Our Burning Planet

RED TIDE, RED FLAG

Mass West Coast lobster walkout the latest in increasing incidence of harmful algal blooms

Mass West Coast lobster walkout the latest in increasing incidence of harmful algal blooms
An estimated five tonnes of rock lobster walked out of the sea this week following a harmful algal bloom that has been developing on the West Coast of the Western Cape. (Photo: Supplied)

The Department of Forestry, Fisheries and the Environment (DFFE) has activated the West Coast Rock Lobster Contingency Plan and issued a Situation Red Alert for coastal communities on the West Coast of the Western Cape following the development of an harmful algal bloom that saw thousands of rock lobsters walk out the sea.

An estimated five tons of rock lobster walked out of the sea this past week following a harmful algal bloom that has been developing on the West Coast of the Western Cape.

Also known as a red tide, it is the latest in increasing incidence of the devastating phenomenon.

Algae are simple plants found in the world’s oceans that produce about 70% of the oxygen in the atmosphere, are a food source for small fish and crustaceans, and play a vital role in marine ecosystems. But too much of a good thing can have dire consequences. 

In certain conditions, microscopic forms of algae called dinoflagellates bloom rapidly as a result of excess nutrients from upwellings in the ocean and gather in dense patches on the ocean’s surface. These harmful algal blooms (HABs) are colloquially termed “red tides” because of the colour of the algae which produce toxins that can be fatal to marine life and harmful to humans who ingest the contaminated seafood.  

The toxins are poisonous to humans when ingested but can also cause respiratory problems and skin irritation. 

This phenomenon often results in another, known locally as crayfish walkouts. Red tides can cause further harm through the depletion of oxygen being used by the overabundance of algae, which can lead to mass walkouts of rock lobsters that try to escape the anoxic conditions.

These mass strandings of West Coast rock lobster are common in South Africa’s late summer and can decimate tonnes of an already severely diminished resource.

Even small red tides can be a serious threat to the health of marine ecosystems and can have devastating impacts on the fisheries economy. 

So it is no wonder that the Department of Forestry, Fisheries and the Environment (DFFE) has activated the West Coast Rock Lobster Contingency Plan and issued a Situation Red Alert for coastal communities on the West Coast of the Western Cape following the development of a HAB.

A statement released by the DFFE on 7 February estimated that the bloom had caused five tonnes of West Coast rock lobster to walkout since the previous day, and cautioned that with more walkouts expected in the coming days, all government role players should be ready to rescue live lobsters on short notice. 

“There has been a build-up of large red tides in the greater St Helena Bay region over the past few weeks,” says the department. “These blooms of phytoplankton presently extend 50km to 60km, dominating waters in the vicinity of Elands Bay, Lambert’s Bay and Doring Bay.”

Save don’t savour

Toxins that may accumulate in the shellfish pose a risk to human health and the department warns the public “not to collect and consume any dead or decayed fish and shellfish washed ashore as a result of the red tide as this could pose a serious health hazard”.

The toxins are poisonous to humans when ingested but can also cause respiratory problems and skin irritation. 

So, none of these lobster will be put on the dinner table and instead “all recovered live lobster will be rehabilitated and will be safely returned to sea once the red tide threat has abated”, says the department. 

Rehabilitation for these critters varies, but a devastating walkout in 2022, when 500 tons of crayfish were stranded, gives some insight into rescue efforts. 


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The lobsters were sent to local crayfish factories where the animals were temporarily stored in oxygenated tanks before later being carried out to sea beyond the HAB and released.

Long story short, climate change is going to… cause upwellings which provide nutrients that cause red tides and lobster walkouts

Rescuing as many as these animals as possible is vital since the Worldwide Fund for Nature has placed the lobster on the Red List as a result of dwindling numbers that have left it close to commercial extinction.

Red flag for a Red List species

While red tides and mass lobster walkouts are common these days, it was not always the case. Across the world’s oceans, HABs appear to be occurring more frequently and South Africa is no exception.

Since 1930 there has been a significant increase in the frequency of HABs – up to sixfold the number of recorded blooms per decade since the 1960s. 

“The most famous examples are the strandings of hundreds of tonnes of rock lobsters in Elands Bay in 1997 and 2000. 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,” says the DFFE.

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“Since the early 2000s these walkouts have been happening every couple of years. We know there was a huge one last year and now it’s happening again,” says Dr Emma Rocke, a marine microbiologist at the University of Cape Town’s oceanography department. 

While the phenomenon is natural, the cause of the steady increase in its occurrence is still unknown.

“The one thing we know for certain is that climate change will result in warmer oceans,” says Rocke. Oxygen minimum zones (OMZs), which are found in the St Helena Bay area, are affected by this warming.

“OMZs are a bit like the lungs of the ocean – they have CO2 and oxygen and if you warm them they are going to release these gases. Like a glass of Coke in the sun, it will become flat.”

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The concern is that OMZs will grow and lobster walkouts will become more frequent, explains Rocke. The system is extremely complex, exacerbated by ocean warming and concentrated in the St Helena Bay area by ocean currents that eddie there.

“Long story short, climate change is going to… cause upwellings which provide nutrients that cause red tides and lobster walkouts,” says Rocke. 

While climate change is the best explanation for this trend, it also signals that the increase is likely to continue into the near future as the climate crisis continues to worsen. DM/OBP

 

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Absa OBP

Comments - Please in order to comment.

  • Gavin Craythorne says:

    The high nutrient level in the Berg and Oligants Rivers from commercial farm run-off could also play a role.

  • Jane Crankshaw says:

    Really interesting info in this article, thank you.

  • sl0m0 za says:

    Climate change plays almost no role in this – over usage of fertilizers is the main culprit and the bst solution to reduce fertilizer usage is to INCREASE atomspheric CO2.

  • Scott Gordon says:

    Interesting article .
    Biology at work . In different parts of our coastline .
    Is run off the cause , why in different places ?
    Yes global warming is a fact , humans are not helping.
    Wonder what research is happening ?
    I assume that the oxygen stealing algae mostly die off , due to lack of ? oxygen ?
    Bombing the sea with oxygen would make it grow faster 🙂
    Am not looking for a Chinese lab to come up with a bio fix , could it not be humanely killed ?

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