Science for Solutions 

A A Special Joint Report with the 

Decision Analysis Series No. 10 National Fish and Wildlife Foundation 

onald F. Boesch, Anderson, Rita A 

dra %: Shumway, . Tes f er, Terry E. 

February 1997 

U.S. DEPARTMENT OF COMMERCE 

William M. Daley, Secretary 

U.S. DEPARTMENT OF THE INTERIOR 

Bruce Babbitt, Secretary 
The Decision Analysis Series has been 

established by NOAA's Coastal Ocean 

Program (COP) to present documents for 

coastal resource decision makers which 

contain analytical treatments of major 

issues or topics. The issues, topics, and 

principal investigators have been selected 

through an extensive peer review 

process. To learn more about the COP or 

the Decision Analysis Series, please 

write: 

NOAA 

Coastal Ocean Office 

131 5 East West Highway 

Silver Spring, MD 209 10 

phone: 301 -71 3-3338 

fax: 30 1 -7 1 3-4044 

Cover photo: The upper portion of photo depicts a brown tide event 

in an inlet along the eastern end of Long Island, New York, during 

Summer 7986. The blue water is Block lsland Sound. Photo 

courtesy of L. Cosper. 
Science for Solutions 

NOAA COASTAL OCEAN PROGRAM Special Joint Report with the 

Decision Analysis Series No. 10 National Fish and Wildlife Foundation 

HARMFUL ALGAL BLOOMS IN COASTAL WATERS: 

Options for Prevention, Control and Mitigation 

Donald F. Boesch, Donald M. Anderson, Rita A. Horner 

Sandra E. Shumway, Patricia A. Tester, Terry E. Whitledge 

February 1997 

National Oceanic and Atmospheric Administration National Fish and Wildlife Foundation 

D. James Baker, Under Secretary Amos S. Eno, Executive Director 

Coastal Ocean Office 

Donald Scavia, Director 
This ~ublication should be cited as: 

Boesch, Donald F. et al. 1996. 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. 46 pp. + appendix. 

This publication does not constitute an endorsement of any commercial product or 

intend to be an opinion beyond scientific or other results obtained by the National 

Oceanic and Atmospheric Administration (NOAA). No reference shall be made to 

NOAA, or this publication furnished by NOAA, in any advertising or sales 

promotion which would indicate or imply that NOAA recommends or endorses anj 

proprietary product mentioned herein, or which has as its purpose an interest to 

cause directly or indirectly the advertised product to be used or purchased because 

of this ~ublication. 
The Assessment Panel 

Donald F. Boesch, Chair 

Center for Environmental and Estuarine Studies 

University of Maryland 

Cambridge, Maryland 

Donald M. Anderson 

Biology Department 

Woods Hole Oceanographic Institution 

Woods Hole, Massachusetts 

Rita A. Horner 

Department of Oceanography 

University of Washington 

Seattle, Washington 

Sandra E. Shumway 

Southampton College 

Long Island University 

Southampton, New York 

Patricia A. Tester 

Southeast Fisheries Science Center 

National Marine Fisheries Service, NOAA 

Beaufort, North Carolina 

Terry E. Whitledge 

Marine Science Institute 

University of Texas at Austin 

Port Aransas, Texas 
THE SECRETARY OF THE INTERIOR 

WASHINGTON 

Harmful algal blooms or as the public knows them, red and brown tides have become an 

increasing menace on our coasts over the last several years. While visiting the Texas coast last 

year, the serious impact these tides are having on our living aquatic resources and in the lives of 

people was brought home to me. At that time I asked the National Fish and Wildlife Foundation 

to see if the staff there could find out what could be done about this problem. 

The report you have in your hands -- Harmful Algal Blooms in Coastal Water: Options for 

Prevention, Control and Mitigation -- is the result of my request, and is this Nation's first 

systematic attempt to find a solution to this growing problem. The report also represents the best 

in intergovernmental cooperation as the report was completed by a partnership with the National 

Oceanic and Atmospheric Administration, Department of Commerce, the Department of the 

Interior, and the National Fish and Wildlife Foundation. 

What we have found is that while there are some steps that can be taken immediately, there are 

no simple answers to all the problems caused by these tides. This means we all must maintain a 

focus on this problem. For my part, I will ask the agencies of the Interior Department to put this 

report to work and to become an active partner in the search for and implementation of solutions. 

I especially want to thank Dr. Donald F. Boesch of the University of Maryland, who chaired this 

important work and the impressive panel that he assembled to help him. 

Well Done. 
Foreword 

I am pleased to release the assessment Harmful Algal Blooms in 

Coastal Water: Options for Prevention, Control and Mitigation, 

conducted for the National Fish and Wildlife Foundation, 

Department of the Interior, and the National Oceanic and 

Atmospheric Administration (NOAA), Department of Commerce. 

The report is the result of deliberations by a panel of experts, 

chaired by Donald F. Boesch of the University of Maryland, and 

is based on the outcome of workshops held in Port Aransas, Texas, 

Seattle, Washington, and Sarasota, Florida, from August through 

November 1996. Regional scientific experts, managers involved in 

reducing or mitigating the effects of algal blooms, and 

representatives of user constituencies participated in each of 

these fact-finding meetings by making presentations and 

participating in discussions. The assessment is intended to 

suggest the direction informed policy at Federal and state and 

local levels might take in dealing with the increasingly serious 

problem of harmful algal blooms. 

The Department of Commerce is particularly interested in this 

environmental problem because it poses a significant threat to 

the Nation's health and economic well-being. Some of these 

blooms produce toxins that are harmful to human beings, fish, 

birds, and marine mammals. Additionally, significant economic 

losses have resulted from blooms that cause closure of fisheries, 

beaches, and water-related activities and the industries they 

support. 

An interagency research effort to assemble the scientific 

knowledge to help understand and predict the occurrence of these 

blooms -- ECOHAB (Ecology and Oceanography of Harmful Algal 

Blooms) -- is underway under the leadership of NOAAts Coastal 

Ocean Program. NOAA is committed to expanding our interagency 

partnerships to explore ways to respond to the additional 

challenges posed in this report. Working together in this way, 

I believe we will move ahead toward finding solutions to this 

priority coastal ocean problem. 

(eL William M. Daley 

Secretary of Commerce 
This assessment was supported principally by the National Fish and Wildlife Foundation and 

the National Oceanic and Atmospheric Administration (Coastal Ocean Program and National Sea 

Grant College Program). Drs. Jerry Clark and Don Scavia, respectively, represented these 

organizations and provided essential encouragement, guidance and assistance throughout the 

planning and execution of the project. Other sponsors providing financial or logistical support for 

the three regional meetings that were held included the University of Maryland Center for 

Environmental and Estuarine Studies, Texas Parks and Wildlife Department, Gulf Coast 

Conservation Association, University of Texas Marine Science Institute, National Marine Fisheries 

Service (Northwest Fisheries Science Center), University of Washington Sea Grant Program, 

Solutions to Avoid Red Tide, Mote Marine Laboratory and the Florida Department of Environmental 

Protection. Dr. Larry McKinney, Mr. Jim Ehman, Dr. Terry Whitledge, Dr. Usha Varanasi, Mr. 

Louie Echols, Major Gen. (ret.) Jim Patterson, Dr. Kumar Mahadaven, and Dr. Kenneth Haddad 

facilitated the participation of these organizations. 

This assessment could not have been successful without the interest and cooperation of many 

technical experts, state agency representatives, resource users, businessmen, and citizens who 

participated in the three regional meetings as presenters, panelists or attendees. Their perspectives 

provided concerns and insights that could not be developed from written reports. 

Ms. Mini Berg provided technical assistance at the regional meetings and in preparation of 

the report. Ms. Deborah Kennedy prepared the figures. Ms. Joyce Meritt and Ms. Joan Thompson 

helped with meeting planning, communication and travel arrangements. Dr. Grant Gross and Ms. 

Sydney Arny of the Chesapeake Research Consortium provided ready assistance and effective 

management of the project. 

Finally, Drs. Shenvood Hall, Daniel Kamykowski, Maureen Keller, Kevin Sellner, Don 

Scavia, Karen Steidinger, Tracy Villareal, and John Wekell and General Jim Patterson reviewed the 

report and provided helpful suggestions toward its improvement. 

To all of these individuals the authors extend their sincere thanks for their commitment, 

interest and assistance. The completion of this assessment would not have been possible at all, much 

less in the short time frame in which we acted, without their utmost cooperation. 
ExecutiveSummary ..................................................... xi 

Introduction ............................................................ 1 

What Are Harmful Algal Blooms ........................................... 3 

Causes and Consequences ................................................. 5 

Neurotoxic Shellfish Poisoning ....................................... 5 

Paralytic Shellfish Poisoning ......................................... 7 

BrownTides ...................................................... 9 

Amnesic Shellfish Poisoning ........................................ 11 

Blooms Resulting in West Coast Fish Kills ............................. 12 

National Trends .................................................. 12 

Prevention ............................................................ 15 

Alteration of Nutrient Inputs ........................................ 15 

Regulating Freshwater Flows ........................................ 17 

Modification of Water Circulation .................................... 18 

Restricting Introductions ........................................... 18 

Controls .............................................................. 21 

Chemical Control ................................................. 21 

Flocculants ...................................................... 22 

Biological Control ................................................ 23 

Options for Control ............................................... 26 

Mitigation ............................................................. 29 

Monitoring and Surveillance ........................................ 29 

Forecasting ...................................................... 30 

Action Alternatives ............................................... 31 

Restoration ...................................................... 34 

Conclusions ........................................................... 37 

Risks ........................................................... 37 

Prevention ...................................................... 37 

Controls ........................................................ 37 

Mitigation ....................................................... 38 

Research ........................................................ 38 

References ............................................................ 41 

Appendix ............................................................. 47 
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 HABs, 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). 

This assessment is limited to an appraisal of scientific understanding, but also reflects 

consideration of information and perspectives provided by regional experts, agency managers and 

user constituencies during three regional meetings. The panel convened these 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. 

The panel developed the following conclusions and recommendations as a result of its 

deliberations: 

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 posed 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. 

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. 

Although pollution and nutrient enrichment are strongly implicated in worsening HABs 

elsewhere in the world, they 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 could well yield positive results in terms of reductions in some 

HABs. In other words, HAB reduction is yet another rationale for advancing existing 
pollution reduction strategies. However, the reduction of the potentially most important 

pollutant, nitrogen, is a daunting challenge because of the importance of difficult-tocontrol 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-related activities also require 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 potential 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. Furthermore, control 

techniques should be evaluated in the context of risk assessments similar to those 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 within small bays. 

t 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 to the immediate expansion of 

simple methods using volunteer observers. 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. 

xii 
Over the last several decades many areas of the world, including the United States, have 

experienced a growing trend in the incidence of harmful algal blooms (Anderson 1989; Smayda 

1990). The episodic proliferation of unicellular marine algae, some of which produce toxins, can 

cause mass mortalities in a variety of marine organisms and cause illness and even death in humans 

who consume contaminated seafood. Some harmful algal blooms can be dense enough to discolor 

the water, while others may produce deleterious effects even if toxic algae are present in low 

concentrations. Some are spatially extensive and persistent, while others are patchy and episodic. 

Harmful algal blooms have long occurred in some regions, such as along the west coast of Florida 

and the extended coastlines of Maine and Alaska, but may be expanding or lasting longer there. 

Others, such as those occurring in Texas and Long Island bays, have developed only in recent years. 

Blooms now threaten virtually every coastal state, cover greater expanses of our coastlines, and 

involve a multitude of species (Anderson 1995). 

Not all harmful algal species produce toxins. Dense blooms of non-toxic species can kill 

marine organisms indirectly by shading, through oxygen depletion, or even mechanical irritation. 

Harmful algae comprise species from several different groups: dinoflagellates, diatoms, microflagellates, cyanobacteria and chrysophytes. An important factor in some microalgal blooms is the 

production of toxins that in human consumers result in paralytic, diarrhetic, neurotoxic, and amnesic 

shellfish poisoning (PSP, DSP, NSP, and ASP); and ciguatera fish poisoning (CFP). Toxins may 

also affect marine mammals and birds. For example, neurotoxins associated with blooms along the 

west coast of Florida caused significant mortalities of endangered manatees in 1996 (Steidinger et 

al. 1996). In addition to risks to human health and natural resources, significant economic losses 

regularly result from closure of fisheries and beaches to protect human health: $7 million from a 

single PSP outbreak in Maine; $25 million from closures related to an NSP outbreak in North 

Carolina; $20 million per event from losses to the tourist industry and local governments for Florida 

red tides; and $15-20 million as a result of closures in harvesting razor clams and Dungeness crabs 

due to a single event of ASP in Washington and Oregon. 

To resolve these issues, federal agencies, including the National Oceanic and Atmospheric 

Administration, Environmental Protection Agency, the National Science Foundation, and the Office 

of Naval Research, are initiating a strategic research program on the ecology and oceanography of 

harmful algal blooms (ECOHAB). To guide this initiative, scientific research and monitoring needs 

were assessed and a national research agenda developed (Anderson 1995). However, issues related 

to the management of HABs have not received comparable attention. What are the environmental 

management options for reducing the incidence and extent of harmful algal blooms (prevention)? 

