Recently, large scale “red tides” have occurred in the northeast (Maine to Cape Cod), along the west coast of
First, the term “Red Tide” is a misnomer. The condition is actually a bloom of algae (phytoplankton). It may be red, brown or other colors. It has nothing to do with the tide.
Most species of phytoplankton are not harmful and serve as the energy producers at the base of the food web, without which higher life on this planet would not exist. Phytoplankton are believed to generate as much as 80% of the world's oxygen supply. The two most common types of marine phytoplankton are diatoms and dinoflagellates.
Occasionally, the algae grow very fast or "bloom" and accumulate into dense, visible patches near the surface of the water. They are not necessarily harmful. During these blooms, most of the phytoplankton eventually die and sink to the bottom, where they are decomposed by bacteria. At night when photosynthesis stops, algae produce carbon dioxide and consume oxygen. These processes deplete the dissolved oxygen necessary for the survival of fish and other organisms, which can cause fish kills in bays and other enclosed water bodies.
A small number of species also produce potent neurotoxins that can be transferred through the food web where they affect and even kill the higher forms of life such as shellfish, fish, birds, marine mammals, and even humans that feed either directly or indirectly on them. Some species, such as the dinoflagellate Alexandrium tamarense and the diatom Pseudo-nitzschia australis produce potent toxins which are liberated when the algae are eaten. People are exposed principally through the consumption of contaminated shellfish.
The recent algal bloom in the northeast (the largest outbreak in 12 years) caused the closure of shellfish beds from Maine to Cape Cod. The predominant species in this outbreak was Alexandrium fundyense. The outbreak caused toxin levels in some clams and mussels to reach record highs and caused the deaths of many gulls and eider ducks.
In Florida, although historical records indicate that algal blooms have occurred for centuries, there is a concern that nutrient runoff from development, farming and phosphate mining may be making the events occur more frequently and last longer. This year, a large algal bloom formed in early January which stretched from
Human health effects of the algal blooms in Florida seem to consist primarily of respiratory problems, especially when winds blow onshore. During a three-month algal bloom event in 2001 Sarasota Memorial Hospital's emergency room admissions for respiratory problems were 54% higher for people living along or visiting the coast than during the same period the next year, when there was no algal bloom.
In Southern California, the recent algal bloom has been more of a curiosity than a hazard (as long as you don’t mind surfing is waves that are the color of dark tea). There have been odor complaints in some areas, especially near coastal lagoons where the algae densities are highest. Although there is speculation that record winter rains plus continuing dry weather runoff containing nutrients may have fueled the present bloom, a connection has not been proved. A positive feature has been the “glow-in-the-dark” water seen at night, created by emissions from the dinoflagellates. Whitewater becomes iridescent blue water and swimmers emerging from the water “glow” and leave blue footprints in the sand.
In the last few years there have been several reported instances of mass deaths of birds and marine mammals associated with the diotom Pseudonitzschia and domoic acid, which is produced by Pseudonitzschia. Recently, domoic acid has been identified as the cause of death of many sea lions throughout central and southern California.
More information on Harmful Algal Blooms can be found at
http://www.surfrider.org/a-z/red_tide.asp and
Rick Wilson
Coastal Management Coordinator, Surfrider Foundation
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