Red TideRed tide is a term people have coined for the phenomenon more correctly known as an algal bloom. Scientists prefer to use the term algal bloom because:
This happens when river, marine, or fresh water algae grow rapidly to form a dense, thick mass. These algae, or more specifically phytoplankton, are single-celled protists, plant-like organisms that can form dense, visible patches near the water's surface. The growth occurs close to the surface as they rely on sunlight to penetrate to perform photosynthesis. Certain species of phytoplankton, such as Dinoflagelate, contain photosynthetic pigments that vary in colour from green to brown to red.
When the algae are present in high concentrations, the water appears to be discoloured or murky, varying in colour from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discolouration, and not all discoloured waters associated with algal blooms are red.
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 are the associated wildlife mortalities among marine and coastal species of fish, birds, marine mammals and other organisms. In the case of Florida blooms, these mortalities are caused by exposure to a potent neurotoxin called brevetoxin which is produced naturally by the marine algae Karenia brevis (see image above). If you or I were to eat these fish poisoned with K. brevis, we could become seriously ill or could even possibly die. What causes these these blooms is still not fully understood. Scientists believe that, low salinity content (<15ppt), warm surface water temperatures, high nutrient concentrations, high light intensity, and calm seas may all play a role. The frequency and severity of blooms in some parts of the world have been linked to increased nutrient runoff from human activities.
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