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Naturally occurring microscopic algae, called phytoplankton, are common in coastal waters. Though phytoplankton are small, they can grow explosively, creating something called a "bloom". In many blooms, these organisms can be so numerous and concentrated that they color the water red, hence the term "red tides".
An intense bloom can produce harmful impacts on marine ecosystems. For example, when masses of algae die and decompose, they can deplete oxygen in the water, causing the water to become so low in oxygen that animals either leave the area or die. A small percentage of algae produce powerful toxins that can kill fish, shellfish, marine mammals and birds, and may directly or indirectly cause illness in people. While both types have harmful impacts, the term, “harmful algal bloom”, is usually associated with blooms that kill with a toxin. “Red tide” is a popular term for harmful algal blooms, however HABs is preferred by scientists as they can be different colors. In some cases, the algae may not produce a discoloration of the water, yet still be present in sufficient numbers to affect shellfish or other marine life.
Shown in this satellite image is ocean color data revealing high concentrations of chlorophyll over a large area (in red), warning scientists of potential HAB activity off the Florida Gulf Coast. Water samples are used to provide data on the algal species to confirm the presence of harmful algae.
Harmful Algal Blooms are considered an environmental hazard because these events can make people sick when contaminated shellfish are eaten, or when people breathe aerosolized HAB toxins near the beach. In addition, HAB events can result in the closure of shellfish beds, massive fish kills, death of marine mammals and seabirds, and alteration of marine habitats. As a consequence, HAB events adversely affect commercial and recreational fishing, tourism, and valued habitats, creating a significant impact on local economies and the livelihood of coastal residents.
Advanced warning of harmful algal blooms (HABs) increases the options for managing these events. The HAB Forecasting System
provided by NOAA, Mote Marine Laboratory, and the Florida Fish and Wildlife Institute, supplies information on the location, extent, and potential for development or movement of harmful algal blooms in the Gulf of Mexico. The forecasting system relies on satellite imagery, field observations, and buoy data to provide the large spatial scale and high frequency of observations required to assess bloom location and movements. Historical and near-realtime data can be accessed through the Harmful Algal Blooms Observing System
Extensive information about HABs can be found on NOAA's National Ocean Service - Harmful Algal Bloom Web site