Cysts of Alexandrium catenella on the west coast of South Africa: distribution and characteristics of germination

Abstract

Cysts of the toxic dinoflagellate Alexandrium catenella (Whedon and Kofoid) Balech were found in the sediments of the southern Namaqua shelf, on the west coast of South Africa, with a maximum recorded abundance of 238 cysts ml⁻¹ wet sediment. Experimental results indicate a short dormancy period of 15–18 days, suggesting that the cyst population does not necessarily serve as an overwintering strategy, but may rather permit rapid cycling between benthic and planktonic stages. Cysts were isolated monthly from sediments and incubated in the laboratory. Cyst germination ranged between 20% and 88% and did not show a clear seasonal pattern. The rate of germination was examined as a function of temperature and light. Cysts germinated within the temperature range 4°–22°C, but germination was highest at 10°C under both light and dark conditions. Although cysts germinated in the dark, germination in the light was higher and required a shorter period of incubation.