The Florida Red Tide

This topic submitted by Andy Black ( at 11:41 PM on 6/9/06.

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The Florida Red Tide and its Impact on SW Florida

Since the first recorded Florida red tide outbreak in 1844, this very dangerous and harmful algae bloom has been studied by scientists. Amazingly, there is still much to learn about the dynamics of this devastating phenomenon. Over the last century red tide blooms have affected almost every county along Florida’s Gulf Coast along with the Florida Keys and some coastal counties along the Atlantic. With blooms ranging from several weeks to over a year, scientists are working to develop a complete understanding of the physical, chemical and biological parameters that lead to red tide's formation and persistence. It has shown to be a very versatile alga, making it able to infest both saltwater as well as brackish water rivers and estuaries. This research will focus on the causes, effects, and management issues the Florida red tide brings to the affected areas, along with the remaining questions scientists still have regarding the harmful algae bloom.


The Florida red tide is in no way a new environmental issue. And although the actual organism responsible for the red tide was never scientifically identified until 1947, there have been anecdotal reports of the apparent effects of red tide along the shores of the Gulf of Mexico dating all the way back to Columbus’ voyage in the 1530’s (Fish). Then, in 1844 the first recorded Florida red tide event was documented. But it was still not until a sweltering fall morning in 1947 in Venice, Florida that the actual organism responsible for the tide was identified (Steidinger).
Originally named Gymnodinium brevis in 1948, the red tide organism has changed names several times within the field of taxonomy. The name was later changed to Gymnodinium breve to adhere with guidelines in the International Cole of Botanical Nomenclature. Then, in 1979 upon new findings concerning the dinoflagellate’s morphology, the name was changed to Ptychodiscus brevis. And then finally in the year 2000 the name Karenia brevis was adopted. This is now what the world can refer to as the Florida red tide (Burkholder).

The Anatomy of a Bloom

Since 1947 much has been learned about K. brevis. Through intense scientific studies we now know the source of the blooms, where they originate, and the effects they have on the surrounding environment. First, to better understand the red tide we must dissect its very source; the dinoflagellate K. brevis.
K. brevis is a very common, unarmored, photosynthetic dinoflagellate that is found year-round throughout the Gulf of Mexico (Start). These year-round concentrations average about one-thousand cells/liter. The cells themselves are typically between 20-45 micrometers long and 10-15 micrometers deep (Fish). Derived from the name “dinoflagellate”, they bare two “whip-like” appendages or flagella that serve in propelling the organism through the water (Burkholder).
Areas of warm waters and high salinity are where K. brevis thrive. This makes the waters of the Gulf of Mexico an ideal environment for the algae (Steidinger). Due to the near-shore effects of the Florida red tide, it is often confused that this is the origination of the blooms. Instead, scientists have found that the blooms originate in the deeper and nutrient-poor waters about eighteen to seventy-four kilometers offshore (Kimm). Every bloom progresses through four major stages. The first stage is the introduction stage. This stage is not yet fully understood by science. The most popular theory suggest that K. brevis goes dormant during parts of the year, in which it settles as sediment on the ocean floor where it later releases itself during periods of warmer waters (Curriero). However, because of the complexity of theory, evidence has not yet been found to completely verify it.
The second stage in the life-cycle of K. brevis is growth. This is where the population, or bloom, steadily increases. As stated before, normal concentrations of the algae are around one-thousand cells per liter. Given the right conditions, it has been found that during the growth stage, K. brevis blooms can more than double this concentration within a few weeks (Fish), making it high enough to begin killing marine life. During this stage the bloom begins forming oxygen depletion zones in the areas it occupies offshore. These oxygen depletion zones are caused by the large amounts of oxygen used by a growing bloom of K. brevis, coupled by the oxygen depleting process of disposing of the fish that have been killed by the toxic bloom (Curriero).
Maintenance is the third stage of the bloom. This is the stage that beachgoers experience. It is where the bloom begins its transport via wind and currents into onshore regions of the Gulf of Mexico. And because of increased nutrient levels found near-shore, the bloom is able to multiply further, allowing the bloom to linger in coastal areas for days, weeks or even months (Fish). Although it is mostly found between the beaches of Clearwater and Sanibel Island, Florida red tide blooms are capable of affecting anywhere on the Gulf coast during this maintenance phase. This is the stage that has been most researched, mainly because it is the most apparent to humans. This is when we see most of the horrible effects of the bloom and where we are most affected (Morris).
The fourth and final stage is dissipation. Water temperature, salinity and nutrient levels of coastal areas all play a factor in the dissipation stage of the K. brevis life-cycle. One reason a bloom may be dissipated or pushed offshore is the introduction of a new water mass, perhaps by freshwater discharges caused by high amounts of rainfall. These can lower salinity levels, lower water temperatures, and create offshore currents, all factors that diminish a once powerful bloom (Curriero).

Effects on Marine Life

The most obvious effect of a K. brevis bloom is its detrimental effect on marine life. Every documented red tide bloom has always been coupled by an astonishing fish kill (Start). Although the blooms mainly affect bottom-dwelling fish such as grouper and grunts, they have been known to kill larger animals such as aquatic birds, dolphins, turtles, and the Florida manatee. There are several mechanisms in which this microalgae enters the body of unsuspecting animals.
The first is known as direct ingestion of cells. Filter feeders such as sponges, zooplankton, and mollusks take in K. brevis while feeding. The algae then remains in the organism’s tissue (Baden). Another way for organisms to attain the harmful algae is by absorption directly across the gills during respiration. This is the most common way fish become poisoned by the bloom (Steidinger). A third transport devise is the bioaccumulation through consumption of prey that carrying the toxin. This is the primary reason for the poisoning of larger animals such as dolphins, aquatic birds, and sea turtles (Baden). Another transport mechanism that is common mainly in mammals and birds is aerosolized transport. This causes respiratory irritation in affected individuals (Fleming).