What actions can be taken in response to blooms to quell or contain them (control)? What steps can 

be taken to reduce the losses of resources and economic values and minimize human health risks that 

do occur (mitigation)? This assessment of prevention, control and mitigation options seeks to 

answer these questions and to provide guidance for policy makers and resource managers at national, 

state and local levels. 
2 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

The specific objectives are to: 

determine the state of understanding of the causes of harmful algal blooms in major 

regions of the United States; 

compare and evaluate the current management efforts related to these blooms; 

evaluate and recommend steps which could be taken to reduce the incidence and 

severity of harmful algal blooms; 

identify feasible actions which should be further developed or evaluated to control the 

spread of harmful algal blooms once they occur, and 

evaluate and recommend procedures for reducing the impact of harmful algal blooms, 

including more effective monitoring, fishery closures, aquaculture practices, and public 

health advisories. 

The assessment was conducted by a Panel of experts-the authors of this reportrepresenting a range of experience in the related scientific and management issues in different parts 

of the United States. The members of the panel were selected by the panel chair, Donald F. Boesch, 

in consultation with the principal sponsors of the assessment, the National Fish and Wildlife 

Foundation and the National Oceanic and Atmospheric Administration. 

The Panel performed the assessment through three regional meetings which addressed the 

most important types of harmful algal blooms: 

Port Aransas, Texas: August 21 -22, 1996; brown tides in Texas and Long Island. 

Seattle, Washington: September 30-October 1, 1996; paralytic and amnesic shellfish 

poisoning and blooms causing fish kills in the Pacific Northwest, California, Alaska and 

New England. 

Sarasota, Florida: November 13- 14, 1996; neurotoxic shellfish poisoning (red tide) in 

the Gulf of Mexico and southeast. 

Regional scientific experts, managers involved in reducing or mitigating the effects of algal 

blooms, and representatives of user constituencies participated in each of these fact-finding meetings 

by making presentations and participating in discussions. A list of these individuals is provided in 

Appendix 1. 

The assessment is intended to suggest informed policy at federal and state levels as it relates 

to environmental protection, resource management, public health, research and development, and 

investment of financial and capital resources. Specific recommendations are highlighted by bold 

facing. A second major goal is to provide background, comparative contexts, and practical advice 

for managers responsible for living resources, environmental protection, public health and tourism 

and recreation. In addition, the assessment aims to serve a useful role in public education and 

awareness. Finally, it provides a frame of reference for better relating research to policy and 

management information needs. The inputs of regional managers and resource users were 

particularly influential in broadening the assessment beyond strictly scientific issues. 
The term "harmful algal blooms" (shortened for convenience here to HABs) has been used 

by the scientific community to describe a diverse array of blooms of both microscopic and 

macroscopic marine algae which produce: toxic effects on humans and other organisms; physical 

impairment of fish and shellfish; nuisance conditions from odors and discoloration of waters; or 

overwhelming effects on ecosystems such as severe oxygen depletion or overgrowth of bottom 

habitats. Although the use of the terms "bloom" or "red tide" conjure up an image of algal 

populations so dense as to be visible, this is not always the case with HABs. Concentrations of only - - 

a few cells per liter of some microalgae may produce 

harmful toxic effects. 

This assessment focused on blooms of microscopic 

algae occurring in the coastal waters of the United States 

which produce toxic effects and impairment of fish and 

shellfish production, either directly or indirectly, via 

degradation of habitats. The focus was on a relatively few 

species of microscopic marine algae which cause the 

following: 

Blooms producing neurotoxic shellfish 

poisoning (NSP). These are caused by the 

dinoflagellate Gymnodinium breve and occur 

along the coasts of the Gulf of Mexico, and 

rarely, the southeast Atlantic coast. 

Blooms causing paralytic shellfish poisoning 

(PSP). Various species of the dinoflagellate 

genus Alexandrium are responsible for PSP in 

New England, northern California, the Pacific 

Northwest and Alaska. 

t "Brown tide" blooms (BTB) caused by very 

small golden brown algae. These seem to be 

a recent occurrence in relatively enclosed 

waters of southern New England, particularly 

Long Island (New York) and Texas. Aureococcus anophagefferens is responsible for 

brown tides in southern New England and a 

similar species, Aureoumbra lagunensis, 

blooms in Texas bays and lagoons. 

80pm Aureoumbra 

Heterosigma 

6 IJm 

Chaetoceros 30 pm 

Blooms of various species of the diatom genus Pseudo-nitzschia produce domoic acid 
4 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

that causes amnesic shellfish poisoning (ASP). Domoic acid poisoning may also be 

experienced by humans, mammals, and birds from consumption of fish and other 

invertebrates. Toxin-producing species of Pseudo-nitzschia occur on the northwest, east 

and Gulf coasts, but no confirmed cases of ASP have occurred in humans in the U.S. 

Blooms which result in catastrophic losses of cultured and wild fish, particularly in the 

Pacific Northwest, but do not cause illness in humans. Such blooms are caused both by 

the raphidophyte flagellate Heterosigma akashiwo and by a few species of the diatom 

genus Chaetoceros, which clog fish gills. 

In the following section, knowledge of the causes and consequences of these harmful algal 

blooms is reviewed. They are treated in the order listed above, with the long-studied NSP and PSPcausing blooms treated first, followed by those which are emerging concerns and less well-studied. 

Several other types of harmful algal blooms were not addressed in this assessment but 

deserve mention. These include blooms of a variety of dinoflagellates: the epibenthic 

Gambierdiscus toxicus which is responsible for ciguatera fish poisoning in tropical waters; the 

"phantom dinoflagellate," PJiesteriapiscicida, known to cause fish mortalities in east coast estuaries 

(Burkholder et al. 1992); and endoparasitic dinoflagellates which infect commercial crab species. 

Blooms of cyanobacteria or "blue-green algae" in east coast estuaries from the Chesapeake Bay to 

Florida Bay and excessive growths of macroalgae ("sea weeds"), which foul beaches, shade 

seagrasses, and deplete oxygen, also cause harm. 
CAUSES AND CONSEQUENCES 

NEUROTOXIC SHELLFISH POISONING 

Massive fish kills off the west coast of Florida have been known since 1844 and, according 

to the writings of sixteenth-century Spanish explorers, the Tampa Bay Indians long noted the 

seasonality of fish kills now associated with red tide blooms. Shellfish toxicity was documented in 

1880 and aerosol-related respiratory symptoms in human inhabitants were described in 1916. 

Between 1844 and 1996, red tides (discoloration, fish kills, respiratory irritation, or shellfish 

poisoning) have occurred in 58 years. Since 1946, when the causative toxic dinoflagellate, 

Gymnodinium breve, was first discovered, red tide has been observed in 42 of the 50 intervening 

years. 

Throughout the Gulf of Mexico and the U.S. South Atlantic Bight, G. breve is found in low 

background concentrations (1-1,000 cellll) except in areas off the west Florida and Texas coasts 

where local circulation may play a role in concentrating cells. While G. breve blooms have occurred 

in many different areas within the Gulf of Mexico, from Yucatkn in the south, along the Tamaulipas 

and Texas coasts, and recently to Alabama, Mississippi and Louisiana waters, they are most frequent 

along the west coast of Florida. Blooms there are especially frequent from Clearwater to Sanibel 

Island, occurring in 21 of the last 22 years. These blooms on the southwest Florida shelf served as 

a source for cells innoculating the U.S. South Atlantic Bight (Florida east coast and North Carolina) 

in 1987-88 (Tester et al. 1991). 

Florida red tides affect humans, wildlife, fishery resources and the regional tourist-related 

economy. As G. breve cells die and break up, they release a suite of powerful neurotoxins, known 

collectively as brevetoxins. Shellfish management regulations include a biotoxin control plan that 

is implemented during red tides to reduce the risk to humans from consumption of toxic molluscs. 

While some illness related to shellfish consumption occasionally has occurred, in general the highly 

cautionary regulations have been quite effective in preventing neurotoxic shellfish poisoning. While 

it is known that aerosols from red tides produce respiratory ailments in many humans exposed, the 

long-term consequences are poorly known, in part because statistics on individuals treated for 

respiratory and other associated maladies are not maintained. Also, it is difficult to assess long-term 

effects of acute exposure among tourists who leave the area. Fish kills, bird kills and occasional 

invertebrate kills are common sights during red tides. In 1996 more than 150 manatees, an 

endangered species, died due to brevetoxin exposure during a prolonged red tide along the southwest 

Florida coast (Steidinger et al. 1996). 

The economic impacts of the Florida red tides are not well-documented but estimates of $15- 

20 million were published in the early 1970s when the blooms lasted for at least three months and 

impacted several counties. The 4-6 month red tide in North Carolina during 1987-88 was estimated 

to have cost the coastal community there $25 million (Tester and Fowler 1990). The 1995-96 west 

Florida red tide, an unusually prolonged one, had severe financial consequences for shellfish 
6 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

growers, beach resorts and tourist-dependent businesses and may have adversely affected real estate 

values. Although these impacts have not been comprehensively quantified, hoteliers and 

restauranteurs in the region testified to unprecedented reductions in business volume. 

G. breve blooms are initiated on the continental shelf or at the shelf edge, rather than in 

nearshore waters where they produce the most deleterious effects. Low concentrations (-4,000 

, ,. . .. ., 

STRAITS OF 

t FLORl DA 

cellsll) of the organism occur in offshore waters throughout 

the year. Bloom initiation is characteristically associated with 

intrusion of deeper, offshore waters onto the shelf. This 

phenomenon is best known for the west Florida shelf where 

blooms may occur any time of the year, but typically occur in 

late summer and fall when more than 70% of the observed 

outbreaks have been initiated. Bloom concentrations first 

appear offshore (18-74 km ) and are associated with fronts. 

Much as weather fronts mark the convergence of air masses, 

ocean fronts separate waters of different temperature and 

salinity characteristics. These fronts are caused by the 

onshore-offshore meanders of the Loop Current, part of the 

Gulf of Mexico current system through which water flows 

along the edge of the shelf and then through Florida Strait, 

eventually to become the Gulf Stream. 

G. breve may grow rapidly in the dynamic nutrient regimes and light conditions along frontal 

gradients, dividing up to once a day, but usually once every 2 to 5 days (Steidinger et al. in press), 

gradually building high densities. G. breve is well-adapted to such environments and can grow 

throughout the water column where there is sufficient light. It has a high photosynthetic capacity 

and can assimilate nutrients (both organic and inorganic) at low light levels. Once growth occurs, 

it takes 2 to 8 weeks to develop into a bloom of fish-killing proportions (1-2.5x105 cells/l) depending 

on physical, chemical and biological conditions. Because of rapid growth and ability to out-compete 

or otherwise exclude other phytoplankton species, G. breve can develop almost monospecific 

surface blooms covering a surface area of 10,000 km2 or more. Although biomass concentration is 

patchy, chlorophyll a values (a good surrogate for biomass) from 10 to >I00 mgl m3 make the 

resultant discolored surface water detectable by satellite color sensors. The Coastal Zone Color 

Scanner which provided data between 1978 and 1986 was able to detect chlorophyll a from G, breve 

cells at densities as much as three orders of magnitude less than are present when discolored water 

is detectable by the human eye, about 10"cells/l (Tester and Steidinger in press). New satellite-borne 

ocean color sensors, which have been recently launched or should be operational in the near future, 

thus offer prospects for routine bloom detection. Of course, the ability to detect subsurface patches 

and distinguish G. breve blooms from those of other algae will limit the use of this technology. 

The fate of a G. breve bloom, whether it will grow denser or larger and, very importantly, 

whether it will be transported onshore and impact beaches and bays, is determined largely by the 

currents on the continental shelf, which are driven by winds, impingement of the Loop Current on 

the shelf, and the fact that the ocean level typically slopes ever-so-slightly down from north to south. 

On the west Florida shelf, currents are complex and include gyres, larger eddies, and filament-like 
Causes and Conseauences 7 

incursions of offshore water across the shelf. These physical processes are capable of moving 

blooms onshore, to the north along the Florida panhandle (via a large clockwise gyre on the northern 

part of the shelf), or south toward the Florida Strait. During some periods there may be little net 

flow, allowing blooms to be maintained within the midshelf zone and occasionally inoculate or reinoculate the nearshore region. The annual cycle of wind stress, northward during the sumer and 

southward in the fall, is responsible for the persistent upwelling (summer) or downwelling (fall) 

found over the west Florida shelf, which can concentrate or disperse blooms and transport them 

toward or away from shore depending on the site and timing of the bloom. Once in nearshore 

waters, transport of the blooms is affected by longshore flows and tidal exchanges with bays. 

G. breve is essentially a continental margin species which can utilize low levels of nutrients 

very efficiently. Dense blooms do not persist at salinities below 24 o/, (parts per thousand), 

conditions that occur in estuaries and coastal waters receiving fresh water from rivers. The offshore 

initiation of red tide blooms cannot be readily prevented. An important question, then, is the degree 

to which a bloom being moved into nearshore waters can be prevented from persisting or 

intensifying by reducing nutrient inputs from the land, including those of human origin. G. breve 

can utilize land-based nutrients and grow rapidly in the coastal waters provided the salinity does not 

fall below 24 01,. Evidence suggests that dense blooms inshore cannot be sustained without inputs 

of "new" nutrients (Steidinger et al. in press). If so, human inputs of nutrient could be responsible 

for extending the duration and impacts of red tides once blooms enter the nearshore zone, including 

bays and canals. 

Dissipation or termination of red tide blooms occurs when blooms are transported out of the 

area or when the integrity of the water mass is weakened by mixing and dilution. Both declining 

water temperature and increasing wind stress contributed to the dissipation of the 1987-1988 G. 

breve bloom off North and South Carolina (Tester et al. 1991). Unfortunately, the roles of densitydependent growth factors, nutrient limitation, and grazing pressure in the decline of red tide blooms 

are not well known. 

