The occurrence of the cyanobacterium Cylindrospermopsis raciborskii in Constance Lake: an exotic cyanoprokaryote new to Canada

Abstract

P.B. Hamilton, L.M. Ley, S. Dean and F.R. Pick. 2005. The occurrence of the cyanobacterium Cylindrospermopsis raciborskii in Constance Lake: an exotic cyanoprokaryote new to Canada. Phycologia 44: 17–25.The tropical and subtropical toxin-producing cyanobacterium, Cylindrospermopsis raciborskii, is reported for the first time in Canada. The species is of particular concern because it appears to be spreading throughout temperate North America and produces toxins that can have serious effects on human health. Cylindrospermopsis raciborskii was found in Constance Lake, Ottawa, Ontario, a shallow mesotrophic to eutrophic hardwater lake (summer average total phosphorus 28–48 μg l−1) where bottom waters can reach sufficiently high temperatures to promote germination of resting stages in the sediments. Peak abundance and biomass occurred in July and August when surface water temperatures were at their maximum. Year to year differences in abundance and dominance over four years of sampling (1998–2001) appeared to be due principally to differences in water temperature rather than nutrients. In the summer of 1998 when biomass was highest over the four years, C. raciborskii contributed 63% of the total phytoplankton biomass and 60% of the cyanobacterial biomass. A warming trend linked to climate change is likely to accelerate the spread and abundance of this potentially toxic species.