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Marie Manandise and Tom Sumner. CoMPLEX, University College London, 4 Stephenson Way, London, NW1 2HE. a. b. RED TIDES: Causes, Consequences and Control of Algal Blooms.
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CoMPLEX, University College London, 4 Stephenson Way, London, NW1 2HE
RED TIDES: Causes, Consequences and Control of Algal Blooms
“Red tides” are massive blooms of a single phytoplankton species which change the colour of the sea (fig. 1). The term red tide is confusing because the colour depends on the pigmentation of the species that blooms. It can also be orange (fig. 2), brown or even bright green.
In contrast to common seasonal algal blooms, their occurrence is not predictable; the conditions required for a red tide to appear are not yet fully understood. Besides, seasonal blooms involve a whole community of algae and not a single species.
Red tides are a natural phenomenon which can be without any consequence. However, some blooms can temporarily disturb the marine ecosystem.
Approximately 200 species are known to cause red tides. The majority of these species belong to the phylum dinoflagellates.
Dinoflagellates are autotrophic protozoans, i.e. unicellular algae. They are primary producers at the basis of the marine food chain. Not all of them are strictly autotrophic as they can also phagocyte organic matter.
Dinoflagellates typically have two flagella which are used for propulsion. Each lies in a groove on the cell surface. The sulcus trails freely, while the cingulum is wrapped around the body (Fig 2).
Most dinoflagellates have a cell wall made out of cellulose plates trapped in intracellular vesicles or alveoli. Xantophophyll pigments are responsible for their brown to golden-brown colour.
What are Red Tides?
When Do They Occur?
The Effects of Red Tides
Figure 4. Fish kill due to oxygen depletion, Narrangasett Bay, USA.
Figure 1. Two examples of red tides a) Cape Rodney, New Zealand b) a bloom of Noctiluca scintillans, La Jolla, California.
Monitoring and Control
Figure 3. Change in N:P ratio in Tolo Harbour between 1982 and 1989, and the occurrence of red tides during the same period.
Reproduced from Hodgkiss and Ho, 1997.
Figure 5. Concentration of chlorophyll a monitored by satellite.
Figure 2. Dinoflagellate anatomy
Barnes R. D., and E. E. Ruppert, 1996. Invertebrate zoology, sixth edition. Ed. Harcourt, Orlando; Dubois P. 2005. Marine biology, course notes (Free University of Brussels); Hodgkiss I. J., and K. C. Ho,1997. Are changes in N:P ratio in coastal waters the key to increased red tieds blooms? Hydrobiologia352: 141-147; Millie D. M., Schofield O. M., Kirkpatrick G. J., Johnsen G., Tester P. A., and B. T. Vinyard, 1997. Detection of harmful algal blooms using photopigments and absorption signatures: a case study of the Florida red tide dinoflagellate, Gymnodinium breve. Limnology and Oceanography42(5): 1240-1251; Tester P. A., and K. A. Steidinger, 1997. Gymnodinium breve red tide blooms: initiation, transport, and consequences of surface circulation. Limnology and Oceanography42(2): 1039-1051; Fig. 1a. N. Godfrey www.niwascience.co.nz; Fig. 1b. Peter Franks, Scripps intstitution of oceanography; Fig. 2. www.geo.ucalgary.ca/~macrae/palynology/dinoflagellates/; Fig. 4. www.geo.brown.edu/georesearch/insomniacs; Fig. 5. sg.geocities.com/myredtide/250m.htm