An Assessment of Florida Red Tide: 

Causes, Consequences and Management Strategies

•

Frank Alcock, Ph.D.

Assistant Professor of Political Science

New College of Florida

Director, Marine Policy Institute at Mote Marine Laboratory

Technical Report #1190

August 2007

1600 Ken Thompson Parkway • Sarasota, FL 34236 • (941)388-4441 • www.mote.org
Acknowledgements

The research and writing of this assessment were made possible by 

a grant from the New Amsterdam Charitable Foundation. Printing, 

dissemination and outreach activities associated with this assessment 

are being made possible by a grant from the Gulf Coast Community 

Foundation of Venice. Additional funding has also been provided by 

Mr. & Mrs. Ronald B. Morris.

The assessment is authored by Frank Alcock, Director of the Marine 

Policy Institute (MPI) at Mote Marine Laboratory. Dr. Alcock’s 

Assigned Research Leave from New College of Florida, where he is an 

Assistant Professor of Political Science, provided the opportunity to 

conduct this assessment. The author would like to thank New College 

President Mike Michalson and Mote Marine Laboratory President 

Kumar Mahadevan for their support with this endeavor.

Chris Pettit, an MPI policy associate, provided research assistance for 

the assessment’s regulatory framework section. Sherry Larkin at the 

University of Florida provided a helpful review of the initial draft of 

the economic impacts section. A number of Mote staff and research 

scientists provided constructive reviews and editorial suggestions at 

various stages. Lawson Mitchell was especially helpful with graphics 

and layout and Susan Stover provided invaluable assistance with 

reference checking. 

The author would like to thank the following individuals for 

taking time to speak about the research and/or policy issues addressed 

in this assessment: Mark Alderson, Julia Birch, Larry Brand, 

JoAnne Burkholder, Don Cheney, Jill Copeland, Stuart DeCew, 

Chris D’Elia, Cindy Heil, Leon Kaganovskiy, Jason Lenes, Pat McDonald, 

Jack Merriam, Frank Muller-Karger, and Mario Sengco. In addition 

to these individuals the author benefitted from the opportunity to 

participate in a July 2006 Workshop on the State of Research on Red Tide 

in the Gulf of Mexico that was sponsored by the National Oceanic and 

Atmospheric Administration, Mote Marine Laboratory and the Florida Fish 

and Wildlife Research Institute. 

Author Contact Information:

Frank Alcock

Marine Policy Institute at Mote Marine Laboratory

1600 Ken Thompson Parkway

Sarasota, FL 34236

(941) 388-4441

alcock@mote.org
The mission of the Marine Policy Institute at Mote 

Marine Laboratory is to strengthen the scientific 

basis of public policy and societal decision making 

for economic development and sustainability of our 

oceans and coastal ecosystems. Working closely with 

Mote scientists and other programs, the Institute 

conducts, integrates and communicates multi-disciplinary research on marine/coastal issues in a manner 

that produces salient, credible assessments and advice 

in policy (legal, economic, social) to decision-makers, 

stakeholder groups, and concerned citizens. 

Dr. Frank Alcock is Director of the Marine Policy 

Institute. Dr. Alcock, Assistant Professor of Political Science at New College of Florida, holds a Ph.D. 

in Political Science from Duke University, an M.A. 

in International Affairs from George Washington 

University and a B.A. in Economics from the State 

University of New York, Binghamton. His experience 

traverses both governmental and academic research 

on sustainable development and trade and global 

environmental politics with a focus on oceans and 

marine policy. He was a Belfer Fellow at the Kennedy 

School of Government, Harvard University and an 

active member of the human dimensions of global 

environmental change research community. 

Barbara J. Lausche, J.D., is the Institute’s Deputy 

Director. She received her J.D. from the Columbus 

School of Law and has 30 years of experience with 

government and non-governmental organizations 

in the U.S. and internationally. Lausche has worked 

with multi-disciplinary teams of scientists building 

institutional capacity and legal frameworks. She has 

worked with the Environmental Protection Agency, 

the Congressional Office of Technology Assessment, 

and was senior environmental staff with the World 

Bank. Lausche serves on the Board of the Island Resources Foundation, co-founded the Science and Environmental Council of Sarasota County and served 

as its honorary Executive Director for five years. She 

is a member of the D.C. Bar, the Commission on 

Environmental Law, the International Union for 

Conservation of Nature and Natural Resources and 

Caribbean co-chair of their Specialists Group on 

Oceans, Coasts and Coral Reefs.

Dr. Michael Orbach is the Institute’s Special Advisor. Dr. Orbach, Professor of Marine Affairs and 

Policy at the Nicholas School of the Environment 

and Earth Sciences at Duke University, holds both a 

Ph.D. and M.A. in Cultural Anthropology from the 

University of California, San Diego and a B.A. in 

Economics from the University of California, Irvine. 

He has worked as a Cultural Anthropologist with 

the National Oceanic and Atmospheric Administration, has held several Governor’s appointments to 

environmental Boards and Commissions, as well as 

several appointments with the National Academy of 

Sciences. Dr. Orbach was an advisor to both the Pew 

Oceans Commission and the U.S. Commission on 

Ocean Policy and is a former President of the Coastal 

Society and the Southern Association of Marine 

Laboratories, Chairman of the Board of Directors of 

the Surfrider Foundation and a member of the Board 

of Directors of the Ocean Conservancy.

Dana O’Mara, M.S., serves as the Marine Policy 

Institute Program Manager. She holds an M.S. in 

Oceanography and Coastal Sciences from Louisiana 

State University. O’Mara has research experience in 

coastal management, marine policy and economic 

issues pertaining to the Gulf of Mexico region and 

beyond. She received a National Oceanic and Atmospheric Administration Coastal Management Fellowship to help develop a Shoreline Access Plan and a 

Shoreline Economic Analysis for the state of Texas.

About the Marine Policy Institute
An Assessment of Florida Red Tide: 

Causes, Consequences and Management Strategies

Table of Contents

Executive Summary ............................................................................................................................................................ 1

Introduction ....................................................................................................................................................................... 2

The Causes of Florida Red Tide.......................................................................................................................................... 3

Red Tide Basics: Bloom Dynamics and Physiology .................................................................................................. 3

 Historical Trends ...................................................................................................................................................... 3

Coastal Pollution and Florida Red Tide.................................................................................................................... 4

 Reasons for Caution with Respect to Linkage................................................................................................ 5

 Reasons for Concern with Respect to Linkage ............................................................................................... 6

 Moving Forward............................................................................................................................................. 8

Consequences: Impacts to Marine Life and Human Health............................................................................................. 10

Brevetoxins............................................................................................................................................................. 10

Impacts to Marine Life........................................................................................................................................... 10

Impacts to Human Health...................................................................................................................................... 11

Consequences: Economic Impacts.................................................................................................................................... 13

Variation in Estimates............................................................................................................................................. 13

National Estimates of Harmful Algal Bloom impacts............................................................................................. 13

 Estimates of Florida Red Tide Impacts................................................................................................................... 14

Management Strategies .................................................................................................................................................... 16

Prevention: Measures to Reduce the Incidence or Extent of Red Tides .................................................................. 16

 Exercising Precaution ................................................................................................................................... 16

 Reducing Non Point Source Pollution ......................................................................................................... 16

Control: Measures to Kill, Neutralize or Remove Red Tide from the Water Column ............................................ 18

 Five Key Evaluative Criteria ......................................................................................................................... 19

 Flocculation.................................................................................................................................................. 20

 Ozone........................................................................................................................................................... 20

 Other Chemical and Biological Agents ........................................................................................................ 22

Mitigation: Measures to Reduce the Impacts of Red Tides..................................................................................... 22

 Improved Monitoring Capacity.................................................................................................................... 22

 Human Dimensions Research...................................................................................................................... 23

 Public Education and Outreach ................................................................................................................... 23

Governance Issues............................................................................................................................................................. 24

The Regulatory Framework for Florida Red Tide................................................................................................... 24

 Federal Governance...................................................................................................................................... 24

 State Governance.......................................................................................................................................... 24

 Local Governance......................................................................................................................................... 26

The Florida Harmful Algal Bloom Task Force........................................................................................................ 26

 External Review...................................................................................................................................................... 27

Conclusion ..................................................................................................................................................................... 29

Appendix: Q&A ............................................................................................................................................................. 30

References ..................................................................................................................................................................... 32

Acronyms ..................................................................................................................................................................... 38

Glossary ..................................................................................................................................................................... 39
Executive Summary

1

Our quality of life in Southwest Florida can be improved 

with a more comprehensive and sustained management 

strategy for Florida red tides. It can also be improved by 

reducing coastal pollution. Both agendas have significant 

implications for the health of our marine environment 

and the coastal economies that depend upon them. In 

recent years, their potential overlap has become a focal 

point of controversy. Coastal pollution is often depicted 

as either the primary cause of red tides or as something 

that’s incapable of affecting them. Neither position stands 

up to scrutiny. 

Red tides have long been a fixture of the West Florida Shelf 

ecosystem and most scientists agree that the initiation of 

blooms and significant stages of their development occur 

offshore and deep in the water column. Once a bloom 

moves inshore, it may benefit from land-based nutrient 

fluxes. These fluxes occur naturally but they can also be 

exacerbated by coastal pollution. Reducing nutrients from 

land may ease the severity and duration of red tides, and 

reduction should be part of a comprehensive management 

strategy that responds to red tides. Reduced nutrient loads 

and better water quality will also generate ecological, 

social and economic benefits that are independent of any 

connection to Florida red tides. 

It is imperative that scientists, policymakers and 

stakeholders move beyond polarized debate surrounding 

the links between coastal pollution and red tide. Conclusive 

scientific evidence of a strong linkage between coastal 

pollution and red tide blooms would no doubt generate 

political momentum for a pollution-reduction agenda. 

However, the nature of nutrient conditions on the West 

Florida Shelf and the variety of nutrient sources that likely 

contribute to red tides make it very difficult to pinpoint or 

assess the relative significance of each source. Conclusive 

evidence remains elusive but Florida needs to act now. 

Florida needs to reduce nutrient loads to its watersheds for 

reasons that go beyond red tide and it needs to develop 

a comprehensive management strategy for red tides that 

goes beyond reducing coastal pollution. 

The Marine Policy Institute (MPI) at Mote Marine 

Laboratory encourages the scientific community to 

intensify its focus on the role of nutrients in red tide 

events. But we caution policymakers and stakeholders 

against thinking about the links between coastal pollution 

and red tide in a vacuum. More thought needs to 

be given to the regulatory processes by which coastal 

pollution will be reduced. The Florida Department of 

Environmental Protection is currently overhauling water 

quality standards for the state’s watersheds that will largely 

dictate improvements. Local ordinances can supplement 

these standards but policymakers, stakeholders and citizens 

should not lose sight of the importance of statewide 

efforts. They should also not lose sight of the fact that 

Florida needs to address a broad portfolio of concerns that 

involve land-sea interactions. Red tide is just one concern 

among many. 

The MPI recommends a multi-pronged approach that 

combines precautionary measures to curb coastal pollution 

with continued research into a diversified suite of control 

technologies and an expansion of measures to mitigate the 

impacts of red tide blooms. Expanded mitigation measures 

should include a robust program on monitoring, detection 

and forecasting along with a robust human dimensions 

research agenda and an aggressive education and outreach 

program. Human dimensions research should include 

projects that assess the impacts of chronic exposure to 

red tide, projects that measure public perceptions and 

knowledge about red tide, projects that measure economic 

activity before, during and after blooms, and projects that 

improve upon interagency coordination and emergency 

response and recovery plans. 

Finally, the MPI recommends that the Florida Harmful 

Algal Bloom Task Force be redesigned, funded and 

reconvened, and that a mechanism be developed to provide 

for periodic external review of Florida’s Harmful Algal 

Bloom research and management programs. In addition 

to strengthening these programs, an external review should 

help to build trust with disaffected stakeholder groups.
Introduction

Red tide blooms have long afflicted the west coast of Florida 

but many believe that the problem is getting worse. For the 

past 20 years, our region has been subjected to debilitating 

blooms on a near-annual basis. The most severe of these 

blooms have persisted for more than a year and have resulted 

in massive fish kills, large underwater dead zones, significant 

marine mammal mortalities, adverse impacts on human health 

and substantial economic losses. 

As red tides have continued to take their toll on Southwest 

Florida, public frustration has intensified. Coastal communities 

want a cause identified or a cure unveiled. Policymakers 

are also frustrated. Decades of research have yielded much 

knowledge about Florida red tides, but the results fail to 

identify a primary nutrient source behind the blooms. State 

and local government officials have expressed their desire to 

address the problem but little consensus has emerged about 

the most appropriate course of action.

Florida red tide presents itself as a priority issue for the newly 

established Marine Policy Institute (MPI) at Mote Marine 

Laboratory. The MPI’s mission is to conduct, integrate and 

communicate multi-disciplinary research on marine policy 

issues in a manner that produces salient, credible assessments 

and advice to decision-makers and the public. The need for 

these services on the issue of red tide is clear. The science of 

Florida red tide is complex, and strongly held viewpoints have 

contributed to the politicization of scientific debates. The MPI 

steps in with the goal of facilitating a constructive dialogue 

among different constituents and forging some consensus 

regarding the benefits and limitations of different management 

options.

The MPI initiated its assessment of Florida red tide with the 

following tasks in mind:

• Survey the broad range of research activity pertaining to 

Florida red tides; 

• Translate research results into language that can be 

understood by policymakers, stakeholder groups and the 

general public;

• Synthesize and integrate the most pertinent research 

findings in a manner that responds to the most pressing 

questions put forth by these groups; 

• Assess alternative management strategies and existing 

regulatory frameworks;

• Provide guidance. 

Importantly, this assessment does not attempt to provide 

a definitive resolution to all of the questions it addresses. 

Definitive answers are possible in some instances but in many 

others they are not. What the assessment attempts to do is to 

contribute to a more constructive dialogue by clarifying areas of 

agreement and disagreement on these questions and outlining 

what is known, what is unknown and how we might learn 

what we don’t know. We hope our audience will look upon 

the assessment as a repository of research and management 

insights and a point of departure for further discussion.

How to Read This Assessment

This assessment is broken down into several sections that cover 

the most relevant and important aspects surrounding Florida’s 

red tide. Each section also includes several subsections. 

“The Causes of Florida Red Tide” addresses bloom dynamics 

and physiology with a view toward understanding the causes of 

red tide. After providing some basic background, the section 

directs its attention toward pressing questions regarding 

historical trends and coastal pollution.

“Consequences: Impacts to Marine Life and Human Health” 

addresses the consequences of red tide with a focus on the 

toxicology of Karenia brevis and its impacts on marine life and 

human health. 

“Consequences: Economic Impacts” extends the discussion of 

the consequences that red tides have on the economy and the 

need for better measures to understand the impacts. 

“Management Strategies” addresses strategies that include 

prevention, mitigation and control measures and the 

implications for each. 

“Governance Issues” provides an overview of the regulatory 

framework pertaining to red tide issues and suggests measures 

to strengthen governance functions. 

“Conclusion” revisits the assessment’s major points. 

2
The Causes of Florida Red Tide

Red Tide Basics: Bloom Dynamics and Physiology

Florida red tides are caused by the toxic dinoflagellate 

Karenia brevis (previously known as Gymnodinium breve), a 

species of phytoplankton found on the West Florida Shelf. 

It is commonly present in background concentrations 

throughout the Gulf of Mexico. It can survive in water 

temperatures ranging from 9 ̊C to 33 ̊C (48 ̊F to 92 ̊F ) with 

optimum growth occurring between 22 ̊C and 28 ̊C (72 ̊F 

and 82 ̊F) and in a wide range of salinities from 24% to 37% 

with optimum growth occurring between 31% and 37% 

(Steidinger et al. 1998). Growth rates 

may also be affected by sunlight and 

shade may play an important role in 

the development of blooms (Walsh et 

al. 2007).

