Paper : Harmful Algal Blooms
This discussion topic submitted by Daniel J. Garnet (
firstname.lastname@example.org) at 12:58 am on 5/17/00. Additions were last made on Sunday, October 27, 2002.
Red tides, now termed Harmful Agal Blooms (HAB), are becoming notorious in the scientific community. Algae serve as the energy producers at the base of the food web and any disturbance in this “base” can cause severe and drastic problems in the entire food web. Most species of algae or phytoplankton are not harmful. Occasionally, the algae grow at an exponential rate and bloom in dense communities. A few species of algae produce potent neurotoxins which, when present in dense concentrations, affect higher forms of life either directly or indirectly such as zooplankton, shellfish, fish, birds, marine mammals and even humans (Anderson). These affects are not only on organisms, but there are also adverse affects found in the “health” of economies that depend on fisheries, shellfish beds and coastal tourism. Public illness and expensive medical treatments are also examples of the affects on economies (Boesch). The prevention, control and mitigation of these Harmful Algal Blooms are extremely important (Bushaw).
The term red tide is no longer used because it is a misnomer. The blooms are not always red but can be yellow, orange, brown, pink or reddish-brown. The blooms also are not dependent on the tides. The term HAB is used to describe a bloom phenomenon that contains toxins or a bloom that causes negative impacts to the environment.
The life cycle of these algal species is very important when determining how to prevent the spread of these blooms. The cysts of the algae remain dormant, buried in deep ocean sediments. These cysts “could” remain dormant for many years if left undisturbed. Germination of these cysts occurs when there is an increase in temperature and sunlight and the result is a free-swimming cell. Cell growth is influenced by a variety of factors, including sunlight, temperature, salinity, and the amount and types of nutrients available in the water (Florida). If these conditions remain optimal, then the cell will grow and divide exponentially. This means that the first cell divides to create two cells, which divides to create four cells, which divides to create eight cells etc. This is the stage when toxicity can occur. After nutrient and sunlight depletion occur, gametes join and form a zygote. The zygote eventually forms a cyst, which falls to the ocean floor and there remains dormant until the cycle is repeated (Anderson).
All species of algae are natural and their blooms have been documented for thousands of years. Winds and currents used to be the only modes of transportation of these blooms but now humans have aided the distribution of these algae. The scientific problem is that the number and diversity of reported HAB incidents have increased during the past twenty-five years and now include almost every U.S. coastal state. This fact worries some scientists and yet others feel that this is a natural occurrence. Currently, there are four accepted possible causes for the increase in HABs.
The first reason, according to scientists, is that there are now improved methods of detection (Bushaw). Scientists that believe this theory claim that the frequency of blooms has not increased but rather that the extent to which outbreaks occur is a greater area than previously studied. Statistical facts have proven that the blooms are more extensive and last longer than previously recorded. Conversely, scientists know that blooms are now being recorded in places where there was no previous record of blooms two decades ago.
The second possible explanation of the increase in blooms is that exotic species of algae may have been introduced via water ballast exchange (Bushaw). This theory has many critics but there is genetic similarity between species of algae in the United States and in other parts of the world. The similarity indicates that dispersal of the algae has occurred but the time this happened and the mode of dispersion has yet to be determined.
A third possibility is that the increase in HABs is due to the failure of grazers to control the algal species’ growth (Bushaw). The main grazers of algae are fish larvae, the microbial food web, bivalves such as clams and mussels, and herbivorous zooplankton. The grazer’s ability to regulate the population depends on biological, chemical, and physical factors as well as timing. The toxins produced by the HABs do not affect all algal consumers. Some are able to consume the algae with no adverse effects while others may experience harmful side effects.
The fourth and final theory is that blooms may result from climate changes, as well as human activities such as increased pollution and nutrient inputs, habitat degradation and the regulation of water flow (Bushaw). There are two main species that appear to bloom in response to an influx of nutrients: cyanobacteria (blue-green algae) and macroalgae. Nutrients that are believed to cause serious HAB problems are nitrogen and phosphorus. There has been a reported higher density of nontoxic algae in nutrient-rich waters caused by animal farm overflows and sewage discharge. This dense alga has also been produced in laboratory cultures enriched with nitrogen and phosphorus. River discharge has also been linked to the increase of HABs due to the nutrient rich water.
Out of 2000 plus species, fewer than 100 produce toxins (Florida); yet HABs create a diverse array of health problems to the environment. There are many cause and effect relationships when looking at the problems associated with HABs. For marine life, HABs can have devastating effects. Most of the toxins affect the nervous system of fishes, causing death by a decrease in respiration. Toxins produced by the algae are released during the bloom phase. The dinoflagellate Gyrodinium aureolum produces a compound that narcotizes fish gills and congests bronchial blood vessels (Bushaw), effectively suffocating the fish. Nearly all fish are susceptible to the toxins and the red tide bloom of 1946-47 is estimated to have killed 500 million fish (Florida). Fish caught during HABs show no evidence of the toxin and are so said safe to eat (Florida)! Bivalve shellfish, such as clams and oysters, which feed by filtering plant matter from the water, may ingest the algae consequently becoming toxic to consumers but not being effected directly (Beauchamp). In many coastal waters, manatee deaths are now being linked to HABs. In 1996, 149 manatee deaths were recorded and attributed to a bloom that occurred in a manatee wintering area (Florida). There have been many other manatee deaths reported since and before this recorded episode. Nontoxic harmful algal blooms can have effects on the environment also. Blooms of macroalgae become so dense that sections of coral reefs and seagrass beds become overwhelmed due to the lack of oxygen and sunlight. Although a bloom may kill large numbers of animals, there are species that do benefit from the blooms and have been doing so for many years. Many of these problems and some totally new problems affect humans.
