Spatial and biological oceanographic insights into the massive fish-killing bloom of the haptophyte Chrysochromulina leadbeateri in northern Norway

•Widespread bloom of haptophyte Chrysochromulina leadbeateri in northern Norway (2019).•Bloom killed farmed salmon causing high direct and indirect gross economic losses.•rRNA gene sequences confirmed genetic similarity with C. leadbeateri from 1991 bloom.•Cell density correlated positively with tem...

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Published in:Harmful algae 2022-10, Vol.118, p.102287-102287, Article 102287
Main Authors: John, Uwe, Šupraha, Luka, Gran-Stadniczeñko, Sandra, Bunse, Carina, Cembella, Allan, Eikrem, Wenche, Janouškovec, Jan, Klemm, Kerstin, Kühne, Nancy, Naustvoll, Lars, Voss, Daniela, Wohlrab, Sylke, Edvardsen, Bente
Format: Article
Language:eng ; nor
Subjects:
Fish kills
Haptophyte diversity
Harmful Algal Bloom
Ichthyotoxic algae
Marine microeukaryotes
Metabarcoding
Mixotrophy
Salmon aquaculture
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Summary:•Widespread bloom of haptophyte Chrysochromulina leadbeateri in northern Norway (2019).•Bloom killed farmed salmon causing high direct and indirect gross economic losses.•rRNA gene sequences confirmed genetic similarity with C. leadbeateri from 1991 bloom.•Cell density correlated positively with temperature and negatively with salinity.•Bloom succession suggests independent initiation from existing local populations. A bloom of the fish-killing haptophyte Chrysochromulina leadbeateri in northern Norway during May and June 2019 was the most harmful algal event ever recorded in the region, causing massive mortalities of farmed salmon. Accordingly, oceanographic and biodiversity aspects of the bloom were studied in unprecedented detail, based on metabarcoding and physico-chemical and biotic factors related with the dynamics and distribution of the bloom. Light- and electron-microscopical observations of nanoplankton samples from diverse locations confirmed that C. leadbeateri was dominant in the bloom and the primary cause of associated fish mortalities. Cell counts by light microscopy and flow cytometry were obtained throughout the regional bloom within and adjacent to five fjord systems. Metabarcoding sequences of the V4 region of the 18S rRNA gene from field material collected during the bloom and a cultured isolate from offshore of Tromsøy island confirmed the species identification. Sequences from three genetic markers (18S, 28S rRNA gene and ITS region) verified the close if not identical genetic similarity to C. leadbeateri from a previous massive fish-killing bloom in 1991 in northern Norway. The distribution and cell abundance of C. leadbeateri and related Chrysochromulina species in the recent incident were tracked by integrating observations from metabarcoding sequences of the V4 region of the 18S rRNA gene. Metabarcoding revealed at least 14 distinct Chrysochromulina variants, including putative cryptic species. C. leadbeateri was by far the most abundant of these species, but with high intraspecific genetic variability. Highest cell abundance of up to 2.7 × 107 cells L − 1 of C. leadbeateri was found in Balsfjorden; the high cell densities were associated with stratification near the pycnocline (at ca. 12 m depth) within the fjord. The cell abundance of C. leadbeateri showed positive correlations with temperature, negative correlation with salinity, and a slightly positive correlation with ambient phosphate and nitrate concentrations. The spatio-
ISSN:1568-9883
1878-1470
DOI:10.1016/j.hal.2022.102287