The Silent Red Tide: A GrowingThreat to Our Marine Life

A Prolonged harmful algal bloom has been devastating South Australia since March with no end in sight, affecting more than 400 marine species.

Dead fish, stingrays, dolphins and sharks are washing ashore, and the disaster has forced local industries to halt operations indefinitely.

Many believe prolonged marine heatwaves are a major factor.

This alarming situation is a stark reminder of the danger harmful algal blooms (HABs) pose to Namibia’s own resource-rich coast.

Here, these events – often called ‘red tides’ – happen when the cold water upwelling in the Benguela Current weakens.

This allows warmer waters to favour the massive growth of algae, which become so dense they tint the water a striking red or brown, giving the phenomenon its eerie name.

Upwelling brings cold, nutrient-rich water from the deep ocean to the surface, fuelling the abundant marine life in Namibia’s rich fishing grounds.

However, the long-lasting HABs upset this delicate balance and can kill the fish communities depend on for food and income.

Namibia’s most recent major red tide occurred in January last year. Pictures of the washed-up marine life circulated widely on social media.

WHAT ARE HABs?

HABs are a phenomenon where microscopic algae reproduce rapidly during favourable environmental conditions, much like a garden being overrun by weeds.

Some forms of these algae produce toxic chemicals that are harmful to ocean life and, in some cases, humans.

Although they form naturally, HABs are becoming both longer-lasting and more frequent due to marine heatwaves (MHW), ocean warming and nutrient pollution.

MHWs are prolonged periods of unusually high ocean temperatures in specific areas, much like heatwaves on land.
While some algae are harmless, they can still clog fish gills. Even worse, their decay drains oxygen from the surrounding waters, causing fish and other organisms to suffocate.

HEALTH CONCERNS

Toxins released by HABs can also cause fish and seabird die-offs as well as allergic reactions among dolphins and whales.

In Namibia, the Unite States and Australia, seals have been reported to be affected by domoic acid.

Produced by some algal blooms, this toxin affects the heart and brain, leading to seizures and heart failure.

It also causes disorientation and lethargy in marine mammals, often one of the first visible signs of poisoning.

For humans, the greatest concern is paralytic shellfish poisoning (PSP) and diarrhetic shellfish poisoning (DSP), which occur after consuming contaminated shellfish.

DSP can trigger severe digestive symptoms such as diarrhoea, nausea and vomiting. PSP can lead to paralysis and, in extreme cases, respiratory failure.

The Benguela upwelling system on Namibia’s coastline is known to host algae species responsible for these illnesses.

The public is urged not to collect washed-up marine life or shellfish after a HAB as it’s likely unsafe for consumption.

Red tides typically appear here during the summer, from October to March.

While HABs generally don’t harm humans through casual exposure, direct contact can cause skin and eye irritation or respiratory symptoms like coughing or shortness of breath.

HABs disrupt marine ecosystems worldwide, including in Namibia. They kill seabirds, harm seals, reduce shellfish harvests, and cause illness in people.

CLIMATE DISRUPTION

Climate change is increasingly contributing to rising sea temperatures and MHWs.

While these ‘blooms’ are a natural phenomenon, their frequency and severity are increasing due to climate change and marine pollution, posing growing threats to both ecosystems and the communities that depend on them.

Addressing climate change at its source is essential. If we don’t, our oceans and coastal communities will bear the cost. 

• Damian Schreiber, marine conservation communications, field and research officer at OCN, involved in seal rescues, education outreach, beach clean-ups, and public awareness. He holds a master’s in ecology and society from the University for Peace (Costa Rica).

In an age of information overload, Sunrise is The Namibian’s morning briefing, delivered at 6h00 from Monday to Friday. It offers a curated rundown of the most important stories from the past 24 hours – occasionally with a light, witty touch. It’s an essential way to stay informed. Subscribe and join our newsletter community.