Paralytic shellfish poisoning (PSP) is a significant problem on both the east and west coasts 

of the U. S. Caused by several closely related species in the genus Alexandrium, PSP toxins are 

responsible for persistent problems due to their accumulation in filter feeding shellfish (e.g., 

Shumway et al. 1988), but they also move through the food chain, affecting zooplankton, fish larvae, 

adult fish, and even birds and marine mammals (Anderson and White 1992; Geraci et al. 1989; 

Shumway 1995). On the east coast, PSP is a serious and recurrent problem from Maine to 

Massachusetts. Connecticut, Long Island (New York) and New Jersey occasionally experience the 

toxin (or Alexandrium) at low levels, but these areas seem to define the southern extreme of this 

organism's geographic distribution. The offshore waters of Georges Bank experienced a serious PSP 

outbreak several years ago, leading to the extended closure of the surfclam fishery and the demise 

of a fledgling roe-on scallop fishery. On the west coast, PSP is a recurrent annual problem along the 

coasts of northern California, Oregon, Washington, and Alaska. Overall, PSP affects more coastline 

than any other HAB problem. 
8 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

It is likely that seasonally recurring outbreaks of PSP are linked to the existence of a dormant 

cyst stage in the Alexandrium life history. This strategy allows the species to deposit dormant cells 

in sediments where they survive through harsh winter conditions and then germinate to initiate new 

outbreaks in subsequent years. Prior to 1972, for example, PSP was restricted to the far eastern 

sections of Maine ("down east") near the Canadian border. That year, however, a massive red tide 

occurred that stretched from southern Maine through New Hampshire and into Massachusetts, 

causing high levels of toxicity in those areas for the first time in recorded history. Virtually every 

year since that event, this region has experienced PSP outbreaks, a result of the successful 

colonization of the area by Alexandrium spp. A similar expansion, with subsequent recurring 

outbreaks of Alexandrium, occurred in the Puget Sound region of Washington in the late 1 970fs, an 

area with no prior history of shellfish poisoning (Nishitani and Chew 1988). Long-term climatic 

variability, which affects temperature, upwelling, and currents or allows cysts to survive in areas 

where they did not before, may be factors in such range extensions. 

PSP occurs over a large geographic range, so a variety of physical mechanisms underlie the 

spreading of Alexandrium blooms. In southern New England, for example, localized blooms occur 

in small, isolated salt ponds and embayments, whereas in the southwestern Gulf of Maine, linkage 

has been documented between the abundance and distribution of Alexandrium and a buoyant coastal 

current that travels from north to south in that region (Franks and Anderson, 1992). Fresh water 

enters the Gulf of Maine from several large rivers in southern Maine, and the freshened coastal 

waters flow south in a manner that is influenced by the amount of rainfall and snowmelt, the local 

wind stress, and the underlying circulation of the Gulf of Maine. Toxic Alexandrium populations 

are closely associated with this buoyant water mass. The long distance transport of Alexandrium 

cells in this coastal current are responsible for PSP outbreaks in southern Maine and Massachusetts, 

and may even be linked to shellfish toxicity on Georges Bank (Anderson and Keafer 1992). The 

hydrographic mechanisms underlying PSP blooms in down-east Maine are more poorly understood 

than those described for the region to the southwest. 

Similarly, on the west coast, blooms can be either localized in distribution (i.e. restricted to 

the inland waters of Puget Sound or the fjords of Alaska) or wide spread along the Pacific Ocean 

coast. In northern California, it is hypothesized that the onset of PSP toxicity is linked to the 

onshore movement of warm, stratified waters following the relaxation of coastal upwelling (Homer 

et al. in press). The relaxation events or downwelling, brought about by a change in wind speed or 

direction, carry established Alexandrium populations toward shore, resulting in rapid increases in 

toxicity in nearshore shellfish. There is currently no evidence that this also occurs in Washington 

or Alaska. 

These are but a few of the physical mechanisms underlying PSP outbreaks in the U.S. Some 

areas are well-studied, and others are virtually unknown. Alexandrium blooms generally do not 

involve large cell accumulations that discolor the water and may be below the water surface where 

they are not visible. Low density populations can cause severe problems due to the high potency of 

the toxins produced by these species. Furthermore, Alexandrium species can grow in relatively 

pristine waters, and it is difficult to argue that anthropogenic nutrient inputs are stimulating the 

blooms. These characteristics are important when considering mitigation and control strategies. 
Causes and Consequences 9 

The economic impact of these outbreaks is significant, though difficult to estimate in total. 

Most of the states listed above operate shellfish monitoring programs, each of which costs $100,000- 

$200,000 per year. Estimates of the losses to shellfisheries and other seafood-related industries are 

few, but one listed the costs of a single PSP outbreak in Maine at $6 million (Shumway et al. 1988). 

Some estimates place the value of the quarantined surfclam resources on Georges Bank at several 

million dollars per year. This resource has been closed to harvest since 1989. On the west coast, 

the shellfish industry in Alaska, which produced 5 million pounds of product in 1917, has been 

greatly reduced (except for aquaculture) as a direct result of persistent product contamination of 

butterclams by PSP (Nev6 and Reichardt 1984). There is a highly restricted recreational shellfish 

industry since many of the state's resources remain permanently closed due to the high costs 

associated with monitoring the state's vast coastline. The value of the sustainable, but presently 

unexploited, shellfish resource in Alaska is estimated to be $50 million per year (Nev6 and Reichardt 

1984). In addition to the risks of PSP from molluscs, there are PSP and domoic acid poisoning risks 

from consumption of Dungeness and other crabs. 

In 1985, a massive bloom of the very small microalga Aureococcus anophageflerens 

occurred in the coastal bays of Long Island, 

New York. Concurrent with the blooms around 

Long Island, blooms were recorded in 

Narragansett Bay (Rhode Island) and Barnegat 

Bay (New Jersey) (Sieburth et al. 1988, Olsen 

1989). The blooms reached very high densities 

and were commonly referred to as "brown tide" 

due to the striking discoloration of the water 

(Cosper et al. 1990). A similar event occurred 

in Texas a short time after an extremely cold, 

windy event in December 1989. Sub-freezing 

temperatures coincident with low tides killed 

millions of finfish and benthic organisms in Laguna Madre (Buskey and Stockwell 1993). The 

decomposition of the dead biomass produced an order of magnitude increase of inorganic nitrogen 

nutrients relative to normal levels (Whitledge 1993). Consequently, high densities of the species 

being described as new to science as Aureoumbra lagunensis developed resulting in the formation 

of a "brown tide," which enigmatically has persisted until this day, seven years later. 

The blooms in Texas and Long Island had substantial ecological and economic effects. In 

both regions the dense algal blooms resulted in decreased light penetration and reductions in the 

extent of seagrass beds, especially in Texas where 20 percent coverage has been lost in water depths 

below one meter (Onuf 1996). In Long Island waters, brown tide blooms (BTBs) had a severe 

impact on commercially valuable bay scallops, affecting bays which contribute more than 80% of 

New York State's bay scallop harvest (Cosper et al. 1987). This fishery is worth an estimated $2 

million per year. In addition other shellfish, including the commercially valuable hard clam, have 

also been affected. 
10 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

The brown tide has recurred in Long Island embayments several years since 1985 and various 

theories exist regarding its formation, such as increased freshwater flow following drought, low 

oxidized nitrogen concentrations, high iron availability, capacity of Aureococcus for growth on 

organic nitrogen sources, decreased exchange with ocean water, and variations in rainfall and 

groundwater inputs (Nixon et al. 1994; Cosper et al. 1990). In contrast to the Long Island BTB 

which has an annual cycle of retreat and redevelopment, Aureoumbra has bloomed continually since 

1989 in Texas embayments and lagoons with a limited water circulation and exchange. Restricted 

circulation promotes nutrient and biomass accumulation by retaining dissolved and particulate 

materials in the ecosystem, thereby maintaining availability of vital elements. In the presence of 

these regenerated nutrients, the growth rate of the BTB organism exceeds advective losses and 

bloom development occurs quickly and persists for long periods of time. 

However, the causes of an initiation of a BTB may be different than the factors responsible 

for the increased prevalence of blooms. The existence of the bloom may even enhance some 

processes for self-perpetuation. One example of this is continual regeneration of nutrients from 

existing biomass. Nevertheless, the persistence of a bloom in the longer term also requires 

additional influx of nutrients from terrestrial or atmospheric sources. Physical mixing of the water 

B~tfln Bay GULF 

0 F 

MEXICO 

column and resuspension of sediments are factors 

that must be considered as potential mechanisms of 

bloom persistence. There is some evidence that there 

may be a benthic phase or a mixing-related 

resuspension of cell aggregates that enhances or 

maintains a BTB (Stockwell et al. 1993). Aside from 

nutrient regeneration and mixing processes, one of 

the prime "maintenance" mechanisms is lack of 

grazing by water column and benthic populations 

(Buskey and Stockwell 1993). These processes 

control levels of phytoplankton biomass under 

normal conditions. Both the Long Island and the 

Texas brown tide organisms were found to retard 

zooplankton grazing in field and laboratory samples 

through an apparent release of inhibiting substances 

(Buskey and Hyatt 1995). Interestingly, microzooplankton grazing was reduced only when 

chlorophyll concentrations exceeded 10 pgll (Buskey et al. 1996). Based on discussions during the 

Port Aransas meeting, other factors which could govern the persistence of BTB include decreased 

competition from the natural phytoplankton assemblage and lower-than-normal loss rates via sinking 

(e.g., via intensified mixing and resuspension) and viral infections. 

Other than reductions in the extent of seagrass beds due to reduced light levels, Texas brown 

tides have not been linked with obvious reductions of other living resources. Whether due to 

population rebound following the 1989 freeze-related mortality, the effects of reduced fishing 

pressure associated with conservation-related regulations, or the contributions of restocking efforts, 

all or any of these factors have allowed populations of highly prized game fish, such as red drum and 
Causes and Conseauences 

spotted sea trout, to increase to higher levels than before the BTB (McEachron and Fuls 1996). How 

these species are fished has, however, also changed. As a result of the heightened turbidity of 

previously clear waters, lures that depend on visibility are not as effective, making fishing less 

attractive to sport fishers. There is some evidence that larval fish populations are reduced in areas 

experiencing a BTB and survival is only 15-20% of controls in laboratory and fish hatchery 

exposures to BTBs. Whether this is of any consequence to the stocks or whether there are delayed 

effects which may result in a future decline in adult populations are unknown at this point. 

Domoic acid has been detected in finfish and shellfish resources on both the east and west 

coasts. This neurotoxin, produced by diatoms in the genus Pseudo-nitzschia, may cause permanent 

short-term memory loss in victims, hence the name amnesic shellfish poisoning (ASP). Another 

term often used for the syndrome is domoic acid poisoning (DAP) because amnesia is not always 

present and there have been no confirmed cases of ASP in humans in the U.S. 

Toxic Pseudo-nitzschia species are present in the 

northeast and Gulf of Mexico and low levels of domoic 

acid have been detected in shellfish on the east coast, but 

not at levels that necessitate quarantine. On the west 

coast, however, domoic acid poisoning has been a 

serious problem affecting razor clams and Dungeness 

crabs in California, Oregon, and Washington. 

The west coast has two different environments to 

consider in terms of harmful algal bloom development. 

The Pacific Ocean coast is associated with upwelling 

events in spring and warmer, thermally stratified water 

in late summer and fall. On the other hand, inland 

waters of Puget Sound and the fjords and inlets of 

Alaska are enclosed areas with restricted water 

exchange. 

Domoic acid production has been confirmed for 

three species of Pseudo-nitzschia on the west coast: P. 

australis, P. multiseries, and P. pungens. Domoic acid 

poisoning first became a noticeable problem in 1991 

when pelicans and cormorants in Monterey Bay 

(California) died or suffered from unusual neurological 

"""4"" t-x_ ./:, WASHINGTON 

KILOMETERS 

I I 

symptoms similar to ASP. Many tons of anchovy catches were recalled or diverted following this 

episode. That same year, domoic acid was identified in razor clams and Dungeness crabs on the 

Oregon and Washington coasts. Since 1991, Pseudo-nitzschia spp. and domoic acid have recurred 

in Monterey Bay, but at relatively low cell numbers and concentrations. Blooms are common in late 

summer and fall when the upwelling season has ended, sea surface temperatures are warmer, thermal 
12 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

stratification is evident, and concentrations of inorganic nutrients are low. On the Washington coast, 

razor clams on some beaches continue to contain low levels of domoic acid, but the source is not 

known. Meanwhile a bloom of mixed Psuedo-nitzschia species occurred in Hood Canal (an arm of 

Puget Sound) in November-December 1994, resulting in toxin levels of about 10 pglg in mussels 

and 14 pglg in phytoplankton (Homer et al. 1996). Closure limits are 20 pglg. 

In western Washington, the economic impact for the 1991 domoic acid event was estimated 

to be between $15 and 20 million based on lost tourist visits (at $25 per digger trip); lost or delayed 

retail sales and lower prices of oysters that were never toxic but were avoided by confused 

consumers (halo effect), lost employment, bankruptcies of local businesses, potential adverse health 

effects (there were no confirmed illnesses due to domoic acid), and costs to the state health 

department for increased testing. 

