Marine Biology (2+1)

Introduction

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.Red tides are not necessarily red and many have no discolouration at all. They are unrelated to movements of the tides.

Red tide is a common name for a phenomenon more correctly known as an algal bloom (large concentrations of microorganisms), an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. It is usually found in coastal areas.

Not all redtides produce toxins. Some do. Even though they do not produce any toxin,their sheer mass could clog the gills or may utilize dissolved oxygen in the sea leading to anoxic conditions. In either case, they could be detrimental to the shellfish, crustaceans and fishes. When contaminated or toxin laden fish are consumed by humans it causes serious health problems such as paralysis, diarrhea, amnesia etc. after which the toxic episodes are known. In recent decades there has been a steady increase in the occurrence of red tides globally and is attributed to pollution.

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 in the 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.