A harmful algal bloom (HAB) contains organisms (usually algae, hence the name) that can severely lower oxygen levels in natural waters, killing marine life. Some HABs are associated with algae-produced toxins. Blooms can last from a few days to many months. After the bloom dies, the microbes which decompose the dead algae use up even more of the oxygen, which can create fish die-offs. When these zones of depleted oxygen cover a large area for an extended period of time, they are referred to as dead zones, where neither fish nor plants are able to survive.
HABs are induced by an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (nitrates, ammonia, urea) and phosphate. These nutrients are emitted by agriculture, other industries, excessive fertilizer use in urban/suburban areas and associated urban runoff. Higher water temperature and low circulation are contributing factors. HABs can cause significant harm to animals, the environment and economies. They have been increasing in size and frequency worldwide,https://en.wikipedia.org/wiki/Urban_runoff a fact that many experts attribute to global climate change. The U.S. National Oceanic and Atmospheric Administration (NOAA) predicts more harmful blooms in the Pacific Ocean.
- J. Heisler, P.M. Glibert, J.M. Burkholder, D.M. Anderson, W. Cochlan, W.C. Dennison b, Q. Dortch, C.J. Gobler, C.A. Heil, E. Humphries, A. Lewitus, R. Magnien, H.G. Marshallm, K. Sellner, D.A. Stockwell, D.K. Stoecker, M. Suddleson (2008). “Eutrophication and harmful algal blooms: A scientific consensus”. Harmful Algae. 8 (1): 3–13. doi:10.1016/j.hal.2008.08.006. PMC 5543702. PMID 28781587.
- Harmful Algal Blooms, Center for Disease Control
- Harvey, Chelsea (2016-09-29). “The Pacific blob caused an “unprecedented” toxic algal bloom — and there’s more to come”. Washington Post.