| Summary: | In the Spring of 2019, a harmful algal bloom (HAB) of Chrysochromulina leadbeateri decimated 14 500 tonnes of caged salmon in the Northern Norwegian coastal regions. C. leadbeateri is a natural part of the marine microbiome along the Norwegian coast, and similar events have happened in the past. To heighten our understanding of how these HABs develops, and capacity of the causal agent as a harmful species, we’ve assessed the environmental and enumeration data of C. leadbeateri density in Northern Troms, collected by Akvaplan Niva during the 2019 HAB, in concurrence with the assessment of several microbial isolation and genomic extraction techniques. The highest cell counts of C. leadbeateri existed in Balsfjorden, where, at most, an estimated ∼49 million cells/L resided at 3 m below the surface. Further, we found a temporal correspondence between an increase in C. leadbeateri cell counts and increased salmon mortality at a locality in Kattfjorden. Generally, there was a higher density of C. leadbeateri at 3, compared with 10 m. This discrepancy could plausibly be attributed to divergent water densities between the two measurement depths. The algal isolation and genomic extraction attempts proved largely unsuccessful. Thus, we provide a series of corrections to the techniques used, to ensure that future attempts may be more efficacious.
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