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What Are Red Tides?

written by: Niki Fears•edited by: Niki Fears•updated: 5/31/2009

Learn about red tides and how they are caused.

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    When certain species of marine algae begin to bloom in wide spread and dangerous ways causing a red coloration due to the concentration of algae in wide spaces of the ocean it is the phenomenon known as a red tide. Red Tides are really think, rather dense patches of certain types of algae, also referred to as phytoplankton, which posses a strong reddish coloration. In such large concentrations they become quite visible as they being to rapidly multiple in the water column and can look like giant waves of red sweeping into shore, giving way to the popular name of a red tide; however, not all such algae are red or cause discoloration.

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    Dangers of Red Tides:

    RedTideOffofCalifornia Red Tides can present several problems for the environment and human health. Algae live near the surface of the water and as they get picked up by the wind they can blow inland. People living near coastal areas where Red Tides have occurred may suffer from a range of health and respiratory problems. Additionally, ingesting shell fish from the affected areas can be extremely hazardous due to the toxins that the algae releases into the water which are absorbed by the shell fish.

    The level of toxins is so high in fact, that the presence of a Red Tide can lead to a massive die off of fish, sea birds, and sea mammals in the effected areas. The toxins attack the neurosystem of fish and other marine life and it is very important to avoid eating contaminated shellfish from a red tide incident.

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    What Are The Causes of Red Tides:

    Red Tides occur when a large, uncontrolled amount of certain types of waste and nutrients enter the marine environment causing the algae which feed upon these nutrients to begin to grow and multiply at a dangerous rate. Agricultural run-off from farming is one of the largest contributors to the burst in growth. In some cases, certain species of algae are going through a normal seasonal sequence of blooming but when they are exposed to this over dose of nutrients their populations begin to boom to harmful and unsustainable levels.

    Red Tides can appear anywhere in the world, in fact in recent years incidences have been reported further north towards Canada than were previously seen. Global warming and the rise of sea temperatures along with the increases in agricultural production to meet the demands of growing populations have both been cited as contributors to this spread of Red Tide.

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    Harmful Algal Bloom Or Red Tide:

    Many are preferring to use the phrase Harmful Algal Bloom (HAB) as opposed to red tides when describing this occurrence. There are several reasons for this shift in terminology, one being the fact that there are different species that occur in the phenomenon of “red tides” many of which may be green or brown or even have a purple, pinkish color or in some cases there is little or no visible color change of the water; hence, red tides may not always be red; therefore, phasing out the term to better identify the problem is the goal of the new term.

    Additionally, the occurrence described as “red tide” does not actually have anything to do with the movements of the ocean's tides, thus, the name can be a bit misleading for those who are not familiar with this environmental problem. (To learn more about what tides actually are, read this article: "What Are Tides?"

    It is important that we take measures to control pollution and runoff that leads to this problem because if Red Tides were to continue to grow and spread, they would cover the upper layers of the water's surface and in addition to the harm caused by their toxins, they could also begin to cut off the supply of sunlight to organisms beneath them, wrecking havoc on the marine and world ecosystem.