What caused the red tide in Jeffreys Bay

The red tide that has been off coast of Jeffreys Bay over the past two weeks is now causing dead fish to wash up on the beaches.

red tide SB
Photo: Stan Blumberg

Red tide can be deadly to marine life like fish, birds and even manatees. And they can have a serious impact on human health, too.

A red tide occurs when the population of certain kinds of algae known as dinoflagellates explodes, creating what’s called an “algal bloom.” Scientists sometimes refer to red tides as harmful algal blooms or HABs.

When millions of these microscopic algae reproduce and cluster in one area of the ocean, they can change the colour of the water.

A rusty shade of red is often seen, though the colour may range from pink or orange to brown or yellow.

A number of factors can cause an algal bloom to grow. Low salinity, a high nutrient content in the water and warmer than usual surface water temperatures are usually cited as contributing to a red tide’s formation.

Photo: Zane Hobson
Photo: Zane Hobson

The water temperature off Jeffreys Bay has been very warm in the past few weeks with temperatures of 27 C being recorded in the canals at Marina Martinique, where sea water is pumped in on a continual basis.

The algae linked to red tides contain a toxin that affects the nervous and digestive systems of animals. Red tides are usually accompanied by a massive die-off of fish, as well as the birds and other animals that feed on fish.

Even larger animals that feed on fish, shellfish and other marine life can be killed if they consume enough of the toxin.

A red tide in Florida, America has been blamed for a significant die-off of manatees, while another red tide in 2012 may have caused a large number of squid deaths in California.

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Humans are also vulnerable to the toxic effects of a red tide. Wave action can release the algae’s toxins into the air, causing respiratory problems among people near the shoreline, particularly those with asthma, emphysema or other respiratory illnesses.

Because the toxins can accumulate in shellfish, red tides often cause outbreaks of parasitic shellfish poisoning (PSP) and amnesic shellfish poisoning (ASP).

Both illnesses affect the nervous systems; ASP can cause dizziness and disorientation, and in extreme cases, PSP can cause respiratory paralysis, resulting in death by asphyxiation.

It is therefore strongly advised not to eat mussels or oysters from the JBay waters right now.

For more on the red tide, click here



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