Red tide

Not to be confused with Crimson Tide and pink tide.
Further information: Harmful algal bloom
A red tide off the coast of La Jolla San Diego, California.

Red tide is a common name for a phenomenon known as an algal bloom (large concentrations of aquatic microorganisms) when it is caused by a few species of dinoflagellates and the bloom takes on a red or brown color. Red tides are events in which estuarine, marine, or fresh water algae accumulate rapidly in the water column, resulting in coloration of the surface water. It is usually found in coastal areas. It kills many manatees every year.[1]

These algae, known as phytoplankton, are single-celled protists, plant-like organisms that can form dense, visible patches near the water's surface. Certain species of phytoplankton, dinoflagellates, contain photosynthetic pigments that vary in color from green to brown to red.

When the algae are present in high concentrations, the water appears to be discolored or murky, varying in color from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discoloration, and not all discolored waters associated with algal blooms are red. Additionally, red tides are not typically associated with tidal movement of water, hence the preference among scientists to use the term algal bloom.

Some red tides are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms. The most conspicuous effects of these kinds of red tides are the associated wildlife mortalities of marine and coastal species of fish, birds, marine mammals, and other organisms.

Overview

Red tide (NOAA)

Red tides in the Gulf of Mexico are a result of high concentrations of Karenia brevis, a microscopic marine algae that occurs naturally but normally in lower concentrations. In high concentrations, its toxin paralyzes the central nervous system of fish so they cannot breathe. Dead fish have been observed to wash up on gulf beaches of Mexico and Texas.[2] Dense concentrations appear as discolored water, often reddish in color. It is a natural phenomenon, but the exact cause or combination of factors that result in a red tide outbreak are unknown.[3] Red tide causes economic harm and for this reason red tide outbreaks are carefully monitored. For example, the Florida Fish and Wildlife Conservation Commission provides an up-to-date status report on the red tide in Florida.[4] Texas also provides a current status report.[5]

Red tide is also potentially harmful to human health.[6] Humans can become seriously ill from eating oysters and other shellfish contaminated with red tide toxin.[7] Karenia brevis blooms can potentially cause eye and respiratory irritation (coughing, sneezing, tear production, and itching) to beachgoers, boaters and coastal residents.[8] People with severe or persistent respiratory conditions (such as chronic lung disease or asthma) may experience stronger adverse reactions. The National Oceanic and Atmospheric Administration's National Ocean Service provides a public conditions report identifying possible respiratory irritation impacts in areas affected by red tides.[9]

The debate over the cause of red tides is controversial. Red tides occur naturally off coasts all over the world. Not all red tides have toxins or are harmful.[10]

Definition

Red tide is a colloquial term used to refer to one of a variety of natural phenomena known as harmful algal blooms or HABs. The term red tide specifically refers to blooms of a species of dinoflagellate known as Karenia brevis.[11] It is sometimes used to refer more broadly to other types of algal blooms as well.

The term red tide is being phased out among researchers for the following reasons:

  1. Red tides are not necessarily red and many have no discoloration at all.
  2. They are unrelated to movements of the tides.
  3. The term is imprecisely used to refer to a wide variety of algal species that are known as bloom-formers.

As a technical term it is being replaced in favour of more precise terminology including the generic term harmful algal bloom for harmful species, and algal bloom for non-harmful species.

The term red tide is most often used in the United States of America to refer to Karenia brevis blooms in the eastern Gulf of Mexico, also called the Florida red tide. These blooms occur almost annually along Florida waters. The density of these organisms during a bloom can exceed tens of millions of cells per litre of seawater, and often discolor the water a deep reddish-brown hue.

The term red tide is also sometimes used to describe harmful algal blooms on the northern east coast of the United States, particularly in the Gulf of Maine. This type of bloom is caused by another species of dinoflagellate known as Alexandrium fundyense. These blooms of organisms cause severe disruptions in fisheries of these waters as the toxins in these organism cause filter-feeding shellfish in affected waters to become poisonous for human consumption due to saxitoxin.[12] The related Alexandrium monilatum is found in subtropical or tropical shallow seas and estuaries in the western Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico and the eastern Pacific Ocean.

Causes

The occurrence of red tides in some locations appears to be entirely natural (algal blooms are a seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents)[13][14] while in others they appear to be a result of increased nutrient loading from human activities.[15] The growth of marine phytoplankton is generally limited by the availability of nitrates and phosphates, which can be abundant in agricultural run-off as well as coastal upwelling zones. Coastal water pollution produced by humans and systematic increase in sea water temperature have also been implicated as contributing factors in red tides. Other factors such as iron-rich dust influx from large desert areas such as the Saharan desert are thought to play a major role in causing red tides.[16] Some algal blooms on the Pacific coast have also been linked to occurrences of large-scale climatic oscillations such as El Niño events. While red tides in the Gulf of Mexico have been occurring since the time of early explorers such as Cabeza de Vaca,[17] it is unclear what initiates these blooms and how large a role anthropogenic and natural factors play in their development. It is also debated whether the apparent increase in frequency and severity of algal blooms in various parts of the world is in fact a real increase or is due to increased observation effort and advances in species identification methods.[18][19]

