Growth responses of Caulerpa taxifolia (Ulvophyceae, Chlorophyta) from the South African aquarist trade. A potential invasive of South African coastal waters

Caulerpa taxifolia (Vahl) C. Agardh is an invasive marine alga in the northern Mediterranean Sea where it poses a serious threat to indigenous fauna and flora. Caulerpa taxifolia obtained through the aquarist trade in South Africa was grown under controlled temperature and irradiance conditions. Two separate univariate studies were performed: i) Temperature treatments of 15°, 20°, 25°and 30°C, all at 90 μmol photons.m-2.s-1 irradiance and ii) irradiance treatments of 20, 75 and 130 μmol photons.m-2.s-1, all at 25°C. The optimum temperature for maximal stolon and assimilator extension was 25°C; the alga showed growth as high as 30°C with slight growth occurring as low as 15°C. Growth of C. taxifolia was similar over the range of irradiance values studied. Maximum mean stolon and assimilator extension were recorded at an irradiance of 75 μmol photons.m-2.s-1. Caulerpa taxifolia commonly available in the South African aquarist trade was shown to have a wide temperature tolerance range, well within the range experienced by the east coast of the country.