If the grass is greener on the other side, it probably gets more manure. Scientists at the Oceanographic Research Institute (ORI) believe that might be the reason for the verdant coats that many of the freshly exposed rocks along Umdloti’s rocky shore have been flaunting of late.
The bright green hairy growth has been adding extra pop to people’s beachfront sunrise pictures, especially those taken at the two large rocks in front of No 9 South Beach Road, whose coats have grown so thick they look like props from The Lorax.
Dr Bruce Mann, retired senior scientist at ORI, said the showy green coats were filamentous green algae that is almost certainly a sign of eutrophication, probably caused by sewage.
A surfer gets ready to paddle out near a rock draped in a luxurious coat of filamentous green algae.
In layman’s terms, eutrophication means there is an overabundance of nutrients, specifically nitrogen and phosphorus, in the water for algae to feed on and grow strong. With eThekwini Municipality’s wastewater infrastructure in tatters, sewage outflows into the ocean have become par for the course, gradually contributing to higher nutrient levels which act as fertilizer for the algae.
For surfers it’s been a winter to remember with consistent big southwest ground swells that shifted a massive amount of sand to create not only great banks, but also expose new rock surfaces to be colonised by marine life.
With nutrients and sunlight in abundant supply, the filamentous green algae swiftly populated the new parcels of beachfront real estate.
Umdloti resident and ORI scientist, Dr Ryan Daly, explained that the intertidal community of marine creatures, including these algae, were completely dependent on how long the rock has been exposed and how high up from the tide the rock is.
Those on the prominent rocks (pictured here) were exposed high enough to get a lot of sunlight on the low tide but still low enough to get sufficient water on the high tide for algae to colonise it and grow.
With the added boost of eutrophication, the algae were able to flourish in a short period of time.
Normally, if newly exposed rock were to remain exposed, barnacles and limpets would start to grow and there would be a succession over time with the algae disappearing and other intertidal creatures taking over. But because the sand in Umdloti moves all the time, Daly expects a different outcome.
“What’s interesting about Umdloti beach is that it’s just so dynamic. Sand moves all the time, new rock pops up, algae colonise it quickly and then it has this growth spurt before anything else colonises it.
“What you’ll probably find with that rock is that it will become high and dry or covered in sand again and then nothing grows on it,” said Daly.