Scientists who study the life cycle of K. 

brevis divide red tide blooms into four 

stages: initiation, growth, maintenance 

and termination. Initiation is 

believed to occur offshore and at 

depth. K. brevis cells are remarkably 

opportunistic when it comes to 

metabolizing nutrients and they 

make use of a broad range of organic 

and inorganic material. Although 

opportunistic, the growth rate of K. 

brevis cells is slow compared to that of 

many other species of phytoplankton. 

K. brevis cells typically undergo one 

cell division every two to three days whereas a number of other 

species of phytoplankton undergo three to four divisions a 

day. Blooms can develop in deeper levels of the water column 

before portions migrate to the surface. Prevailing ocean and 

wind currents can transport the bloom closer to shore or move 

it along the coast. Given that blooms initiate and develop 

in a nutrient-poor environment, the blooms often maintain 

themselves by recycling or regenerating nutrients. Factors 

such as predation, changing nutrient ratios, limited nutrient 

availability and dilution of water masses have been suggested 

as precursors to bloom termination. Relief to coastal areas also 

results from the transport of the bloom out of the area (Tester 

and Steidinger 1997, Steidinger et al. 1998). 

Historical Trends

Although long-term historical trends remain a topic of debate 

among harmful algal bloom (HAB) researchers (ICES 2007), 

a number of authoritative scientific organizations have stated 

that harmful algal blooms are getting worse around the world 

(U.S. Commission on Ocean Policy 2004, HARRNESS 

2005, FDEP 2006). Some of the factors believed to play a 

role in this worldwide trend include nutrient enrichment, or 

eutrophication, resulting from population growth and land use 

practices, and warmer water temperatures due to global climate 

change. Although the general trend appears to be worsening, 

trends for specific HABs can embody more uncertainty. This 

is particularly true for HABs that start offshore like K. brevis. 

Southwest Florida has endured red tide blooms on a near-annual 

basis over the past two decades and the 2005 bloom was one of 

the most severe on record. However, Florida red tide blooms 

of similar intensity and duration have 

been confirmed as far back as 1948-

49, and anecdotal evidence suggests 

that severe blooms have scourged the 

region for hundreds, if not thousands, 

of years. There is broad consensus that 

Florida red tides have been especially 

active in recent years but putting this 

decade into historical perspective is 

extremely difficult due to a lack of data 

suitable for exposing historical trends.

Even though red tide blooms have 

long been a fixture of the West Florida 

Shelf marine ecosystem, many people 

believe that they are getting worse 

in terms of frequency, intensity and 

duration. Such perceptions have 

been reinforced by increased media 

attention on the topic and a recently 

published article in the scientific journal Harmful Algae (Brand 

and Compton 2006). 

In the journal article, Brand and Compton argued that Florida 

red tides were substantially more abundant in the 1994-2003 

period than they were in the 1954-63 period. The authors 

also noted changes in seasonal patterns of Florida red tide 

blooms and their relative intensity inshore vs. offshore. The 

authors hypothesized that increased nutrients from terrestrial 

sources can explain these patterns. Brand and Compton 

based their conclusions on an analysis of a historical red tide 

database compiled and maintained by the Florida Fish and 

Wildlife Research Institute (FWRI). FWRI has argued that 

the database is generally unsuitable for analyzing historical 

trends because of the nature of the data and the methods by 

which they were collected prior to 1998. On other questions 

pertaining to the origins, growth and trajectory of past blooms, 

the FWRI suggests that the database can be quite helpful 

(FWRI 2007b).

Microscopic view of Karenia brevis cell

3
One of the fundamental tenets of scientific inference concerns 

the need for an unbiased sampling protocol. Bias occurs 

when samples are not representative of the broader population 

being studied. In order to infer historical trends from red tide 

data, researchers must ensure that the timing and location of 

sampling efforts do not vary in response to expectations or 

observations of red tide. Red tide researchers also must make 

every effort to ensure that variation in their measurements of 

red tide reflects actual patterns of change in red tide blooms 

rather than changes in the way they are studying those blooms. 

Consistency and reliability in sampling procedures are essential 

to these efforts. 

The majority of historical red 

tide measurement data that 

exist in the FWRI database 

consist of event response 

data — that is, data were 

gathered only after a bloom 

had already been verified in a 

particular place at a particular 

time. Systematic sampling 

protocols — those that take 

measurements at consistent 

locations and consistent 

periods of time were only 

used sporadically prior to 

1998. With the increase 

in coastal population since 

the 1950s and the advances 

in detection technologies 

(including satellite imagery) 

it is difficult to determine 

whether changes in event response data truly reflect changes 

in the nature of red tide blooms or our better ability to detect 

them. Attempting to make inferences from datasets that mix 

event response data with systematically collected data can be 

especially problematic. Finally, the variety of organizations 

collecting red tide data, the types of information collected and 

the measurement techniques used have varied considerably 

over time in Southwest Florida. This introduces additional 

concerns with respect to the consistency and reliability of the 

data compiled by FWRI. 

Can these sampling concerns be alleviated through the 

application of statistical techniques? This question is at the center 

of the debate surrounding the FWRI database. In their analysis, 

Brand and Compton employed a set of statistical techniques to 

reduce the sampling bias. Statisticians commissioned by the 

FWRI to analyze both the Brand and Compton article and the 

FWRI database have called into question the techniques used by 

Brand and Compton as well as their conclusions (FWRI 2007d). 

The MPI is not qualified to resolve this ongoing debate but given 

the accessibility of the database and transparency of the statistical 

techniques used by Brand and Compton, qualified experts will 

be able to assess the relative merits of these competing claims. 

Importantly, the FWRI position that the pre-1998 data in the 

historical database are unsuitable for determining historical trends 

implies that we will not be able to confirm for the foreseeable 

future whether or not Florida red tides are indeed worsening. 

Under such circumstances, the MPI encourages policymakers to 

operate under the assumption that Florida red tides may very 

well be getting worse.

Coastal Pollution 

and Florida Red Tide

Coastal pollution has been 

a focal point of contention 

between some scientists and 

stakeholder groups. Some 

have expressed doubts over 

the importance of terrestrial 

nutrient sources in explaining 

red tide blooms and others 

believe them to be a major 

contributing factor. In many 

cases the disagreement has 

been semantic with scientists 

equating “cause” with initiation 

and stakeholders equating 

“cause” with the appearance 

of blooms in coastal regions. 

This debate, at times quite 

tense, can evolve into a more constructive dialogue as both sides 

better understand and acknowledge the reasons for contending 

viewpoints.

K. brevis is highly adept at utilizing both organic and inorganic 

nutrients. The relative importance of different nutrient sources 

varies over the stage of a bloom and it is possible that the specific 

combination of nutrient sources that are responsible for a major 

bloom varies from year to year. Most scientists agree that red 

tide blooms initiate offshore before being transported inshore by 

wind and ocean currents. They express skepticism that terrestrial 

nutrients affect the early stages of a bloom. However, when a 

bloom moves inshore, most acknowledge that runoff can help 

maintain the life of a bloom or affect its growth. How much a 

role these sources play remains unclear. Complicating the issue 

further, coastal nutrients can be categorized as either “natural” 

— present during even pre-historic times — or anthropogenic 

— the result of human activities. Distinguishing between the 

two can be difficult in nature. 

Red tide blooms have long plagued Florida’s coastline. 

This picture shows a fish kill from the 1960s.

4
Reasons for caution with respect to linkage

For those who perceive coastal pollution to be a major 

contributing factor to the occurrence of red tide blooms, it is 

important to acknowledge that there is a substantial amount 

of research on the physiology of K. brevis cells and transport 

of red tide blooms that cautions against arguments linking 

coastal pollution to red tide. 

One of the most important features of 

K. brevis that rarely registers in public 

debates is its slow growth rate. 

K. brevis cells are remarkably 

opportunistic in using a broad range 

of nutrients. They are by no means 

picky eaters. But their slow growth rate 

provides other phytoplankton species 

better access to available nutrients 

in eutrophic, or high-nutrient, 

environments. When nutrient 

levels are lower, in oligotrophic 

environments, K. brevis is better 

suited to compete with these other 

phytoplankton species. Its niche, or 

ecological specialization, seems to 

be the use of organic nutrients and 

very low concentrations of inorganic 

nutrients (FWRI 2007c). Simply 

stated, K. brevis can survive and even 

thrive where other species cannot.

These observations provide some 

insight into an important puzzle for 

Florida red tide researchers: how 

does K. brevis come to dominate an 

ecosystem when it should be outcompeted by other species of phytoplankton that grow more 

rapidly? These insights also pose a problem for arguments 

claiming that coastal pollution causes Florida red tides. 

Inland waterways and coastal estuaries contain a number 

of phytoplankton communities that will absorb most 

nutrients found in coastal runoff. It is difficult to specify 

a plausible delivery mechanism that allows nutrients from 

runoff to bypass a gauntlet of other phytoplankton species 

and become accessible to K. brevis during its initiation and 

development away from the coastline. This makes theories 

about nutrient-enriched coastal runoff pouring into the 

Gulf and triggering red tide blooms problematic. For 

blooms that have established themselves along the coastline 

the picture is more complex. 

Before the mid-1970s, scientists believed that red tide 

blooms initiated and grew around inshore passes. However, 

after a review of historical data from blooms in the 1950s 

and 1960s, scientists concluded that red tide blooms 

originated about 10 to 50 miles offshore (18 to 74 km) 

on the mid West Florida Shelf (Steidinger et al. 1998). 

Although a few scientists have questioned whether the 

offshore initiation theory should be accepted as fact, the 

use of satellite data and more vigilant monitoring programs 

have since confirmed a number of 

offshore blooms and tracked their 

transport to inshore waters by ocean 

and wind currents. Importantly, 

red tide blooms can develop 

throughout the water column and 

what we witness — and track — at 

the surface is often an incomplete 

picture of the scale and movement 

of what is happening with a given 

bloom below the surface (Weisberg 

and He 2003; Walsh et al. 2003). 

It often appears that small red tide 

blooms move inshore, then rapidly 

increase in scope and intensity around 

inlets. This reinforces the perception 

that these blooms are being fueled 

by coastal runoff. However, blooms 

tend to concentrate along a rapid 

change in water density such as 

temperature and salinity fronts that 

mark the boundary between two 

distinct water masses. Early stages of 

blooms have been found associated 

with density gradients well offshore. 

Density gradients are also found 

around inlets and in the mouths of 

estuaries. Given what is known about the growth rates of 

K. brevis and the physical oceanography of the West Florida 

Shelf some scientists suspect that people are witnessing 

upwelling and accumulation more than expansion and 

intensification.

So what nutrient sources do scientists think account for red 

tide blooms if not coastal runoff? There have been dozens of 

theories involving suspected nutrient delivery mechanisms 

for K. brevis. Scientists stress that these mechanisms are not 

mutually exclusive. Many likely operate in concert with 

one another. Scientists also stress that no single source can 

account for all the nutrients required to sustain a major 

bloom (Vargo et al. 2007; Walsh et al. 2007). 

K. brevis cells multiply at a significantly slower 

growth rate when compared to other species of 

phytoplankton. Over a three day period one K. 

brevis cell will develop into four or five cells. Over 

the same period one cell of other phytoplankton 

species can develop into thousands of cells.

Day One

K. brevis

Day Three

K. brevis

Day One

other phytoplankton

Day Three

other phytoplankton

5
Apart from land-based nutrient sources there are a handful of 

atmospheric and oceanic sources that are receiving increased 

attention from scientists. Upwellings of deep, nutrientenriched water along the continental shelf are viewed as 

playing a potential role in the initiation of offshore blooms. 

These nutrients result from the accumulation and reprocessing 

of marine life from the water column. Robust nutrient 

reservoirs are common to most large water bodies such as 

oceans and gulfs below their thermoclines, where colder, 

saltier water mixes with warmer, fresher water. While there 

seems to be some correlation between upwelling in the Gulf 

of Mexico and a couple of red tide blooms, recent FWRI data 

suggest that these upwellings can benefit other phytoplankton 

communities as much — if not more — than they benefit 

K. brevis (C. Heil, pers. comm. March 2007; J. Lenes pers. 

comm. June 2007).

A second significant source of nutrients may be trichodesmium. 

Trichodesmium is a cyanobacteria found throughout the 

world’s oceans. Trichodesmium blooms often precede 

and/or accompany K. brevis blooms. Trichodesmium can 

provide significant nutrients to K. brevis through a process 

known as nitrogen fixing. With adequate supplies of iron, 

trichodesmium can fix nitrogen from the atmosphere and 

excrete it in a form that can be used by K. brevis, subsequently 

resulting in the growth of a red tide bloom. In recent 

decades, increased desertification in Africa and the resulting 

transoceanic dust clouds have meant more iron deposits in 

the Gulf of Mexico. The increases in iron deposits seem to 

coincide with trichodesmium blooms that are accompanied by 

red tide (Mulholland et al. 2006; Walsh el al. 2007). Notably, 

rainfall may facilitate nutrient delivery mechanisms involving 

trichodesmium in addition to increasing coastal runoff (J. 

Lenes pers. comm. June 2007).

A third significant source of nutrients is rotting fish. Since 

dead fish often drift to the bottom before floating to the top, 

a massive fish kill triggered by a bloom could conceivably lead 

to the dispersal of a large amount of nutrients throughout the 

water column. Rough estimates of the biomass of fish killed 

during a red tide bloom indicate that this source could be a 

significant contributor to the overall nutrient budget (Vargo 

et al. 2007). 

It is highly likely that the predominant nutrient source 

changes over the course of a bloom and it remains unclear 

whether a particular combination of sources is common to all 

blooms (Walsh et al. 2007). The table on page 7 attempts to 

capture some of the most important ingredients in the recipe 

for Florida red tides.

Reasons for concern with respect to linkage

For those who are quick to downplay the potential links 

between coastal pollution and red tide, it is important to 

acknowledge some concerns and observations that have been 

expressed by stakeholders and scientists. 

Regardless of the factors responsible for initiating a bloom, 

once it moves inshore, the bloom will be able to use any 

nutrients that it can access. Even if a number of important 

stages of red tide bloom development occur beyond the reach 

of coastal runoff, any contribution that pollution makes to 

the frequency, scope, intensity and/or duration of a red tide 

bloom once it arrives inshore is of consequence. If coastal 

pollution does nothing more than extend the duration of red 

tide blooms, it still remains of paramount concern because the 

duration of a given bloom is often the most significant factor 

in its overall impact on coastal communities. 

Although there is no conclusive scientific evidence linking 

specific sources of coastal pollution to Florida red tides, there 

are a number of unresolved questions that caution against 

dismissing it as inconsequential. The questions pertain to the 

amount of nutrients being discharged into watersheds and 

groundwater tables from non-point sources, the range and 

intensity of terrestrial nutrient fluxes into the Gulf of Mexico 

and the fate of dissolved organic vs. inorganic nutrients as they 

move through the ecosystem. 

In their analyses of sediment cores from Charlotte Harbor, 

Turner et al. (2006) conclude that the present nitrogen loading 

to the estuary is about three times what it was before the 

1800s. The analyses also suggest that improved water quality 

treatment facilities and land use practices resulted in stable or 

slightly lower nitrogen loading from rivers between 1980 and 

the early 1990s. It projects higher loads after 1998 because of 

continued population growth.

Estimated nitrogen loads to Tampa and Sarasota bays have been 

lowered substantially since the 1970s, although assessments 

of Southwest Florida estuaries from Venice through the Ten 

Thousand Islands paint a bleaker picture of current water 

quality conditions (Conservancy of Southwest Florida 2005; 

Charlotte Harbor National Estuary Program 2005; Sarasota 

Bay Estuary Program 2006; Tampa Bay Estuary Program 

2007). This seems consistent with the notion that the net 

changes to nutrient loads in Florida’s waterways since the 

1972 Clean Water Act vary from watershed to watershed 

with predominant composition and sources of nutrient loads 

changing over time. 

