Dr. Donald Boesch - Harmful Algal Blooms

Harmful Algal Blooms: Options for Prevention, Control and Mitigation

An Assessment Conducted for the National Fish and Wildlife Foundation and the National Oceanic and Atmospheric Administration Coastal Ocean Program.

Results published in:

Boesch, D. F., D. M. Anderson, R. A. Horner, S. E. Shumway, P. A. Tester, and T. E. Whitledge. 1997. Harmful Algal Blooms in Coastal Waters: Options for Prevention, Control, and Mitigation. NOAA Coastal Ocean Program Decision Analysis Series No. 10. NOAA Coastal Ocean Office, Silver Spring, MD. 46pp. + appendix.

Executive Summary

This report is the product of a panel of experts in the science of blooms of unicellular marine algae which can cause mass mortalities in a variety of marine organisms and cause illness and even death in humans who consume contaminated seafood. These phenomena are collectively termed harmful algal blooms or HABs for short. As a counterpart to recent assessments of the priorities for scientific research to understand the causes and behavior of HAB's, this assessment addressed the management options for reducing their incidence and extent (prevention), actions that can quell or contain blooms (control), and steps to reduce the losses of resources or economic values and minimize human health risks (mitigation).

The panel convened three regional meetings during the latter half of 1996 to solicit information and opinions from scientific experts, agency managers and user constituencies in Texas, Washington, and Florida. The panel's assessment limited its attention to those HABs that result in neurotoxic shellfish poisoning, paralytic shellfish poisoning, brown tides, amnesic shellfish poisoning, and aquaculture fish kills. This covers most, but certainly not all, HAB problems in the U.S. Harmful algal blooms are increasing in frequency or severity in many U.S. coastal environments and worldwide. Beyond aesthetic impairment, such blooms pose increasing risks to human health, natural resources and environmental quality. Whether the increase in HABs is a direct result of human activities, cyclic or longer-term variations in climate, or other natural factors, the greater risks demand improved precautions for the protection of human health, more concerted efforts to manage activities which may cause HABs, and renewed consideration of control strategies.

If possible, it is obviously preferable to prevent HABs in the first place rather than to treat their symptoms. Many scientists have suggested that increases in HABs are somehow linked to increased pollution of the coastal ocean, particularly by plant nutrients. Indeed, there are few other causes, other than climate change, that could conceivably be responsible for such widespread increases in HABs during the last half of the 20th Century. However, pollution and nutrient enrichment have not been unequivocally identified as the cause of any of the HABs considered in this assessment. Nonetheless, conscientious pursuit of goals for reductions of pollution, including excess nutrients, which have been established for many U.S. coastal waters would probably yield positive effects in terms of reductions in HABs. In other words, HAB reduction could provide an additional rationale to advance existing pollution reduction strategies. However, the reduction of the potentially most important pollutant, nitrogen, is a daunting challenge because of the importance of difficult-to-control nonpoint sources from agriculture and fossil fuel combustion. Careful assessment and precaution against introductions and along-coast transfers of HAB cells and cysts via ballast water and aquaculture seeding activities also require greater attention.

Although controlling HABs by the application of chemicals or flocculants or the introduction of biological control agents is fraught with difficulties related both to effectiveness and the potential for undesirable side effects, such controls deserve more careful attention than they have received heretofore. In addition to the need for expanded U.S. research on this topic, much can be learned from the experiences of Asian nations and from risk assessments applied in evaluating chemical and biological controls in land-based agriculture. The applicability of controls may be limited to more managed and constrained circumstances, for example in association with aquaculture or in small bays.

The conservative procedures used to protect public health from exposure to algal toxins have been largely successful to this point. The incidence of mortality and serious illnesses in the U.S. has been relatively low. However, in order to contend with potentially increased and more diverse risks from HABs in an era of declining governmental resources to support labor-intensive monitoring, more sophisticated and reliable detection methods are now required. In addition, the medical community should be better informed and prepared to treat individuals suffering HAB toxicity. Individuals visiting or living on the shore or consuming seafood also need to be better informed about the risks, but not unduly alarmed. Responsible public education and communication must receive increased attention.

The expanded research being initiated by federal agencies on the Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) should seek to contribute understanding toward prevention, control and mitigation strategies. However, a factor limiting the evaluation, much less application, of prevention, control and mitigation strategies has been the lack of focused research programs in these areas. Federal and state agencies with responsibilities for resource management, environmental protection and public health should support applied research directly addressing prevention, control and mitigation, including: evaluation of the effectiveness and side-effects of chemical, physical and biological control agents; development of better detection and measurement of toxins and HAB species for application in monitoring; ballast water treatments; and determination and treatment of the effects of chronic exposure on human health.

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