Spatial and temporal variations of a saxitoxin analogue (LWTX-1) in Lyngbya wollei (Cyanobacteria) mats in the St. Lawrence River (Québec, Canada)

The concentration of the saxitoxin analogue LWTX-1 was quantified in samples of the benthic filamentous cyanobacterium Lyngbya wollei (Farlow ex Gomont) Speziale and Dyck collected in two fluvial lakes of the St. Lawrence River (Canada) over the 2006–2013 period. The study was aimed at documenting the spatial (between fluvial lakes, between sites within each lake) and temporal (inter-annual, monthly) variations of toxin concentration in relation with hydrological (water level), physical (water temperature, conductivity, transparency), chemical (nutrients in overlying water) and biological (L. wollei biomass and mat condition) characteristics. Toxin concentration was hypothesized to vary seasonally with biomass accumulation and environmental conditions. Toxin concentrations measured in Lake Saint-Louis (51 ± 40 μg LWTX-1 g−1 DM, N = 29 days in 2007, 2009–2011) were double those in Lake Saint-Pierre (25 ± 31 μg LWTX-1 g−1 DM, N = 26 days in 2006–2008, 2012–2013); however, August 2007 measurements taken from both lakes did not differ significantly. Ten of the twelve highest values (>100 μg LWTX-1 g−1 DM) were obtained from Lake Saint-Louis, between April and October in 2007, 2010 or 2011. Under ice samples showed intermediate concentrations of LWTX-1 (42 ± 9 μg LWTX-1 g−1 DM, N = 2). Concentrations of LWTX-1 were positively correlated with Secchi depth (r = 0.59, p < 0.001), L. wollei biomass (Spearman r = 0.31, p < 0.01) and %N in filaments (r = 0.48, p < 0.001), suggesting toxin production was linked to mat growth and metabolism rather than water quality. Although LWTX-1 has been reported to have a low toxicity, monitoring of L. wollei abundance is required to assess the environmental and human health risks posed by this taxon in the St. Lawrence - Great Lakes system.