Red tide is the expression used to refer to the phenomenon caused when algal blooms become so numerous that they paint the seawater red. The issue here is that the great amount of the algae depletes the water of oxygen and it also releases a toxin that causes illness in humans and species in the water, birds, and other mammals.

There are several factors that create the perfect environment for algal blooms to multiply. These can be warm ocean water temperatures, low salinity, calm seas, and rain. Besides this, the algae that cause red tide can be transported by the wind over great distances.

The most common forms of alga that causes red tide include:

  • Alexandrium fundyense 
  • Alexandrium catenella 
  • Karenia brevis 

Red tides are common everywhere and occur in both salty and fresh water.  Humanity has been able to cope with them.  However, since the 1980s the occurrence of such events has increased. 

Red tide algae produce a toxin that is released into the water.  The reason why these toxins are released is still unknown.  Organisms such as krill and fish are not affected by the toxin, so they will graze on the algae.  Nevertheless, the organisms that feed on these ones become poisoned due to the accumulation of the toxin on the prey´s body.

Today, red tides affect a great number of countries, causing sea life to be reduced. The National Ocean Service has been studying ways in which the occurrence of a red tide can be forecasted. The idea is for affected nations to have the opportunity to prepare.

Satellites have allowed scientists to better track and monitor the harmful algae. Along with this, an antidote is in development.