Gymnodinium catenatum is a dinoflagellate belonging to the Phylum Dinophyta, Kingdom Protista. Dinoflagellates are unicellular, contain the pigments Cholorpylls a and c, and xanthophylls, contain cellulose in their cell wall, carry out oxygenic photosynthesis, and thrive in a marine environment (Madigan, 736). Dinoflagellates have a transverse flagellum that attaches laterally and a longitudinal flagellum that extends lengthwise from the lateral groove (Raven, 366). Dinoflagellates are very resilient organisms. They are able to form resting cysts when low nutrient levels persist. The cysts drift to the ocean floor, where they can remain viable for years. Cysts can be transported to other locations by the current of the ocean or in the hulls of ships. When nutrient conditions are favorable, the cysts germinate forming free swimming cells (Raven, 365).
Dinoflagellates are a basic part of the marine food web. Mass occurrences of the phytoplankton are termed algal blooms. In most cases, this is beneficial to the marine ecosystem because it is an abundant food source. Mussels, small fish, and even large fish feed upon the dinoflagellates. However, some of the algal blooms can cause massive fish kills, the contamination of mussels, and a disruption of the marine ecosystem. The harmful algal blooms (HAB) are classified into two divisions: toxin producers, which can contaminate seafood and kill fish, and high-biomass producers, which can cause anoxia and death of marine life after reaching dense concentrations (Geohab, 7).
Gymnodinium catenatum belongs to the first group of HAB's. It is responsible for the red tides off the coast of Africa and California and is known to cause Paralytic Shellfish Poisoning (PSP). About 100 cases have resulted in death and thousands of cases causing illness (Fisheries Western Australia, 2). G.catenatum produces saxitoxin as a secondary metabolite. Saxitoxin is a neurotoxin that disables the sodium pump (deCarvalho, 552). Mussels feed upon dinoflagellates such as G. catenatum. The toxin accumulates and concentrates in the filter feeders and humans ingest the shellfish (Raven, 364).
The symptoms for the PSP include a variety of gastrointestinal and neurological symptoms. Symptoms for a mild case include headache, nausea, vomiting, diarrhoea, and a tingling sensation around the lips, gradually spreading to the face and neck. However, in an extreme case of PSP, the symptoms are much more severe. A person may experience muscle paralysis, respiratory difficulty, and death may occur 2-24 hours after ingestion. The only treatment for Paralytic Shellfish Poisoning is the stomach pumped and in extreme cases artificial respiration (Fisheries Western Australia, 2).
It is difficult to determine if shellfish are contaminated with saxitoxin or some other toxin caused by dinoflagellates. Infected mussels cannot be identified visually. Some precautions may be taken to prevent PSP. People should avoid eating shellfish in areas where red tides are known to occur or during times when a red tide is prevalent. About twenty species of dinoflagellates have been shown to produce saxitoxin. If a red tide is present, the chances increase for the mussels to have ingested dinoflagellates that produce saxitoxin. Another precaution is cooking and discarding cooking fluids afterward. This decreases the amount of poison ingested by the consumer. If the shellfish are left in the preparatory liquid, they can absorb more of the poison. However, the only true prevention is to avoid eating shellfish totally or to have the shellfish tested by the public health department (Fisheries Western Australia, 3).
Harmful algal blooms not only pose a threat to human health, but they also affect humans economically. In Japan, HAB's cause an estimated loss of one billion yen per year occurs due to the death of finfish and shellfish in aquaculture sites. In 1996, several molluscs were removed from the market because tests revealed toxin levels well above standards set by the World Health Organization. Estimates for the confiscation of the molluscs and the hospital treatments of the poisoning cases were about 50 million in US dollars (Geohab, 9). Harmful algal blooms have occurred throughout history. However, there is an increase in the frequency of the HAB's. Human activity affects the occurrence of algal blooms. Sewage and agricultural runoff provide dinoflagellates with the high nutrient levels needed for reproduction. Transportation to different locations is provided by the ship's ballast waters (GeoHab, 10).
Increased awareness of the toxins produced by the dinoflagellates may reduce the number of illnesses related to the consumption of the shellfish. However, the algal blooms are devastating economically. Due to the increased occurrences of HAB's, scientists are researching preventative methods. Research for reducing the population in an algal bloom of G. catenatum occured in Japan in 1998. A red tide of G. catenatum in Yatsushiro Sea was dramatically reduced with the growth of Polykrikos kofoidii. The tests showed that more than 50% of P. kofoidii predated on the natural population of G. catenatum. The P. kofoidii successfully contributed to the cessation of G. catenatum (Matsuyama, 91).
References
1) deCarvalho, Mamede; Jacinto, Jorge; Ramos, Natalia; Journal of Neurology, "Paralytic Shellfish Poisoning: Clinical and Electrophysiological observations," Vol. 245, Issue 8, 1998, pp 551- 554..
2) Madigan, Michael; Marinko, John; Parker, Jack; Brock Biology of Microorganisms, Prentice Hall, NJ, 2000, pp 735-739.
3) Matsuyama, Yukihiko; Miyamoto, Masahide; Kotani, Yuichi: Aquatic Microbial Ecology, "Grazing Impacts of the Heterotrophic Dinoflagellate Polykrikos kofoidii on a bloom of Gymnodinium catenatum," Vol 17, pp, 91-98, 1999
4) Raven, Peter; Evert, Ray; Eichhorn, Susan; Biology of Plants sixth edition, W.H. Freeman and Company Worth Publishers, 1999, pp364- 366.
5) Fisheries Western Australia, "Marine Biotoxins" http://www.wa.gov.au/westfish/sf/broc/fhinfo/fhinfo04.html
6) GEOHAB: Global Ecology and Oceanography of Harmful Algal Blooms, 1998. http://www.phys.ocean.dal.ca/~jhurst/SCOR/GEOHAB/GEOHAB.html
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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