Effects on Humans

The most apparent symptom of a K. brevis bloom in humans is experienced through aerosolized transport. As blooms experience coastal surf regions, the brevetoxins are easily aerosolized and released into the air. The toxin then is inhaled by beach going humans who experience symptoms such as paroxysmal coughing, tearing, rhinorrhea from irritated eyes and nasal passages (Backer). Although these symptoms can be experienced as extreme, they cease promptly upon leaving beach areas and have not shown any signs of long term side-effects (Fish).
The second and most dangerous way humans are affected by K. brevis blooms is through the digestion of shellfish such as clams, oysters, and muscles that have been contaminated by the toxin. These bottom dwelling organisms tend to contain high concentrations of the K. brevis toxin during bloom episodes and are responsible for neurotoxic shellfish poisoning (NSP) in humans. Symptoms of NSP include loss of motor coordination, pupil dilation, and mild diarrhea (Morris). In some rare cases these stroke-like symptoms have resulted in severe paralysis and even death (Steidinger).

Impact on Southwest Florida

The most obvious impact of onshore K. brevis blooms in Southwest Florida is the loss of marine life. The red tide’s impact on fish can be extreme. However, the most noted impact is that of endangered species such as manatee. In 1996 a red tide bloom was responsible for the death of 149 manatees (Twilley), which feed on seagrass containing the lethal toxin. Dolphins are sometimes also extremely impacted by blooms. In the spring of 2004, 107 dolphins in the Florida Panhandle died after eating smaller fish that had been infected with the K. brevis toxin. This was the fist documented, but most likely not the first case of dolphins being directly impacted by a bloom (Twilley).
Another factor affected by K. brevis blooms is Florida’s tourist industry. Estimated millions of dollars are lost by Gulf Coast tourist beach areas every time there is a significant red tide bloom (Tomerlin). The stinging aerosolized toxin and massive amounts of dead fish that wash up on the beach deter potential beachgoers. Coupled with tourism is the fishing industry that is also directly affected by red tide blooms. Any time there are concentrated amounts of K. brevis, all shellfish harvesting must cease until the bloom is over, which could be months long and cost the fishing industry millions of dollars in lost profit (Tomerlin). Also, fish populations are often greatly depleted, causing fisherman to lose profit on species such as Mahi Mahi, Grouper, and sea trout (Tomerlin).

Unanswered Questions
Despite the intense research conducted towards the Florida red tide, there is still much unknown about this brevetoxin. A few of these outstanding questions are: What exactly causes a bloom to begin its growth stage? What ultimately causes the die-off of a bloom? Where exactly do the blooms originate? What can be done to control future out breaks? These are all great questions that scientists will continue to probe as they work cooperatively to carry out intense studies regarding the K. brevis blooms (Fish). As for now, they will have to await the next bloom to grow to study its creation and effects.

Work Cited

Backer, Lorraine C. et al. Occupational Exposure to Aerosolized Brevetoxins during Florida Red Tide Events: Effects on a Healthy Worker Population. Environmental Health Perspectives, May 2005. Vol. 113: 5.

Baden, Daniel G. et al. Natural and Derivative Brevetoxins: Historical Background, Multiplicity, and Effects. Environmental Health Perspectives, May 2005. Vol. 113: 5.

Burkholder JM, Noga EJ, Hobbs CH, Glasgow HB. New “Phantom” Dinoflagellate is the Causative Agent of Major Fish Estuarine Fish Kills. Nature, 1992. Vol. 358: 407-10.

Curriero, F.C. The Association Between Extreme Precipitation and Waterborne Disease Outbreaks in the United States. American Journal of Public Health, 2001. Vol. 91: 1194-1199.

Fish and Wildlife Research Institute. Florida Fish and Wildlife Conservation Commission. 2006.

Fleming, Lora E., et al. Overview of Aerosolized Florida Red Tide Toxins: Exposures and Effects. Environmental Health Perspectives, May 2005. Vol. 113: 5.

Kimm, Karen L. et al. The Red Tide Toxin, Brevetoxin, Induces Embryo Toxicity and Developmental Abnormalities. Environmental Health Perspectives, 2001. Vol. 109: 4.

Morris, J. Glenn. Harmful Algal Blooms: An Emerging Public Health Problem with Possible Links to Human Stress on the Environment. Annu. Rev. Energy Environment, 1999. Vol. 24: 367-90.

Start: Solutions to Avoid Red Tide, Inc. 2004-2006.

Steidinger, K., et al. Harmful Algal blooms in Florida. HAB Task Force Technical Advisory Group, 1999.

Tomerlin, A., Adams, C. The Economics of Harmful Algal Blooms (HABs). Florida Sea Grant Program, 1999. Vol. 98.

Twilley, Robert R., et al. Confronting Climate change in the Gulf Coast Region: Prospects for Sustaining Our Ecological Heritage. Union of Concerned Scientists & Ecological Society of America, 2001.

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