Notable occurrences

See also

References

  1. ↑ "Discover NOAA's Coral Reef Data". www8.nos.noaa.gov. Retrieved 2009-08-22.
  2. 1 2 "Red Tide in Texas, Current Status". Texas Parks and Wildlife. 15 September 2015. Retrieved 30 September 2015.
  3. ↑ "Red Tide FAQ". www.tpwd.state.tx.us. Retrieved 2009-08-23.
  4. ↑ Florida Fish and Wildlife Research Institute. "Red Tide Current Status Statewide Information". research.myfwc.com. Retrieved 2009-08-23.
  5. ↑ "Red Tide Index". www.tpwd.state.tx.us. Retrieved 2009-08-23.
  6. ↑ "Harmful Algal Blooms: Red Tide: Home". CDC HSB. Retrieved 2009-08-23.
  7. ↑ "Red Tide FAQ - Is it safe to eat oysters during a red tide?". www.tpwd.state.tx.us. Retrieved 2009-08-23.
  8. ↑ Kirkpatrick, B., L.E. Fleming, D. Squicciarini, L.C. Backer, R. Clark, W. Abraham, J. Benson, Y.S. Cheng, D. Johnson, R. Pierce, J. Zaias, G.D. Bossart, and D.G. Baden. 2004. "Literature Review of Florida Red Tide: Implications for Human Health Effects." Harmful Algae. Volume 3. Pages 99 to 115.
  9. ↑ "Harmful Algal Bloom Operational Forecast System". www.tidesandcurrents.noaa.gov/hab/. Retrieved 2012-02-14.
  10. ↑ Gregg W. Langlois, Pamela D. Tom. "Red Tides: Questions and Answers". U.S. Government. Retrieved 2009-08-23.
  11. ↑ "Harmful Algal Blooms (HABs): Red Tide". U.S. Centers for Disease Control and Prevention. Retrieved 2 Oct 2011.
  12. ↑ "Red Tide Fact Sheet - Red Tide (Paralytic Shellfish Poisoning)". www.mass.gov. Retrieved 2009-08-23.
  13. ↑ Trainer, VL; Adams, NG; Bill, BD; Stehr, CM; Wekell, JC; Moeller, P; Busman, M; Woodruff, D (2000). "Domoic acid production near California coastal upwelling zones, June (1998)". Limnol Oceanogr 45: 1818–1833. doi:10.4319/lo.2000.45.8.1818.
  14. ↑ Adams, NG; Lesoing, M; Trainer, VL (2000). "Environmental conditions associated with domoic acid in razor clams on the Washington coast". J Shellfish Res 19: 1007–1015.
  15. ↑ Lam CWY, Ho KC (1989) Red tides in Tolo Harbor, Hong Kong. In: Okaichi T, Anderson DM, Nemoto T (eds) Red tides. biology, environmental science and toxicology. Elsevier, New York, pp 49–52.
  16. ↑ Walsh; et al. (2006). "Red tides in the Gulf of Mexico: Where, when, and why?". Journal of Geophysical Research 111: C11003. Bibcode:2006JGRC..11111003W. doi:10.1029/2004JC002813.
  17. ↑ Cabeza de Vaca, Álvar Núnez. La Relación (1542). Translated by Martin A. dunsworth and José B. Fernández. Arte Público Press, Houston, Texas (1993)
  18. ↑ Sellner, K.G.; Doucette G.J.; Kirkpatrick G.J. (2003). "Harmful Algal blooms: causes, impacts and detection". Journal of Industrial Microbiology and Biotechnology 30 (7): 383–406. doi:10.1007/s10295-003-0074-9. PMID 12898390.
  19. ↑ Van Dolah, F.M. (2000). "Marine Algal Toxins: Origins, Health Effects, and Their Increased Occurrence". Environmental Health Perspectives 108 (suppl.1): 133–141. doi:10.2307/3454638. JSTOR 3454638. PMC 1637787. PMID 10698729.
  20. 1 2 "PARALYTIC SHELLFISH POISONING (PSP)". Sabah Fish Department.com. Retrieved 2013-01-11.
  21. ↑ University of Florida Marine and Natural Resources, IFAS Extension
  22. ↑ HAB 2000
  23. 1 2 3 "Red tide warning". New Straits Times. 2013-01-06. Retrieved 2013-01-07.
  24. 1 2 "2 Red Tide deaths in Sabah". Daily Express. 2013-01-06. Retrieved 2013-01-11.
  25. ↑ (R/V) Oceanus, National Science Foundation
  26. ↑ Moore, Kirk. "Northeast Oysters: The bigger danger, growers assert, would be the label of endangered". National Fisherman. Retrieved 2008-07-31.
  27. ↑ Fimrite, Peter (2011-09-17). "Red tide killing abalone off California". The San Francisco Chronicle.
  28. ↑ "Texas Gulf Coast Sees Largest Algae Bloom In Over A Decade". Huffington Post. 2011-10-18.
  29. 1 2 MUGUNTAN VANAR (2013-01-07). "Sabah issues red tide alert". The Star Online. Retrieved 2013-01-07.
  30. ↑ Herald-Tribune
  31. ↑ Netburn, Deborah (11 August 2014). "Massive 'Florida red tide' is now 90 miles long and 60 miles wide". Orlando Sentinel. Retrieved 30 September 2015.
  32. ↑ Israel, Dale G. (June 25, 2015). "12 persons hospitalized in Bohol for red tide poisoning".
  33. ↑ "Rijkswaterstaat, do not swim between Katwijk and Scheveningen". Dutch Public Broadcasting, NOS. 3 August 2015. Retrieved 30 September 2015.

External links

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