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Red tide growing in greater St Helena Bay area along the West Coast

A policeman watches crayfish walk out of the sea at Elands Bay due to a red tide some years ago. File photo: Brenton Geach

A policeman watches crayfish walk out of the sea at Elands Bay due to a red tide some years ago. File photo: Brenton Geach

Published Jan 17, 2021

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CAPE TOWN - A harmful algal bloom, better known as a red tide, has been building up at Elands Bay on the West Coast, about 220km north of Cape Town, and has resulted in several marine species washing up on the beach, the environment, forestry, and fisheries department said on Sunday.

These included, rock lobsters, octopus, white mussels, and some fish species. Weather conditions were not favourable at the moment as a north-westerly wind was currently blowing and keeping the algal bloom concentrated in the bay, the department said in a statement.

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"Notwithstanding the red tides, West Coast rock lobster catches are still good and this indicates that oxygen levels are still high. The new moon spring tide occurred two days ago, thus limiting the possibility of a mass stranding within the next 10 days."

The department had activated its West Coast rock lobster contingency plan and issued a "situation yellow" alert and placed all government role-players on standby, the department said.

In terms of the contingency plan, the environment department is the lead department, supported by the West Coast District Municipality, Cederberg Municipality, South African Police Service, South African National Defence Force, and the Western Cape provincial administration.

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"These role-players are currently preparing for a situation red because beaching has taken place and there is a possibility that there may be beaching in excess of 10 tons at a single or multiple localities in the area.

"As is often the case in summer and late summer, there has been a build-up of large red tides in the greater St Helena Bay region over the past few weeks. These blooms of phytoplankton presently extend 50-60 km in the vicinity of Elands Bay, Lambert’s Bay, and Doring Bay," the department said.

Red tides are a natural phenomenon in coastal waters caused by a dense accumulation of microscopic algae. Some of the algal species are harmful because they contain toxins, which are poisonous to humans.

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Poisoning may either take place through the consumption of contaminated seafood or by toxic aerosols or water-bound compounds that cause respiratory and skin irritation.

Other red tides cause harm through the depletion of oxygen (anoxia), which affects all marine creatures, and can lead to mass mortalities of the entire marine communities or mass walkouts of rock lobsters that try to escape the anoxic conditions.

In the Benguela upwelling region off the West Coast of Southern Africa, red tides have periodically led to rock lobster strandings. The best known examples are the strandings of hundreds of tonnes of rock lobsters in Elands Bay in 1997 and 2000.

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In 2014, an extensive and long-lasting red tide occurred for the first time along the South Coast, extending from Knysna to beyond Port Elizabeth and causing wide-scale mortalities of fish.

ANA

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environment

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