Knysna, Sedgefield and surrounds are currently observing the red tide phenomena around our coast line. We have seen many warnings issued by various departments, but the spectacular natural show being put on by Mother Nature seem to have been overlooked. With beautiful summer evenings currently experienced, we invite visitors and residents alike, to observe these beautiful occurrences from Brenton and Noetzie whilst these warnings are in place.
The term ‘red tide’ is misleading as the sea water may actually turn brown, orange, purple, yellow, or even black. The phrase is also a misnomer since it has nothing to do with tidal fluctuations. The colour in the water is caused by the dense concentration of very tiny microscopic plants called phytoplankton. On the South African coast the most common type of microscopic plants are known as dinoflagellates.
Red tides are most common along the west and south coasts of the Cape in late summer and autumn. During this period the prevailing southerly winds cause the cold nutrient-rich water from the deeper parts of the ocean to rise up by a process known as upwelling. When the dormant phytoplanktons reside in the sediments in the deep ocean, in an environment which is dark and oxygen poor, they are known as dinoflagellate cysts. During a bloom period each single cell may replicate itself one million times in two to three weeks. When all these conditions combine the result is a bloom known as red tide.
OBSERVE: A spectacular event that takes place in the ocean during red tide is the glow of phosphorescence. The bloom of algae is accompanied by an increase of microscopic plankton, which glows in the dark when disturbed by waves. The result is a brilliant light show of turquoise glowing waves as they break along the shoreline at night.
NOTE: Please note that red tides can produce crayfish and mussels which are poisonous.