6
7

The above table highlights some of the main factors involved in the nutrient delivery mechanisms that can contribute to the initiation 

and development of Florida red tides. Each factor is depicted as an ingredient with an accompanying description of its impact. Note 

that some ingredients (trichodesmium blooms, coastal runoff) are enhanced by others (dust, rainfall). Some ingredients may be more 

or less important at different stages of a bloom and it is unlikely that red tide blooms are dependent on any single ingredient – they 

can still occur when one or more are missing. The more ingredients that are present, however, the greater the likelihood of a bloom. 

Recipe for Florida Red Tides

Ingredients Impact

Initial Factors

Upwellings Upwellings of deep, nutrient enriched water along the continental

shelf are viewed as playing a potential role in the initiation of

offshore blooms.

Saharan Dust Dust clouds from the Sahara Desert contain iron. When deposited

in the Gulf of Mexico the iron can boost trichodesmium blooms and

their production of nutrients.

Rainfall Rainfall may enhance a number of nutrient delivery mechanisms

including those that involve atmospheric deposition (see

trichodesmium discussion) and terrestrial fluxes.

Proximate Nutrient Sources

Trichodesmium Blooms Trichodesmium blooms often precede and/or accompany Florida red

tides. Trichodesmium can provide significant nutrients for red tide

blooms through a process known as nitrogen fixation.

Trichodesmium uses iron to fix nitrogen from the atmosphere and

excrete it in a form that can be used by a red tide bloom.

Grazing and Excretion Similar to the above mechanism whereby nitrogen is created as a

byproduct of Trichodesmium blooms, other species of plankton

consume one another and excrete nutrients as byproducts of their

metabolic processes.

Terrestrial (land-based) Fluxes Terrestrial fluxes can include a variety of organic and inorganic

nutrients that result from human activities as well as natural

physical processes. While a substantial portion of these nutrients

are absorbed before escaping into the Gulf, some may become

accessible to red tides.

Benthic (sea bottom) Fluxes The benthos or sea bottom serves as a significant reservoir of

nutrients. A rich variety of marine life utilizes these nutrients but it

remains unclear whether or not significant amounts can flux or

escape into the water column in a manner that allows Karenia brevis

to access them.

Self-Sustaining Mechanisms

Regenerated Nutrients K. brevis, in association with bacteria, may be particularly adept at

regenerating nutrients from metabolic byproducts as well as the

nutrients that are released when cells die. While this should not

contribute to bloom growth it may allow red tide blooms to

maintain themselves until more nutrients become available.

Dead Fish Dead fish can disperse a large amount of nutrients throughout the

water column. As red tides become larger and more intense they

begin to kill more fish. The fish kills result in the release of

additional nutrients that can intensify the bloom.
Statewide, substantial improvements have been made 

with respect to controlling point source pollution over the 

past 30 years, but non-point source pollution appears to 

have steadily increased over this time. Increased levels of 

nutrients and decreased levels of dissolved oxygen continue 

to persist in many of Florida’s waterways (FDEP 2006). 

The relationship among changing patterns of land use, 

associated nutrient loads and their impacts on macroalgal 

and phytoplankton communities is complex. Some changes 

to coastal algal communities reflect less coastal pollution, 

while some reflect more. One study links the reduction of 

nutrient loads from point source pollution to lower total 

phytoplankton densities and to a declining dominance 

of a single opportunistic species in the Tampa Bay area 

(Johansson and Lewis, 1992). Another study links increases 

in macroalgal populations in the coastal waters of Lee County 

to terrestrial fluxes that are believed to be associated with 

non-point sources (Lapointe and Bedford 2006). Another 

study links changes in background nutrient ratios to both 

land use practices and algal communities across a long stretch 

of coastline in Southwest Florida (Heil et al. 2007). Given 

these findings it seems plausible that land use activities could 

affect nutrient conditions in a manner that renders particular 

coastal regions vulnerable to takeover by an incoming red tide 

bloom. And once blooms arrive inshore, terrestrial nutrient 

fluxes can contribute to them. 

A number of potential relationships between terrestrial 

nutrient fluxes and Florida red tides have been examined 

or hypothesized. One study does provide evidence of 

a correlation between rainfall, river flow and red tide 

duration (Dixon 2003) and additional anecdotal data on 

specific blooms are suggestive (L. Brand, unpublished data). 

Rainfall and river flow should increase terrestrial runoff, 

which can send pulses of a variety of organic and inorganic 

nutrients downstream. While a substantial portion of 

these nutrients will be absorbed by other phytoplankton 

communities before reaching a red tide bloom, some could 

become accessible to red tides. 

Other arguments propose indirect mechanisms linking 

coastal pollution and red tide through groundwater releases. 

Hu et al. (2006) argue that Florida’s active 2004 hurricane 

season could have triggered pulses of groundwater release in 

offshore springs that provided substantial nutrients to the 

2005 red tide bloom. There has also been speculation about 

the potential for polluted groundwater releases closer to the 

shoreline and their potential impact on blooms (Lapointe 

and Bedford 2006; Paytan 2006). Additional speculation 

exists regarding the potential for terrestrial nutrient fluxes 

to be stored in benthic sediments in a manner that can 

be accessed by K. brevis (Brand and Compton 2006; L. 

Brand, pers. comm. June 2007). More research needs to 

be conducted before these hypothesized nutrient delivery 

mechanisms can be ruled out as significant contributors to 

the overall nutrient budget.

A final area of concern involves the relative importance of 

dissolved organic nutrients for K. brevis. As noted earlier, 

recent research suggests that K. brevis is adept in using 

dissolved organic nutrients (Bronk et al. 2004; Bronk et 

al. 2006). Urea, in particular, is readily metabolized by 

K. brevis. In recent decades, the composition of many 

fertilizers has shifted toward higher urea content. Scientists 

have suggested that this shift may be linked to increased 

coastal eutrophication and higher incidences of certain 

types of algal blooms (Anderson et al. 2002; Glibert et al. 

2006). Urea concentrations have not been monitored with 

any regularity in the coastal waters of Southwest Florida 

until recently and this has alarmed some stakeholders who 

point to the potential impacts of fertilizers (Zollo 2006).

Moving Forward

The amount of data collected on red tides and associated 

environmental conditions has increased substantially over 

the past few years to the point where data collection has 

outpaced data analysis. A rigorous analysis of recently 

collected data can be expected in the next couple of years 

along with a renewed emphasis on nutrient dynamics in 

conjunction with a new $4.7 million grant from NOAA to 

address nutrient questions (NOAA 2006). 

There are three approaches that the red tide research 

community might consider in helping to resolve unanswered 

questions relating to nutrient dynamics: 

• Sharpen the focus on nutrient uptake during the 

course of a bloom. 

This approach would imply an expansion of efforts 

to track and monitor red tide blooms and an 

accompanying intensification of event sampling efforts 

in terms of their spatial and temporal coverage. This 

approach could prove especially helpful to isotopic 

tracing efforts. Isotopic tracing is a technique used 

to trace chemical compounds from different sources. 

It has recently provided some clues to the nutrient 

sources used by K. brevis (Havens 2004; Lapointe and 

Bedford 2006). The technique’s utility is hampered, 

however, when a mobile organism quickly utilizes its 

available nutrients and where more than two sources 

8
are potential contributors of nutrients. Both conditions 

appear to be present in the case of K. brevis but both 

can be accommodated - to a certain degree - by more 

frequent sampling over a longer period of a bloom’s life 

cycle (C. Heil, pers. comm. June 2007). 

• Sharpen the focus on specific areas where nutrient 

terrestrial fluxes and K. brevis are suspected to interact. 

Studies that target estuaries, inlets and shoreline coastal 

areas may yield insights on terrestrial nutrient fluxes 

that have escaped detection in laboratory analyses and 

theoretical discussion. An intense focus on these areas 

would also allow for long-term studies of red tide’s 

impact on particular marine species and ecosystem 

habitats.

• Sharpen the focus on different sources of coastal pollution 

in an effort to more accurately assess their magnitude, 

disposition and impacts on coastal ecosystems.

While many forms of coastal pollution have been 

reduced over the past few decades, non point source 

pollution has increased. Net changes to nutrient loads 

vary from waterway to waterway. Importantly, we do 

not monitor the vast majority of non point sources of 

pollution as much as we estimate them (FDEP 2006). If 

we are underestimating non point source pollution and 

associated nutrient loads and these loads are affecting 

our coastal environment in subtle but important ways 

then it follows that coastal pollution could be directly 

or indirectly affecting patterns of red tide. 

In sum, much of what we know about Florida red tide 

casts doubt on the notion that coastal pollution can trigger 

the initiation or development of red tide blooms offshore. 

This does not mean that terrestrial nutrient sources are 

unrelated to red tide blooms. Once blooms arrive inshore, 

there are a number of reasons to suspect that coastal 

pollution can exacerbate them, as has been observed for 

other phytoplankton and macroalgal species. Resolving 

the slow growth rate of K. brevis with its apparent ability 

to dominate a phytoplankton community remains a key 

research puzzle. Vigorously testing a variety of terrestrial 

nutrient hypotheses will be necessary to confirm or refute 

them and dispel lingering suspicions and uncertainties. 

9
Consequences: Impacts to Marine Life 

and Human Health 

Karenia brevis, the organism responsible for Florida red tide 

blooms, produces a powerful collection of neurotoxins called 

brevetoxins. The release of these brevetoxins during a bloom 

can have substantial impacts on marine life that include 

massive fish kills and significant mortality events for birds and 

marine mammals. Large fish kills can occasionally generate 

hypoxic, or oxygen deficient, zones that amplify the impacts 

on a broader spectrum of marine life (FWRI 2007, NOAA 

2006). The extent to which red tides affect populations of 

ecologically and economically important fisheries over time 

and space is poorly known. Human 

health impacts usually take the form of 

neurotoxic shellfish poisoning (NSP) 

and respiratory irritation. Adverse 

impacts might also result from longterm exposure to brevetoxins but 

research on the chronic effects of 

Florida red tide is in its infancy.

Brevetoxins

More than 30 years of research on the 

toxicity of K. brevis has resulted in an 

increasingly complex picture (Fleming 

et al. 2005; Baden et al. 2005). Until 

1981, only one specific brevetoxin had 

been identified and scientists thought 

the lethality of a given red tide bloom 

was directly related to its cell and toxin 

concentrations. Since then, a number 

of additional brevetoxins produced 

by K. brevis have been identified and 

characterized. 

Brevetoxins typically affect organisms by opening up the sodium 

channels of nerve cell membranes and causing the nerve cells 

to depolarize. This leads to disruptions of muscle function and 

subsequent respiratory and cardiac distress. Different brevetoxins 

and their derivatives can vary in their potency, especially when 

they are modified in a laboratory setting or metabolized by other 

species in nature. Certain structural features of these derivatives 

appear to have distinct physiological consequences on neuronal, 

pulmonary and enzymatic regulatory systems of organisms 

(Baden et al. 2005). Scientists also recently discovered that K. 

brevis produces brevenal, a natural antagonist that counteracts 

the effects of the brevetoxin. 

It is not known whether the specific combinations of different 

brevetoxins and the balance between brevetoxins and brevenal 

in a specific K. brevis cell reflect different stages of the cell’s life 

cycle, environmental conditions or both. 

The important point is that the toxicity of a given K. brevis

cell can vary, as can the amount and combination of toxins it 

releases in its environment. Once released, the potential effects 

of the brevetoxins can evolve as marine life metabolizes them.

Impacts to Marine Life

Marine life is exposed to brevetoxins by eating them, breathing 

them or touching them. The toxins 

can also pass through cell membranes, 

including the blood-brain barrier and 

skin tissue (Kemppainen et al. 1991; 

Apland et al. 1993). Different forms 

of marine life vary in their reaction to 

the toxins.

Fish kills are both an early warning sign 

for humans and a sad hallmark of red 

tide blooms. Fish kills of up to 100 

tons of fish per day have been estimated 

during active red tides. Fish are exposed 

to brevetoxins by swimming through 

blooms and ingesting forms of marine 

life that have become contaminated with 

toxins. They are thought to be killed 

through lack of muscle coordination and 

paralysis, convulsions and respiratory 

failure (Kirkpatrick et al. 2004). 

Little research has been conducted on 

the effects that red tide has on specific 

fish communities. Smith (1975; 1979) 

documented the decimation and subsequent re-colonization 

of an offshore reef fish community in the Gulf of Mexico 

following a single red tide event in 1971. This event appeared 

to have caused a hypoxic “dead zone” offshore of Tampa Bay 

and Sarasota and Manatee counties, similar to the dead zone 

that occurred during the summer of 2005. Smith estimated 

that 80-90% of the reef fishes were killed by the red tide and 

that all the species that disappeared from the reefs re-colonized 

the area within a year. However, Smith believed that several 

years may be required to re-establish the community to its 

former structure in terms of relative abundance of each species. 

Because Smith’s work was narrowly focused and targeted only 

one reef fish community and a single red tide event, much 

remains to be learned about the ecological effects of red tide on 

economically and ecologically important fisheries. 

The two pictures shown above are of a patient’s lungs 

before and after a brevenal treatment. The picture on 

the right reveals more yellow, orange and red areas.

These areas reflect better lung function than the 

corresponding white areas in the picture on the left. 

Brevenal is natural antagonist to brevetoxins produced 

by K. brevis cells. It was discovered in 2004 and is 

being evaluated as a possible treatment for cystic 

fibrosis, a debilitating lung disorder.

10

©William Abraham at Mount Sinai Miami Beach
Fish mortality often results from acute exposure but many 

species appear to withstand lower levels of exposure over time 

and accumulate toxins in their organs. Until recently, it was 

unclear whether lower trophic species could accumulate and 

transfer brevetoxins to higher trophic species but a number 

of mortality events involving manatees and dolphins have 

confirmed that this can happen. There are, in fact, a 

variety of potential vectors through which brevetoxins can 

work their way through the food web. Acute and chronic 

mortality events are both possible, and significant time lags 

have been known to occur between the presence of a red 

tide bloom and a mortality event later linked to a bloom.

Red tide events have been implicated 

in manatee deaths dating back to 

1962 (Steidinger et al. 1998). The 

most severe episode occurred in 1996 

when 149 manatees were killed by 

brevetoxin exposure. There was no 

significant lag time that year between 

the dissipation of the red tide and 

the last manatee death. Subsequent 

lung pathologies revealed that the 

brevetoxins were inhaled (Bossart 

et al. 1998). The respiratory tract, 

liver, kidneys and brains of the 

manatees were primary targets of 

the brevetoxins and the effects were 

thought to be chronic rather than 

acute (Kirkpatrick et al. 2004). 

During a 1982 event there was a 

lag of approximately three weeks 

between the dilution of K. brevis 

cell concentrations below levels that 

should be lethal to manatees and 

the last manatee death. Necropsies 

revealed tunicates (a filter-feeding 

organism that can accumulate toxins) 

in the manatee stomachs (O’Shea 

et al. 1991). A 2002 red tide event 

killed 34 manatees and necropsies 

suggested that brevetoxin adhering to 

the surface of seagrass that was eaten 

by the manatees was the likely vector. 

In 2004, 107 bottlenose dolphin deaths were reported 

weeks after a red tide dissipated. A subsequent investigation 

linked the dolphin mortality event to menhaden (a plankton 

eating fish) that had accumulated brevetoxins in their organs 

(Flewelling et al. 2005). Toxic seagrass was again thought to 

be the primary culprit in the most recent manatee mortality 

event that also saw another lag between the dissipation of 

red tide and 27 manatee deaths (Spinner 2007). Considered 

together, these mortality deaths reveal a number of potential 

pathways for brevetoxins to work their way through a food 

web over the period of a month.

