Seasonal community dynamics and toxicity potential of cyanobacteria in Lough Arrow, an oligo-mesotrophic lake in the north-west of Ireland

Favourable water quality is paramount to ensuring the protection of natural habitats and the resources they provide. Phytoplankton are an important assessor of the health of aquatic ecosystems, particularly in lakes. As such, the characterisation of phytoplankton communities over time enables a detailed assessment of a water body’s ecological condition. This study examined the characteristics of cyanobacteria in Lough Arrow, a lake in Ireland’s northwest, over the course of a year to ascertain their community dynamics as well as potential for cyanotoxin production. DGGE analysis of 16 S rRNA gene amplicons for spherical cyanobacteria revealed seasonal shifts in Lough Arrow, with greater diversity in the summer and autumn. Non-metric multidimensional scaling showed that seasonal changes in the cyanobacterial community were largely driven by changes in environmental factors such as temperature and conductivity. The presence of the toxigenic species Microcystis sp. was confirmed from DGGE profiles. Analysis for the potential production of microcystin toxins in the lake was undertaken via qPCR analysis of the mcyE gene. No significant difference between the summer and autumn seasons was observed. Microcystin concentrations, estimated via the application of an ELISA assay, showed very low concentrations in the lake (max conc. 0.027 µg/l), which were not significantly different between the summer and autumn. The species richness and abundance of cyanobacteria in Lough Arrow was seasonal; responding dynamically to changes in environmental factors. The presence of Microcystis sp. and potential for microcystin production detected in the summer and autumn seasons indicating that the establishment of a tailored monitoring plan could be of benefit for better ascertaining and managing water quality parameters and potential risks to human and animal health.