Cylindrospermopsis raciborskii, a toxic invasive cyanobacterium in South African fresh waters

Abstract

Cylindrospermopsis raciborskii, a problem-causing cyanobacterium capable of releasing potent toxins, has become increasingly prevalent in South African freshwaters, especially in the lower reaches of the Orange River. This organism was first detected during the summer (January to March) of 2000 in the lower reaches of the Orange River. During this period, and again in 2003 and 2005, it formed severe summer blooms, occasionally reaching concentrations of 1 000 000 cells ml^–1. Blooms of C. raciborskii lead to several problems including taste and odours, as well as making water treatment difficult (conventional treatment processes were unsuccessful). Fish kills were also reported during the time of the bloom. According to the World Health Organisation, cyanobacterial concentrations greater than or equal to 100 000 cells ml^–1 may be detrimental to human health. It seems as if this organism is slowly spreading into other freshwater systems in the country. While it was restricted mainly to the lower Orange River system during 2000, it has since been found in low concentrations in a large number of rivers throughout South Africa. The spread of this organism should be monitored, because it may have devastating consequences for the precious and scarce water resources in the country. The primary aim of this paper is to act as a report on the presence of C. raciborskii in the lower Orange River and as a warning of its potential to form blooms in other South African freshwaters. A short overview of its distribution of this species in South Africa is provided, as well as a brief summary of environmental conditions during the 2005 bloom period. Management recommendations are also listed.

Keywords: Orange River, toxins, cylindrospermopsin, blooms, Cyanobacteria, blue-green algae

African Journal of Aquatic Science 2008, 33(1): 17–26