Catastrophic losses of cultured and wild fish sometimes occur due to species of phytoplankton that do not cause illnesses in humans. Blooms of the raphidophyte flagellate Heterosigma 

akashiwo have caused kills of pen-reared salmonids in Washington in 1989 and 1990, and wild fish 

in 1994. Losses to the fish growers, including higher insurance rates as well as lost production, are 

about $4-5 million per year when blooms occur. The mechanism by which Heterosigma kills fish 

is not known, but may involve an ichthyotoxin (R.A. Cattolico, presentation to the Panel, 1 996), or 

production of superoxide hydroxy radicals or hydrogen peroxide (Yang et al. 1995). Heterosigma 

blooms cause problems at high cell densities, usually exceeding lo7 cells/l. Blooms often start in 

shallow back bays of Puget Sound and spread into the sound, carried by tides and currents. This 

species is a vertical migrator, usually occurring in surface waters during the day and at depth during 

the night. Vertical stability of the water column is probably an important factor in maintaining 

blooms. 

Fish kills are also caused by the diatoms Chaetoceros convolutus and C. concavicornis 

(possibly also C. danicus) which do not produce a toxin, but have long setae armed with short 

secondary spines. Chains of cells apparently become lodged between secondary lamellae in the fish 

gills and cause blood hypoxia as a result of mucus production. Chaetoceros blooms kill at low cell 

densities, sometimes as low as 1 O4 cellsll. These diatoms may be restricted to near-surface waters 

or mixed throughout the water column depending on local hydrographic conditions. Most fish 

growers have their own phytoplankton monitors who sample at the pen sites on a daily basis from 

April through September. They also rely on reports from other phytoplankton monitoring programs. 

Economic losses are about half a million dollars per event. 

The foregoing sections highlight several of the major HAB phenomena that affect the U.S. 

For Florida NSP red tides there is no evidence of increased frequency of blooms, but the 1995-96 

persistent bloom left the impression in many that these blooms are lasting longer and covering more 
Causes and Conseauences 13 

area. Similarly, the recent occurrence of G. breve blooms in Texas, North Carolina, Louisiana, 

Mississippi, and Alabama where there they have historically been extremely rare or unknown raises 

concerns about their proliferation. Although PSP events have been experienced for hundreds of 

years in northeastern and northwestern Canada, these outbreaks now affect extensive areas in New 

England and Washington State where fewer problems existed 20 years ago. Brown tides have 

become persistent problems in Texas and Long Island bays, but were unknown to those regions 7 

and 12 years ago, respectively. ASP has emerged as a concern on the east and west coasts, but was 

unknown to science before 1987. 

The nature of the HAB problem has thus changed considerably over the last two decades in 

the United States. Where formerly a few regions were affected in scattered locations, now larger 

geographic areas, including most coastal states, are threatened, in many cases by more than one 

harmf~l or toxic algal species. These trends are not unique to the U.S., as a global expansion of the 

HAB problem over the last several decades has been suggested by several analysts (Anderson 1989; 

Smayda 1990; Hallegraeff 1993). Given the many different manifestations of HABs and their 

impacts and the increased monitoring and reporting in recent years, it is difficult to tabulate these 

events to document statistically an increasing trend. Most international experts would agree, 

however, that the number of toxic blooms, the economic losses from them, the types of resources 

affected, and the number of toxins and toxic species have all increased dramatically in recent years, 

lending credence to our general observations of trends for U.S. waters. 

There are many potential reasons for the increased incidence of HABs (Anderson 1989), 

some of which simply reflect our improved ability to detect toxins at low levels or to network with 

colleagues familiar with particular toxin syndromes. Nevertheless, based on abundant evidence that 

the events are more numerous and more dangerous, one has to suspect that human activities may be 

involved via growth stimulation due to nutrient inputs; alteration of the "integrity" of coastal 

ecosystems through pollution, habitat destruction, and harvesting of resomces; climate change; or 

dispersal of HAB species or strains via shipping and other materials transportation. In addition, the 

increased use of coastal waters for aquaculture might provide other mechanisms for the transport of 

harmful algal cells and their growth in new areas, but aquaculture also leads to increased monitoring 

to ensure that a safe product is produced. 

The implications of expansion of HABs are significant, not just because of the ecolromic 

costs of severe and recurrent blooms, but also because state and federal agencies responsible for 

protecting the public health and the viability of fisheries industries are forced to struggle with a broad 

array of toxins and potentially toxic resources. In addition, subtle and significant ecosystem impacts 

are only now beginning to be considered or recognized. These may be caused by the movement of 

toxins through food webs or by selective mortality of critical components of these webs. Effects on 

marine mammals and birds which are at the top of food chains have been observed and it is 

conceivable that entire year-classes of finfish and shellfish species could be impacted if toxic blooms 

devastate larval or juvenile populations. 

If one accepts that the expansion of HABs is real, and that it has many causes, both natural 

and human-assisted, what can be done about them in a practical sense? What information is needed 

to efficiently manage the affected fisheries resources, protect public health, support aquaculture 

development, and contribute to policies for the protection and management of coastal environments? 

If human activities are making the HAB problem worse, how can that be demonstrated, and what 
14 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

steps should be taken to minimize further impacts? These are important practical issues, and the 

apparent trends in HAB incidence make them even more pressing. Management of these phenomena 

and other impacts are considered in subsequent sections in the context of prevention, control and 

mitigation. It should be clear from this brief review that there is considerable disparity in the 

knowledge of causes of different types of HABs. This variation in understanding has obvious 

implications regarding the feasibility of these management approaches. 
As used here, prevention refers to environmental management options for reducing the 

incidence and extent of harmful algal blooms before they begin, not controlling or mitigating them 

after they occur. The options are problematic both because of uncertainties about what 

environmental factors cause the blooms and because of the difficulties of regulating those factors. 

Other than actions taken to moderate the effects of society on global climate change, the potential 

options are limited to controls on materials flowing into the coastal region (mainly nutrients and 

fresh water, but potentially trace elements and toxic pollutants as well), modifications of physical 

conditions which might favor HABs (e.g., poor water circulation), and restrictions on activities 

which might result in the inadvertent transfer of harmful species into environments where they do 

not now occur. 

There has been a rapid increase in the 

loading of coastal waters of developed nations with 

plant nutrients, particularly nitrogen, since World 

War 11, coincident with the growing disposal of 

sewage fiom expanding populations, increased use 

of chemical fertilizers and animal production in 

agriculture, and increased fossil fuel combustion 

(producing nitrous oxides which fall back on the 

earth). Consequently, it is tempting to attribute the 

apparent increase in HABs to human eutrophication 

(e.g., Smayda 1990); indeed there is strong 

evidence for this for some HABs in Europe and 

Japan (see papers in Smayda and Smimizu 1991). 

It is now well-documented that anthropogenic 

nutrient enrichment is responsible for increase 

phytoplankton production and biomass, decreased 

water clarity, loss of submersed aquatic vegetation 

due to shading, and sometimes severe oxygen 

depletion in many U. S. coastal waters. While this 

is a prime suspect for blooms that become harmful 

when high concentrations of algae develop, it is less 

likely a factor for those blooms which are harmful 

when cells are present at low densities (e.g., for 

PSP). There may be a good prima facie case to 

implicate human nutrient inputs where blooms are 

recent or worsening phenomena (e.g., brown tides). 

Nitrogen is a critical element for life. The 

availability of nitrogen controls the productivity of 

ecosystems and explains why coastal regions 

produce more harvestable resources than the 

open ocean. However, growing evidence is 

demonstrating that human activities (including the 

use of artificial fertilizers, planting of nitrogen-fixing 

crops, fossil fuel burning, and the mobilization of 

nitrogen stored in soils and trees) have at least 

doubled the global rate of nitrogen entering the 

land-based nitrogen cycle. Excess nitrogen is 

causing serious and long-term environmental 

consequences including increased concentrations 

of the greenhouse gas nitrous oxide, formation of 

photochemical smog, losses of mineral nutrients 

essential for long-term soil fertility, acidification of 

soils and waters, and increased transport of 

nitrogen by rivers into estuaries and coastal waters 

(Vitousek et al. in press). Riverine nitrogen fluxes 

in temperate zones of the North Atlantic Ocean 

basin have increased from pre-industrial times by 

2 to 20 fold (Howarth et al. 1996). These 

increases result mainly from nonpoint sources, 

particularly agriculture and the atmospheric 

deposition of oxidized nitrogen from fossil fuel 

combustion. Algal blooms, depletion of dissolved 

oxygen, and loss of seagrasses are among the 

consequences of the resulting over-enrichment of 

the coastal marine environment. 
16 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

The accumulation of biomass that accompanies the appearance and growth of some HABs 

requires that a considerable amount of vital nutrients be available. However, the types of nutrients 

preferred differs widely among various microalgae. Recent evidence indicates that when a certain 

preferred nutrient substrate, such as nitrate, is depleted from the water column HAB species are often 

capable of using other substrates for their nutrition (Carlsson and Grankli in press). Thus, not only 

the quantity of any one or two particular nutrient(s), but the relative proportions of a whole array of 

nutrients (quality of the total nutrient pool), may influence the development of a nuisance bloom. 

For example, as one moves away (in time or space) from a new nutrient source, the mouth 

of a river, for example, algae typically deplete inorganic nitrogen (nitrate and ammonium) first and 

leave other substrates behind (Butler et al. 1979). Later in the bloom sequence, the dissolved and 

particulate organic matter produced from the initial uptake is often available to support subsequent 

blooms either directly (through dissolved organic matter uptake) or after remineralization of the 

organic matter to ammonium. Even in regions where total nitrogen inputs have been reduced, a 

change in the relative amounts of organic and inorganic nitrogen in the remaining nitrogen pool may 

affect bloom development. The brown tide blooms evidenced in Long Island embayments may be 

a prime example of this as they typically develop during summer, after the concentration of inorganic 

nitrogen in the water has been depleted to very low levels. This was similarly observed for 

Narragansett Bay (Smayda and Villareal 1989). In such instances, a more effective control program 

for nutrient inputs to the coastal waters could reduce the accumulation of HAB biomass and possibly 

the duration of the bloom conditions. Immediate effects may not be evident, however, due to the 

possible existence of sedimentary nutrient reservoirs. 

Nutrients that may be responsible for the large biomass accumulations include various 

inorganic and organic forms of nitrogen, phosphorus, and other growth factors such as iron. 

Intensities of nutrient loadings, the proportion of the various plant nutrients, remineralization rates, 

and grazing pressures all potentially affect which algal species will bloom. Some of the Long Island 

bays presently experiencing BTBs had earlier experienced dense "green tides" (reviewed in Ryther 

1990) as a result of runoff from duck farms. Although the duck farms sources have been greatly 

reduced, the concentrations and composition of nutrients (e.g., proportions of inorganic and organic 

forms of nitrogen) may now favor the proliferation of Aureococcus as opposed to green algae. 

At present, it cannot be concluded with certainty that any of the HABs considered here would 

be eliminated with rigorous control of anthropogenic nutrient inputs, but it is possible that such 

inputs may be factors in bloom intensity and persistence for BTB, Heterosigma, and Gymnodinium 

breve blooms. Nutrient management strategies may be particularly useful in preventing some HABs 

in estuaries and embayments that have restricted water circulation. Nutrient reduction strategies are 

being pursued in many of these more enclosed water bodies for reasons other than HAB prevention. 

Notable among these are the Comprehensive Conservation and Management Plans (CCMPs) 

developed under the National Estuary Program (NEP) for many of the nation's estuaries, including 

the HAB-affected Peconic Bay, Albemarle-Pamlico Sound, Tampa Bay, Sarasota Bay, Charlotte 

Harbor, Corpus Christi BayILaguna Madre and Puget Sound. Although implementation of these 

plans is often lagging-particularly with regard to nitrogen which is difficult to control because of 

its multiple sources, high solubility, and growing atmospheric inputs--considerable progress has 

already been made in reducing point-source loadings of nutrients in such estuaries as Tampa Bay and 
Prevention 17 

Sarasota Bay (Sarasota Bay National Estuary Program 1999, where water clarity and the conditions 

for growth of seagrasses have improved. 

Point and non-point source reductions of nutrient inputs into coastal waters 

should be rigorously pursued as a key element of estuarine and coastal 

management where restricted flushing of the receiving waters or sheer 

magnitude of the loadings suggest that there are negative impacts of 

eutrophication. The potential benefits of reductions of nutrient loadings in 

terms of decreased frequency and severity of HABs should be made a more 

explicit consideration in relevant estuarine and coastal management programs, 

such as those in the National Estuary Program. 

Flows of fresh water into many coastal ecosystems are subject to human alteration through 

water use and diversion and modifications of the watershed, e.g. deforestation, impoundments and 

stream channelization. Flows are, to a certain degree, subject to human control and regulation. Can, 

then, freshwater flows be managed in such a way as to reduce the frequency, extent, and severity of 

HABs? 

Regulation of freshwater inflows might be an important consideration only with the Gulf of 

Mexico red tide organism, G. breve. Although G. breve tolerates a wide salinity range, it seems only 

to proliferate in consequential blooms at salinities above 24 "/, . Resource managers in Florida are 

concerned that projected reductions in freshwater flow into Gulf Coast estuaries, as a result of 

growing demand for potable water, may result in increased salinities and deeper intrusion of red tides 

into these estuaries. Incursion of G. breve blooms into Texas bays and unusual blooms along the 

Mississippi and southeastern Louisiana coasts in the fall of 1996 also seemed to be associated with 

higher than normal salinities. These observations suggest that managing inflows of fresh water, 

when available, may prevent encroachment of red tide into estuaries. However, it must be kept in 

mind that nutrients, which may stimulate blooms, are also delivered with fresh water. 

It should also be pointed out that Heterosigma blooms in Puget Sound and Alexandrium 

blooms in the southwest Gulf of Maine seem to occur when freshwater influx increases (in the latter 

case in combination with onshore winds). In contrast to the shallow estuaries of the Gulf Coast, 

however, management of freshwater flows to prevent such blooms is not a feasible management 

action. 

