Harmful algal bloom (HAB)

What is HAB?

A harmful algal bloom (HAB) is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. 

Example?

• the production of neurotoxins which cause mass mortalities in fish, seabirds, sea turtles, and marine mammals
• human illness or death via consumption of seafood contaminated by toxic algae
• mechanical damage to other organisms, such as disruption of epithelial gill tissues in fish, resulting in asphyxiation
• oxygen depletion of the water column (hypoxia or anoxia) from cellular respiration and bacterial degradation

Why does it suddenly occur?

• The primary human contribution to HABs is thought to be nutrient pollution -- from, amongst other things, agriculture, sewage outfalls and mining -- creating a more favorable, nutrient-rich environment in coastal waters in which certain groups of phytoplankton can thrive.
• Climate change may also be making some coastal environments more hospitable to harmful phytoplankton species.
• Many species of phytoplankton are also transported around the world in ships' ballast water and discharged in areas where they did not previously occur. Others are distributed accidentally through the transfer of shellfish for aquaculture.

Advantages and disadvantages of HAB?

Advantages

Although not a danger, some harmful algal blooms produce beautiful displays of bioluminescence when disturbed at night, especially by breaking waves.

Disadvantages

They kill fish, birds, mammals

They cause illness and sometimes lead to death when people eat shellfish or fish that have concentrated the nerve poisons produced by the blooms. The most common symptoms include nausea, vomiting, abdominal cramps, diarrhea, and neurological disorders.

What kind of studies being done now with HAB?
Harmful algal bloom and eutrophication : nutrient sources,composition and consequences (Donal et al,2002)

The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change (J.M et al,2012)