Many such neurotoxins act to interfere with sodium ion movement in mammalian nerve cells. Red tides have been recorded from South Africa, Peru, Japan. Locally, red tides occur along the Cape west coast where conditions are occasionally optimal for rapid population growth. In March 1989. a particularly severe red tide at Betty's Bay caused mass deaths of large invertebrates including perlemoen. The responsible organism has been identified as Gymnodinium nagasakiense.
Red tides can also occur in upper beach tidal pools left by a high spring tide.
Within a few days, optimal conditions can create a tidal pool filled with blood-red water. The next high spring tide that occurs two weeks later will clean out the tidal pools and the process can be repeated when conditions are again right. The effects of a severe red tide on the marine life of a particular area may be devastating and can last for many years. Particular care about eating shellfish should be taken by visitors who are unfamiliar with conditions prevailing at the time of their visit to the Cape coast. Biology of Plants, third ed.