Skip to content


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.

Microalgal toxins and their chronic effects need to be recognized as major threats to animal health, sustained fisheries, endangered species, and ecosystems.  It is recognized that algal 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, place certain populations at increased risk.  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.

Additional Resources

Brooks, B.W., Lazorchak, J.M., Howard, M.D., Johnson, M.V.V., Morton, S.L., Perkins, D.A., Reavie, E.D., Scott, G.I., Smith, S.A. and Steevens, J.A., 2016. Are harmful algal blooms becoming the greatest inland water quality threat to public health and aquatic ecosystems?. Environmental toxicology and chemistry35(1), pp.6-13.

Burkholder, J.M., Shumway, S.E., and Glibert, P.M. 2018. Food Web and Ecosystem Impacts of Harmful Algae, S.E. Shumway, J.M. Burkholder, S.L. Morton (Eds.), Harmful Algal Blooms: a Compendium Desk Reference, John Wiley & Sons, Ltd., Hoboken, New Jersey (2018), pp. 243-301

Dolah, F.M.V., Roelke, D. and Greene, R.M., 2001. Health and ecological impacts of harmful algal blooms: risk assessment needs. Human and Ecological Risk Assessment: An International Journal7(5), pp.1329-1345.