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Harmful Algal Blooms (HABs)

Algae, single celled plant-like marine organisms, are critical to life on Earth. Marine algae range from microscopic single celled organisms (phytoplankton) to larger mulitcellular seaweeds like kelp. As photosynthesizers, harvesting energy from sun to produce their own food, algae are the base in many marine food webs. Oxygen is another product of photosynthesis, and single-cell algae (phytoplankton) living in the ocean are responsible for half of the oxygen produced on Earth.


Pseudo-nitzschia, a marine algae that can cause domoic acid poisoning.

Algae as a group are immensely important to the functioning of our planet, but there are a few dozen species of algae which can cause serious problems. These species become noticeable during periodic events known as "harmful algal blooms" (HABs). Algae can grow at rapid rates (bloom) and overgrow other species, alter habitats, or deplete oxygen (though algae produce oxygen while they are alive, the decomposition of large amounts of dead algae can deplete oxygen). Some algae are capable of producing powerful toxins that are harmful or deadly to other species. Impacts of HABs include fish kills, injuries to marine invertebrates and marine mammals, and even human illness or death.


Alexandrium, a marine algae that can cause paralytic shellfish poisoning.

The causes of HABs are not fully understood. In some cases, environmental changes such as alteration in water flow or water temperature have been observed to coincide with HABs. In many aquatic ecosystems, nutrients (such as nitrates and phosphates) are scarce and this limits algae growth. When additional nutrients are available through runoff from land, pollution or changes in water circulation, this natural control on algal growth is removed, often resulting in rapid growth of aquatic algae. Scientists suspect that increases in nutrients may also play a role in some HAB events. HABs are a threat to living resources, fishing, tourism, and human health. The number and intensity of HAB events appear to be increasing.

Is Shellfish Safe?

HABs Resources

Additional Resources

Detecting Harmful Algal Blooms in the Pacific Northwest

NANOOS Awarded Funds to Study 2015 West Coast Bloom

NOAA Funds HAB Forecasting System

Phytoplankton Bloom in Hood Canal 2016

NANOOS Ocean Technology Transfer Grant for 2014-2017

Overview of 2015 HAB Event

How are HABs Monitored?



HABs Research

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