Seasonal diversity and dynamics of haptophytes in theSkagerrak,Norway, explored by high‐throughput sequencing

Abstract

Microalgae in the division Haptophyta play key roles in the marine ecosystem and in global biogeochemical processes. Despite their ecological importance, knowledge on seasonal dynamics, community composition and abundance at the species level is limited due to their small cell size and few morphological features visible under the light microscope. Here, we present unique data on haptophyte seasonal diversity and dynamics from two annual cycles, with the taxonomic resolution and sampling depth obtained with high-throughput sequencing. From outer Oslofjorden, S Norway, nano- and picoplanktonic samples were collected monthly for 2 years, and the haptophytes targeted by amplification of RNA/cDNA with Haptophyta-specific 18S rDNA V4 primers. We obtained 156 operational taxonomic units (OTUs), from c. 400.000 454 pyrosequencing reads, after rigorous bioinformatic filtering and clustering at 99.5%. Most OTUs represented uncultured and/or not yet 18S rDNA-sequenced species. Haptophyte OTU richness and community composition exhibited high temporal variation and significant yearly periodicity. Richness was highest in September–October (autumn) and lowest in April–May (spring). Some taxa were detected all year, such as Chrysochromulina simplex, Emiliania huxleyi and Phaeocystis cordata, whereas most calcifying coccolithophores only appeared from summer to early winter. We also revealed the seasonal dynamics of OTUs representing putative novel classes (clades HAP-3–5) or orders (clades D, E, F). Season, light and temperature accounted for 29% of the variation in OTU composition. Residual variation may be related to biotic factors, such as competition and viral infection. This study provides new, in-depth knowledge on seasonal diversity and dynamics of haptophytes in North Atlantic coastal waters.

Haptophyte Diversity and Vertical Distribution Explored by 18S and 28S RibosomalRNAGene Metabarcoding and Scanning Electron Microscopy

“…Nutrients measurements were performed on samples collected at eight different depths (1, 2, 4, 8, 12, 16, 20, and 40 m) as described in Egge et al. ().…”

“…To compare our 18S OTUs to the OTUs obtained by HTS of samples from the same station taken in two earlier years (Egge et al. ,b), we ran MegaBLAST (Morgulis et al. ) with the OTUs of the previous study as query sequences, and our OTUs as subject sequences.…”

“…() and Egge et al. (,b). These studies identified an abundance of new haptophyte sequences (OTUs) and new haptophyte lineages, which could not be assigned to a cultured and genetically characterized taxon.…”

“…; Egge et al. ,b; Liu et al. ), each of them further improving the methodology and providing new insights about the diversity and distribution of the group.…”

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“…The OTU is then closed, and its radius (or diameter, depending on the method used) from the centroid is that global similarity value. There is no consensus on which global similarity value should be used because taxa evolve at different rates Caron et al, 2009;Nebel et al, 2011); a 97% value is commonly used in protist studies (Edgcomb et al, 2011a;Massana et al, 2015), although higher values are also used (Egge et al, 2015).…”