Impacts to Human Health

Humans can be exposed to brevetoxins through ingestion 

of contaminated seafood. Brevetoxins are tasteless, odorless 

and heat and acid stable. They cannot be easily detected nor 

removed by food preparation procedures (Baden et al 1997; 

Kirkpatrick 2004). To date, shellfish are the primary vector, or 

pathway, for human brevetoxin exposure. Shellfish reported to 

be associated with neurotoxic shellfish 

poisoning (NSP) when contaminated 

with brevetoxins include oysters, 

clams, scallops and other filter feeders. 

Thankfully, NSP is considered one 

of the milder forms of paralytic 

shellfish poisoning with no known 

fatalities. Typical NSP symptoms 

include gastrointestinal symptoms 

(nausea, diarrhea, and abdominal 

pain) accompanied by occasional 

neurological symptoms (headache, 

vertigo, incoordination). In severe 

cases respiratory failure has been 

reported (Kirkpatrick et al. 2004). 

Importantly, there have been no 

reported cases of NSP in Florida 

resulting from ingestion of 

commercially harvested shellfish. The 

Florida Department of Agriculture 

and Consumer Services maintains a 

very cautious protocol with respect to 

closing shellfish fisheries and allowing 

shellfish products on the market. 

To date, all known cases of NSP that 

have been linked to the brevetoxins 

from a red tide bloom have involved 

illegal recreational harvesting activity. 

There have not been any reported cases 

of brevetoxin exposure in humans that 

resulted from ingestion of finfish species. However, the 2004 

dolphin mortality event discussed above suggests that some 

fish species can accumulate brevetoxins in their abdominal 

organs. Accordingly, recreational fishers should only eat the 

fillets of fish caught in the vicinity of a red tide bloom and 

avoid eating any fish that appears to behave unnaturally. 

Filter feeding shellfish (clams, oysters and mussels) 

concentrate the brevetoxins and can cause neurotoxic 

shellfish poisoning (NSP) in humans. Florida’s 

Department of Agriculture and Consumer Services 

has a very conservative safety protocol that closes 

shellfish harvesting areas when red tide cell counts 

exceed 5,000 cells per liter (fish mortalities are rare 

below 100,000 cells per liter). A shellfish harvesting 

area is not reopened until cell counts drop below 5,000 

K. brevis cells per liter and bioassay tests confirm the 

shellfish are not toxic. This can take an additional two 

to six weeks after red tide is gone from a harvest area.

To date, there have been no reported cases of NSP 

attributed to commercially produced shellfish in the 

presence of a red tide bloom (FDACS 2002).

11
Humans can also be exposed to brevetoxins through 

inhalation. K. brevis cells are fragile organisms that 

are easily broken open by wave action along the beach. 

When this happens, the brevetoxins are released and 

can become aerosolized. When a red tide bloom is near 

the shoreline, the aerosol of contaminated sea spray will 

contain toxins that can be carried inland with the prevailing 

winds. Studies to date show the toxins can travel at least 

a mile (1.6 km) inland from the shore, and the distance 

is highly variable and dependent upon environmental 

conditions, such as wind speed and direction (Kirkpatrick 

et al. in prep). Inhalation of aerosolized brevetoxins causes 

respiratory irritation, bronchial constriction, coughing and 

a burning sensation in the 

eyes, nose and throat. Less 

frequent reported symptoms 

include pulmonary distress, 

dizziness, tunnel vision and 

skin rashes (Kirkpatrick et 

al. 2004). In animal models, 

many of the respiratory 

symptoms are greatly 

reduced by administering 

common medicines like 

antihistamines, inhaled 

steroids, bronchodilators 

or anticholinergics before 

exposure. Bronchodilators 

will reverse most respiratory 

symptoms after exposure 

(Abraham et al. 2005). 

Asthmatics and other 

segments of the population 

with chronic respiratory 

ailments are especially 

sensitive to brevetoxins. 

A series of studies have 

shown that when people 

with chronic respiratory 

problems are exposed to red 

tide blooms, a greater proportion demonstrate symptoms 

than those without chronic respiratory ailments (Singer et 

al. 1998; Abraham and Baden 2001; Fleming et al. 2005, 

Fleming et al, 2007). The most severe symptoms appear to 

occur in those with the most serious underlying respiratory 

ailments (Fleming et al. 2005; Fleming et al. 2007). 

Symptoms also tend to persist longer in these populations 

than in persons without any underlying respiratory 

conditions (Kirkpatrick et al. 2007). 

Whether inhalation can result in additional neurological 

or immunological problems is one of the focal points of 

future research on the health effects of red tide. Laboratory 

studies of manatees and other animals suggest that these are 

possibilities, particularly if exposure to red tide is chronic 

(Benson et al. 1999; Fleming et al. 2001). A recent study 

of emergency room visits to a Sarasota hospital during the 

months of September through December in 2001 and 2002 

is noteworthy. A large red tide bloom affected the area during 

Fall 2001 but not 2002. Although the overall number of 

emergency room visits did not significantly change from one 

year to the other, there were some suggestive findings. When 

separated by ZIP code, coastal residents had a 54% increase 

in emergency room visits 

during the red tide year with 

31%, 44%, 56% and 64% 

increases in pneumonia, 

asthma, bronchitis and upper 

airway disease, respectively 

(Kirkpatrick et al. 2006). 

Although the study’s 

findings are limited by its 

short duration and lack of 

data on a number of factors 

that could contribute to the 

observed variation, it will 

compel researchers to further 

investigate the potential for 

chronic impacts.

Scientists from Mote Marine Laboratory perform human health studies 

to determine the effects of red tide on the human population.

12
Consequences: Economic Impacts

Florida red tides impose significant economic costs in localized 

areas but the cumulative impacts for an entire coastal region 

affected by a bloom are difficult to calculate. Estimates 

of economic impacts are highly inconsistent and heavily 

dependent upon the assumptions of the analyst. Given the 

likelihood of displaced economic activity, economists need to 

better understand how consumers respond to red tide events 

before they can provide accurate impact assessments. Better 

data on tourist and recreational activity in the presence of red 

tide events will be critical for these assessments.

Variation in Estimates

Based upon a subset of HAB outbreaks from 1987-2000, 

Hoagland and Scatasta (2006) offer an estimate of $82 

million for the total economic costs of all HABs that affect 

the entire United States. The Hoagland and Scatasta study 

uses the same methodology as Hoagland et al. (2002) and 

Anderson et al. (2000) which had previously estimated 

average annual economic losses between 1987 and 1992 at 

$50 million. With respect to the most recent figure of $82 

million, the authors estimate that recreation and tourism 

impacts amount to an average of $4 million year. Compare 

this with an estimate by the public relations director of the 

St. Petersburg/Clearwater Visitors and Area Convention 

Bureau of $240 million in potential losses for the Tampa 

region from the 2005 Florida red tide bloom (Moore 2006; 

NOAA 2007). 

So, one economic assessment suggests that the sum total 

of all economic impacts to the tourism sector across 

the country averages around $4 million a year, while 

another claim estimates the economic impacts to be $240 

million in a single metropolitan area. The reason for the 

remarkable variation lies in the different assumptions and 

methodologies employed in different instances. The authors 

of the nationwide studies adopted a conservative set of 

assumptions and focused on a wide range of data sources 

while the estimate from the St. Petersburg/Clearwater 

Visitors and Area Convention Bureau results from a simple 

extrapolation.

Part of the difficulty with calculating economic impacts results 

from the fact that much of the economic activity affected by 

a red tide bloom is displaced rather than lost. A family that 

refrains from eating at a waterfront restaurant when a bloom 

is active may instead eat at another restaurant further inland. 

The waterfront restaurant loses some revenue as a result of 

this decision but the inland restaurant gains a comparable 

amount. The net impact on the broader community of 

which the family is a part is probably negligible. If a family 

changes their vacation plans as a result of a red tide bloom, 

traveling to Orlando instead of Tampa, then Tampa loses 

revenue but not the state of Florida. If a family chooses to 

travel to California instead of Florida because of red tide, 

then the state of Florida loses revenue but not the country 

as a whole. The counterintuitive result is that the broader 

the regional scope of analysis, the less significant some types 

of economic impacts may appear. Generally speaking, the 

diversified nature of the U.S. economy mitigates many of 

types of adverse economic impacts from natural hazards.

With the $240 million estimate cited by the St. Petersburg/

Clearwater Visitors and Area Convention Bureau, the public 

relations director noted that Fort DeSoto beach visitors had 

increased 6% in 2005 before a red tide bloom began affecting 

the area. At the end of the year beach visits were only up 2% 

for the year. Inferring that the red tide bloom resulted in a 

4% reduction in beach visitors, the director projected a 4% 

loss onto the entire metropolitan tourist industry – $6 billion 

in annual revenues – to arrive at the $240 million figure 

(Moore 2006). Given the nature of displaced economic 

activity, this type of extrapolation can be misleading.

National Estimates of Harmful Algal Bloom Impacts

Anderson et al. (2000; see also Hoagland et al. 2002) define 

economic impacts “to mean lost gross revenues in the relevant 

product or factor markets, expenditures for environmental 

monitoring and management or other costs that would not 

have been incurred in the absence of HABs.” They focused on 

four types of costs: 1) public health; 2) commercial fisheries; 3) 

recreation and tourism and 4) monitoring and management 

costs. The authors based their analysis on a survey of experts 

from different coastal states and a literature review. Some 

additional data sources were consulted when possible. Public 

health costs accounted for the largest portion of nationwide HAB 

impacts (45%), followed by commercial fisheries losses (37%). 

Recreation/tourism losses (14%) and monitoring and mitigation 

costs (4%) accounted for the smallest portions. These figures 

did not include economic multiplier effects, which attempt to 

account for a ripple effect that occurs when economic losses in 

one segment of the economy affect the level of activity in others. 

Ripple effects are highly sensitive to local market structure and the 

authors of the national estimates decided to forgo using a single 

economic multiplier and/or calculating separate multipliers for 

each localized HAB event (Anderson et al. 2000).

The national HAB study authors highlight the fact that their 

estimates are conservative and they discuss a number of data 

and methodological challenges. Valid, reliable data that could 

be compared across cases were difficult to obtain. Few states 

13
have conducted economic assessments of HAB impacts or 

collected data that could be used to generate reliable estimates. 

Where data were available, extrapolations were often made to 

compensate for incomplete or underreported measurements. 

For instance, the authors used a rule of thumb of multiplying 

the number of reported shellfish poisoning cases by ten to 

account for the significant underreporting of cases (Hoagland 

et al. 2002). With respect to commercial fisheries, the authors 

expressed their desire to obtain measures of lost consumer and 

producer surpluses in relevant markets due to shifts in supply 

and demand curves. Most HAB impact studies instead measure 

and report changes in the gross value of sales, which often fail to 

accurately reflect welfare changes. Anderson et al. (2000) and 

Hoagland et al. (2002) also discuss 

the relevance of the “malleability” 

of capital and labor or the costs of 

switching these factors to their next 

best alternative activity. The less 

malleable productive factors are the 

less capable a given economy will be 

in mitigating the economic losses 

that result from a red tide bloom.

Estimates of Florida 

Red Tide Impacts

While the national HAB 

assessments provide a useful 

template for analyzing the 

economic impacts of a variety 

of HABs, the economic losses 

associated with Florida red tides 

are likely to manifest differently 

from those in other regions. 

Public health costs, which account 

for the largest share of impacts in 

the national assessment, are closely 

tied to shellfish poisonings. Cases 

of neurotoxic shellfish poisoning 

(NSP) from Florida red tide are 

rarer, sporadic and less severe than 

other forms of shellfish poisonings around the country. Public 

health costs therefore represent a much smaller portion of 

economic costs associated with red tide blooms in assessments 

done to date. If stronger evidence were to link red tide exposure 

to chronic respiratory and/or immune system problems, then 

estimates of public health costs would increase substantially.

Commercial fishery losses associated with K. brevis can be 

significant but are usually localized. Martin (1987) estimates 

that a 1986 K. brevis bloom along the coast of Texas caused 

the loss of $2 million in oyster production (Martin factored 

in a multiplier in estimating the total economic impacts to 

be near $6 million). During the 2002-03 HAB season, the 

Florida shellfish aquaculture and oyster industries lost $6 

million in dockside sales and up to 20% of planted clams 

(NOAA 2004).

Only a couple of estimates of cleanup costs have been 

provided in the literature. Habas and Gilbert (1975) 

estimated the cleanup costs for an extreme 1971 event to 

be approximately $800,000. Hoagland et al. (2002) cite a 

personal communication with Sarasota County officials stating 

that cleanup costs for the county average around $63,000 per 

year. The authors use this citation as a basis for estimating 

an annual average of $170,000 in 

cumulative costs across all Florida 

counties during a red tide bloom. 

Monitoring costs in Southwest 

Florida are difficult to precisely 

calculate because monitoring 

activity is funded as part of an 

overall research agenda. Red 

tide research funding has been 

inconsistent until the turn of the 

century. For the past five years, it 

has averaged more than $1 million 

per year (Heil 2007). 

Unlike some of the other regions of 

the U.S. that have been subjected to 

HABs, Florida’s greatest economic 

concern lies with its tourism and 

recreational sectors. Florida’s 

coastal economies generated 

$402 billion in 2003, or 77% of 

the state’s total economy (Kildow 

2006). Tourism generated $63 

billion in 2005, with $8.3 billion 

generated in the recreational 

fishing sector alone (Hauserman 

2006). Nationwide, Florida ranks 

No. 1 among destinations for Americans who swim, fish, dive 

and otherwise enjoy the state’s many beaches, coastal wetlands 

and shores. We should thus expect that Florida’s economic 

vulnerability to impacts in the tourism and recreational sectors 

to be higher than that of other regions. The $240 million 

estimate of Tampa area losses from the 2005 red tide event 

may be excessive, but the conservative averages in the national 

HAB assessments are likely too low.

There have only been a few studies focused on recreation and 

tourism impacts from Florida red tide. Habas and Gilbert 

Florida’s economy relies more heavily on its tourism and 

recreation sectors than other areas of the United States that are 

affected by harmful algal blooms. The economic losses associated 

with Florida red tides can climb into the millions of dollars and 

have an especially significant impact on beach communities.

14
(1975) estimated the economic damage to the Southwest 

Florida tourism industry from a 1971 red tide bloom to be 

approximately $20 million ($95 million in 2006 dollars), 

with the most significant effects occurring in the hotel, 

restaurant, amusement and retail sectors. Although outside 

of Florida, Tester et al. (1988) estimated the recreation and 

tourism effects from a 1987 K. brevis bloom to be $29 million 

across four coastal counties in 

North Carolina (the bloom was 

transported to the East Coast by 

the Gulf Stream). Hoagland et 

al. (2002) suggest that some of 

these losses were likely offset by 

positive effects in other counties 

as tourists redirected their 

vacation activity elsewhere. 

Adams et al. (2000) used a 

time series analysis to measure 

recreational and tourism impacts 

to Sarasota and Manatee counties 

from recent red tide blooms. 

The study showed a negative 

impact on beach attendance 

but no statistically significant 

economic impacts to the business 

community. The authors once 

again speculated that this could 

have been due to displacement of 

economic activity to other areas 

of the county. In a subsequent 

study (Larkin and Adams 2006), 

the authors employ a similar 

method to look at the impacts 

of red tide on business activity in 

two smaller ZIP code areas (Fort Walton Beach and Destin). 

With a more localized scope, the authors were able to find 

evidence of a 29% to 35% decline in average monthly 

revenues for restaurant and lodging businesses during months 

of red tide incidence. These losses amounted to $2.8 million 

to $3.7 million a month – significant sums for the waterfront 

business community.

