other toxins of varying potency. Brevetoxins are most commonly associated with shellfish due to accumulation via filter feeding but have been found in a variety of marine organisms, including other molluscs and crustaceans.
How much brevetoxin is a harmful dose?
An acute toxin dose for humans has not been established for brevetoxin as only limited data are available on intoxications in humans and data for oral toxicity in mice is sparse. No human fatalities have ever been reported.
What are the symptoms
Mild intoxication may involve gastro-intestinal symptoms (nausea, vomiting, diarrhoea, numbness of extremities and face) which resolve in a day or two. More severe poisoning may cause one or more of the following neurological symptoms which can occur within minutes up to 18 hours after consumption, and may last for a few days:
- Loss of co-ordination of muscles and partial limb paralysis
- Hot-cold temperature reversal
- Headaches
- Slurred speech
- Fatigue
- Respiratory discomfort/distress.
If neurological symptoms occur, seek medical attention. Treatment involves supportive care for managing the symptoms.
No chronic effects have been documented although there is very little research in this area.
What can be done to inactivate or eliminate brevetoxins?
- Brevetoxins are heat-stable, so are not destroyed by cooking or freezing.
- They are not visible and have no smell or taste.
- Once seafood is contaminated with brevetoxin, it can only be purged naturally. Purging time varies between species, ranging from weeks to months.
Brevetoxin risk is managed through monitoring of seawater for toxic algae (conducted regularly in commercial shellfish growing areas in Australia) and testing of seafood for brevetoxins. Microscopic identification of Karenia to species level is difficult and molecular testing may be required. Brevetoxin analysis is conducted via LC-MS/MS in commercial laboratories.
Karenia blooms are often associated with fish-kills and toxins may also be aerosolised by coastal winds and waves, causing respiratory discomfort in humans (throat irritation, sneezing, coughing and itchy eyes).
Recommendations for Seafood Consumers
- Stay Informed: Regularly check updates from SA Health and the Department for Environment and Water for the latest advisories on seafood safety and water quality.
- Purchase Responsibly: Buy seafood from reputable sources that adhere to safety guidelines and can verify the origin of their products.
- Avoid Foraging: Refrain from collecting shellfish or other seafood from affected beaches, as they may be contaminated.
- Support Local Industries: Consider supporting local fisheries and aquaculture businesses that are implementing safe practices and have been cleared by health authorities.
- Advocate for Sustainability: Engage in conversations about these impacts and support initiatives aimed at reducing environmental impacts on marine ecosystems.
Conclusion
The ongoing harmful algal bloom in South Australia serves as a stark reminder of the delicate balance within our marine environments and the far-reaching consequences of ecological disturbances. As consumers, staying informed and making conscientious choices can contribute to the resilience of both our health and the seafood industry. Please note that Brevetoxin illness in humans is rare internationally and has not been recorded in Australia to date.
Where can I access more information?
- EFSA Scientific opinion on Marine biotoxins in shellfish – Emerging toxins: Brevetoxins group (2010). EFSA Journal; 8(7):1677
- Watkins S.M., Reich A., Fleming L.E., Hammond R. (2008). Neurotoxic Shellfish Poisoning. Marine Drugs 6, 431-455
- Food and Agriculture Centre of United Nations (FAO), (2004). Food and Nutrition Paper 80, Marine Biotoxins, Chapter 5, Neurotoxic shellfish poisoning (NSP). http://www.fao.org/3/y5486e/y5486e00.htm