Limiting the intrusion of red tide into Gulf Coast estuaries by maintenance of 

reduced salinity conditions should be an expressed consideration in freshwater 

flow allocation and estuarine management. 
18 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

For some HABs in relatively confined coastal waters, there is concern that restricted water 

exchange may allow blooms to persist. For example, the Texas bays and lagoons plagued by brown 

tide have poor water circulation and exchange as a result of the small astronomic tidal range and 

restrictions by occluded passes, tidal flats and causeways. Consequently, the residence time of water 

in parts of the Laguna Madre is about one year. For these reasons, some environmental and fishing 

advocates have suggested that brown tides could be reduced or eliminated by increasing circulation 

through the removal of currently in-place causeways and replacing them with high-rise bridges. 

Another suggestion was to open passes through the long, uninterrupted stretch of Padre Island to 

increase direct exchange between Laguna Madre and the Gulf of Mexico. It is not clear that such 

passes would have the desired effect, either on sufficiently reduced residence time or on the blooms 

themselves. Cells could still be present in the smaller bays off Baffin Bay where the bloom seems 

to be reinitiated periodically. Increased circulation could move the cells to new areas. Furthermore, 

there may be other undesirable and possibly unpredictable consequences (e.g., increasing storm 

surge) of opening new passes. There would also be considerable engineering challenges, not to 

mention costs, in keeping these passes open and providing required infrastructure. Similar reengineering of coastal hydrodynamics has also been a topic for discussion for Long Island estuaries, 

although they are better flushed than the Laguna Madre. 

Major modifications of water circulation for preventing HABs are not presently 

justified by available knowledge, but the effects of water exchange on HABs 

should be an expressed consideration in managing features such as inlets, 

channels and causeways which affect circulation. 

Ballast Water 

Introductions of organisms from one region 

to another via ships' ballast waters have had 

significant impacts on coastal ecosystems. In some 

cases, nonindigenous species have become 

established which, because of a lack of predators or 

competitors, dramatically proliferated in the new 

environment. Most of the species for which ballastwater introduction has been documented are marine 

invertebrates (NRC 1996), although evidence has 

been presented that toxic dinoflagellates have been 

introduced into Australian waters via ballast water 

(Hallegraeff 1991) and genetic tracers suggest that 

there have been transfers among strains of some 

HAB species between widely separated parts of the 

-- 

In its recent report of this title, the National 

Research Council (1996) assessed potential 

control strategies for reducing the risk of 

introductions of nonindigenous species by ship's 

ballast water. Changing ballast at sea is 

currently the favored technique, but is limited by 

vessel safety considerations and the lack of 

ability to remove all ballast and associated biota. 

Development of shipboard treatment is 

recommended, with the most promising 

techniques (based on safety, effectiveness and 

operational feasibility) being fine screening and 

application of low concentrations of biocides. 
Prevention 19 

world (Scholin and Anderson 1993). These genetic methods are, however, unable to indicate 

whether this dispersal occurred in the very recent past (i.e. within the last 50 years) or several million 

years ago. HAB species are more likely to survive ballast-water transport if they form cysts and 

reside in ballast tank sediments. Kelly (1993) incubated a variety of planktonic algae from ballast 

sediments collected from ships entering ports in the state of Washington, but none of these was a 

known HAB species. There is yet no evidence that any of the HAB species considered here has 

been introduced via ballast water into areas where they now cause problems, but two issues should 

be kept in mind. First, the behavior of many HABs suggests that seeding of areas where blooms 

have not occurred or re-seeding where blooms have died out is important. This suggests that even 

short-distance transport of cysts or planktonic organisms themselves could stimulate blooms. 

Second, even though the nominal species may be indigenous, the introduction of new genetic strains 

of the organism that prosper better in the receiving environment or are better able to escape pathogen 

control than the indigenous populations could also lead to blooms. 

More attention should be directed to evaluating the role of ballast water transfers as a 

mechanism for inoculating areas with HAB species. Particular attention should be directed to the 

transfer of spores and cysts in ballast tank sediments. Where significant risk is demonstrated, 

appropriate control strategies should be required as suggested by the National Research Council 

(1996). Some of the strategies recommended by the NRC, e.g., fine screening, may not be as 

effective for organisms less than 50 pm in size as for larger invertebrates. 

Except where the potential for introduction of HAB species is extremely low, 

engineering or operational strategies developed to reduce ballast-water 

introductions of invertebrates should be designed to ensure the destruction or 

elimination of HAB species and their cysts. 

Shellfish and Finfish Transfers 

There is a potential for introducing HABs into waters in which the algal species or specific 

strain is not resident when shellfish and finfish (including eggs and fry) are transported from site to 

site during normal stocking procedures. No specific cases of introduction of HAB species in 

contaminated shellfish seed (small bivalves transplanted for grow-out) have yet been documented. 

Although it is possible that algal species could survive ingestion by the bivalve, introduction via 

shellfish seed is improbable given the conditions of transfer. On the other hand, transfer of stock 

with large volumes of sediment, seaweed, or detrital material attached to shells is more likely to 

result in algal transfers as well. Precautions should be taken when transporting shellfish from a 

bloom-prone region to one which is not, particularly if substantial sediment is included and the alga 

of concern forms cysts. 

State agencies should carefully consider and appropriately regulate the risks of 

inter- and intra-state transfer of HAB species via shellfish seeding and transfer 

operations. Where such risks exist, it is prudent to prohibit such transfers or 

require an intermediate transfer step whereby shellfish can be 'depurated' or 

washed prior to introduction into the receiving environment. 
20 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

One mechanism for HAB dispersal or proliferation is through 

dredging and disposal of marine sediments containing resting stages of HAB 

species. Large numbers of cysts or spores are often found in bottom 

sediments of areas subject to HABs, maintained in a resting state either 

because of internal (e.g. maturation) or external (e.g. low temperature, low 

light, anoxia) inhibition of germination (Anderson et al. 1987). Dredging 

or other activities that displace sediments can thus disperse a harmful 

species to new areas or initiate a bloom near the dredge site. Dispersal can occur through the 

transport of dredged material by barge or by the resuspension of sediments by dredging activities 

and subsequent dispersal by currents. Bloom initiation can result when cysts are exposed to 

favorable environmental conditions during dredging or spoil disposal. For example, in many areas, 

90% or more of the cysts of toxic Alexandrium species are buried below the sediment surface, 

typically in anoxic sediments (Anderson et al. 1982). Since cyst germination requires oxygen, most 

of these buried cysts will remain dormant and never germinate unless they are resuspended, as might 

occur during a dredging operation. A bloom might then occur at or near the dredge site, or in distant 

waters where the spoil is dumped. Dredging during certain seasons will be less likely to result in 

cyst germination than at other times, and care with sediment resuspension and transport can 

minimize dispersal. At present, there are no federal regulations in this regard, although the Army 

Corps of Engineers requires testing for a host of other chemical and biological parameters prior to 

approval of a dredging permit. 

State and federal agencies must take HAB cysts into account when regulating 

coastal zone activities such as dredging or dredge spoil disposal. Effective policy 

decisions on these issues will require current information on the regional 

distribution and abundance of HAB cysts and a knowledge of the physiological 

and environmental controls on cyst germination in that region. Surveys for cysts 

may be required prior to issuance of permits. 
Efforts to control insects, diseases, and fungi are common agricultural practices on land, but 

similar attempts to control unwanted plants or animals in the ocean are rare or more limited in scope. 

The significant impacts of HABs on public health, the economy, and ecosystems provide rationale 

for considering similar controls, but research on this topic has been extremely limited, especially in 

the United States, presumably because of over-riding concerns about environmental impacts, costs, 

and effectiveness. Forty years ago, attempts were made to control the Florida red tide dinoflagellate 

Gymnodinium breve through the large-scale application of copper sulfate to 16 square miles of ocean 

using crop-dusting aircraft (Rounsefell and Evans 1958). Copper sulfate is commonly used to 

control freshwater algae in lakes and reservoirs. The results of that aerial treatment were initially 

effective, but several of the treated areas developed new red tides several weeks later. The 

conclusion reached at the time was that the use of copper sulfate for bloom control should only be 

considered in local situations to give short-term, temporary relief from blooms. Since that time, 

HAB control has not been seriously considered in the United States, although other 

countries-notably Japan and China which farm the ocean heavily-have invested in research on the 

topic. Control of HABs remains largely untested on major blooms, however, as field applications 

have been restricted to shallow ponds used for shrimp and fish mariculture or on waters in the 

immediate vicinity of fish cages. 

General approaches to direct control include: 1) chemicals that kill or disrupt red tide cells 

during blooms; 2) clays or other materials that flocculate algal cells and other particles in the water 

column into larger particle aggregations, which thereby sink more rapidly to the ocean floor; and 3) 

biological agents such as zooplankton grazers or lethal pathogens such as viruses, bacteria, or 

parasites. 

Attempts to use chemicals to control directly HAB algal cells in blooms encounter many 

logistical problems and environmental objections. The use of copper sulfate in the 1957 Florida red 

tide control effort (Rounsefell and Evans 1958) highlights several of these problems, the most 

significant being that the chemicals are likely to be non-specific and thus will kill co-occurring algae 

and other organisms indiscriminately. Efforts to find a "magic chemical bullet" that will somehow 

kill only a specific, targeted HAB species may be futile, as it is difficult to imagine a unique 

physiological target for a chemical that is characteristic only of one phytoplankton species. For 

example, about 35 years ago the Bureau of Commercial Fisheries conducted a major program to 

screen chemicals that could be used for controlling Florida red tides. Approximately 4,700 

compounds, predominantly organic in nature, were evaluated (Marvin 1964). Of these, only 6 were 

found to be suitably potent against G. breve without causing excessive mortality of other marine 

organisms. Unfortunately, when these six were re-tested against G. breve using natural seawater 

culture medium, cell mortality proved to be low and variable, possibly because natural seawater 

contains chemicals inhibiting the effectiveness of the toxicants tested. More testing was planned, 

but the lack of subsequent published data suggests that this program was terminated before fwther 
22 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

tests could be conducted. The failure of this program to identify a promising chemical does not 

mean that such chemicals do not exist, but rather that the process of finding one is long and 

laborious. 

Chemical control of blooms is thus an area where some careful research is needed. Even if 

a chemical with ideal properties is found, environmental objections to its application are likely to 

be significant. Each candidate chemical will require extensive testing for lethality, specificity, 

persistence, and general safety, and each must meet regulatory concerns, such as those imposed on 

industrial discharges, regarding acute and longer-terms effects in coastal environments. Although 

direct chemical control of HABs may not be a strategy of choice given other more benign 

alternatives, the success of this approach in terrestrial systems (e.g. application of herbicides and 

pesticides) suggests that it should not be completely ruled out, in discrete applications where 

collateral effects are minor or confined. 

While it is not prudent to invest in a major search for chemical compounds that 

might destroy HAB cells, a small-scale effort could be justified concentrating on 

chemicals and application procedures that are already accepted for use in the 

control of aquatic weeds and pests such as the water hyacinth or Eurasian 

milfoil. Furthermore, before significant effort is expended to evaluate chemical 

control strategies, risks to other resources must be evaluated and the receptivity 

of federal and state agencies and the general public to this approach assessed on 

a regional basis. In addition, the persistence and effects on co-occurring 

organisms of toxins released by chemicals which disrupt algal cells should be 

evaluated. 

A flocculant is a material that, when added to water, scavenges co-occurring particles as it 

falls to the sediments below. Inorganic flocculants (e.g., aluminum sulfate or various ferric salts) 

are commonly used to purify fresh water in reservoirs. Macromolecular flocculants are synthetic 

molecules that collect particles by means of a process called bridge formation. Huge polymer 

molecules are very effective in this regard, the most common being polyacrylamide (Shirota 1989). 

One non-chemical flocculant that shows considerable potential is clay. The natural waterclearing properties of clays are evident during and immediately after storms when the seawater near 

the mouth of rivers becomes turbid from clay minerals eroded fiom land. This turbidity decreases 

dramatically several days later and the seawater can become very clear. This is a result of 

flocculation. The clay particles adsorb inorganic and organic materials, algae, and other particles 

to form a "floc" which continues to grow in size as it accumulates particles, and eventually falls to 

the bottom sediments. 

Japanese (reviewed in Shirota 1989) and Chinese (Yu et al. 1994 a,b,c) researchers have 

studied the theory behind clay as a flocculant in seawater, and both groups have tested a variety of 

natural and treated clays on HAB species in culture. Depending on the treatment used, removal of 
Controls 23 

95-99% of the targeted cells in cultures has been accomplished following additions of clay. In field 

trials, the Japanese have used clay to treat natural HAB blooms on several occasions. On a small 

scale, clay was dispersed in the vicinity of culture cages where fish were dying during a 

Cochlodinium red tide (Shirota 1989). This was deemed very effective by the fishermen, as virtually 

no fish mortality was observed and the bloom was eliminated. Japanese workers also looked into 

application of the clay from aircraft as a strategy for large-scale bloom treatment and concluded that 

airborne dispersal of clay is feasible, but expensive (Shirota 1989). Chinese workers are now 

applying clay flocculation methods to the treatment of unwanted algae in shallow mariculture ponds 

(Yu et al. 1994 a,b,c), but it is not yet known whether costs are low enough and removal efficiencies 

high enough for use in more open coastal waters. 