Another potential impact for waterfront businesses and 

residential communities lies in property values. Anderson 

et al. (2000) opted against including property values as 

a type of economic impact in their national study due to 

the difficulty of calculating these impacts. Waterfront real 

estate values can be affected by a variety of factors and 

attributing variation in these values to red tide blooms can 

be problematic. But the possibility remains that an intense 

bloom and/or recurring blooms could depress the demand 

for real estate and adversely impact property values over both 

the short and long term. Local government revenues derived 

from property taxes could also be affected.

An important observation from the above discussion is the need 

for better understanding market behavior before, during, and after 

the presence of a red tide bloom. Adams et al. (2002) provided 

some preliminary insights along 

these lines through a telephone 

survey of 1,006 individuals living 

in Manatee and Sarasota Counties. 

The survey collected demographic 

data, gauged public awareness and 

knowledge of Florida red tide and 

asked questions about the effects of 

red tide on behavior. The results 

suggested that recreational activities 

were significantly affected, but 

in different ways. Fishing, beach 

and water activities were the most 

heavily affected activities and more 

likely to be postponed rather than 

redirected. Restaurant, lodging 

and other forms of retail patronage 

were less affected. Restaurant 

patronage was redirected more 

often than it was delayed but the 

other forms of patronage were 

more often postponed. The results 

suggest that a significant portion 

of recreational and tourist activity 

may be redirected but a significant 

portion might also be postponed 

indefinitely or lost. 

15

The above photo shows residential homes on North Manasota 

Key along Lemon Bay. The substantial property values along 

Southwest Florida’s coastline are linked to the natural beauty 

of the area. Recurring red tides are a potential threat to these 

property values.

©Lucy Keith, Wildlife Trust
Management Strategies 

A NOAA Research Plan for Prevention, Control and 

Mitigation of HABs (NOAA 2001; Boesch et al. 1997) 

subdivides HAB management options into three types of 

activities: prevention, control and mitigation. Preventive 

measures attempt to stop blooms from occurring, minimize 

their incidence or limit their extent. Control measures focus 

on limiting impacts by killing or neutralizing the toxicity of 

the causative organisms and/or removing the organisms and 

their toxins from the water column. Mitigation measures 

seek to limit the impact of the blooms without dealing 

directly with the causative organisms themselves. 

The HAB management terminology might be confusing to 

those familiar with the mitigation vs. adaptation debate in 

the context of climate change. In climate change discourse, 

mitigation strategies denote actions aimed at reducing the 

extent of climate change, typically pollution control in 

the form of reduced carbon emissions, while adaptation 

strategies denote actions to minimize the impacts of climate 

change (IPCC 2007). HAB prevention measures are thus 

analogous to climate change mitigation strategies and 

HAB mitigation measures are analogous to climate change 

adaptation strategies. There is no conceptual counterpart 

to HAB control measures on the issue of climate change. 

To limit the potential confusion, this section will refer to 

alternative HAB management options by directly referring 

to the type of activities they involve with the operative HAB 

management terminology in parentheses.

The key point made in this section is the importance of 

combining all three types of activities into a comprehensive 

response strategy. A limited strategy that focuses on only 

one type of management activity will be insufficient given 

the complex nutrient dynamics that shape the lifecycle 

of Florida red tides and the limitations of the current 

generation of control technologies.

Prevention: Measures to Reduce the Incidence 

or Extent of Red Tides

Exercising Precaution

There is some skepticism regarding prevention strategies 

for Florida red tides given their long history, their offshore 

origins and the uncertainty regarding the nutrient delivery 

mechanisms that sustain them. Some may view the notion 

of prevention measures as futile. They may note that 

Florida red tides have encroached upon Florida long before 

it was populated and suggest that they will likely continue 

to do so long into the future. If anthropogenic inputs 

are assumed to be unrelated to the frequency, intensity or 

duration of red tide blooms then one might conclude that 

little can be done in terms of prevention. Even if a less 

rigid posture is adopted toward the potential links between 

anthropogenic factors and red tide, some may still resist a 

strategy incorporating preventive measures on account of 

uncertainty. This logic suggests that such measures only be 

considered after clear linkages have been confirmed. 

The logic suggesting that preventive measures should be 

resisted on account of uncertainty is inconsistent with the 

precautionary principle. As noted earlier, there are reasons 

to suspect that coastal runoff can exacerbate Florida red 

tides. More importantly, some of the measures suggested 

by prevention advocates have important ecological benefits 

apart from any connection to Florida red tide. Lowering 

the amount of nutrients that are discharged into Florida’s 

watersheds is a top priority for prevention advocates that 

engage in red tide debates. Reduced nutrient loads will 

improve water quality throughout watersheds, in addition 

to lowering the intensity of terrestrial fluxes when a red tide 

is in close proximity to the coastline. 

Reduced loads may or may not lead to a discernible change 

in red tide patterns but they will certainly improve the 

health of Florida’s watersheds.

An important issue that prevention advocates need to 

consider, however, is the modalities of reducing nutrient 

loads and the most appropriate venues for affecting change. 

The major sources of water quality impairment in Florida 

include domestic and industrial wastewater, urban and 

suburban stormwater, agricultural runoff and hydrological 

changes. Water quality problems in Florida were historically 

associated with domestic and industrial point sources but 

stricter regulatory controls and new wastewater treatment 

technologies have substantially reduced pollution from these 

sources. Non point sources now account for most of the 

water quality problems in the state with urban stormwater 

and agricultural runoff being the primary concerns. And 

unlike point source discharges, non point sources are 

difficult to measure, monitor and control. 

Reducing Non Point Source Pollution

The methods of regulating non point sources typically 

revolve around certification and permitting of best 

management practices and associated technologies, along 

with periodic monitoring of water bodies. This departs 

from the direct measurement and continuous monitoring 

of discharges that are subject to point source regulations. 

Permitting for stormwater pollution is conducted through 

16
6

As noted, the sequence illustrated below generally will take five years and will be repeated 

continuously to refine what is known about the basin and evaluate success in restoring impaired 

waters.

DEP

District

Group 1 

Basins

Group 2 

Basins

Group 3 

Basins

Group 4 

Basins

Group 5 

Basins

NW 

OchlockoneeSt. Marks Apalachicola-Chipola 

ChoctawhatcheeSt.Andrews Bay Pensacola Bay Perdido Bay 

NE Suwannee Lower St. Johns 

N/A

Nassau-St. Marys Upper East Coast 

Central Ocklawaha Middle St. Johns Upper St. Johns Kissimmee Indian River Lagoon 

SW Tampa Bay Tampa Bay Tributaries 

Sarasota Bay-PeaceMyakka Withlacoochee Springs Coast 

S

Everglades West 

Coast Charlotte Harbor Caloosahatchee Fisheating Creek Florida Keys 

SE Lake Okeechobee St.Lucie-Loxahatchee 

Lake Worth LagoonPalm Beach Coast 

Southeast Coast 

Biscayne Bay Everglades

This map of Florida illustrates the 29 basin management areas that fall within Florida’s six water management districts. The 29 areas are also 

divided into five groups, represented by different colors that coincide with a rotating schedule of assessment and impairment designation, the 

assignment of Total Maximum Daily Loads (TMDLs), and the formulation and implementation of Basin Management Action Plans (BMAP)s.

17
the U.S. Environmental Protection Agency’s (EPA) 

National Pollution Discharge Elimination System (NPDES) 

stormwater permit program. The program has consisted of 

two phases. Phase I, initiated in 1990, addresses large and 

medium municipal storm systems along with a number of 

categories of industrial activity. Phase II, initiated in 1999, 

addresses additional sources, including municipal systems 

not regulated under Phase I and small construction activity 

disturbing between one and 5 acres (FDEP 2007). 

In October 2000, EPA authorized the Florida Department of 

Environmental Protection (FDEP) to implement the NPDES 

stormwater permitting program in the State of Florida in all 

areas except Indian Country lands. As the Pollution Discharge 

stormwater permitting authority, FDEP is responsible for 

promulgating rules and issuing permits, managing and 

reviewing permit applications, and performing compliance 

and enforcement activities. Florida also has separate 

stormwater/environmental resource permitting programs and 

local stormwater/water quality programs, which have their 

own regulations and permitting requirements (FDEP 2007).

A comprehensive effort is also under way to bring Florida 

into compliance with the Clean Water Act’s Total Maximum 

Daily Load (TMDL) provisions. In 1998, several Florida 

environmental groups filed a lawsuit against the U.S. 

Environmental Protection Agency (EPA) for its failure to 

enforce the provisions in the Clean Water Act. Total Maximum 

Daily Loads are the amount of each pollutant a water body can 

receive without violating water quality standards. Because of 

the lawsuit, a Consent Decree was issued in 1999 that required 

the EPA and the FDEP to expedite their assessment of Florida 

waterways and establish TMDLs in those that are impaired. 

Florida responded by passing the 1999 Watershed Protection 

Act requiring the FDEP to establish a priority ranking and 

schedule for analyzing impaired waters and a methodology for 

determining which water bodies are impaired. In accordance 

with the Watershed Protection Act the FDEP has adopted 

an Impaired Waters Rule and accompanying TMDL Program 

(Florida Senate 2003). FDEP’s five-year report on the 

Program discusses some significant challenges that FDEP will 

have to overcome to satisfy the terms of the Consent Decree 

(FDEP 2005). If FDEP cannot fulfill its obligations by 2012, 

the EPA may step in and impose more stringent regulations.

The new TMDL Program assigns Florida’s 52 watersheds to 29 

basins and divides them into five groups that are evenly spread 

across Florida’s six water management districts. 

A five-year basin rotation schedule will allow for an assessment of 

each basin once every five years. The initial assessment is the first 

of five phases in the TMDL development cycle. It is followed 

by a second phase of coordinated monitoring that supplements 

initial assessments and clarifies the status of potentially impaired 

water bodies. The third phase develops TMDLs in response to 

an impaired waters designation, the fourth incorporates multiple 

TMDLs and allocates loads to specific sectors as part of a 

comprehensive Basin Management Action Plan (BMAP). The 

fifth phase implements the BMAP. 

Initial assessments have been completed for all 29 basins and 

FDEP is in the process of developing Total Maximum Daily 

Loads and Basin Management Action Plans. Nutrient load 

reductions that are mandated through this process will require 

significant expenditures. Allocating loads will be especially 

contentious and litigation is expected (FDEP 2005). 

If a more definitive link between terrestrial runoff and red 

tide is established, the most likely regulatory response will 

take the form of more stringent criteria for NPDES permits, 

stronger enforcement penalties for noncompliance and Total 

Maximum Daily Loads that are incorporated into the Basin 

Management Action Plans. State legislation that addresses red 

tide specifically is, of course, possible. And local permitting 

requirements and water quality enhancement programs can go 

beyond what is required by the state. But beyond requiring 

supplementary best management practices, most substantive 

measures would likely need to be harmonized with NPDES 

permitting requirements and TMDLs that are integrated into 

BMAPs. 

NPDES permitting requirements, Total Maximum Daily 

Loads and Basin Management Action Plans are critical venues 

for water quality measures directed at red tides because they 

are in the process of being developed and they will dictate 

Florida’s water pollution reduction efforts independent of any 

confirmed linkage to red tide.

Control: Measures to Kill, Neutralize or Remove Red Tide 

from the Water Column

There are a variety of ways to control, kill and/or remove K. 

brevis cells from the water column. It is easy to do this in a 

small, contained environment like a laboratory. Controlling 

red tide blooms at the scales we normally find them in the 

marine environment is far more challenging. Research is being 

conducted on a handful of technologies that remain potentially 

viable for field settings, but the conditions under which these 

control technologies can be used will be limited in the near 

term. The most likely applications will be found in intercoastal 

waterways and canals. Open-water applications pose the most 

difficult challenges for control technologies, and technological 

fixes for large-scale blooms would appear to remain a remote 

possibility over the short-to-medium term.

18
Five Key Evaluative Criteria

Policymakers need to consider a number of criteria when 

evaluating potential control technologies that might be 

deployed against a red tide bloom: 

1. Does a considered technology effectively kill, contain 

or neutralize K. brevis cells and/or the brevetoxins they 

produce? As noted, there is no shortage of physical, 

chemical and biological materials that can accomplish 

this. 

2. Does the considered technology pose less of an 

ecological risk than letting the bloom run its course? 

Destroying K. brevis cells is relatively easy. Doing so 

without harming any other form of marine life is not. 

Importantly, the ecological risks associated with a 

given technology should not be considered in isolation. 

Red tides will significantly alter marine ecosystems 

and the decision not to intervene with a viable control 

technology reflects the acceptance of some level of risk. 

In many of the hypothetical scenarios under which a 

control technology would be used, the targeted area 

will have already suffered fish kills and benthic (sea 

floor) mortality events. The additional ecological risks 

associated with deploying a control technology under 

such circumstances are often far less than it would 

be if we were to consider deploying it in a pristine 

marine environment. Conversely, it is also possible 

for a control technology to exacerbate problems by 

increasing the amount of toxin released into the 

environment when K. brevis cells are destroyed and/or 

disturbing ecological balances that may or may not be 

related to the presence of red tide.

3. Is it logistically feasible to deploy a considered 

technology in a manner that will render it effective? 

It is this criterion that undermines the viability of a 

number of potential technologies that work well in 

laboratory settings. Two logistical factors are especially 

important. One is the total biomass of an active red 

tide bloom and the space it covers. When the 2005 

red tide bloom was discovered moving in from the 

bottom of the West Florida Shelf, it already covered 

an area of 500 square miles, the equivalent of 250,000 

football fields. At this size, researchers estimated that 

it would take a single vessel spraying a chemical agent 

a full year to cover the corresponding surface area just 

one time. The other is the importance of deploying 

the considered technology at sufficient concentrations 

throughout the water column. Red tide blooms 

often develop below the surface. Simply treating the 

surface of the water with a given control agent may 

prove futile. The depth problem is compounded by 

ocean currents that may upwell and transport new K. 

brevis cells into an area that has recently been treated. 

This can occur even after the entire water column 

in a given area has been cleared. Collectively, these 

logistical concerns limit the foreseeable applications of 

most of the control technologies under consideration. 

Treating small segments of semi-protected areas with 

modest tidal flows is much more realistic than treating 

a moderate-to-large bloom in the open water. Largerscale applications remain a future possibility for 

some technologies, though, especially when they’re 

combined (e.g. algicidal and/or biotoxin-degrading 

bacteria in association with clay or another carrier). 

Logistical obstacles could also conceivably be overcome 

by deploying a given technology at the appropriate 

depth shortly after a new bloom initiated. However, 

we currently have no way of detecting blooms at this 

very early stage. 

4. Economic cost is another criterion that must be 

considered. The cost of deploying a control technology 

needs to be considered in relation to the potential 

economic losses that the control technology is seeking 

to prevent. Logistical feasibility and cost are often 

related. Deploying a number of control technologies 

at a sufficient scale to substantially impact a bloom 

is often both logistically unfeasible and too costly 

to seriously consider. Some deployments of control 

technologies may be logistically possible but still too 

costly. While policymakers should seriously consider 

spending $100,000 to prevent $1 million in damages, 

spending $1 million to protect against $100,000 in 

damages makes little sense. When considering a range 

of potentially viable control technology options, cost 

will become a significant factor in determining the 

most appropriate control technology for deployment.

5. The final criterion that warrants consideration is 

public perception. While related to actual ecological 

risks and economic costs, public perception toward the 

use of a particular control technology remains a factor 

that affects policy decisions. Public resistance can 

generate a number of social and political ramifications 

that are distinct from economic and environmental 

costs. These ramifications no doubt already factor 

into policy decisions — as well they should.

19
Flocculation

Flocculation refers to a process by which a substance is added 

to a solution to create a “floc” that removes fine particulates 

by binding with them and causing them to clump together. 

