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. Although they are a small percent of the algal species, toxic algae blooms have a large impact.
A broad classification of HABs distinguishes two groups of organisms: the toxin producers, which can contaminate seafood or kill fish, and the high-biomass producers, which can cause anoxia and indiscriminate kills of marine life after reaching dense concentrations. Some HABs have characteristics of both.
The impact of harmful microalgae is particularly evident when marine food resources are affected. Shellfish and in some cases finfish are often not visibly affected by the algae, but accumulate the toxins in their organs. The toxins may subsequently be transmitted to humans and through consumption of contaminated seafood become a serious health threat. Toxic blooms have caused large-scale marine mortality events and have been associated with various types of shellfish poisonings around the world. No illness has occurred due to the consumption of Maryland seafood.
Cyanobacteria, aka Bluegreen Algae, can produce many different toxins including skin irritants, liver toxins, and neurotoxins. Harmful cyanobacteria in Maryland include Anabaena, Aphanizomenon, Lyngbya, Microcystis and more.
Dinophysis spp are known to produce okadaic acid or other toxins responsible for Diarrhetic Shellfish Poisoning, DSP.
Pseudo-nitzschia has been shown to produce very low levels of domoic acid in Maryland. Shellfish feeding on toxic Pseudo-nitzschia can accumulate the toxin leading to Amnesic Shellfish Poisoning, ASP, in people or animals that consume the the shellfish.
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