The Trophic Transfer of Toxins throughout the Food Web

A Case Study on the Economic and Medical Impacts of Red Tide.

By Lucaya Luckey-Bethany.
Based on the interview with Dr. Gabriel Vargo.


This case study is also available in the following formats:

Adobe PDFOpen DocumentWord Document


AbstractThe Broad PictureIndications of a Growing ProblemGoalsQuestions and ScenariosBibliography


Red Tide is a naturally occurring phenomenon in which single-celled algae proliferate at an alarming rate; eventually becoming visible to the naked eye.  Human pollutants are exacerbating this natural problem.  The toxins produced by these algae are gradually being ingested by larger organisms and are quickly moving up the food web into species harvested for human consumption.  This case study will display the significant medical and economic implications from red tide and its subsequent affects on all organisms.

The Broad Picture

“Trophic transfer” is defined as “dietary bioaccumulation… considered the major mechanism for contaminant accumulation in organisms higher up in the food web”; in other words, toxins ingested by single-celled organisms are subsequently eaten by larger and larger organisms, compounding the amount of toxin at each level in comparison to the amount of tainted food eaten. 

Red tide is considered to a very rapid growth, (or “bloom”) of specific types of algae, (one species contains a red pigment which eventually becomes visible from above).  While scientists are attempting to discover the true catalyst for this natural phenomenon, human pollutants such as waste materials are a possible contributing factor to the increased cases of red tide that have been documented in the past few years.  The introduction of nitrates from human waste materials into the ocean waters can serve as a type of fertilizer which may promote the growth of natural algae.

While the food web was once considered a veritable “chain”, recent studies have indicated a much larger amount of interaction than originally perceived, thus resulting in a web of constant cause-and-effect relationships.  Sea creatures that use ocean plants as a primary source of nutrients are affected first, while those preying upon the smaller grazing organisms quickly become affected.  Alarmingly high levels of marine mortality rates may be a first indication of toxic algae levels found in some water supplies.  These toxins will eventually poison shellfish and other popular seafoods for human consumption.  This results in dangerous poisons introduced to the human digestive system.  Four of the five most documented types of human poisoning have already been found in the United States, and the Fifth case is predicted to make an appearance very soon. Amnesic Shellfish Poisoning (ASP) comes from Domoic Acid and can be fatal, within 24-48 hours one may experience sever gastrointestinal discomfort and some alarming neurological affects, some resulting in death.  In 1987 four people died of this poisoning in the United States.  Ciguatera Fish Poisoning (CFP) results from the toxin ciguatoxin or maitotoxin and is possibly fatal, there is no way to test the food before consumption to see if the toxin is present and treatment of the poison can take years for a full recovery.  The Center for Disease Control in Atlanta estimates that only 2-10% of all Ciguatera poisonings are actually documented, while 50,000 people who live in tropic or sub-tropic areas suffer from Ciguatera annually.  Diarrhetic Shellfish Poisoning (DSP) is the only one that has not yet reached the U.S. and is also non-lethal—a full recovery is expected within three days, although rehabilitating gastrointestinal problems are expected to occur.  Neurotoxic Shellfish Poisoning (NSP) is almost identical to CFP but much less severe; however, wave action in the shallow coastal regions can create an aerosol from the toxin brevetoxin which will result in asthma-like symptoms in beach-goers.  Paralytic Shellfish Poisoning (PSP) is possibly fatal, and total heart failure can occur within 24 hours of ingesting the toxin saxitoxin, there is no antidote yet survivors are expected to recover fully.

Economically, the red tide can prove disastrous.  The disintegration of the commercial fishing industry is only one of many possible losses in necessary revenue.  Beach closings and a fall in tourism can spell disaster for many coastal cities and Caribbean island countries.  Clean-up efforts can become monumental, and the monetary affects of treatment not only for subsequent poisonings, but also bacterial infections stemming from massive amounts of decomposing marine life on the local beaches can become financially devastating affects.   Some sort of concentrated and comprehensive effort to find both a cause and possible antidote for algae toxicity must be employed as quickly as possible in order to preserve the world’s oceans.

Indications of a Growing Problem

Evidence of a  continued red tide are beginning to alarm ocean scientists and economists alike, scientist Don Anderson and a highly specialized team of algae researchers have discovered the possibility that the Alexandrium cells within red tide algae have produced cysts, or seed-like forms of the algae which embed themselves in seafloor sediments off of the coast of New England after the dissipation of the red tide that has recently plagued Massachusetts.  These cysts lie dormant until growing conditions become once more favorable—this leads to the prediction that red tide is a phenomenon just waiting for the right moment to invariably strike.

Continued red tide could have disastrous affects, when considering those casualties that have already occurred from a temporary problem.  In 1991 over one hundred pelicans were found dead near Monterey Bay, California—their deaths attributed to the high toxicity of the fish found in their stomachs after the red tide troubled the area.  In past years of red tide instances off the coast of Massachusetts 14 humpback whale corpses were beached within one month, in the year 2004 alone 107 dolphin deaths were attributed to the red tide, and in 1996 over 150 manatees were killed off the coast of Florida; this was approximately ten percent of the entire endangered species population.

Economically, the results are equally staggering.  Estimates in the 1970s found that an average-sized bloom lasting three to four months could cost the state of Florida alone over 20 million dollars, and the 1995-96 bloom cost over double that figure.   Today’s findings are even more alarming: the cost of red tide clean-up, beach closings, and medical treatments can and will cost over 50 million dollars per year.  

Governor Mitt Romney has declared a state of financial crisis in Massachusetts, asking for more than 24 million dollars in order to deal with the current red tide problem, and findings have shown that the commercial fishing industry is losing more than 3 million dollars a week during a red tide event.

Beach closings and inaccessible marine tourist hotspots have also had a drastic impact on the tropical and subtropical economy.  One third of all Americans visit the United States’ coastal regions each year, a total of 910 million trips and spending almost $44 billion.  This money goes towards supporting the local economies—hotels, restaurants, and private entrepreneurs alike.  Fishing is also an American pastime which has significant monetary ramifications.  There are an estimated 35 million anglers who were estimated to spend $ 38 billion in 1996 alone, and the numbers are only increasing.  That is one out of every six Americans of age sixteen spending over $1,000 in pursuit of their sport.  The sport of kayaking or canoeing was a $99 million-dollar industry in 1996—also, these industries provided nearly seven million jobs in that year and generated sales reaching $450 billion, most of which were attributed to the recreation and tourist economic activity.

With continued affects from red tide manifesting themselves, the tourist economy will crumble as endangered species take on new onslaughts, leaving devastating numbers behind.


The catalyst which begins the algal bloom process is the first culprit to identify, once that is completed, there must be a concentrated effort to stem the red tide, as well as a genuine cut-back on human waste materials dumped into the oceans.  Continued protection of endangered species must be increased, as well as a more in-depth analysis of the implications of a food web where all organisms form a very intricate global relationship.  Only through continued research and a certain open-mindedness for the necessary fund to be granted can the destructive process of red tide be stopped before there are more cases of economic, medical, and biological crisis.

Questions and Scenarios

Provide short but concise answers to the following questions:

  1. Are there any potential benefits that could result from the red tide? If so, what could they be and how could they help benefit society?
  2. What are some theories of how algal blooms occur and how they are sustained?
  3. What are some harmful implications of red tide that have not been addressed in this case study?
  4. Assume you are putting together a proposal for an inland community to help financially support red tide research, how would you convince them that this is a sound and necessary investment?