With respect to red tide blooms, the targeted particulates 

are K. brevis cells and toxins. Although most HAB research 

has focused on clay flocculation, a variety of substances can 

serve as flocculants. Recent research has begun to explore the 

viability of using sand, shells, sediment and other naturally 

occurring substances as flocculants. 

Clay flocculation can be considered as one of the only HAB 

control technologies with a partially successful track record 

in the marine environment. In Asia, it has been used with 

some measure of success to protect aquaculture facilities 

from HABs (Maruyama et al. 1987; Shirota 1989; Choi et 

al. 1999). Treatment of an area affected by a bloom involves 

spraying the area with clay slurry from a boat. As the slurry 

floats down through the water column it binds with the algae 

cells, clumps together and drifts down to the sea bottom. 

Ideally, the cells become trapped on the bottom and die. 

Dosage and water flow are critical issues, however. If the 

slurry concentration is too high, it may rupture the cells 

while they remain suspended in the water column causing 

the release of toxins. Higher dosages may also pose greater 

risks to other forms of marine life that have not already been 

killed by a bloom. If the slurry concentration is too low, 

it may fail to remove many cells from the water column. 

Moderate levels of water flow appear to be conducive to 

flocculation dynamics, but they can also increase the rates 

of re-suspension of cells away from the sea floor. Lower flow 

rates may reduce flocculation rates but help keep the floc on 

the sea bottom (Sengco 2007).

Research targeting K. brevis cells has demonstrated the 

technology’s potential under controlled conditions. The 

results suggest that treatments during periods with minimal 

to modest tidal flows may be effective in highly targeted 

areas. Moderate to strong tidal flows and/or high winds in 

the immediate wake of a treatment can re-suspend the cells 

off the sea floor and impede the efficacy of the treatment. 

Benthic impacts resulting from dead K. brevis cells and their 

associated toxins can vary but they do not appear extensive 

so long as there is adequate mixing during a complete tidal 

cycle. In fact, research results suggest that some benthic filter 

feeders may benefit from having the brevetoxins trapped in 

the sediment as opposed to suspended in the water column 

(Sengco and Anderson 2004; Archambault et al. 2004; 

Haubois et al. 2005).

Phosphatic clay is one of the most effective flocculants but there 

are concerns with nutrients, heavy metals and radionuclides 

in Florida’s phosphatic clay. Alternative clays from outside of 

Florida have been considered but transport costs are a major 

concern (Anderson et al. 2004). New research is exploring 

the viability of using sand and other sediments from dredging 

activities as well as a chitin composite of crustacean shells as 

flocculants (Sengco 2007).

Flocculation remains a potentially viable weapon against 

Florida red tide, but its applications may be limited to smallscale treatments and its efficacy will vary with environmental 

conditions. Medium-to-large scale applications remain 

possible over the long term, perhaps in conjunction with 

chemical or biological agents. Flocculation must also 

overcome lingering challenges with regard to ecological 

risks, economic costs and public perception.

Ozone

Ozone is a molecule consisting of three oxygen atoms. It 

must be maintained at low temperature and high pressure 

and it becomes highly unstable as temperatures rise and fall. 

It has a very high oxidation potential. Ozone is toxic but 

dissipates very rapidly and does not remain in the water. 

Many municipal drinking water systems kill bacteria with 

ozone instead of the more common chlorine. Ozone can 

be produced on demand with electricity and is often a 

cost-effective method of treating water. It does not require 

transportation and storage of hazardous chemicals and once 

it has decayed it leaves no taste or odor in drinking water.

Ozone offers a number of potential advantages as a control 

technology for Florida red tide. Unlike most other control 

technologies, it will destroy brevetoxins in addition to 

killing or inhibiting K. brevis cells (Pierce et al. 2003; 

Pierce et al. 2004). It will also oxidize decaying fish and 

reoxygenate waters than have lost oxygen and become 

anoxic as a result of a bloom. Its major disadvantage is its 

toxicity. Although the toxicity only lasts for seconds after 

release into the water column, high concentrations of ozone 

will kill indiscriminately and the possibility of degassing 

into the atmosphere can pose a serious danger to humans 

conducting the treatment if strict protocols aren’t followed 

(Schneider et al. 2003). 

Ozone stands out among control technologies in terms 

of efficacy and cost in small-scale applications. Logistical 

considerations limit the scope of ozone treatments beyond 

small-scale targets. Its ecological and occupational risks are 

short-lived but significant.

20
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Address: 1301 Constitution Ave, NW 

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Telephone: 202-566-1744 

Email: docket-customerservice@epa.gov
Other Chemical and Biological Agents

One of the only attempts to control a red tide bloom in open 

waters took place in September and October of 1957. Onehundred-and-five tons of copper sulfate was dispersed along a 

32 mile stretch of the west Florida coast (from Anclote Key to 

Pass-a-Grille Beach), approximately three miles offshore. The 

total area covered was approximately 16 miles. The copper was 

initially distributed from burlap sacks dragged behind ships 

but this proved ineffective for covering large areas, so crop 

dusting planes were used. The effects were immediate as cell 

concentrations dropped from 10 million cells per liter to zero 

across most of treated area. Within two weeks, however, bloom 

concentrations returned to high levels in two of five monitored 

areas. Collateral damage to the ecosystem from the copper 

treatment was not monitored. In addition to its potential for 

ecological damage and limited efficacy, the cost of the copper 

sulfate treatment has since discouraged decision makers from 

seriously considering it as a viable control method (Rounsefell 

and Evans 1958; Sengco, in prep). 

A number of additional tests have since been conducted to 

find chemicals that could kill or inhibit K. brevis. Marvin 

and Proctor (1964) tested more than 4,000 compounds and 

found none to be effective within acceptable levels of cost and/

or ecological risk. Research continues on potentially viable 

chemical agents but issues of cost, efficacy, collateral damage 

and the logistical challenges of dispersing the chemicals at an 

appropriate concentration throughout the water column have 

remained daunting.

In addition to chemical agents, researchers are experimenting 

with algicidal bacteria as potential control agents for K. brevis. 

These bacteria are ubiquitous on the West Florida shelf and they 

can influence the growth and decline of blooms through direct 

or indirect interactions. The bacteria need not kill K. brevis to 

be effective, but may render them vulnerable to predation from 

other micro-organisms (Sengco, pers. comm. March 2007). 

Combining algicidal bacteria with other chemical compounds 

or flocculants is possible, and precedent does exist for similar 

approaches in the form of bioremediation of oil spills, that is 

using bacteria in combination with other compounds to clean 

up the spills. The major challenges for biological agents are 

the same as for chemical agents. Can sufficient amounts of 

bacteria be cultured to substantially impact a bloom and at 

what cost? If artificial production requirements are eased by 

the bacteria’s ability to grow in the presence of a bloom, what 

will happen to the large bacteria population after the bloom 

subsides and how will it affect the balance of the larger bacterial 

community in the broader ecosystem? These questions remain 

at the forefront of research on biological agents to control red 

tide.

Mitigation: Measures to Reduce the Impacts of Red Tide

HAB mitigation strategies focus on limiting the impacts of 

HABs without addressing the causative organism, K. brevis,

directly. A variety of activities can be considered within this 

category, including efforts to learn more about the natural 

and human dimensions of Florida red tides and efforts 

to effectively communicate that knowledge as a means of 

reducing harmful impacts.

Improved Monitoring Capacity

Efforts to detect, monitor, track and predict red tides are an 

integral component of a sound mitigation strategy. Preparation 

for - and responses to - red tide blooms become more difficult 

when detection provides little warning, when monitoring 

is inconsistent and when prediction models provide little 

guidance. These efforts can also play an important role in 

prevention and control strategies. The earlier red tide blooms 

are detected and the longer they are tracked, the easier it will 

be to determine the conditions under which different nutrient 

sources become relevant in the development and maintenance 

of a bloom. This will inform prevention strategies. Early 

detection and accurate projections of bloom movement are also 

likely to be vital to the efficacy of most control technologies. 

Initiatives to better detect, monitor, track and predict red tides 

are ongoing at the state, regional and federal levels. At the state 

level, the Florida Fish and Wildlife Research Institute (FWRI) 

engages in an ongoing monitoring and sampling program with 

weekly updates made available through its website. 

At the regional level, an Action Plan for Harmful Algal Blooms 

and the Gulf of Mexico Coastal Observing System was recently 

developed in conjunction with a regional workshop on the 

topic (NOAA/CSC 2004). The workshop recommended 

that a Harmful Algal Blooms Observing System (HABSOS) 

be developed and integrated into existing observing systems 

including the Integrated Ocean Observing System (IOOS) 

and the Gulf of Mexico Coastal Observing System (GCOOS). 

Although initially focused on the Gulf of Mexico, NOAA 

officials envision that HABSOS will be expanded into a 

national program. The purpose of the program will be to 

provide updates on the location of existing blooms, early 

alerts to new blooms, forecasts of bloom movements and 

probabilities that new blooms would occur. HABSOS remains 

under development. 

An existing tool that already performs some of these functions 

is the NOAA HAB Bulletin. Currently operational in the Gulf 

of Mexico, the HAB Bulletin is proving useful for Florida’s 

22
state managers in making decisions about when and where 

to monitor the hundreds of miles of coastline and associated 

shellfish beds. As new technologies and modeling tools become 

available, the HAB Bulletin should improve. 

The importance of robust monitoring capacity for an effective 

mitigation strategy is not lost on Florida’s foremost authorities 

on oceans and coastal management. The Florida Oceans & 

Coastal Resources Council continues to list capacity building 

measures for observing systems as a high priority in its Annual 

Science Research Plan (Florida Oceans & Coastal Resources 

Council 2007). 

Human Dimensions Research

A far greater amount of research effort 

has been directed toward the physical 

dimensions of Florida red tides when 

compared to efforts that focus on its 

human dimensions. This asymmetry 

reflects both a dearth of social scientists 

working on HABs and a poor track 

record of integrating natural and social 

science research agendas on a variety 

of marine environment problems that 

include HABs. These deficiencies 

can hamper the ability to effectively 

mitigate HAB impacts because 

effective mitigation strategies often 

entail managing human behavior more 

so than the HABs themselves. 

The significance of human dimensions 

research has recently been recognized 

by the HAB research community in its Human Dimensions 

Research Strategy for Harmful Algal Blooms (Bauer 2006 

or HARR-HD). HARR-HD outlines six areas of human 

dimensions research with accompanying recommendations. 

Two of the research areas outlined in HARR-HD are discussed 

in earlier sections of this report: socioeconomic impacts and 

human health impacts. A third, recreational and drinking 

water impacts are less relevant with Florida red tides but can 

be considered in the context of water quality. The remaining 

three areas are risk communication, interagency coordination 

and public education and outreach.

Risk communication research is critical for educating and 

informing the public in a manner that allows it to understand 

the probability of a HAB event, trust the message and 

respond in ways that help them reduce their vulnerability 

and promote their recovery. Key areas of risk communication 

include determinates of organizational trust, risk perceptions, 

social amplification of risk, media engagement and message 

development and design. Institutional research, including 

interagency coordination, is critical for understanding 

institutional incentives, gaps and overlaps in governance 

authority and opportunities for reform. In the presence of a 

red tide bloom, the public wants to know who’s in charge and 

what can be done to alleviate the problem. Can emergency 

response strategies be developed that are akin to those in place 

for other natural hazards? Can local governments and state 

agencies improve their coordination efforts during red tide 

blooms? Do laws need to be changed in order to improve 

our overall response strategy? The next section offers some 

preliminary observations with respect to governance issues 

but more thorough assessments and 

analyses are needed. 

Public Education and Outreach

Public education and outreach is 

perhaps the most vital component 

of an effective mitigation strategy. 

Southwest Florida benefits from a 

combination of active research and 

stakeholder organizations. Mote 

Marine Laboratory, the Florida Fish 

and Wildlife Research Institute 

(FWRI) and the Florida Department 

of Health have partnered with a 

grassroots network known as START 

(Solutions To Avoid Red Tide) to form 

the Red Tide Alliance. The Alliance 

seeks to educate the public about the 

effects of the Florida red tide and other 

harmful algal blooms. Regional and 

local chapters of the Sierra Club are also very active in their 

public education and advocacy campaigns that target Florida 

red tide. Although these and a handful of other organizations 

disseminate red tide information in the Southwest Florida 

region, coordination and consistency are sometimes lacking. 

And few have adequate feedback mechanisms that can 

ascertain the effectiveness of their respective education and 

outreach activities. 

While differing priorities and perspectives may preclude 

a sweeping consensus on all aspects of red tide research, 

management and policy preferences, greater effort can be made 

to broaden collaboration among the range of organizations 

and stakeholder groups that are active on the issue of red 

tide, especially with respect to public education. These 

efforts should include Chambers of Commerce and Tourist 

and Visitor’s Bureaus in addition to environmental advocacy 

groups. Future public education and outreach initiatives 

23

The above picture shows a Slocum Glider, also 

referred to as an Autonomous Underwater Vehicle 

(AUV). The glider is designed to monitor area waters 

at varying depths in order to detect harmful algal 

blooms and the conditions under which they form.
should be designed in a manner that builds upon other areas 

of human dimensions research including institutional analysis 

and risk communication. These initiatives should also include a 

variety of ongoing surveys to assess program effectiveness.

Governance Issues

The Regulatory Framework for Florida Red Tide

There is a complex array of laws and organizations operating 

at federal, state and local levels that pertain or could pertain 

to Florida red tide. Interplay occurs “vertically” between 

different levels of government and “horizontally” across 

different physical domains and issue areas. Different physical 

domains include marine vs. terrestrial areas and areas with 

national park and/or wetlands designations. Different 

issues can include those involving wildlife, environment, 

water provision, health and a variety of economic activities 

like agriculture, fisheries, mining, etc.

Federal Governance

The most relevant organizations at the federal level include the 

Environmental Protection Agency (EPA), the National Oceanic 

and Atmospheric Administration (NOAA), the National 

Institutes of Environmental Health Sciences (NIEHS), the 

Army Corps of Engineers (ACE), the National Centers for 

Disease Control and Prevention (CDC), the National Park 

Service (NPS) and the National Science Foundation (NSF).

The respective roles of these agencies vis-à-vis their state 

counterparts are collaborative in many areas, clearly 

demarcated in some and contested in others. Collaboration is 

most notable with respect to research. The federal government 

plays a vital role in the provision of research funding and 

infrastructure that are critical to effective management 

strategies. NOAA, NIEHS, EPA and NSF provide varying 

degrees of funding for HAB research programs working 

closely with state agencies. An important piece of legislation 

for research funding is the Coastal Zone Management 

Act. The Management Act authorizes a variety of programs 

and initiatives to encourage coastal states to develop and 

implement coastal zone management plans. Another is the 

Harmful Algal Bloom and Hypoxia Research and Control Act. 

Enacted in 1998, this Act recognized that many of our nation’s 

coastal areas were suffering from HABs and hypoxia each year, 

threatening both coastal ecosystems and human health. The 

Act was reauthorized in 2004 to provide an updated research 

framework for addressing HABs that requires stronger 

consultation with local resource managers (HARRNESS 2005). 

Demarcation of federal authority is most salient with respect 

to the spatial dimension of red tide issues. The federal 

government maintains authority over activities in U.S. waters 

beyond nine miles from the Gulf of Mexico coastline of U.S. 

states. Deployment of red tide control technologies in federal 

waters would likely require an National Pollution Discharge 

Elimination System permit from the EPA. Activities 

undertaken in areas designated as national parks fall under 

the jurisdiction of the National Park Service. Construction 

activities undertaken in areas designated as wetlands require 

permits from the Army Corps. The Army Corps and EPA also 

maintain a degree of authority over activities affecting navigable 

waters, although the definition of “navigable” remains subject 

to judicial interpretation (Meltz and Copeland 2007).

