Harmful Algal Bloom Information System for Kachemak Bay, Alaska

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This Harmful Algal Bloom (HAB) Information System provides information on current water temperatures in Kachemak Bay and how these temperatures may affect the development of HABs and resulting shellfish toxicity. HABs are large increases in the amounts of toxic species of marine algae, also known as phytoplankton, that can cause human illnesses such paralytic shellfish poisoning (PSP). PSP events can cause illness in people, primarily from eating shellfish that filter phytoplankton for food and may concentrate toxins in amounts dangerous to both people and marine mammals.

Current Water Temperature (F) at Seldovia Harbor, Kachemak Bay

Kachemak Bay National Estuarine Research Reserve water quality station (SEQA2)

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The top graph shows the potential for HAB growth in Kachemak Bay, Alaska based on current water temperature at Seldovia Harbor. The bottom graph shows concentrations of PSP toxins measured in shellfish tissue at several Kachemak Bay locations, with results grouped by week. Different methods are used for shellfish testing (listed below). Phytoplankton species that cause PSP grow slower at colder temperatures and faster in warmer temperatures. The temperature ranges for HAB growth (top graph) are represented as: Low Growth Potential (green band), Moderate Growth Potential (orange band) and Maximum Growth Potential (pink band). Maximum Growth Potential indicates the temperature range most likely to promote the growth of HAB species, but other factors, such as nutrients, also play a role.

This HAB Information System provides information to help in making decisions about whether or not to recreationally harvest shellfish. It is NOT a direct measure of current shellfish toxicity. It is ALWAYS recommended to check advisories from the Alaska Departments of Health and Social Services (ADHSS) and Environmental Conservation (ADEC) before harvesting shellfish. The regulatory limit for human shellfish consumption is 80 micrograms (ug) of toxin per 100 grams (g) of shellfish tissue. See the links below.


  • Commercially available shellfish, including oysters, are regularly tested for HAB toxins under a State of Alaska regulatory program. Tested shellfish should be considered safe for consumption, unless state advisories are issued.
  • Recreationally harvested shellfish are NOT routinely tested for toxins.
  • Toxin concentrations in shellfish may change rapidly, therefore past toxin test results may not represent current conditions.
  • Water temperatures vary throughout Kachemak Bay, with shallow areas and sub-bays often having warmer waters than at Seldovia Harbor. The Seldovia temperature observations should only be used as a guide for other areas around Kachemak Bay.


Microscopic marine algae, referred to as phytoplankton, are important as the primary base of ocean food webs. Most of the many different phytoplankton species provide an important marine food source and are not harmful. Some phytoplankton species can produce toxins that make people sick. Large increases in the amounts of these plankton are referred to as harmful algal blooms (HABs). In Alaska, there are three species that can cause illnesses, including Alexandrium, which causes PSP from saxitoxins; Pseudo-nitzschia,  which causes amnesic shellfish poisoning (ASP); and Dinophysis, which causes diarrhetic shellfish poisoning (DSP). PSP is the most common illness that has occurred in Alaska. Different methods for testing shellfish toxins include mouse bio-assay (MBA), enzyme-linked immunosorbent assay (ELISA), high performance liquid chromatography (HPLC), and receptor binding assay (RBA). The links below provide more information.

In Kachemak Bay, researchers with the NOAA National Centers for Coastal Ocean Science (NCCOS) have conducted long-term phytoplankton research and monitoring to better understand the environmental conditions that trigger HABs and affect the degree of their toxicity. The NOAA/NCCOS Kasitsna Bay Laboratory, located in Kachemak Bay, and its partners continue to monitor and study HABs to determine how to better detect and ultimately forecast future blooms. The goal is to provide local community members with advanced warning information for their decisions on shellfish harvesting, which can reduce their risks from the adverse health effects associated with HABs.

Phytoplankton growth increases with more sunlight and with higher water temperature, as long as there are also sufficient nutrients in the water to sustain growth. NCCOS Kachemak Bay research indicates that the algal species causing PSP start growing faster when water temperatures levels are between 48º to 53ºF (9º and 12ºC), and that growth accelerates more at even higher temperatures. However, blooms are also affected by light levels, nutrients, water circulation, and freshwater run-off.

The HAB Information System provides an index for potential growth of HABs in Kachemak Bay based on the observed surface water temperature. Water temperature is one of the known variables influencing HABs in Kachemak Bay; research is underway to investigate other environmental conditions that may also trigger HABs, such as nutrients. Before harvesting shellfish, it is recommended to first check the HAB Information System to identify ocean temperatures for which eating recreationally harvested shellfish should be limited or avoided to reduce exposure to potential HAB toxins. This site provides data on past toxin testing. It does not guarantee that all recreational shellfish will be safe for consumption. Commercially available shellfish, including oysters, are regularly tested for HAB toxins under a State of Alaska regulatory program and should be considered safe for consumption, unless state advisories are issued. Information on monitoring and research programs, and the State of Alaska shellfish harvest program are provided in the links below  

Kachemak Bay Long-term Phytoplankton Monitoring Program

Within Kachemak Bay, several organizations are involved in the study and monitoring of phytoplankton that can lead to HABs. The Kachemak Bay National Estuarine Research Reserve and NOAA/NCCOS Kasitsna Bay Laboratory conduct ongoing phytoplankton and HAB monitoring, especially during the summer months. For annual reports, additional data, and more program information:

Learn More About Recreational and Commercial Shellfish Harvest

Know Before You Dig- Recreational Shellfish Harvesting Information for Alaska
If you choose to harvest shellfish in Alaska, it is important that you know the facts about Paralytic Shellfish Toxin (PST), know the species you plan to harvest, and know the symptoms of paralytic shellfish poisoning and get help quickly! For more information:

Shellfish Poisoning Resources, Alaska Public Health
The Alaska Section of Epidemiology keeps Alaskans safe from communicable diseases, injuries, and environmental, occupational, and other health hazards. For more information:

Commercial Shellfish Resources, Alaska Dept of Environmental Conservation
The Alaska Food Safety and Sanitation Program protects public health at regulated food, seafood and public facilities to prevent illness, injury and loss of life caused by unsafe sanitary practices. For more information on commercially harvested shellfish: 

Alaska Commercial Shellfish 
The following links provide information about shellfish farming operations and PSP testing.

HABs and Marine Biotoxins in Alaska 
The following links describe the harmful phytoplankton species and marine biotoxins in Alaska and how they cause harm to fish, marine mammals, and sometimes even humans.


Marine biotoxins

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