The principal environmental concern about the use of clay as a flocculent relates to the effect 

of sedimented particles on bottom-dwelling (benthic) organisms. Filter-feeding benthic organisms, 

for example, are known to stop filtering when 

suspended sediment concentrations are elevated. 

However, benthic organisms inhabiting sediments, 

as opposed to rock or reef substrates, are generally 

well-adapted to survive the deposition of fine 

sediments provided it is not overwhelming. 

Another concern is that clay treatment might 

deposit so much algal biomass that oxygen 

depletion becomes a problem in bottom waters. 

Furthermore, no studies have been conducted on 

the possible impacts of flocculation and 

sedimentation of toxin-containing organisms, 

either in the release of their toxins or in possible 

encystment in bottom sediments. If clay is to be 

seriously considered as a bloom control strategy, 

an area for future study is clearly the fate and 

effects of sedimented toxins, as well as the effects 

of the clays themselves on benthic organisms 

Evidence that claylorganic aggregates falling down 

on organisms inhabiting bottom sediments are not 

detrimental is found in the studies of Portmann 

(1970) and Howell and Shelton (1970) who 

investigated the effects of clay from pottery 

operations on the bottom fauna of two bays near 

Plymouth, U.K. As a result of the area's pottery 

industry, China clay was distributed over 48 square 

kilometers, accumulating in bottom sediments at 

the very high loading of 188 kg per square meter. 

Fish and benthic organisms were abundant in the 

area, however, and many seemed to thrive with 

the clay substrate. Shirota (1989) reports that 

claylorganic floc is an excellent food source for 

sea cucumbers, so it is likely that some benthic 

animals would benefit from the nutrition in the 

material carried to the bottom with the clay. 

The application of clays to flocculate and thereby remove cells of HAB algae 

from the water column may constitute a relatively benign control strategy under 

feasible circumstances. Rates of removal of cells due to clay flocculation, degree 

of release of toxins from flocculated cells, physical and toxic effects on benthic 

organisms, and the consequences of organic loading from sedimented blooms 

on near-bottom oxygen conditions will require further evaluation. 

A variety of organisms could conceivably be used to control HABs, but in reality, biological 

controls have many logistical problems and are far from operational. Introduction of non-indigenous 

species or strains pose unknown risks and may be irreversible. Biological control is used extensively 
24 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

in agriculture, such as in the release of sterile male insects or the use of pheromones to control insect 

pests (Hokkanen and Lynch 1995), but there are concerns about the concept of releasing one 

organism to control another. Such concerns are likely to be greatly magnified in the marine 

environment, because there is little precedent for such activities. Despite examples where such an 

approach has had negative long-term consequences on land, there are cases where the approach has 

been both effective and environmentally acceptable (e.g., sterile male releases for control of the 

Mediterranean fruit fly). Biological controls of marine HABs could be via predators (animals which 

graze on planktonic algae), parasites, or microbial pathogens. 

Zooplankton 

One obvious group of organisms to consider as biological control agents is the small animals 

(zooplankton) which co-occur with algae and eat them as food. In nature, zooplankton grazing may 

be an important factor limiting the growth of algal populations and thus preventing blooms. Martin 

et al. (1973) suggested that marine ciliates could be cultured and used for control of G. breve cells. 

Likewise, Shirota (1989) indicated that the Japanese considered the use of zooplankton such as the 

copepod Acartia clausi in controlling HABs. However, both Shirota (1 989) and Steidinger (1 983) 

provide calculations that illustrate the logistical impracticality involved in growing zooplankton 

predators in the laboratory in sufficient quantity to control blooms. Both authors arrive at estimates 

that are unrealistic with respect to cost, space, and facilities. Grazing control for the Texas brown 

tide is being evaluated for isolated embayments and lagoons (Buskey et al. 1996) where the volume 

to be treated may not be as prohibitive. But here too the density of grazers required is probably not 

achievable. While zooplankton grazing may be a factor that normally keeps blooms in check, the 

suggestion that zooplankton can be added or stimulated in order to control blooms once they occur 

is problematic because of the more rapid growth of populations of microalgae than those of their 

animal grazers. 

Viruses 

Viruses have the potential to be highly specific and effective control agents. They are 

abundant in coastal seawater and have recently been recognized as having significant effects on the 

dynamics of phytoplankton blooms. In Norway, the collapse of a bloom of the coccolithophorid 

Emiliania huxleyi occurred simultaneously with the appearance of many viruses in the surrounding 

water and inside the algal cells (Bratbak et al. 1993). Similarly, Nagasaki et al. (1994 a,b) linked 

the collapse of a Heterosigma bloom to the appearance of virus particles within the cells. Viruses 

have also been observed inside many cells during brown tides on Long Island (Sieburth et al. 1988; 

Milligan and Cosper 1994) and there is some indication that a virus may have affected the Texas 

brown tide in a portion of Corpus Christi Bay (D. Stockwell, personal communication). 

On a theoretical level, there are a number of features which make viruses attractive as 

biological control agents (Suttle 1995). First, viruses replicate rapidly, releasing hundreds of viral 

particles when a host cell is disrupted. During a HAB, the rate of viral propagation would 

potentially be accelerated because infection depends upon the frequency with which the virus 

encounters host cells. Another important feature is that viruses tend to be host-specific. This means 
Controls 25 

that a single algal species could be targeted, leaving closely related, co-occurring organisms 

unaffected-the ultimate "magic bullet". In reality, however, viruses are sometimes so host-specific 

that they are unable to infect different genetic strains of the same host species. A bloom population 

of an algal species in nature is often a mixture of different genetic strains of that species. This is 

perhaps the reason many viruses co-exist with their host species, rather than destroying them. 

Because one can expect a co-existence to have developed between viruses and HAB species over 

time, viral control of an established bloom will likely require the introduction of a virus or viruses 

which are isolated from a location or time where the bloom is not present (perhaps even from other 

parts of the world). Whether such viruses exist is a primary question, and whether they could be 

used effectively in control remains unknown as well. 

Another limitation is that environmental regulations concerning the release of a viral 

pathogen might be highly restrictive, given the uncertainties involved. The ability of some viruses 

(e.g. HIV) to switch hosts would support concerns that a control strategy might have unexpected 

consequences within the community of planktonic organisms. Some effort should be devoted to 

further exploration of this avenue of biological control, but the probable limitations of this strategy 

should be recognized as well. 

Parasites 

There are a variety of different parasite species which can infect marine organisms, including 

algae. For example, the dinoflagellate Amoebophrya ceratii is a well known intracellular parasite 

of other, free-living dinoflagellates (Nishitani et al. 1984). The highly virulent nature of parasite 

infection of dinoflagellates has led to the suggestion that these might be effective in controlling HAB 

populations (Taylor, 1968). 

A key issue with respect to biological control is that of host specificity, as the technique 

would be ideal if an introduced parasite would only attack the targeted HAB organism and then dieoff after the demise of the bloom. This is, however, an area where little is known with respect to 

HAB species. Resolution of these specificity issues is needed, although an argument can be made 

that absolute host specificity should not be a requirement. In agriculture or in pest management 

(e.g., mosquitoes), biological and chemical control agents are seldom species-specific and in many 

cases have been employed without unacceptable side effects. 

Bacteria 

New work by Japanese scientists suggests that bacteria could play an important role in 

controlling HABs. An intriguing example is the Gymnodinum mikimotoi-killing bacterium described 

by Ishida (in press). A bacterial strain isolated at the end of a G. mikimotoi bloom exhibits strong 

and very specific algicidal activity against this dinoflagellate species. Cultures of G. mikimotoi are 

completely destroyed within 24-38 hours of the time the bacterium is introduced to a culture. A 

second example of a potentially specific bacterial-algal relationship was reported by Furuki and 

Kobayashi (1 990) who found that a Cytophaga species (bacterium) isolated from the declining phase 

of a Chattonella (alga) bloom was lethal to that alga and could be cultivated in sea water only when 

that sea water was spiked with disrupted cells of Chattonella. As in many other areas involving 
26 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

biological control of HABs, the status of studies on bacteria thus far has been confined to basic 

scientific investigations of the nature of the interaction. No practical efforts have yet been attempted 

to use bacteria to control HABs. 

Studies are needed to determine if viruses, bacteria, or parasites exist that can 

be effective pathogens to targeted HAB species. Once pathogenic isolates are 

established, they must be tested for specificity and efforts must be made to 

understand the dynamics of infection and replication. The environmental 

impacts of the release of non-indigenous organisms need to be carefully 

considered before biological controls can be used in practice. 

OPTIONS FOR CONTROL 

The concept of HAB control is a scientifically challenging and politically charged topic that 

has not received serious attention from the scientific community in the United States. Each of the 

strategies described above has potential benefits and disadvantages, but all require significant 

research and risk assessment before they can be applied on a larger scale to control naturally 

occurring algal blooms. In theory, they can be applied to an established bloom for short-term, 

temporary control, or at specific places and times in the early stages of bloom development in an 

attempt to reduce the size of the seed or inoculum populations. The latter strategy is especially 

appealing if a discrete initiation zone actually can be identified for a HAB, in which treatment might 

result in long-term reduction in bloom size or frequency. 

With both the Long Island and Texas brown tides it may be possible to define such initiation 

zones. In Texas, the Baffin Bay system appears to be a location where blooms are sustained from 

year to year, with adjacent waters being more sporadic with respect to biomass development. 

Around Long Island, areas such as Flanders Bay in the Peconic Bays are often the first to show signs 

of the brown tide, with adjacent waters blooming in subsequent weeks. In Florida, G, breve blooms 

seem to have an offshore initiation zone (Steidinger 1983; Tester and Steidinger in press), although 

it may be large. In the Gulf of Maine, the Casco Bay area is thought to be a source region for 

blooms of Alexandrium tamarense that affect several hundred miles of coastline (Franks and 

Anderson 1992). Where the times and places of bloom initiation can be discretely defined, control 

efforts applied then and there could cover a small area but potentially have a significant impact on 

bloom magnitude and spatial extent. 

Furthermore, since neither the Texas nor the Long Island brown tide organisms nor G. breve 

have been shown to have a dormant, benthic stage in their life histories, these species appear to rely 

on the persistence of sparse populations of cells in the water column for the "seed" population that 

initiates future blooms. Reduction in the size of a bloom in one year through control efforts in an 

initiation zone might thus reduce the geographic extent of a bloom that year, and reduce the size of 

future blooms as well. 

In some situations, it may be worthwhile to consider controlling an established bloom as it 

threatens nearshore fisheries or coastal aesthetics, rather than focusing on source populations. For 
Controls 27 

example, should control measures along the west coast of Florida be considered at times when the 

red tide is established in nearshore waters, even though it is likely that the problem is more 

widespread and will likely recur? Short-term relief fiom dead fish, toxic shellfish, and airborne 

aerosols might be desirable to citizens, tourists, and local businesses, even if winds and currents 

bring another bloom to those waters a few weeks later. Clearly, policy decisions of this type require 

a thorough understanding of bloom transport and growth dynamics, and of the cost, effectiveness, 

and environmental impacts of control strategies. 

An obvious question central to the Panel's deliberations is whether HABs can and should be 

controlled. The first issue, that of feasibility, can only be addressed through detailed laboratory, 

mesocosm, and field studies using the most promising of the approaches listed above. The more 

important question is whether control should even be attempted-whether the benefits outweigh the 

potential impacts. One argument is that any discussion of controls is premature because there is 

insufficient knowledge of the physiology, oceanography, and bloom dynamics of HAB species on 

which to base control strategies. We cannot control what we do not understand. In addition, there 

is the concern that human efforts to control these natural phenomena may have undesirable 

consequences. Steidinger (1 983) argued that Florida red tide control, even if it were feasible, should 

be carefully considered before it is pursued because the red tides and associated fish kills may have 

an ecological function similar to fires or other perturbations in terrestrial ecosystems, which help to 

maintain biological diversity and productivity. Conversely, it can be argued that human activities 

may be stimulating HABs in the first case, thus remedial intervention may be justified. In any case, 

the high likelihood that any attempt to control a HAB will have consequences to other organisms 

requires a precautionary approach to application of chemical, physical or biological controls. 

It is easy to understand why individuals who are economically or personally affected by 

HABs would strongly advocate control strategies. However, the drive to control HAB phenomena 

must demonstrate that the problems are severe, long-lasting, and worth the cost and potential 

environmental impacts of the control strategy. 

Even then, it must be recognized that there are 

presently no proven control techniques and that 

bloom dynamics and environmental conditions may 

limit or exclude the application of effective 

controls. Certain types of HABs seem the most 

amenable to control-such as those in isolated 

embayments or those which totally dominate planktonic ecosystems so that few co-occurring species 

will be impacted by the treatment. Likewise, 

blooms for which discrete initiation zones can be 

identified seem appropriate for consideration in this 

regard. Concerns and reservations about controls 

increase when blooms produce toxins which might 

The severe impacts of the protracted 1995-96 red 

tide along the Florida Gulf Coast on coastal 

residents and businesses led concerned citizens to 

establish Solutions to Avoid Red Tide (START). 

