Red Tides

This topic submitted by Carrie Bishop ( cellen78@aol.com) at 4:42 PM on 6/9/03.

A swim in a tropical stream, Corcovado Natl Park.

Tropical Field Courses -Western Program-Miami University



Red Tides
Carrie Bishop
Tropical Marine Ecology, 2003


Red Tide, also referred to as Harmful Algal Blooming (HAB), occurs when phytoplankton that contains reddish pigments, “blooms” or grows very rapidly and becomes visible from the surface of the water. These blooms can be harmless, or can contain toxins that can cause the death of sea creatures. This phenomenon can also cause adverse reactions in the human body, through skin and respiratory irritation or through food poisoning (if an affected shellfish is ingested). Red Tide (which has no association with real tides) can be problematic for coastal economies if seafood production is shut down, or if beaches are not available for use by tourists.

My inspiration for studying “red tide” came when visiting Fort Myers, Florida, during spring break 2003. Everyone around me (including myself) seemed to be coughing. I attributed my cough to a virus, but my fellow visitors seemed to think it was “red tide”. By the end of the trip it was a joke, that we had all contracted “red tide disease”. There is an actual basis for scientists to be interested in studying HABs, There seems to be an increasing number of these events occurring, and although they do not seem to do dramatic damage to marine ecosystems, they are a menace to the human communities in coastal areas. Investigation into the cause of increased HAB activity could lead us to discover if human activity is creating an environment that is favorable for these blooms. There are several local, national, and global initiatives that are taking steps to study HABs, and make an effort to safeguard ecological and commercial value of coastal marine ecosystems. The amount of research concerning human health effects from HAB organisms and their toxins is limited, and may become a field of increased interest in coming years.

It is believed that algal blooming has been occuring for millennia. References to red tide events can be found in the Bible, in Chinese documents from the T’ang Dynasty, and in American Indian Lore from Alaska. Specifically in the Caribbean, HAB events date back to the 1500s. Florida records stretch back only to 1844, when the first suspected fish kill by HAB occurred. The worst red tide on record in Florida was from 1946-1947, and University of Miami researchers identified and named the organism responsible (G. breve) during this event. In an effort to stop red tides, state officials in 1957 tried to spray copper sulfate from crop dusters onto Gulf waters, but discontinued this due to damage to other sea life. The longest red tide bloom in Florida history lasted from September 1994 to April of 1996. Currently, there are moderate to high blooms with fish kills and respiratory irritation along the western coast of Florida.

Phytoplankton are marine algae that consist of a single cell; they range in size from 1/1000 of a millimeter to 2 millimeters. Some phytoplankton have use of a flagella for movement, while others rely on currents to move in the water. They require certain nutrients to live and must have access to oxygen, light, and carbon dioxide. There are about 4000 known types of planktonic microalgae, 80 of which are known to be toxic, and 200 which are known to be noxious. The number of harmful species is thought to be underestimated, there are approximately three to four added each year.

A bloom is an increase in population that leads to a peak. The impact of HABs depends on the concentration of the harmful species. There is a minimum cell concentration required for toxicity of all harmful algae. Experts suggest several reasons that blooms may occur, including Global warming, increased nutrient availability, and El NiĖo events. In laboratory experiments scientists can demonstrate that algae growth increases with increased quantities of nutrients, but can’t link this with HAB events in nature due to the complex relationships between harmful and non-harmful species. Temperature variations can induce changes in circulation patterns, and affect the geographic range and magnitude of blooms. Phytoplankton may have an unexpected level of complexity in their interactions with the marine environment, making determining the cause of blooms difficult.

Due to the fact that some toxins are extremely dangerous at very low levels of concentration, we must find reliable ways of detecting toxin concentration in seawater. The traditional methods have been bioassays (often with a mouse), but animal assays have received criticism and researchers are searching for new ways of reading toxin level in the water. Two promising methods have emerged, one is a biochemical assay using radioactive toxin that will be replaced by the natural toxin if it is present in the water, and the second is high performance liquid chromatography (HPLC) which can isolate and identify specific chemical compounds. The biochemical assay is a preferred method for investigations of a specific toxin; the HPLC can be used for a variety of different toxins with little or no changes to the HPLC equipment.

Shellfish can carry toxins that have accumulated in their cells, as can crabs, fish, and some gastropods. When ingested by humans, these can be devastating. Algal toxins may be several times more toxic that cobra venom, and more than one thousand times more toxic than cyanide. Some harmful algae damage their victims by producing mucilage or sharp spines that cause mechanical clogging or lesions of the gills. Fish kills can also be caused by a reduction in oxygen in the water. Although humans are most concerned with the death of fish that affect our economy, there are many other species in the ecosystem that can be damaged by an anoxic area. The research regarding toxins affect of marine ecosystems shows us that there are many different paths the toxin can take through the food chain, and that the phytoplankton are extremely complex in their interaction with other sea life. Specifically in Florida, over 200 manatees were found dead or dying during the spring of 1996. High densities of the algae G. breve were found in the waters in this area. Experimentation found that the specific toxin released by G. breve (saxitoxin) has a high affinity for binding to nerves of several marine mammals. Each of the algae behaves in a slightly different way, making these studies extremely complex.

