Algae are a natural and important part of the marine ecosystem. However sometimes environmental conditions mean algae populations grow very quickly, leading to a 'bloom'. Sometimes these blooms are clearly visible to the naked eye (e.g. red or green colouration to the water) but not always.
Not all algal blooms are harmful. However, blooms that do cause harm to the marine environment and/or human health are called harmful algal blooms (or HABs).
Impacts
HABs are a common and serious issue in Tasmania. Tasmania has multiple species of algae that can form HABs under the right conditions. The severity and impact of a HAB can vary based on a range of factors, including the species in the bloom, environmental conditions and size of the bloom.
HAB events can have the following impacts:
- Fish kills: HABs can reduce oxygen levels, making it hard for fish to breathe. Some blooms also release biotoxins that irritate and damage fish gills and internal organs. This can lead to large numbers of fish deaths.
- Seafood safety: Some HABs release toxins which accumulate in filter-feeding species. These toxins can cause serious illness if eaten. Rock lobster, oysters, mussels, abalone, periwinkles, sea urchins can all accumulate these toxins.
- Seafood industry: HABs regularly lead to temporary seafood harvest closures when seafood from an area may not be safe to eat. This ensures seafood in shops and restaurants is always safe to eat. Other temporary restrictions may also be put in place to protect human health and the marine environment. These restrictions can impact market access and export potential. They also require ongoing monitoring to protect consumer safety.
Preparing for HABs
The government is preparing for future HAB events in Tasmanian waters through stakeholder workshops, planning, and centralising coordination for HAB monitoring and management.
Integrated biotoxin management plan
NRE Tas is currently developing a statewide integrated biotoxin monitoring program. The program will improve our ability to rapidly detect and respond to HABs by:
- Centralising all biotoxin testing and regulation within NRE Tas; and,
- Creating a biotoxin management plan that covers all relevant species and fishing zones across Tasmania.
Marine Heatwaves and Related Events Response Plan
Harmful algal blooms may be associated with marine heatwave events.
The Tasmanian Marine Heatwave and Related Events Response Plan outlines how Tasmania will respond to marine heatwaves and related events, such as HABs.
Tasmanian Marine Heatwave and Related Event Response Plan (PDF 1Mb)
Workshops
We're working with fishers and aquaculture operators to get ready for possible HAB impacts this summer (2025-26).
We convened a HAB Preparedness Information Workshop. The aim was to bring together key stakeholders, including representatives from government agencies, industry, and academic institutions, to share knowledge and coordinate strategies that enhance the collective readiness for HAB events in Tasmanian waters.
We also hosted three summer industry preparedness workshops with representatives from wild fisheries, shellfish aquaculture and finfish aquaculture. This ensures industry had the latest information and provided a forum for sharing ideas on how we could be better prepared for heatwaves and related stressors (including HABs).
Learn more
Frequently asked questions
How do I know seafood is safe to eat during a HAB event?
Commercial seafood is closely monitored to make sure it is safe to eat.
National guidelines establish:
- When seafood should be tested for biotoxins; and,
- When fishing and harvesting operations should be closed due to biotoxins.
Commercial seafood is only sold when it has passed all necessary safety requirements.
For recreational fishers,
public health warnings are issued by the Department of Health when seafood in an area is unsafe to eat due to a HAB.
How are biotoxins monitored in Tasmania?
Tasmania has a biotoxin monitoring program in place through
ShellMAP. It monitors for both harmful algae and the biotoxins they may produce.
ShellMAP publishes a
weekly biotoxin bulletin that provides a summary of HAB monitoring results from the previous week.
How does the South Australian HAB event translate to Tasmania?
The latest research shows that the
South Australian algal bloom is made up of different types of the Karenia species.
Karenia has previously been identified in Tasmania through routine monitoring activities. All historical detections of Karenia in Tasmania have been below the regulatory limit for closing fishing and harvesting operations.