Holidaymakers along South Africa’s West Coast are being met with unsettling scenes as patches of discoloured seawater, piles of dead shellfish and even glowing waves after dark point to renewed red tide activity in the region.
The phenomenon, which tends to surface during the warmer summer months, is a naturally occurring marine event but one that can carry serious risks when conditions intensify, according to Musson, as reported by EWN.
Red tide develops when microscopic algae called dinoflagellates rapidly multiply in coastal waters, sometimes reaching extreme concentrations. These blooms are especially common along the West Coast because of the Benguela Current, which drives cold, nutrient-rich water up from the depths through a process known as upwelling. When these nutrients reach the surface, they create the perfect environment for algae populations to surge.
While algae are a normal and essential part of ocean ecosystems, problems begin when blooms become too dense or toxic. At very high levels, certain dinoflagellate species release toxins that can be deadly to marine life and dangerous for people.
One of the biggest concerns during red tide events is shellfish. Mussels and oysters feed by filtering large volumes of seawater, which means toxins present during a harmful bloom can build up inside their bodies. Even shellfish that look fresh and healthy can be contaminated.
Consuming affected shellfish can lead to paralytic shellfish poisoning, a condition that may cause tingling, numbness and, in severe cases, difficulty breathing. Less serious exposure can still result in intense stomach illness similar to severe food poisoning. Crucially, neither cooking nor freezing shellfish makes them safe to eat.
Musson stresses that shellfish found washed up on beaches should never be consumed, warning that heat and freezing do nothing to neutralise the toxins involved.
Marine life is also heavily impacted when blooms collapse. As dense algal masses die and decompose, oxygen levels in the water can drop sharply. This oxygen depletion can trigger fish die-offs and has been known to force West Coast rock lobsters out of the water as they search for air. Smaller marine animals, including shellfish, may suffocate when algae clog their gills, which explains the dead organisms often seen scattered along affected shorelines.
Despite the alarming scenes, not every algal bloom is hazardous. Algae form the foundation of the ocean food chain, and lower concentrations are both normal and beneficial. Authorities keep a close watch for situations where blooms turn toxic or dangerously dense, issuing warnings when activities like swimming or shellfish harvesting become unsafe.
South Africa runs extensive shellfish testing programmes along the West Coast, with frequent sampling aimed at protecting consumers from contaminated seafood.
The glowing waves that have drawn crowds at night are also linked to dinoflagellates, but these displays are usually harmless. The light appears when the water is disturbed, triggering a chemical reaction within the organisms. According to Musson, bioluminescent water is often safe to swim in, provided there are no official warnings, strong odours or signs of widespread marine deaths.
Current advisories remain in place for sections of the West Coast between Hondeklip Bay and the Olifants River estuary, where red tide activity has been most intense. Authorities continue to urge the public to avoid collecting or eating wild shellfish in these areas and to steer clear of beaches if foul smells or mass fish deaths are present.
‘When in doubt, stay out – and definitely don’t eat anything you’ve picked up yourself,’ Musson cautions.
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