October 27-31, 2013
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This cyanobacterial bloom has the typical appearance of a thick layer of green paint. The bloom was found to consist of toxic species in the genus Microcystis. (Photo by W. Carmichael)
This massive “red tide” of the dinoflagellate Noctiluca stretched for more than 20 miles along the southern California coast. Non-toxic blooms such as these can cause extensive mortalities of plants and animals in shallow waters when the bloom biomass decays, stripping oxygen from the water. (Photo by P. Franks)
Harmful algal blooms are caused by species of tiny plants—phytoplankton—some of which produce potent chemical toxins. Fueled by periodic abundances of nutrients in the ocean, these algae multiply and proliferate until they can cover tens to hundreds of miles of coastal ocean. (Photo by D. Anderson)
Dead fish from a Karenia brevis bloom in Texas. At high concentrations, toxins produced by this organism can cause massive fish kills. (Photo by Brazosports)
A spectacular “red tide” bloom (non-toxic) of Noctiluca scintillans in New Zealand. (Photo by M. Godfrey)
Researchers are investigating the use of natural clays in Florida’s Sarasota Bay as a potential tool to mitigate harmful algal blooms, or “red tide” (Photo by J. Culter)
Seaweeds (macroalgae) can also cause harm. For example, expansive blooms of several Caulerpa spp. occurred off the Florida coast in 1997 and 2001. Caulerpa spp. can grow year-round and have transformed some reefs into “Caulerpa meadows” where more than 70% of the coral surface is now dominated by these macroalgal HAB species. (Photo by B. LaPointe)
When shellfish accumulate dangerous toxins after filtering algae from water as food, public health is at risk. State and federal agencies monitor these shellfish for biotoxins and close affected areas, posting signs like this. Note that although the water appears clear, there is a danger present. (Photo by J. Kleindinst)
An example of foam produced during a Phaeocystis bloom in the North Sea. This material is unsightly and bothersome to coastal residents, but it also can coat fishermen?s nets, causing fish avoidance.
Harmful AlgaeStatement of Purpose
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The primary objective of this site is to serve as a comprehensive resource for information about harmful algal blooms.
What are Harmful Algal Blooms (HABs)?
Marine and fresh waters teem with life, much of it microscopic, and most of it harmless; in fact, it is this microscopic life on which all aquatic life ultimately depends for food. While most of these species of phytoplankton and cyanobacteria are harmless, there are a few dozen that create potent toxins given the right conditions. Harmful algal blooms may cause harm through the production of toxins or by their accumulated biomass, which can affect co-occurring organisms and alter food-web dynamics. Impacts include human illness and mortality following consumption of or indirect exposure to HAB toxins, substantial economic losses to coastal communities and commercial fisheries, and HAB-associated fish, bird and mammal mortalities. To the human eye, blooms can appear greenish, brown, and even reddish- orange depending upon the algal species, the aquatic ecosystem, and the concentration of the organisms.
These outbreaks are commonly called red tides, but scientists prefer the term "harmful algal blooms" (or HABs). The term red tide erroneously includes many blooms that discolor the water but cause no harm, and also excludes blooms of highly toxic cells that cause problems at low (and essentially invisible) cell concentrations. Therefore, harmful algal bloom is a more appropriate descriptor.
Last updated: May 1, 2013
The Harmful Algae Page is supported by a National Oceanic and Atmospheric Administration Center for Sponsored Coastal Ocean Research Coastal Ocean Program (NOAA/CSCOR/COP) grant to the National Office for Harmful Algal Blooms at Woods Hole Oceanographic Institution, Dr. Don Anderson, Director.