Does oligotrophication induce cyanotoxin production and accumulation in food webs of Arctic/alpine lakes?

Sammanfattning

Arctic/alpine lakes in Sweden are facing nutrient declines, i.e., oligotrophication, and intensified nitrogen (N)-limitation due to climate change and associated landscape alterations. These changes are expected to promote nitrogen-fixing cyanobacteria (N2-fixers) in primary producer communities in benthic biofilms of the lakes. Many N2-fixers are able to produce potent, harmful cyanotoxins. This study investigated whether increases in dominance of N2-fixers affected the prevalence and accumulation of cyanotoxins – including microcystins and nodularins (as a group; MC), cylindrospermopsin, and anatoxin-a – in benthic biofilms and macroinvertebrates from nine Swedish Arctic/alpine lakes. Cyanotoxins were commonly detected in the samples. Cyanotoxin concentrations quantified by enzyme-linked immunosorbent assay (ELISA) and by liquid chromatography–mass spectrometry (LC-MS) were generally positively correlated. Data showed strong positive correlations of the relative biomass of N2-fixers with the concentrations of cylindrospermopsin and anatoxin-a but not MC in biofilms. Most macroinvertebrate samples had higher cyanotoxin concentrations than the biofilms, indicating trophic transfer and bioaccumulation of cyanotoxins. Yet, cyanotoxin bioaccumulation did not differ among functional feeding groups of the benthic macroinvertebrates, possibly due to limited numbers of samples collected. Benthic macroinvertebrates are the key prey for fish including Arctic char and brown trout in Arctic/alpine lakes. Thus, with increases in dominance of N2-fixers in benthic biofilms driven by lake oligotrophication and intensified N-limitation, fish likely will face increased exposure to cyanotoxins in diet or in water. This study highlights the importance of monitoring cyanotoxin risks in Arctic/alpine lakes, and the necessity of further investigating cyanotoxin bioaccumulation in the food web components especially fish.