Perhaps the first grass-roots organization formed 

specifically to address HABs, START is "dedicated 

to funding and promoting efforts to control and 

manage toxic red tide, keeping it from area waters 

and beaches" and has expressed concern that 

little effort is being expended on research on 

possible solutions. START'S activities have 

heightened attention to prevention and control 

strategies by managers, scientists, and the public. 

be released during treatment or when blooms are 

widespread. 
28 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

It is premature to conclude whether HAB control strategies are feasible, 

applicable or advisable, because the knowledge base and experience are not sufficient 

to provide the information needed to judge effectiveness and weigh benefits against 

costs. Research on potentially feasible control methodologies should thus be pursued, 

concurrent with field and laboratory studies to better understand the ecological 

mechanisms underlying HABs. 
Under mitigation we consider the steps that can be taken to reduce the losses of resources 

and economic values and to minimize human health risks that occur as a result of blooms that are 

otherwise not prevented or controlled. These include better monitoring and surveillance to reduce 

the risk of ingestion or exposure to toxins, improved forecasting to allow more time to protect 

resources and avoid risks, restoration of affected resources, and a variety of alternative actions to 

minimize effects which might occur. Because prevention and controls are unlikely to provide much 

relief from HABs in the near term, special attention should be given to more immediate 

improvements in mitigation of their effects. 

Coastal states that experience toxic phytoplankton blooms are mandated under the National 

Shellfish Sanitation Program of the Interstate Shellfish Sanitation Commission (ISSC) to have 

shellfish monitoring programs designed to protect public health. While these programs have proven 

highly effective, they are not meant to address the biology of the causative organisms and their 

bloom dynamics. In recent years not only has there been an extension in the range of known HAB 

species, but previously unknown toxic species have emerged as well. Further, increased pressure 

on shellfish resources by non-traditional user 

groups (such as immigrants who harvest 

previously unutilized seafood species which are 

not monitored for HAB toxicity) coupled with 

increased demand for underutilized species has put 

severe pressures on monitoring programs already 

facing extreme financial and personnel limitations. 

Difficulties in sample collection, transport 

and testing of shellfish are compounded in many 

areas by the lack of staff, especially in regions with 

extensive coasts or remote regions. Some regions 

have been successful in developing a volunteer 

network to help collect samples. Even with such 

assistance most state programs lack adequate 

hnding for increased sample analyses. 

Monitoring of offshore waters poses an 

extreme situation. Collection of samples from 

Georges Bank, for example, is complicated by the 

great distance from the shore, large area, and the 

fact that these are federally controlled waters. 

Dockside monitoring of offshore shellfish catch 

has been suggested, but appears infeasible. The 

Representatives of the Washington Department of 

Health and the California Department of Health 

Services spoke to the Panel about the difficulties 

of maintaining adequate surveillance while the 

variety of HAB threats was increasing at the same 

time that financial and human resources devoted 

to monitoring programs were static or declining. 

The numbers of samples collected in California 

has greatly increased through use of volunteers, 

but this has stressed the fixed resources available 

for laboratory analysis. Consequently, there is a 

great need for more rapid, automated analysis. In 

Washington, an outbreak of domoic acid in razor 

clams along the ocean coast was fortuitously 

detected because curious field agents decided to 

collect a few unscheduled samples. The fishery 

was closed on an emergency basis two weeks into 

the season and exposure of large numbers of 

people to the toxin was narrowly averted. Because 

of budget pressures experienced by state 

agencies throughout the country, there is 

widespread concern among those charged with 

protecting public health from HABs that the line of 

protection of public health is becoming alarmingly 

thin. 
30 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

shellfish involved (usually surfclams and mahogany quahogs) have a short shelf life and this, 

coupled with the potential problem of disposal of tons of toxic shellfish, make dockside testing after 

harvest an unreasonable alternative to regular monitoring. A further complication is the individual 

variability of toxicity in these shellfish. Samples have been collected with individual toxicity 

ranging from non-detectable to over 2,000 pg saxitoxin-equivalents/lOO g of tissue. Further 

complicating monitoring is the species-specific and tissue-specific binding and elimination of toxins. 

Other regions with offshore blooms present similar difficulties. 

Phytoplankton monitoring has been proposed as an early warning system in several areas. 

For example, a program of citizen collection of phytoplankton samples from piers has been 

developed in California (G. Langlois, presentation to the Panel, 1996) and is now being implemented 

in New England. While this may provide a good indicator assessment for fish farms in the Pacific 

Northwest and G, breve in the Gulf of Mexico, it should be pointed out that it has not been possible 

to correlate the presence or abundance of the causative organism with outbreaks of PSP toxicity 

during the past forty-plus years in Maine (Shumway et al. 1988). In Alaska, Hall (1982) found that 

this may reflect inadequate sampling frequency rather than inadequacy of the general approach. In 

spite of these limitations, Canadian shellfish growers recently argued for the maintenance of some 

type of phytoplankton monitoring program, noting that it serves as an early warning system to allow 

them to identify toxin-free periods for harvesting and marketing product (Bates and Keizer 1996). 

Implementing a volunteer patrol (coastal and beach) to observe and map discolored water or dead 

fish has been suggested as an early warning system for the eastern Gulf of Mexico. This would help 

meet the need for accurate, up-to-date information requested by local businesses and the general 

public. 

There is a chorus from the management and private sectors to produce a rapid, reliable, 

inexpensive (<$5.00 ea) "dip-stick" test for the various HAB toxins, although these sectors may fail 

to realize that the largest cost of toxicity monitoring will remain sample acquisition and processing 

rather than the analysis itself. Obviously, "dip-stick" tests will need to be sensitive and specific. 

There are test kits under development for at least five toxin groups, yet none is currently reliable for 

management purposes. Fast through-put, laboratory-based monitoring awaits the development and 

approval of receptor-based assays or ELISA tests using toxin antibodies. Future possibilities for 

monitoring include the use of in situ sensors, species-specific probes, and, for some HABs, air-borne 

optical instrumentation. 

Research and development agencies should support development of "dip stick" 

tests for phycotoxins and assist the ISSC and Food and Drug Administration to 

speed their testing and approval for routine use in HAB risk management. 

Further development of phytoplankton monitoring approaches should also be 

pursued, to help focus monitoring of toxins or toxicity levels. 

Effective forecasting of the occurrence, intensity and distribution of HABs depends on 
Mitigation 3 1 

understanding the interplay of underlying physical and biological processes. The ECOHAB 

(Ecology and Oceanography of Harmful Algal Blooms) program to be implemented by federal 

science agencies offers the prospect of developing the understanding of key processes, emphasizing 

the development of predictive models and forecasts. Ideally, information on the life cycle 

requirements, cell physiology and behavior of the HAB species in a region should be available to 

develop a conceptual model of bloom dynamics. That knowledge, coupled with local meteorological 

and circulation models (even first order empirical, statistical models) could help identify conditions 

both necessary and sufficient for bloom initiation. Pertinent field conditions most easily measured 

by automated in situ devices, sensors on moorings and remotely operated vehicles (ROVs), remote 

sensing (sea surface temperature, ocean color), and air-borne spectral radiometers hold promise for 

detecting or tracking spatially explicit bloom phases for some species. However, some algae 

produce harmful effects at fairly low cell densities or occur at depth in the water column and would 

escape such detection. Some HABs result in discolored water patches that can be visually observed 

by overflights in such areas as the Texas and Long Island bays and Puget Sound, and by satellite in 

open shelf areas in the Gulf of Mexico and the U.S. South Atlantic Bight. These patches can be 

tracked, correlated with local wind and current conditions, and mapped. Coupled with forecast 

models, these satellite, aircraft of in-situ observations can be used to re-initialize or correct models 

to yield more accurate near real-time predictions. 

The development of forecast models integrated with near-real time sensing 

systems should be pursued as an important goal of research programs on the 

ecology of HABs. 

Accurate Information and Public Education 

Public confusion concerning algal bloom has in the past resulted in over-reaction, causing 

harm to fishery or tourism industries that had little or no relationship to a particular bloom. 

Conversely, a cavalier or too lax attitude in come cases could result in illnesses, or even deaths. Not 

all HABs pose similar health risks. Public health officials and health care providers need accurate 

and up-to-date information. The public also requires responsible reports to guide their consumer and 

recreational choices. Any HAB mitigation strategy should include an educational component for 

researchers, resource managers, public health officials, health care providers and user groups. 

Providing relevant information on the potential causes and effects of HABs to the medical 

community as well as the general public should act to reduce the level of anxiety, promote realistic 

expectations and allow individuals to develop their own contingency plans. Timely dissemination 

of accurate information to the press by managers and scientists should be a priority. The press, in 

turn, should accept the obligation of reporting this information promptly and factually, avoiding 

sensationalism. 

Aquaculture and Fishery Harvesting 

Efforts to mitigate the impacts of HABs on shellfish and finfish farms are both difficult and 

complicated. One of the few opportunities available for mitigation for shellfish growers during 
32 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

HABs is short-term filtration of water to hatcheries, but this is not a practical solution in the longterm. Moving shellfish crops to another area is usually not possible and, if the shellfish are already 

contaminated with harmful cells, e.g. Alexandrium, moving them may contaminate the other area. 

Floating net-pens used to raise fish, however, can be moved from affected areas to uncontaminated 

waters, but this often entails regulatory approval or permitting, logistically challenging movement 

of the pens and the fish in them, and the assumption that clean water will be available at the new 

site. Such movements are costly, dangerous and labor intensive. Fish growers usually stop feeding 

their fish at the first sign of a bloom in order to reduce fish activity and metabolism, but this is also 

costly in terms of reduced growth of the fish. Fish farms sometimes are able to pump harmful algaefree water from depth into their pens, but this assumes that the farm has the necessary pumping 

equipment and the bloom remains in the surface water. This is not always the case, e.g., Heterosigma 

is a vertical migrator and Chaetoceros can often occur throughout a 50-my well-mixed water column. 

Both finfish and shellfish farmers from all geographic regions of the U.S. have repeatedly 

expressed a need for more advanced warning from regulatory agencies when blooms occur. For 

example, determination of the most likely bloom areas in Long Island bays provides valuable 

information for shellfish reseeding operations. Finfish farmers in the Pacific Northwest also would 

benefit from an expedited permitting processes for relocating their stocks when HABs occur. 

Some shellfish hatcheries have added potassium permanganate or copper sulfate to the water 

(both algicides) to kill blooms. Ozonation is also being investigated for "depuration" of shellfish 

contaminated with brevetoxin. Although ozonation has some promising applications, its widespread 

effectiveness and reliability remain to be demonstrated. 

Human Health 

Few primary care and emergency-room physicians in HAB-prone areas are familiar with 

symptoms of algal toxicity, thus hindering quick and reliable diagnosis and treatment. Consequently, 

there is reason to believe that human health effects of algal toxicity are under-reported. Better 

information on symptomology and treatment should be provided to health-care providers, 

particularly where the exposure of large numbers of people cannot be prevented by regular public 

health precautions, for example where beach-goers and coastal residents are exposed to toxic 

aerosols. In such cases, the longer-term consequences of acute exposure, for example after a 

vacationer goes back home and suffers a respiratory infection or other malady, are particularly 

problematic. The chronic exposure to algal toxins (as might be experienced by a beach resident in 

a red tide region, or a subsistence shellfisher) deserves increased attention by the medical research 

community. 

Recreation and Tourism 

As reviewed under Causes and Consequences, HABs have significant economic impacts not 

only from the loss of fish and shellfish, but also as a result of impairment of the use and enjoyment 

of coastal areas and their resources. This includes: simple aversion to boating or fishing in turbid 
Mitigation 33 

waters (as seen in the case of brown tides in Texas and Long Island); prohibition of recreational 

fisheries (for example, razor clam harvesting in Washington); halo effects on the sales of fish and 

shellfish in markets and restaurants as a result of public concern and misinformation about the safety 

or wholesomeness of the product; cancellation or abbreviation of vacations and recreational uses as 

a result of noxious blooms; and diminished property values. Beyond the dollars and cents, the 

quality of life of coastal residents and visitors has been considerably diminished by HABs, such as 

the extended 1995-1996 red tide on the Florida Gulf coast. 

Representatives of the hospitality industry 

in Florida who met with the Panel indicated that p --o a- *A e o 

they sometimes lost business because the public I 1 

learned from the press that the entire region was 

being affected red when the outbreak was 

in fact patchy and localized. problems 

have been observed for resort areas on the Texas 

coast during and following red tide (Gymnodinium 

location and severity of red tide, based on a well- I groundless fear for the safety'G seafood. 'charter 

At the kmel's Sarasota meeting, hoteliers, 

restauranteurs, and sport-fishing businessmen 

related the significant impacts on their businesses 

of the unusually persistent red tide during 1995 

and 1996. Overseas tourists had vacations ruined 

by noxious beachfront conditions. Many U.S. - - . - 

breve) incidents. ~~tt~~ reporting through the 

popular news and information perhaps 

including daily or weekly advisories about the 

organized network of observers would improve this 

situation as well as reduce the exposure of the cancellations, even though the fishing grounds 

were unaffected. The costs to the regional uninformed visitor when blooms are severe. In 

order to avoid unwarranted panic, however, this 

information service would have to be accompanied 

tourists canceled their reservations based on news 

reports, even during times when beaches were not 

affected. Restaurants also reported sharp drop-off 

of customers and revenues. ~resumablv out of 

by a carefully developed educational effort. 

Beyond the physical discomfort caused by brevetoxin aerosols, beach use is also affected by 

the sight and smell of windrows of dead fish on the beach. Although this has not been routinely 

done, it should be feasible to reduce the stranding of dead fish on limited sections of beach by the 

use of floating booms, such as those used for oil spill control, or net enclosures. An additional 

problem and cost is the removal of dead fish from the beaches. During the 1995-96 red tide 

outbreak, many tons of dead fish were removed from beaches. In addition to the costs of physical 

removal, disposal into landfills required the payment of tipping fees and consumed landfill capacity. 

Similar disposal problems confront fish farmers in the Pacific Northwest when Heterosigma or 

diatom blooms result in significant fish mortality. A Sarasota County commissioner asked whether 

the dead fish could be macerated and disposed of offshore. The Panel was unable to examine all 

aspects of the feasibility of this option but noted that existing regulations may pose obstacles. 

