U.S. Commission on Ocean Policy - Joint Ocean Commission Initiative

Harmful Algal BloomsThe term harmful algal bloom (HAB) is used to describe destructive concentrations ofparticular algal species in ocean waters. These blooms are sometimes called red tidesbecause the high algal density can make the ocean surface appear red, but they may alsobe green, yellow, or brown, depending on the type of algae present.The Nature of the ProblemThe underlying physical, chemical, and biological causes for most harmful algal bloomsare not well understood, but an increase in distribution, incidence, duration, and severityof HABs has been documented within recent decades (Figure 23.1). In many areas, increasesin nutrients in coastal waters, from point and nonpoint sources of pollution, and highernumbers of invasive species released from ships’ ballast water mirror the increase in HABevents, suggesting a possible causal connection. 7,8 However, others have suggested thatthe apparent increase in HAB events is simply a result of more frequent and effectivemonitoring. Additional research is needed to understand why blooms form in a specificarea, how they are transported, and what causes them to persist.HABs become a health concern when they produce high concentrations of potent toxinsin ocean waters. When these toxins are concentrated in fish and other seafood consumed byhumans, they can lead to paralytic, diarrhetic, neurotoxic, or amnesic shellfish poisoning.Most of these toxins cause harm only if ingested; however, some enter the air from sea sprayand can cause mild to severe respiratory illnesses when inhaled. These health effects are notrestricted to human populations; fish, birds, and marine mammals also fall victim to red tidepoisoning. The Great Lakes and large estuarine systems are also affected by HABs. Lake Eriecontinues to experience blooms of a blue green alga called Microcystin sp. This alga is capableof producing toxin compounds called microcystins that have been implicated in bird andfish kills and can result in gastrointestinal problems in humans.Annually, HABs are believed to cost the nation’s fishing and tourism industries morethan $50 million directly, with a likely multiplier effect that pushes the total economicloss to $100 million. 9,10 This can be catastrophic to low-income fishing communities, aswitnessed in Maryland in 1997 during an outbreak of Pfiesteria piscicida (a species ofdinoflagellate) associated with widespread fish kills. 11 Tourism was hurt by news coverageof seafood poisonings, and reports of red tides had a swift and chilling effect on oceansideresort visits, beach-going, and boating. Aquaculture can also be severely damaged byHABs, which can cause rapid fish kills and result in harvesting moratoria.HABs are of particular concern in areas where the water contains high concentrationsof dissolved nutrients. These areas are incubators for many types of algal blooms, nontoxicas well as toxic. The nutrients create conditions for rapid growth of large and densealgal blooms. When the algae die, their decomposition consumes the dissolved oxygenthat other organisms need for survival.Improving Understanding, Detection, and PreventionHABs constitute significant threats to the ecology and economy of coastal areas. While thepreferred course of action is prevention, effective treatments are also needed. The currentavailability of biological, chemical, or physical treatments is extremely limited. The ecologyof each bloom is different, and the required environmental conditions are not completelyunderstood for any particular algal species.The most likely and immediate solution for reducing the number and severity of HABsis to control nutrient inputs to coastal waters. (Nutrient pollution is further discussed inChapter 14.) Prevention may also be strengthened through careful facility siting decisionsand tighter controls on invasive species. However, for better long-term management, acomprehensive investigation of the biology and ecology of HABs will be needed to increaseour understanding of options for prevention, prediction, and control.344 A N O CEAN B LUEPRINT FOR THE 21ST C ENTURY