Thousands of rock lobster, many sharks and other marine species beached on the West Coast around Elandsbaai and Doringbaai. The cause of the mass die-off is is called a ‘red tide’.
A red tide is an event that occurs on the coastline when algae — a plant-like organism — grows out of control. The name comes from the fact that overgrown algae can cause the water to change colour. Red tides can be hazardous to human health and sea life.
When these algae blooms occur, all oxygen in the water column disintegrates. Nothing escapes. Deceased sharks, West Coast rock lobster, hagfish and other species have been photographed along the beach.
This incident is similar to the one which occurred at the V&A Waterfront’s harbour in May last year, 2021. The strange colour of the water had many locals wondering if sewerage was being pumped into the water, causing masses of dead fish to float to the surface.
Similarly to the Elands Bay die off today, the cause was that of deoxygenation, or an algae bloom, which is a common natural phenomenon, said Ingrid Sinclair from the Two Oceans Aquarium.
The colour of the water depends on the type of algae, bacteria or dinoflagellates present, Mark Fitzie, also from Two Oceans Aquarium, confirmed. The colour of the algae determines the colour we see — for example, red or blue. The milky-blue colour at the V&A was enhanced due to the harbour being a confined basin, coupled with ammonium and oils released from fatty fish like mackerel.
Unfortunately, all marine life dies in these instances. Species like muscles and anemones are able to close themselves up as a protection measure, but not for long periods of time. What’s left is a red graveyard and crustacean coated beach.
As mentioned above, algal blooms are a natural occurrence. Scientists have, however, expressed that the frequency of these events can be altered by human activity. For example, nutrient-rich run-off in rivers caused by farming, Fitzie added.
Additionally, biotoxins released during some algal blooms can have knock on effects. Other species like whales and seals can be implicated either directly by these biotoxins or as a result of a lack of food — the latter being the main cause linked to the mass seal deaths reported in the Western Cape last year.
Important to note; the creatures effected by algae blooms cannot be consumed by humans. They are toxic and can be harmful.
The restoration of deoxygenated ecosystems results from the the ebb and flow of tides, wind and movement. The remedy here is aeration and time.
Picture: Sea Search