Red tides

From time to time especially near the coast, the sea becomes bright red literally over-night. This phenomenon is called a red tide. Red tides occur world-wide in warm seas. They are massive blooms of phytoplanktons. At the peak of a red tide there may be hundreds of thousands of cells in a single drop. Red tides aren’t always red. They can be orange, brown or green in colour. Only around 6% of all phytoplankton species are known to cause red tides. In red tide discoloration of sea water usually caused by dinoflagellates. But many other organisms like cyanobacteria, diatoms and chrysophyta can also cause red tides.

There are many factors that influence red tide event. Warm ocean surface temperatures, low salinity, high nutrient content, calm seas and rain followed by sunny days during the summer months are some of them. Algae related to red tide can spread or be carried long distances by winds, currents storms or ships.

Because of this phenomena there can be happen harmful algal blooms. About the third of red tide organisms produce poisons. Among them there are most powerful toxins too. These toxic substances may be lethal to fish and other marine life. It may be a threat to human health, fisheries, coastal aesthetics and the economy. Mussels, clams, crabs and other shellfish often tolerate the toxin by storing them away in the digestive gland, kidney, liver or other tissues.

People who eat the shellfish can suffer nausea, diarrhea, vomiting, numbness and tingling, loss of balance and memory, slurred speech, shooting pains, paralysis, and even death. And these organisms release toxic air born irritants which can cause sore throats, eye irritation and skin complaints.