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Biotoxins from HABs are transferred throughout the food web when toxic algal cells are eaten by zooplankton, fish, and shellfish that are, in turn, eaten by other animals and humans. (G. Wikfors)


Ecosystem impacts of many different types can be linked to toxic and non-toxic HABs.   Impacts include loss of shellfish, loss of habitat, seagrass die-backs, and altered food web interactions that decrease preferred higher trophic level species.  An example of a species causing such impacts is the microalga Aureococcus anophagefferens, the cause of the mid-Atlantic brown tide, and the related species, Aureoumbra lagunensis, the cause of brown tides along the Texas coastline.  These species have had substantial ecosystem impacts that include a reduction in light penetration, a reduction in the extent of seagrass beds, and a reduction in the growth rates of hard clams.  Brown tides have also caused mass mortalities of mussel populations in Rhode Island and in Long Island waters.  Recurrent blooms have had severe impact on bay scallops, affecting more than 80% of New York's commercially valuable harvest.

It is recognized that harmful algae and their toxins can influence ecosystems from both the top-down (i.e., affecting predators and influencing grazing) and from the bottom-up (i.e., affecting plankton and benthic communities).  Acute or chronic exposure to HABs and their toxins, either directly or through the food web, puts these populations at increased risk.

Impacts of HABs on Higher Vertebrates

Acute or chronic exposure to HABs and their toxins, either directly or through the food web, place certain populations at increased risk.  Microalgal toxins and their chronic effects need to be recognized as major threats to animal health, sustained fisheries, endangered species, and ecosystems.  Long-term effects of biotoxins on the health of aquatic animals include increased susceptibility to disease, immunosuppression, abnormal development, and the induction of tumors.  Animals at all trophic levels that are exposed to biotoxins in the long term through their diet may die or display impaired feeding and immune function, avoidance behavior, physiological dysfunction, reduced growth and reproduction, or pathological effects.

Impacts of HABs on Aquaculture and Wild Harvest

Adverse effects ranging from reduced growth and reproduction to mass mortalities may lead to increased occurrence and severity of disease, significant losses in harvestable resources, or to spoiled or contaminated products - outcomes that result in substantial economic damage and adverse health consequences for consumers.  Aquaculture operations are particularly vulnerable to toxic and harmful algal events because of the inability to move or protect certain kinds of stock when a HAB event threatens.

Last updated: July 31, 2012