Clearly, alternative disposal options should be evaluated using a common-sense, relative-risk 

approach. 

A variety of estimates of economic impacts from HABs are presented in the literature and 

were offered to the panel during its three regional meetings. However, there is a consistent lack of 

comprehensive assessments of regional economic impacts of HABs. This is important information 

not only for determining where best to focus efforts to reduce avoidable economic impacts, but also 

for determining the justifiable costs of prevention and control efforts. 
34 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

Endangered Species 

HABs have now been determined to be responsible for the mortality of at least three 

endangered marine mammals: Florida manatees (brevetoxins) and humpback whales and bottlenosed dolphins (saxitoxins). While it may prove difficult to mitigate these impacts, greater 

understanding of the nature and extent of these impacts is required. Stranded and ill marine 

mammals and birds should be routinely examined for symptoms and presence of algal toxins. The 

1996 manatee mortality incident clearly indicates that much more monitoring of at-risk species is 

required. Coupled with improved knowledge about the distribution of and environmental factors 

associated with HABs, this may reveal management options to reduce exposure, for example by 

regulating freshwater flows to protect manatees from red tide. 

Federal and state agencies with resource stewardship and public health 

responsibilities, working in conjunction with outreach officers from universities 

and research institutions, should develop and widely distribute clear and factual 

leaflets and public advisories concerning HABs and their risks. Special 

materials should be distributed to health care providers, which present 

information about symptoms and treatments. During HAB events, agencies 

should provide regular reports to the public via the news media concerning the 

distribution and intensity of outbreaks and recommended precautions. 

Technical assistance to resource users should be increased to provide timely 

advisories based on forecasts and monitoring and advice on practical steps that 

can be taken to minimize losses. In areas with finfish net-pen aquaculture, 

permitting processes should be streamlined to allow timely tactical relocation 

of pens. 

Economic studies should be undertaken to document regional and national costs 

of HAB impacts and made available to inform policy-makers. 

Restoration efforts have thus far been limited to reseeding efforts (bottom planting of 

hatchery-reared juvenile scallops) in the Peconic Bay system (New York) after mortalities resulting 

from BTB. These efforts have been only partially successful. The bay scallop comprised a 

multimillion dollar fishery on Long Island prior to the first occurrence of Aureococcus blooms in 

1985. Three successive years with brown tides caused extensive mortality of adult scallops and 

severely limited larval recruitment; the impact of the brown tide is magnified by the short lifespan 

of the bay scallops. By the fall of 1988, virtually no native stock remained in the Peconic Bays and 

the fishery was essentially eliminated. 

Tettelbach and Wenczel (1993) and the Long Island Green Seal Committee attempted to 

reseed bay scallops at three sites. Enough scallops survived at one of the sites to spawn, but another 

bloom ofAureococcus apparently prevented successful recruitment. Heavy recruitment was noted 

in 1991 after similar reseeding efforts; however, these scallops were quickly obliterated by a 
Mitigation 35 

shell-boring parasite and another summer brown tide. A good crop of scallops realized in 1994 

raised the hopes of baymen that the worst was over, but, due to a major brown tide in 1995, both 

1995 and 1996 were poor seasons and the outlook for 1997 is dim. Transfer of bay scallop spawners 

has been successful (Peterson et al. 1996) and could, theoretically, be successful in restocking areas 

affected by brown tides. However, in the Peconic Bays areas of optimum scallop growth often 

coincide with areas of intense BTBs. Furthermore, it is currently not possible to predict with any 

degree of certainty the likelihood of a bloom, making restocking with spawners risky. 

The other cases in which the living resources themselves may be damaged include fish kills 

from Gulf of Mexico red tides or loss of fishery resources resulting from larval mortality or declines 

in seagrasses in Texas estuaries affected by BTB. In Texas, hatchery stock enhancement of some 

finfish species is already being conducted, although as discussed under the Causes and Consequences 

section it is not clear that these stocks have yet suffered. Nonetheless, it may be feasible to restore 

lost seagrass beds in Texas and Long Island estuaries, but not until the BTB subsides and light 

conditions improve. 

Restoration of resources damaged by harmful algal blooms is limited to 

restocking of shellfish and replanting of seagrasses, but such efforts will not be 

successful until the threats of recurrent blooms subside. 
36 

Prevention, Control, and Mitigation of Harmful Algal Blooms 
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 increasing blooms are a direct 

result of human activities, cyclic or longer-term variations in climate, or other natural factors, the 

greater risks posed demand improved precautions for the protection of human health, more 

concerted efforts to manage activities which may cause HABs, and renewed consideration of 

strategies to control blooms once they occur. 

It is obviously preferable to prevent HABs in the first place rather than just 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, it is difficult to imagine 

another cause, other than climate change, that could be responsible for the widespread increases in 

HABs witnessed during the last half of this century. Although pollution and nutrient enrichment are 

strongly implicated in worsening HABs elsewhere in the world, they 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 of the bays and estuaries of the United States could well yield 

positive results in terms of reductions in HABs. In other words, HAB reduction is yet another 

rationale for advancing existing pollution reduction strategies. However, the reduction of the 

potentially most important pollutant, nitrogen-containing materials, is a daunting challenge because 

of the importance of nonpoint sources of nitrogen 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-related transfers also require greater 

attention. 

Although controlling HABs through the application of chemicals or flocculants or the 

introduction of biological control agents is fraught with difficulties related to effectiveness and 

potential side effects, such controls deserve more careful attention than they have received 

recently. In addition to the need for expanded U.S. research on this topic, much can be learned 

fiom the experiences of Asian nations. Furthermore, control techniques should be evaluated in the 

context of risk assessments such as those applied in evaluating chemical and biological controls in 
Prevention. Control. and Mitiaation of Harmful Alaal Blooms 

land-based agriculture. The applicability of controls will probably be limited to more managed and 

constrained circumstances, for example in association with aquaculture or within 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 the increased number and diversity of 

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 

to the immediate expansion of simple methods using volunteer observers. Moreover, the 

medical community should be better informed and prepared to recognize and 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 so that they are cautious but not unduly alarmed. Responsible 

public education and communication should receive increased attention. 

Research being initiated by federal agencies on the Ecology and Oceanography of 

Harmful Algal Blooms (ECOHAB) should seek to contribute basic understanding of the causes 

and behavior of HABs which would inform prevention, control and mitigation strategies, 

particularly regarding: 

the role of anthropogenic nutrient sources in stimulating and sustaining blooms and the 

potential effectiveness of nutrient control strategies in reducing blooms; 

the effects on blooms of trophic alterations, such as changing grazing pressure, that result 

from human over-harvesting or habitat changes; 

the importance of "seeding" in the genesis of blooms and mechanisms for inoculation; 

critical stages of bloom formation and propagation that may be suitable targets for 

control strategies; 

the role and potential impacts of parasites and predators in suppressing blooms; 

molecular or other indicators of harmful algal species which may improve the sensitivity 

and reliability of monitoring; 

remote sensing of blooms that provides advanced warning and supports tactical 

mitigation; and 

modeling of physical and biological processes which may be applied in forecasting the 

occurrence and movement of harmful algal blooms. 

Even with such advances in basic understanding, a critical factor limiting the evaluation, 
Conclusions 39 

much less application, of prevention, control and mitigation strategies is the lack of focused, applied 

research on solutions. Federal and state agencies with responsibilities for resource 

management, environmental protection, and public health should support research directly 

addressing prevention, control, and mitigation, including: evaluation of the effectiveness and 

side-effects of chemical, physical, and biological controls; development of better measurements 

of toxins and HAB species for application in monitoring; ballast water treatments; and effects 

of chronic exposure on human health. Such a focused, applied research effort, in consort with the 

expanded research on ecology and oceanography of blooms, would substantially increase the 

Nation's ability to protect public health and natural resources. 
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SPEAKERS AND PANELISTS PARTICIPATING IN THE REGIONAL MEETINGS 

PORT ARANSAS, TEXAS, AUGUST 21-23,1996 

Dr. Edward J. Buskey 

Dr. Hudson DeYoe 

Mr. Jim Ehman 

Mr. Wallace Kelly, Jr. 

Mr. Walt Kittleberger 

Dr. Darcy J. Lonsdale 

Dr. Larry McEachron 

Dr. Larry D. McKinney 

Dr. Robert Nuzzi 

Dr. Christopher P. Onuf 

Mr. Robert B. Wallace, Jr. 

Marine Science Institute, University of Texas at Austin 

Port Aransas, TX 

Corpus Christi Bay National Estuary Program 

Corpus Christi, TX 

Gulf Coast Conservation Association 

Houston, TX 

Coastal Bend Guides Association 

Corpus Christi, TX 

Lower Laguna Madre Foundation 

Port Mansfield, TX 

Marine Sciences Research Center, State University of New 

York, Stony Brook 

Texas Parks and Wildlife Department 

Rockport, TX 

Texas Parks and Wildlife Department 

Austin, TX 

Suffolk County Department of Health Services 

Riverhead, NY 

National Biological Service 

Corpus Christi, TX 

Coastal Bend Bays Foundation 

Corpus Christi, TX 
48 

Prevention, Control, and Mitigation of Harmful Algal Blooms 

Mr. Brian Bernier 

Mr. Kevin Bright 

Dr. Raymond Carruthers 

Dr. Rose Ann Cattolico 

Mr. Frank Cox 

Ms. Janet Kelly 

Mr. Gregg Langlois 

Mr. Steve McKnight 

Mr. Dave Molenaar 

Mr. Raymond RaLonde 

Mr. Tim Sample 

Dr. Chris Scholin 

Dr. Usha Varanasi 

Dr. John Wekell 

Global Aqua-USA 

Seattle, WA 

ScanAm Fish Farm 

Anacortes, WA 

U.S. Department of Agriculture 

Beltsville, MD 

Department of Botany, University of Washington 

Seattle, WA 

Washington Department of Health 

Olympia, WA 

Seattle, WA 

California Department of Health Services 

Berkeley, CA 

Global Aqua-USA 

Seattle, WA 

Quinault Indian Nation 

Taholah, WA 

University of Alaska Marine Advisory Program 

Anchorage, AK 

U.S. Food and Drug Administration 

Seattle, WA 

Monterey Bay Aquarium Research Institute 

Moss Landing, CA 

National Marine Fisheries Service 

Seattle, WA 

National Marine Fisheries Service 

Seattle, WA 
Appendix 49 

Dr. Daniel Baden 

Mr. Ed Chiles 

Mr. Dennis Hart 

Dr. Gary Kirkpatrick 

Dr. Tom Lee 

Mr. Dan Leonard 

Ms. Katherine Moulton 

Ms. Carole Nikla 

Dr. Richard Pierce 

Ms. Gloria Raines 

Dr. Gary Rodrick 

Dr. Richard Shriner 

Dr. Karen Steidinger 

Dr. Richard Stumpf 

Dr. Gabriel Vargo 

Rosenstiel School of Marine and Atmospheric Science 

University of Miami, Miami, Florida 

Anna Maria Island, FL 

Hart's Landing 

Sarasota, FL 

Mote Marine Laboratory 

Sarasota, FL 

Rosenstiel School of Marine and Atmospheric Science 

University of Miami, Miami, FL 

Englewood, FL 

Colony Beach and Tennis Resort 

Long Boat Key, FL 

Holiday Inn 

Sarastoa, FL 

Mote Marine Laboratory 

Sarasota, FL 

Manasota '88 

Palmetto, FL 

Department of Food Sciences and Human Nutrition 

University of Florida, Gainesville, FL 

Sarasota, FL 

Florida Department of Environmental Protection 

St. Petersburg, FL 

U.S. Geological Survey 

St. Petersburg, FL 

Department of Marine Science, University of South Florida 

St. Petersburg, FL 
No. 1. Able, Kenneth W. and Susan C. Kaiser. 1994. Synthesis of Summer Flounder Habitat 

Parameters. 

No. 2. Matthews, Geoffrey A. and Thomas J. Minello. 1994. Technology and Success in 

Restoration, Creation, and Enhancement of Spnrtina nlternzflora Marshes in the United States. 2 

vols. 

No. 3. Collins, Elaine V., Maureen Woods, Isobel C. Sheifer and Janice Beattie. 1994. 

Bibliography of Synthesis Documents on Selected Coastal Ocean Topics. 

No. 4. Hinga, Kenneth R., Heeseon Jeon and Noelle F. Lewis. 1995. Marine Eutrophication 

Review. 

No. 5. Lipton, Douglas W., Katharine F. Wellman, Isobel C. Sheifer and Rodney F. Weiher. 

1995. Economic Valuation of Natural Resources: A Handbook for Coastal Resource 

Policymakers. 

No. 6. Vestal, Barbara, Alison Rieser et al. 1995. Methodologies and Mechanisms for 

Management of Cumulative Coastal Environmental Impacts. Part I -- Synthesis, with Annotated 

Bibliography; Part I1 -- Development and Application of a Cumulative Impacts Assessment 

Protocol. 

No. 7. Murphy, Michael L. 1995. Forestry Impacts on Freshwater Habitat of Anadromous 

Salmonids in the Pacific Northwest and Alaska--Requirements for Protection and Restoration. 

No. 8. Kier (William M.) Associates. 1995. Watershed Restoration--A Guide for Citizen 

Involvement in California. 

No. 9. Valigura, Richard A., Winston T. Luke, Richard S. Artz and Bruce B. Hicks. 1996. 

Atmospheric Nutrient Input to Coastal Areas - Reducing the Uncertainties.