The greatest threat to human life is through consumption of bivalve shellfish that have been contaminated with the toxins produced by the algae. There are several toxins that produce some very nasty health problems in humans. Amnesic Shellfish Poisoning (ASP) is a syndrome that can be life threatening. Pseudo-nitzschia sp. secretes the toxin domoic acid, which causes ASP. Both gastrointestinal and neurological disorders occur in infected people (Anderson). Symptoms include nausea, vomiting, abdominal cramps, and diarrhea. Neurological symptoms can also appear within 48 hours of consumption. They include dizziness, headache, seizures, short-term memory loss, respiratory failure and coma. Ciguatera Fish Poisoning (CFP) is a syndrome produced by the ingestion of shellfish contaminated by many different species of algae that secrete ciguatoxin/maitotoxin (Anderson). CFP produces gastrointestinal, neurological and cardiovascular symptoms. The same symptoms as ASP are seen in CFP and also sweating, numbness, and reversal of temperature sensation. These can all lead to paralysis and death. Okadaic acid produced by Dinophysis sp. is responsible for Diarrhetic Shellfish Poisoning (DSP). Gastrointestinal symptoms occur within 30 minutes of consumption and include incapacitating diarrhea, nausea, and chills. Gymnodinium breve produces brevetoxins causing Neurotoxic Shellfish Poisoning (NSP). This syndrome is nearly identical to CFP. Toxic aerosols are produced by wave action, which can produce respiratory asthma-like symptoms in patients (Beauchamp). Paralytic Shellfish Poisoning (PSP) is another life threatening syndrome caused by the production of saxitoxins in many algal species (Anderson). Symptoms are purely neurological and include ataxia, giddiness, fever, rash and staggering. In severe cases respiratory arrest occurs within 24 hours of consumption.
There is no antidote for most if not all of these syndromes. Supportive therapy is usually the action taken and some of the toxins just have to run their course in 3-4 days with or without medical treatment.
Many economies are damaged by the loss of coastal fisheries and shellfish beds. An average of $100 million per year nationwide in losses is attributed to HABs. For fisheries, insurance rates rise, unemployment and bankruptcies rise and retail sales decline due to scares and public resources are diverted to monitoring programs. A recent outbreak of Pfiesteria in the Chesapeake Bay resulted in an estimated $43 million loss for the local seafood industries (Bushaw). The 1991 domoic acid/ASP outbreak in Washington had a negative impact on the entire city (Bushaw). Tourism dropped significantly and an estimated $18 million was lost for local fisheries.
HABs have a large impact on coastal waters and their prevention and control is a major interest to many groups. The answer to the problem of controlling and preventing HABs is not straightforward and is very complex. There are many state and federally funded research programs working right now trying to find the best possible way to mitigate the effects of HABs and trying to develop prevention for future outbreaks. Current research is focused on (1) identifying toxins, (2) developing tests for studying HAB species, (3) developing rapid and inexpensive tests for identifying HABs in coastal waters, (4) evaluation of specific procedures to rid HABs from waters, and (5) isolation and characterization of natural bacterial and viral populations that could possibly be used to control HABs (Bushaw). Many scientists believe that there is no way and no reason to eradicate HABs. HABs often occur over thousands of square miles of water and are not restricted to the surface. Any biological or chemical means of attacking these algae may adversely effect other forms of marine life. Many scientists believe that the disturbance the HABs cause is beneficial to the growth and renewal of the ecosystem much like “gap” areas created in rainforests when trees fall (Boesch).
In summary, like anything in nature, there is no easy way to solve this problem. Many scientists still are not even sure that HABs are problems. There seem to be as many causes to the increase in HABs over the past two decades as there are problems produced by the HABs. In order to preserve animals like manatees, various fish and to keep ourselves safe we are all going to have to be more conscientious about the waste we put in to our environment. Our government is going to have to enforce tougher laws on dumping and we as humans are going to have to help out the environment by finding some way that loss due to HABs can be minimized.
1. Anderson, Don. Woods Hole Oceanographic Institute. “Harmful Algae Page”
2. Beauchamp, Richard A. Hendricks, Kate. Odener, Mike. Wiles, Kirk. Texas Department of Health. Bureau of Food and Drug Safety.
3. Boesch, Donald F. Anderson, Donald M. Horner, Rita A. Shumway, Sandra E. Tester, Patricia A. Whitledge, Terry E. Harmful Algal Blooms in Coastal Waters: Options for Prevention, Control and Mitigation. Feruary, 1997
4. Bushaw-Newton, K.L. and Sellner, K.G. 1999. Harmful Algal Blooms. In: NOAA’s State of the Coast Report. Silver Spring, MD: National Oceanic and Atmospheric Administration. No copyright, Government of United States of America.
5. Florida Department of Environmental Protection, Florida Marine Research Institute. “Red Tide, Florida’s Unwelcome Visitor”. February, 1998
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