Microbial community dynamics during a harmful Chrysochromulina leadbeateri bloom in northern Norway

Abstract

In late spring 2019 a harmful algae bloom occurred across multiple, interconnected fjords and bays in northern Norway. This was a major event causing severe fish mortality at several salmon aquaculture facilities in the region. The reported focal taxon and suspected agent of fish mortality was a Chrysochromulina leadbeateri-like prymnesiophyte that was morphologically identical to the UiO-035 isolate collected from a similar bloom from the same region in 1991. This study reports on succession dynamics of the marine microbiome via detectable changes in abundance of 18S and 16S rRNA gene amplicon sequence variants and closely related taxa of the focal strain C. leadbeateri UiO-035. This taxon co-bloomed with a diverse group of microeukaryotes and prokaryotes and their temporal succession dynamics revealed high variability with strong shifts in abundance during the event. These blooming patterns were poorly connected to environmental conditions suggesting that other factors such as biological interactions may be at least as important in shaping the dynamics of this type of harmful algae bloom. A deeper understanding of microbiome succession patterns during these rare but destructive bloom events will help guide future efforts to generate predictive models and anticipate deviations from the natural bloom cycles of the northern Norwegian fjord systems that are home to large scale aquaculture activities.