Red Tide events affect the coastal economies due to decreased tourism and destruction of shellfish farming and fishing. The discoloration of the water often turns off tourists, and although they’ve been deemed “red” tides, they can be green, brown, red, or even white. These blooms can also give off a foul smell that discourages visitation of beaches. Allergic reaction to blooms also dampens the spirit of beachgoers. Shutting down fishing industries has an obvious impact on the economy of a marine society.

Humans are affected not only financially by the HAB events, but physically as well. There are six known syndromes to HAB organisms: ciguatera fish poisoning, paralytic shellfish poisoning, neurotoxic shellfish poisoning, diarrhetic shellfish poisoning, amnesic shellfish poisoning, and Pfiesteria-associated syndrome. These syndromes are caused by consuming tainted foods or through inhaling airborne toxins. Symptoms range from eye irritation and respiratory irritation to paralysis and death.

There are many community initiatives to study and share information regarding HAB events. ECOHAB, EUROHAB, and GEOHAB (Global Ecology and Oceanography of HAB) are large-scale measures to investigate the HABs and their affect of the ecosystem of our earth. There are local organizations in Florida, including START (Solutions to Avoid Red Tide), and The Red Tide Alliance (which includes The State of Florida Fish and Wildlife Conservation Commission's Florida Marine Research Institute (FMRI) which is the State agency responsible for the study of harmful algal blooms (HABs); Mote Marine Laboratory, a not-for-profit marine research laboratory and START). These organizations share interest in red tide’s affect on the economics, public health and natural resources of our earth.

The current abilities of humans to control or prevent HABs are limited. The best we can do is early warning when harmful species reach critical concentrations. The next goal is to forecast harmful events up to 7 days before they occur, in an effort to move fish and harvest shellfish before they are killed. The final stage would be to control the bloom completely, by adding one of several substances to the water. One such substance is ozonated seawater, which in experimental trials reduces, but did not completely prevent, the release of toxins by K. brevis. A second possibility is the introduction of Nannochloris sp. containing y –APONIN, in an effort to convert K. brevis to a non-motile form.

The amount of information regarding HABs is relatively small compared to other scientific fields. Red tide will continue to be studied and information shared in an effort to control HAB events in Florida and throughout the world.

Internet Resources:

The Harmful Algae Page. National Office for Marine Biotoxins and Harmful Algal Blooming. March 29, 2003 http://www.whoi.edu/redtide/whathabs/whathabs.html

Florida Marine Research Institute. Florida Fish and Wildlife Conservation Commission. March 29, 2003. http://www.floridamarine.org/features/default.asp?id=1018

START: Solutions To Avoid Red Tide, Inc. March 29, 2003. http://www.start1.com/

The Red Tide Alliance. March 29, 2003. http://www.redtideonline.com

The Mote Marine Red Tide Update Page. Mote Marine Laboratory. March 30, 2003. Director Mike Henry. http://www.marinelab.sarasota.fl.us/~mhenry/rtupdate.phtml

Florida Environment.com. March 30, 2003. http://www.floridaenvironment.com

Journal Sources:

The degradation of Karenia brevis toxins utilizing ozonated seawater. Harmful Algae. Volume: 2, Issue: 2, June, 2003. pp. 101-107. Schneider, Keith R.; Pierce, Richard H.; Rodrick, Gary E.

High affinity binding of red tide neurotoxins to marine mammal brain. Aquatic Toxicology. Volume: 46, Issue: 2, July, 1999. pp. 139-148. Trainer, Vera L.; Baden, Daniel G.

Recreational exposure to aerosoloized brevotoxins during Florida red tide events. Harnful Algae. Volume: 2, Issue:1, March 2003. pp. 19-28. Backer, Lorraine C.; Fleming, Lora E.; Rowan, Alan; Cheng, Yung-Sung; Benson, Janet, Pierce, Richard H.; et. al.

Studies of the effect of Y-APONIN from Nannochloris sp. On the Florida red tide orgainsm Karenia brevis. Toxicon. Volume:41, Issue: 2, February, 2003. pp. 245-249. Derby, Melissa L.; Galliano, Michael; Krzandwski, Joseph J.; Martin, Dean F.

The diversity of harmful algal blooms: a challenge for science and management. Ocean and Coastal Management Volume: 43, Issue: 8-9, 2000. pp. 725-748. Zingone, Adriana; Oksfeldt Enevoldsen, Henrik


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