Water governance is perhaps the most contested area with 

respect to the parameters of federal vs. state government 

authority on a red tide-related issue. Water governance 

can be thought to include both water provision and water 

pollution. The previous discussion of preventive measures in 

the context of Florida’s Total Maximum Daily Load program, 

EPA oversight and the Clean Water Act offer a glimpse into 

the vertical interplay between state and federal authorities on 

this issue.

State Governance

Some of the relevant organizations within Florida that 

operate on the state and regional levels include the Florida 

Fish and Wildlife Conservation Commission (FWC) 

and its Fish and Wildlife Research Institute (FWRI), the 

Florida Department of Environmental Protection (FDEP) 

and its five Water Management Districts, the Division of 

Environmental Health within the Florida Department of 

Health (FDOH) and the Florida Department of Agriculture 

and Consumer Services (FDACS). 

FWRI oversees most of Florida’s red tide research programs 

and provides the most centralized source of information on red 

tide queries as it acts as the State’s “first responder” to reported 

blooms. The FWRI can be considered the counterpart to 

and/or research partner for a number of federal agencies that 

support red tide research programs. 

Another centralized entity that could offer additional 

governance and oversight of red tide-related activities is the 

Florida Harmful Algal Boom Task Force. The task force will 

be discussed in the next section.

The FDEP can best be considered Florida’s counterpart to 

the EPA. As discussed in the section on preventive measures, 

the FDEP is currently involved in a massive effort to assess 

24
the impairment status of Florida’s waterways, develop a Total 

Maximum Daily Load Program and implement the program 

through a suite of Basin Management Action Plans. FDEP is 

also responsible for issuing environmental resource permits in 

conjunction with water use and wetlands activities. 

Many of FDEPs water governance responsibilities are carried 

out through its five Water Management Districts. Chapter 

373 of the Florida Statutes gives the Florida Department of 

Environmental Protection “general supervisory authority” 

over the districts and directs the Department to delegate water 

resources programs to them where possible. Pursuant to these 

delegations, the districts are authorized to administer flood 

protection programs and to perform technical investigations 

into water resources. The districts are also authorized to 

develop water management plans for water shortages in 

times of drought and to acquire and manage lands for water 

management purposes under the Save Our Rivers program. 

Regulatory programs delegated to the districts include programs 

to manage the use of water, aquifer recharge, well construction 

and surface water management. Although district charters were 

changed in the 1970s to include issues of water quality, only a 

small portion of their budgets are allocated to quality issues and 

FDEP retains authority over the TMDL program. The FDEP 

is also responsible for implementing the State Water Resource 

Plan and has the power to implement programs to attempt 

to mitigate problems with water resources, such as red tide.

FDEP engages with numerous state and local organizations in 

carrying out its water governance mandates. 

The Florida Department of Health’s Division of 

Environmental Health is mandated by Chapter 381, among 

other statutes, to conduct an environmental health program 

that will “detect and prevent disease caused by natural and 

The above chart shows the substantial number of organizations that interact with the Florida Department of Environmental Protection (FDEP) on water 

management issues. The regulatory frameworks (laws and governing authorities) that are potentially relevant Florida red tides can be highly complex.

25

©FDEP 2006
man-made factors in the environment.” This is different than 

the FDEP mandate in that it focuses directly on the health 

of the environment and the public, giving this organization 

the ability to address the wider consequences of red tide in 

terms of human health. This mandate can conflict with or 

overlap that of the FDEP or other agencies. In addition, the 

Division of Health does not possess the ability to effectively 

monitor and regulate those whose 

actions are potential factors in 

the exacerbation of red tide and 

other water problems.

The Florida Department of 

Agriculture and Consumer Services 

(FDACS) has crosscutting 

authority over a number of issues 

that pertain or could pertain to 

red tide. FDACS plays a key 

role in the TMDL program with 

respect to the development of 

best management practices for 

agriculture, it is charged with the 

enforcement and administration 

of Florida’s Commercial Fertilizer 

Law, and it has responsibility for 

maintaining the safety protocols 

for the State’s aquaculture shellfish 

harvesting program. 

In addition to the statutes 

governing the environment and 

health of Florida’s waterways, 

there are a multitude of statutes 

that address the economic sectors 

most commonly identified as 

affecting water quality in Florida. 

Various statutes, task forces and commissions address mining, 

agribusiness, development, fertilizer manufacturing and 

distribution, roadway development and petrochemical runoff, 

sewage treatment and several other areas that are relevant to 

coastal pollution. 

Local Governance

While the state and federal government continue to sort through 

their respective governance and oversight responsibilities, it is 

local communities that most often bear the brunt of a given 

bloom’s impacts. Cleanup of fish kills is the responsibility of 

local governments but this appears to be done on an ad hoc basis 

independent of local laws and ordinances. It does not appear 

that local governments in Southwest Florida have emergency 

response plans for red tides that are comparable to those for 

hurricanes and other natural hazards, but this is something 

that local governments could consider. Advance planning for 

timely cleanup of fish kills, centralized information sources 

for bloom forecasts and beach advisories and concerted efforts 

to provide tourist and recreational options in lieu of activities 

affected by red tide blooms can all help to mitigate the impacts 

of a red tide bloom.

Local governments have also 

become active in terms of 

preventive measures. A recent 

Sarasota County Fertilizer 

and Landscape Management 

Code requires a set of best 

management practices for various 

aspects of fertilizer use within 

the county. Sanibel Island has 

also passed a similar ordinance. 

Industry interest groups have 

attempted to preempt these and 

future ordinances by lobbying 

for legislation that would 

establish statewide standards for 

fertilizer use (Whittle 2007). 

 While there may be specific 

elements of proposed ordinances

that will require statewide 

harmonization, the notion of 

uniform ordinance for the entire 

state or a regulatory ceiling for 

local governments seems unwise 

and inconsistent with FDEP’s 

watershed management strategy. 

FDEP is developing standards 

and programs that are tailored to 

individual basins and watersheds. The level of regulation for 

non-point source pollutants will vary from basin to basin and 

from watershed to watershed. A model fertilizer ordinance 

could prove useful in establishing a benchmark for local 

governments to consider, but it shouldn’t be embedded in 

legislation that inhibits the flexibility of FDEP’s watershed 

management approach or that prevents local communities 

from tailoring local ordinances to their specific needs. 

The Florida Harmful Algal Bloom Task Force

The Florida Harmful Algal Bloom Task Force was first 

established in 1997 as an ad hoc advisory body to address 

harmful algal bloom (HAB) issues in Florida waters. Members 

included representatives from government, universities and 

the public and private sectors. In 1999, the Task Force was 

26

The above photo shows an example of a “no-mow” zone 

along a seawall in Sarasota County. This is an example of a 

bast-management practice for homeowners who live along 

waterways. Floridians are discussing the merits of mandating 

such practices through local government ordinances. 

©Sarasota County
legislatively authorized via statutes Ch. 370.06092, F.S. 

and Ch. 370.06093, F.S., and charged with: 1) reviewing 

the status and adequacy of information for monitoring 

physical, chemical, biological, economic and public health 

factors affecting harmful algal blooms in Florida; 2) 

developing research and monitoring priorities that included 

detection, prediction, mitigation and control; 3) developing 

recommendations that could be implemented by state and 

local governments and 4) developing recommendations 

to the Florida Marine Research Institute (now the Florida 

Fish and Wildlife Research Institute). The legislation also 

expressed its intent for the Task Force to develop its priorities 

and recommendations with a view toward complementing 

the work being carried out by the cooperative federal-state 

program known as Ecology and Oceanography of Harmful 

Algal Blooms (ECOHAB-Florida). Continuation of the 

Task Force after the completion of its reporting requirements 

was left to the discretion of FWRI.

The Task Force commissioned a Technical Advisory Group 

that prepared its lone report in 1999 (Steidinger et al. 1999). 

Although many important research findings can be traced 

back to the recommendations of this initial report, there 

have been a number of significant HAB events, emerging 

issues and advances in HAB research since it was released. 

The FWRI announced its intentions to revisit and update 

the Task Force’s report in Fiscal Year 2006-07 but this has 

yet to be done. The need to perform the functions outlined 

in the Florida HAB Task Force’s legislative mandate is as 

strong today as it was when it was established. Funding and 

reconvening this body could allow for a number of effective 

governance functions to be performed. However, some 

observations are warranted: 

1. Greater consideration should be given to the 

relationship between the functions of the Florida 

HAB Task Force and the most appropriate structure 

for fulfilling those functions. Important governance 

functions that the Task Force could fulfill include: 1) 

organizing and prioritizing the scientific questions and 

management concerns pertaining to red tide and other 

harmful algal blooms in Florida; 2) summarizing the 

best available science that can address these questions 

and concerns; 3) identifying the resources needed to 

address unanswered questions or concerns; and 4) 

providing mechanisms for programmatic assessment, 

external review and mediation of scientific disputes. 

The language of the 1999 legislative mandate speaks 

to these functions in varying degrees.

2. Although the Florida HAB Task Force had nominal 

representation from government, universities and 

both the public and private sectors, the overwhelming 

majority of Task Force members were representatives 

of state regulatory agencies. The Technical Advisory 

Group that worked in concert with the Task Force 

was comprised of scientists, most from the same 

regulatory agencies represented on the Task Force with 

a few others from independent research laboratories 

and academia. This arrangement is well suited for 

enhancing communication and collaboration between 

regulators and researchers, but it only allows for modest 

input from stakeholder groups and local governments. 

Consideration should be given to reconstituting the 

Task Force in a manner that provides for a greater 

balance between state and local policymakers as well 

as a broader range of stakeholders that are affected by 

HABs in Florida.

3. Consideration should be given to establishing an 

External Review Committee that is distinct from 

the Technical Advisory Committee. Members of the 

External Review Committee should have minimal ties 

to the Florida HAB research community and minimal 

ties to Florida stakeholder groups. In addition to 

assessing the state’s research and management programs, 

the review committee could be used to mediate 

scientific disputes that may arise among members of 

the Technical Advisory Group and/or between this 

group and other HAB researchers that are critical of 

a particular area of work. If the Florida HAB Task 

Force is not reconstituted in a manner that includes an 

External Review Committee then consideration should 

be given to creating or commissioning a separate body 

to perform this function.

External Review

The frequency and severity of red tide outbreaks over the 

past decade has put a considerable amount of stress on our 

Southwest Florida communities. Frustration with red tide 

has strained community relationships with state regulatory 

agencies and red tide researchers. The community wants 

to be assured that existing answers to their most pressing 

questions about red tide represent accurate depictions of 

the best available science and that researchers are doing 

everything they can to reduce the uncertainties in their 

answers. Regardless of how or why trust breaks down, when 

it does, it becomes very difficult for the people most directly 

involved in the red tide research program to provide the 

necessary assurances. Under such circumstances, an external 

review of the program conducted by qualified experts that 

are unaffiliated with it could prove invaluable. It could help 

mediate some of the most contentious scientific disputes, 

27
endorse program areas that are performing well, outline 

measures for improvement and help to restore trust with 

disaffected stakeholders. 

To a limited degree, this Marine Policy Institute assessment 

attempts to make a constructive contribution along these 

lines. But the Institute currently lacks the range and depth of 

expertise necessary to definitively resolve the most contentious 

scientific disputes and it lacks the formal independence 

necessary to function as an impartial external review body. 

The Marine Policy Institute thus recommends that a separate 

mechanism be developed to provide this function for Florida’s 

HAB research and management programs. 

The previous section discusses the possibility of redesigning 

the Florida Harmful Algal Bloom Task Force in a manner 

that provides for external reviews. Two additional models 

for conducting external reviews can be found in the Florida 

Bay Science Oversight Panel and the Maryland Blue Ribbon 

Citizens Pfiesteria Action Commission. 

Responding to mounting concerns over the role of 

nutrient loads in the deterioration of Florida Bay, the U.S. 

Department of Interior commissioned an independent 

scientific assessment in 1993 (Boesch et al. 1993). After the 

initial assessment, a Florida Bay Science Oversight Panel was 

established as an independent peer-review group charged 

with providing regular, broad, technical and management 

review of the Interagency Florida Bay Science Program. It 

continues to review agency plans, strategies for program 

development, scientific quality of research, modeling and 

monitoring and research results (NOAA 2000).

Maryland’s Blue Ribbon Citizens Pfiesteria Action 

Commission was appointed in 1997 by then-Governor Parris 

Glendening in response to an apparent outbreak of a harmful 

alga known as Pfiesteria piscicidia in Chesapeake Bay. The 

commission was charged with making recommendations for 

managing the risks associated with Pfiesteria and minimizing 

the likelihood of future outbreaks. The commission conducted 

intensive investigations into the myriad scientific and public 

policy aspects of the Pfieisteria issue. Many scientific briefings 

were held to inform legislative committees, government 

committees, the public and the scientific community. The 

political momentum generated by the Commission’s findings 

was largely responsible for Water Quality Improvement 

Act of 1998 (Boesch 1997; Maginen 2001). Despite its 

regulatory impact, concerns have since been expressed about 

the interplay between science and politics in the Maryland 

case (Belousek 2004).

Discussions with individuals involved with these external 

review mechanisms suggest that the Florida Bay model is 

perceived as less politicized while the Citizens Pfiesteria 

Action Commission is perceived as having greater impact on 

the regulatory process. The Marine Policy Institute does not 

endorse a particular model for external review, but suggests that 

further discussion of the strengths and weaknesses associated 

with different models take place. The MPI also recommends 

the following guidelines for conducting external review.

1. Define the mandate and parameters for an external 

review team before selecting external reviewers; 

2. Use area of expertise, scientific qualifications and 

impartiality (minimal ties to Florida research 

organizations and stakeholder groups) as primary 

criteria for selecting external reviewers;

3. Allow the selection process to be administered by an 

organization or individual that is trusted by a broad 

range of scientists and stakeholders;

4. Allow for stakeholder input on prospective candidates 

prior to final selection. 

An external review does not guarantee that the scientific 

disputes will be resolved or that all stakeholder groups will be 

happy with the outcomes. In the absence of such a review, 

however, efforts to politicize red tide research will likely persist 

as long as red tides continue. The absence of a formal review 

process will also encourage disaffected stakeholders to attempt 

their own external reviews in a manner that is likely to neglect 

the guidelines outlined here.

28
Conclusion

Scientific uncertainty regarding the potential linkages 

between coastal pollution and Florida red tide should not 

detract from progressing with agendas that address both. 

Florida needs to reduce coastal pollution — in the form of 

nutrient loads to Florida watersheds — for reasons other 

than red tide. And it needs to deploy a comprehensive 

management strategy for combating red tides that goes 

beyond reducing nutrient loads.

Decades of research have contributed to an impressive body 

of knowledge on K. brevis, its life cycle, and the conditions 

that lead to red tide blooms on the West Florida Shelf. 

Given what we know, it will be very difficult to prevent the 

periodic recurrence of Florida red tides. 

But there are actions that we can take to improve the way 

that we deal with them. 

• We can take precautionary measures that reduce 

potential human contributions to red tides with the hope of 

easing the intensity and duration of blooms. 

• We can push forward with field studies with 

existing control technologies that have the potential for 

removing or destroying K. brevis cells in small areas under 

specific conditions. 

• We can explore the potential for new technologies 

that may be able to expand the range and conditions under 

which they can be effective. 

• We can undertake a variety of activities that will 

improve our ability to predict, monitor, and track blooms 

and to better prepare, respond and recover from them. 

• We can improve the oversight of our research 

and management of Florida red tide — and harmful algal 

blooms more generally — by funding and improving upon 

existing governance mechanisms. 

Collectively, these actions can help reduce the impact that 

Florida red tides have on our coastal communities and 

improve our quality of life. 

29
Appendix: Q&A

The following set of questions and answers synthesizes and 

integrates the most pertinent research findings and policy 

recommendations from this report.

Are Florida red tides getting worse?

