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What are HABs?

At the base of the food chain in most freshwater and marine systems are phytoplankton, single-
celled photosynthetic algae. The rapid growth of cells of one or several species of phytoplankton can
form an algal bloom. While blooms are often harmless and can be beneficial to the functioning of marine and freshwater ecosystems, there is increasing awareness that blooms can also be indicative of
eutrophication, ecosystem disruption, or altered environmental states.

Some algal blooms can have negative impacts to the environment, human health, or the economy
and are thus termed Harmful Algal Blooms (HABs). Mechanisms that classify a particular organism as harmful can be physical (gill irritation, viscosity and gelatinous barriers which lead to gill clogging and death), large blooms leading to anoxia, and/or production of phycotoxins or allelopathic deterrents to grazers.

Marine toxins can cause human illness and fatalities, marine mammal and bird mortalities, and fish
kills. Many of the negative impacts to humans and marine organisms are related to toxic shellfish
ingestion. Toxins produced by phytoplankton accumulate in filter feeding organisms such as bivalve
shellfish and filter feeding fishes such as sardines and anchovies. As a result, the California
Department of Public Health monitors the shellfish industry for phycotoxins that cause paralytic and amnesiac shellfish poisoning (PSP, ASP), and provides alerts for non-commercial harvesting and recreational users of the coastal environment.