What is Red Tide?

WHOI

WHOI

WHOI

The term “Red Tide” has been in the news lately as a result of this summer’s red tide event on the coast of Maine in the United States.  Red tide is a phenomenon caused by microscopic algae blooms,  during which algae become so numerous that they discolor coastal waters (hence the name “red tide”). The algal bloom may also deplete oxygen in the waters and/or release toxins that may cause illness in humans and other animals.  Scientists actually prefer the term “Harmful Algal Blooms” (HAB) as the term “red tide” erroneously includes many blooms that discolor the water but cause no harm, and also excludes blooms of highly toxic cells that cause problems at low (and essentially invisible) cell concentrations. Therefore, harmful algal bloom is a more appropriate term.

There are approximately 4,000 species of microscopic algae in the oceans with about 300 of these being identified with periodic explosions of growth or blooms.  These single species blooms are what discolor the water surface changing it to colors of red, brown, yellow, purple, green or white depending on the species of algae.  When these have properties that are considered harmful to humans and other life, they called “Harmful Algal Blooms”. 

Since the 1980s, there has been a significant increase int he incidence of HABs worldwide.  In many areas, the HABs are occurring more frequently, over larger areas and lasting longer.  Countries affected by these algal bloom  events include: Argentina, Australia, Brazil, Canada, Chile, Denmark, England, France, Guatemala, Hong Kong, India, Ireland, Italy, Japan, the Netherlands, New Zealand, Norway, New Guinea, Peru, the Philippines, Romania, Russia, Scotland, Spain, Sweden, Thailand, the United States, and Venezuela. 

WHOI

Harmful Agal Blooms can create potent toxins given the right conditions and may cause harm through the production of toxins or by their accumulated biomass, which can affect co-occurring organisms and alter food-web dynamics,  The potential impacts  are many including:

• Some toxic species can cause a variety of human ailments, contracted either through inhaling airborne toxins, skin contact or, more commonly, eating contaminated shellfish. These toxins may cause amnesia, stomach cramps, nausea, memory loss, paralysis and even death.
• Some species are merely unpalatable to other marine life because of gelatinous envelopes or other characteristics and they exact their harmful effects by essentially “starving” the food chain. Other species can cause physical damage, as the blooms of species which contain barbs that lodge among gill tissues of fish, causing death. Such blooms can cause a great deal of financial damage by killing farmed fish, which are grown in crowded aquaculture pens.
• HABs can cause substantial economic losses to coastal communities through loss of tourism and impact on commercial fishing. 

The causes of the HAB “epidemic” is somewhat disputed as some scientists belive it is the result of increased monitoring, but most agree with the following:

• The primary human contribution to HABs is thought to be nutrient pollution — from, amongst other things, agriculture, sewage outfalls and mining — creating a more favorable, nutrient-rich environment in coastal waters in which certain groups of algae can thrive.
• Climate change may also be making some coastal environments more hospitable to harmful algae species.
• Many species of algae are also transported around the world in ships’ ballast water and discharged in areas where they did not previously occur. Others are distributed accidentally through the transfer of shellfish for aquaculture.

It appears that the Harmful Algal Bloom phenomenon is becoming more of a problem worldwide.  One impact that we at Ocean Power Magazine are pondering is what would be the impact to wave or tidal power generating equipment if ensconced in an algae bloom?  Just another hurdle that  will have to be traversed on the path to ocean power generation.  Researchers and scientists at NOAA , Woods Hole Oceanographic Institute and many others around the world, continue to monitor and study this harmful but sometimes beautiful phenomenon.

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Posted by Tracey Smith on Aug 13 2009. Filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry