Spatial abundance and distribution of picocyanobacterial communities in two contrasting lakes revealed using environmental DNA metabarcoding

Freshwater picocyanobacteria (Pcy) are important yet understudied components of lake ecosystems. Most previous studies have relied on cell abundances to assess Pcy dynamics in largely oligotrophic lakes, while little is known about spatial diversity and dynamics across different lake types. In the present study we assessed the horizontal-spatial abundance and community structure of Pcy in two contrasting (oligotrophic and hypertrophic) New Zealand lakes using epifluorescence microscopy and 16S rRNA metabarcoding. Pcy abundance and community composition differed significantly both between and within the oligotrophic and hypertrophic lakes. While spatial variability was observed in both study lakes, these differences were particularly pronounced in the oligotrophic, morphometrically complex Lake Wanaka where cell abundances were typically higher in bays than open-water sites and community structure differed significantly between sites. Community structuring appeared to be driven by localised environmental conditions, with different factors influencing each lake. These results suggest that single spot-samples are insufficient to gain an understanding of Pcy dynamics and consequently, phytoplankton dynamics in lakes.

Automated summary

This study used epifluorescence microscopy and 16S rRNA metabarcoding to assess the horizontal-spatial abundance and community structure of freshwater picocyanobacteria (Pcy) in two contrasting lakes in New Zealand. Significant differences in Pcy abundance and community composition were found between and within oligotrophic and hypertrophic lakes, with spatial variability particularly pronounced in the oligotrophic Lake Wanaka. The study suggests that single spot-samples are insufficient to understand Pcy dynamics and phytoplankton dynamics in lakes.