Oceanic heterotrophic flagellates are dominated by a few widespread taxa

Abstract

Marine heterotrophic flagellates (HFs) form a diverse and ecologically relevant functional group of bacterial grazers and nutrient remineralizers in oceanic waters. Despite playing a crucial role in marine biogeochemical cycles, there is still a lack of information on which specific taxa dominate HF assemblages and what are their patterns of distribution in a global context. In the present work, we addressed this issue by analyzing amplicon sequencing data sets retrieved from samples taken in tropical and subtropical oceanic regions at depths from surface to 4000 m. Only a few dozens of widespread taxa, mostly affiliating to MAST clades, Picozoa, Bicosoecida and Chrysophyceae, seemed to dominate surface HF assemblages. The majority of these dominant HFs were present at relatively constant abundances, while others were influenced by temperature or displayed a patchy distribution. In the deep ocean, only a handful of taxa belonging to Bicosoecida and Chrysophyceae, together with Diplonemea and Kinetoplastida, explained most of the HF signal. Co‐occurrence networks between HF and prokaryotic taxa at the surface ocean revealed two main clusters influenced by temperature that did not seem to show specific patterns of interaction. However, some correlations emerged outside these thermal groups that could represent new prey–predator interactions. Overall, we identified the putatively most ecologically relevant HF taxa in the ocean, which become promising targets for further experimental and genomic studies.

Antarctic lake phytoplankton and bacteria from near‐surface waters exhibit high sensitivity to climate‐driven disturbance

“…This was reflected in low phytoplankton biomass and undetectable photosynthetic efficiency ( F V / F M ), suggesting that the phytoplankton are indeed under high excitation pressure and adapt by downregulation of their photosynthetic apparatus. Last, the moat appears to be a suitable habitat for a variety of HNANs, including those of the Stramenopile MAST phylum, Bicosoecida, a dominant picoeukaryote (<3 μm) clade within marine systems (Obiol et al, 2021 ).…”

On the origin of TSAR: morphology, diversity and phylogeny of Telonemia

“…To investigate the global distribution of telonemids in marine waters and to determine which clades were the most abundant and most diverse, we used the Tara Oceans and Malaspina Expedition metabarcoding dataset corresponding to the V9 and V4 regions of the 18S rDNA gene, respectively [ 29 , 30 ]. We obtained the Tara Oceans OTU dataset from Richter et al [ 31 ].…”

metaPR2: a database of eukaryotic 18S rRNA metabarcodes with an emphasis on protists

“…Stoeck et al 2009). In marine waters, metabarcoding studies extended quickly and now tackle more focused questions, for example analysing the distribution of protist groups in the ocean as a function of their size (De Vargas et al 2015), the diversity of heterotrophic protists in the deep layers of the ocean (Giner et al 2020; Obiol et al 2021), detailed biogeographic distribution of specific taxa (e.g. Malviya et al 2016; Yau et al 2020), factors structuring marine plankton communities (Logares et al 2020; Sommeria-Klein et al 2021), and the seasonal succession of taxa (e.g.…”