Possibly. Harmful algal blooms (HABs) appear to be getting 

worse throughout the world. Some of the forcing factors 

believed to play a role in the worldwide trend are increased 

nutrient enrichment resulting from population growth and 

land use practices and increased water temperatures due to 

global climate change. Although the general trend appears 

to be worsening, trends for specific HABs can embody 

more uncertainty. This is particularly true for offshore 

HABs such as Karenia brevis, the organism that causes 

Florida red tides. Southwest Florida has endured red tide 

blooms on a near-annual basis over the past two decades, 

and the 2005 bloom was one of the most severe on record. 

However, Florida red tide blooms of similar intensity and 

duration have been confirmed as far back as 1948-49, 

and anecdotal evidence suggests that severe blooms have 

scourged the region for hundreds, if not thousands of years. 

There is broad consensus that Florida red tides have been 

especially active in recent years, but putting this decade 

into historical perspective is extremely difficult due to a lack 

of data suitable for determining historical trends. 

Can coastal pollution exacerbate Florida red tides? 

Probably. The recipe for Florida red tides is complex. 

The relative importance of different ingredients - nutrient 

sources and other environmental factors - varies over the 

different stages of a bloom and it is possible that the specific 

recipe responsible for red tides varies from bloom to bloom. 

Terrestrial nutrient fluxes are one of many ingredients that 

can contribute to a red tide bloom, and coastal pollution 

exacerbates these fluxes. Most scientists agree that red tide 

blooms initiate offshore before being transported inshore 

by wind and ocean currents. They believe coastal runoff 

is unlikely to affect the early stages of a bloom, but when a 

bloom moves inshore, they acknowledge that runoff can play 

a role in intensifying or prolonging a bloom. Assessing the 

relative importance of terrestrial nutrient sources, including 

coastal pollution, remains a top research priority.

What impacts do Florida red tides have on marine life 

and human health?

Karenia brevis, the organism responsible for Florida red 

tide blooms, produces a powerful collection of neurotoxins 

called brevetoxins. The release of these brevetoxins can cause 

massive fish kills and significant mortality events for sea 

birds and marine mammals. Large fish kills can occasionally 

generate hypoxic zones, or areas of low oxygen, that can kill 

even more marine life. The extent to which red tides affect 

populations of ecologically and economically important 

fisheries over time and space is poorly known. Human 

health impacts usually take the form of neurotoxic shellfish 

poisoning (NSP) and respiratory irritation. Adverse impacts 

could also result from long-term exposure to brevetoxins, 

but research on such chronic effects of Florida red tide in 

humans is in its infancy.

What impacts do Florida red tides have on the economy?

Florida red tides impose significant economic costs in 

localized areas, but the cumulative impacts for an entire 

coastal region affected by a bloom are difficult to calculate. 

Existing estimates are highly inconsistent and heavily 

dependent upon the assumptions of the analysts. Given the 

likelihood of displaced economic activity, economists need 

to better understand how consumers respond to red tide 

events before they can provide accurate impact assessments. 

Better data on tourist, recreational and real estate activity 

in the presence and absence of red tides will be critical for 

future assessments in Florida.

What management options exist for responding to Florida 

red tides?

There are three types of management options for dealing 

with Florida red tides: 

1. Measures that reduce potential human contributions to 

red tide (preventive measures);

2. Measures to control or eliminate red tide when it occurs 

(control measures);

3. Measures to reduce the impacts of red tide when it occurs 

(mitigation measures). 

Effective management strategies should incorporate all three 

options. Excess nutrients in our watersheds give rise to a 

variety of problems that we need to avoid. A precautionary 

approach to Florida red tides that incorporates the 

reduction of nutrient loads as a part of a general nutrient 

management strategy will yield benefits that go far beyond 

impacts on red tide. Research on control technologies 

30
should continue. Given the limited applications for the 

most viable technologies projected over the short term, 

the research portfolio should remain diversified. A more 

substantial effort should also be made to improve efforts 

to mitigate red tide’s impacts. Mitigation measures should 

include a robust program on monitoring, detection and 

forecasting, but it should also include a robust human 

dimensions research agenda and an aggressive education 

and outreach program. This would include projects that 

measure public perception and knowledge about red tide, 

projects that measure economic activity before, during and 

after blooms and projects that improve upon interagency 

coordination and emergency response and recovery plans. 

 

What regulatory mechanisms exist for reducing coastal 

pollution?

There is a widespread consensus that Florida needs to reduce 

the amount of non-point source pollution that makes its 

way into ground and surface waters. The most relevant 

regulatory mechanisms for realizing these reductions fall 

under the jurisdiction of the U.S. Environmental Protection 

Agency (EPA) and the Florida Department of Environmental 

Protection (FDEP). FDEP is currently overhauling Florida’s 

water regulatory framework in the shadow of federal 

oversight. The overhaul includes assuming responsibility 

for permitting under the National Pollution Discharge 

Elimination System (NPDES), assessing all of the state’s 

waterways and establishing Total Maximum Daily Loads 

(TMDLs), or water quality standards, for those designated 

as impaired, and developing 29 Basin Management Action 

Plans that implement the TMDLs across all 52 of Florida’s 

watersheds. These regulatory changes under existing law 

have as great a likelihood of reducing nutrient loads and 

improving water quality in Florida as would new laws enacted 

as a direct response to red tides. Supplemental ordinances 

from local governments may improve local conditions, but 

Florida’s future water quality will largely be determined by 

rigorous enforcement of permitting requirements, as well as 

the new standards being developed and the programs being 

designed to implement them. 

Are there any viable control technologies for combating 

Florida red tides?

There are a variety of ways to control, kill and/or remove 

K. brevis cells from the water column. It is easy to do this 

in a small, contained environment but controlling red tide 

blooms at the scales that we normally find them in coastal 

and marine environments is far more challenging. Research 

is being conducted on a handful of viable technologies, but 

the conditions under which these control technologies can 

be used will be limited in the near term. The most likely 

applications might be found in intercoastal waterways and 

canals. Open-water applications pose the most difficult 

challenges for control technologies, and technological fixes 

for large-scale blooms remains unlikely over the short to 

medium term.

How can oversight of Florida’s red tide research and 

management activities be improved?

The governance of both research and management can be 

improved upon by redesigning, refunding and reconvening 

the Florida Harmful Algal Bloom Task Force, and creating 

a mechanism that provides for periodic external reviews 

of the entire HAB program. The Florida Harmful Algal 

Bloom Task Force was first established in 1997 as an ad hoc 

advisory body to address harmful algal bloom (HAB) issues 

in Florida waters. In 1999 it was legislatively authorized to 

provide a handful of governance and oversight functions, 

but it has since become dormant. The need to perform 

the functions outlined in its original legislative mandate 

is as strong today as it was when it was established. The 

composition of the Task Force would benefit from a broader 

and more balanced representation of societal interests. 

Florida’s HAB research and management programs could 

also benefit from periodic external reviews. External reviews 

could help mediate some of the most contentious scientific 

disputes, endorse program areas that are performing well, 

outline measures for improvement, and help to restore trust 

with disaffected stakeholders.

31
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tide-induced bronchial responses [abstract]. International 

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Abraham, W.M., A.J. Bourdelais, A. Ahmed, S. Serebriakov, 

and D.G. Baden. 2005. Effects of inhaled brevetoxins 

in allergic airways: toxin-allergen interactions and 

pharmacologic intervention. Environmental Health 

Perspectives 112:632–637.

Adams, C. M., D. Mulkey, A. Hodges, and J. W. Milon. 

2000. Development of an economic impact assessment 

methodology for occurrence of red tide. Gainesville, FL: 

Institute of Food and Agricultural Sciences, Food and 

Resource Economics Department, University of Florida. 

Staff Paper SP 00-12. 

Adams, C., S. Larkin, D. Mulkey, A. Hodges, and B. 

Ballyram. 2002. Measuring the Economic Consequences 

and Public Awareness of Red Tide Events in Florida. St. 

Petersburg, FL: Harmful Algal Task Force, Florida Fish 

and Wildlife Conservation Commission. 156 p.

Anderson, D.A. 1997. Turning back the harmful red tide. 

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ACE – Army Corps of Engineers

BMAP – Basin Management Action Plan

BMP – Best Management Practice

CDC – National Centers for Disease Control and Prevention

ECOHAB – Ecology and Oceanography of Harmful Algal Bloom program

EPA – Environmental Protection Agency

FDACS – Florida Department of Agriculture and Consumer Services

FDEP – Florida Department of Environmental Protection

FDOH – Florida Department of Health

FWC – Florida Fish and Wildlife Commission

FWRI – Florida Fish and Wildlife Research Institute

GCOOS – Gulf of Mexico Coastal Observing System

HAB – Harmful Algal Bloom

HABSOS – Harmful Algal Blooms Observing System

ICES – International Council for the Exploration of the Seas

IOOS – Integrated Ocean Observing System

IPCC – Intergovernmental Panel on Climate Change

MPI – Marine Policy Institute

NIEHS – National Institutes for Environmental Health Sciences

NOAA – National Oceanic and Atmospheric Administration

NPDES – National Pollution Discharge Elimination System

NPS – National Park Service

NSF – National Science Foundation

TMDL – Total Maximum Daily Load

List of Acronyms

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Acute - Rapid onset, severe, intense

Acute Toxicity - Adverse effects from short-term exposure

Aerosol - Fine particles or liquid droplets dispersed in the air

Algicidal Bacteria - Bacteria ubiquitous on the West Florida 

Shelf which can influence the growth and decline of algal 

blooms through direct or indirect interactions

Anoxic - The absence of oxygen

Anthropogenic - Caused or influenced by humans

Benthic - Relating to the bottom of a sea or lake or to the 

organisms that live there

Best Management Practices - Effective, practical, structural or 

nonstructural methods which prevent or reduce the movement 

of sediment, nutrients, pesticides and other pollutants from 

the land to surface or ground water, or which otherwise protect 

water quality from potential adverse effects

Biomass - The total mass of living matter in a given habitat

Bioremediation - The use of biological agents, such as bacteria 

or plants, to remove or neutralize contaminants, as in polluted 

soil or water

Biota - The animals, plants, fungi, etc., of a region or period

Bloom - The sudden development of conspicuous masses of 

organisms, as algae, in a body of water

Brevenal - A natural antagonist produced by Karenia brevis, 

counteracting the effects of brevetoxin

Brevetoxin - A neurotoxin produced by Karenia brevis

Chronic - Continuing a long time or recurring frequently

Chronic Toxicity - Adverse effects from repeated exposure over 

long periods of time

Cyanobacteria - A photosynthetic bacterium, generally bluegreen in color and in some species capable of nitrogen fixation

Dead Zone - A zone of oxygen-depleted coastal waters too low 

to support most life in bottom and near-bottom waters, and 

which is largely attributed to anthropogenic nutrient pollution. 

Also referred to as hypoxic zones

Desertification - The rapid depletion of plant life and the loss 

of topsoil at desert boundaries and in semiarid regions, usually 

caused by a combination of drought and the overexploitation of 

grasses and other vegetation by people

Dinoflagellate - Any of numerous one-celled organisms found 

mostly in the ocean, usually having two flagella of unequal 

length and often an armor-like covering of cellulose

Ecosystem - A community of organisms together with their 

physical environment, viewed as a system of interacting and 

interdependent relationships

Estuary - The wide lower course of a river where it flows into 

the sea; estuaries experience tidal flows and their water is a 

changing mixture of fresh and saltwater

Eutrophication - Excessive nutrients in a lake or other body 

of water, usually caused by runoff of nutrients (animal waste, 

fertilizers, sewage) from the land, and which causes a dense 

growth of plant life

Flocculation - The process by which a substance or “flocculant” 

is added to a suspension in order to remove fine particulates by 

binding with them and causing them to clump together and 

sink to the bottom

Flux - A flow, discharge or transfer

Groundwater - The supply of fresh water found beneath the 

Earth’s surface, usually in aquifers, which supply wells and 

springs

Groundwater Table - The top zone of soil and rock that is 

saturated with water and which may be only a foot below the 

ground surface or it may be hundreds of feet down

Human Dimensions - Refers to the suite of social, cultural 

and economic aspects of human behavior with respect to 

ecosystems. and can include both the impacts of human activity 

on ecosystems and ecosystem impacts on human activity

Hypoxic - Referring to low oxygen

Inorganic - Not involving organisms or the products of their 

life processes; of mineral origin

Lipid Soluble - Organic compounds that are oily to the touch 

and are insoluble in water

Load - The total amount of material (pollutants) entering a 

water body from one or multiple sources

GLOSSARY

39
Macroalgal - Large aquatic photosynthetic plants that can been 

seen without the aid of a microscope

Mitigation - Measures taken to reduce adverse impacts 

Neurotoxin - A toxin that damages or destroys nerve tissue

Nitrogen Fixation - Conversion of atmospheric nitrogen gas 

into forms useful to plants and other organisms by lightning, 

bacteria, and blue-green algae; it is part of the nitrogen cycle

Non point Source Pollution - Pollution sources that are diffuse 

and without a single identifiable point of origin, including 

runoff from agriculture, forestry, and construction sites

Observing System - A collection of one or more sensing 

elements (human and/or instrument) that reside on fixed or 

mobile platforms

Oligotrophic - When water bodies which are nutrient poor 

and contain little aquatic plant or animal life

Organic - Characteristic of, pertaining to, or derived from 

living organisms; made of carbon and hydrogen as the basic 

building blocks

Oxidation - A chemical reaction that increases the oxygen 

content of a compound and/or removes electrons from an atom

Ozone - An unstable, poisonous allotrope of oxygen, O3, 

that is formed naturally in the ozone layer from atmospheric 

oxygen, and is also produced in the lower atmosphere by the 

photochemical reaction of certain pollutants; it is a highly 

reactive oxidizing agent used to deodorize air, purify water, and 

treat industrial wastes

Phosphatic Clay - The very fine mineral byproduct of the 

phosphate ore beneficiation process

Phytoplankton - A subcategory of planktonic species found in 

fresh and saltwater and which drift near the surface of the water 

where there is plenty of sunlight for growth 

Plankton - Tiny, often microscopic, organisms that inhabit the 

water column of oceans, seas and bodies of fresh water 

Point Source Pollution - The pollution that comes from a 

specific, identifiable source, such as a pipe or channel

Precautionary Principle - The precautionary principle asserts 

that when there are threats of serious or irreversible damage 

to the environment, lack of full scientific certainty should not 

be used as a reason for postponing cost-effective measures to 

prevent environmental degradation.

Predation - The act or practice of capturing another creature 

(prey) as a means for securing food

Proximate - Close in terms of time and/or space

Runoff - The discharge of water over land into surface water or 

groundwater, and which can carry pollutants from the air and 

land into receiving waters

Stormwater - Rainfall that does not infiltrate the ground or 

evaporate because of impervious land surfaces, but instead flows 

onto adjacent land or watercourses or is routed into drain/sewer 

systems

Terrestrial - Of or pertaining to land

Thermocline - An abrupt and dramatic temperature gradient 

that marks the transition between warm surface waters and the 

cooler waters below

Tidal Flow - The water current caused by the tides

Total Maximum Daily Load (TMDL) - a pollution “budget” 

that stipulates the maximum amount of pollution a water body 

can assimilate without violating water quality standards

Transoceanic - Extending across or traversing the ocean

Trichodesmium - A form of cyanobacteria found throughout 

the world’s oceans and which can provide nutrients through the 

process of nitrogen fixation

Trophic Species - The multiple organisms that make up a food 

chain or web. Higher trophic species refer to those at the top of 

the food chain

Upwelling - A process in which cold, often nutrient-rich waters 

from the ocean depths rise to the surface

Wastewater - Spent or used water from an individual home, 

community, farm or an industry that contains dissolved or 

suspended substances

Watershed - Land area that delivers runoff water, sediment, and 

dissolved substances to a major river and its tributaries 

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