1/31/2024 0 Comments Seasonality core manualThe warm oligotrophic subtropical gyres of the major ocean basins are the largest biome in the planet, and these nutrient-poor regions are expanding in size ( Irwin and Oliver, 2009). This trophic transfer may represent a critical mechanism sustaining the upper levels of mesopelagic trophic webs. There, a large and diverse community of heterotrophic protists thrives on sinking particulate matter, preys upon the prokaryotic populations ( Rocke et al., 2015 Ollison et al., 2021) and removes a similar percentage of the prokaryotic standing stock compared to the epipelagic realm ( Rocke et al., 2015). The available observational data is rich in horizontal spatial and temporal coverage, yet lacks vertical resolution, particularly below the photic zone ( Ollison et al., 2021). Recent applications of molecular tools such as metabarcoding ( de Vargas et al., 2015 Choi et al., 2020), metagenomics and single cell genomics ( Latorre et al., 2021), have significantly sharpened our understanding of protist diversity, distributions, and functionality, from basic trophic modes to complex metabolic pathways, and emphasized their importance in channeling marine productivity to upper trophic levels. They are responsible for ~50% of annual planktonic photosynthetic primary productivity (PP), of which they consume ~66%, plus an additional 10% of bacterial PP ( Calbet and Landry, 2004 Steinberg and Landry, 2017). These groups occupy distinct niches in the marine food web, playing essential roles in biogeochemical cycles ( Mitra et al., 2014 Worden et al., 2015). They include primary producers (autotrophs), heterotrophs (phagotrophs and parasitic), and a substantial collection of lineages exhibiting varying degrees of mixotrophic strategies ( Mitra et al., 2016). Marine protists encompass a large and heterogeneous community representing the majority of the eukaryotic diversity on the oceans ( Worden et al., 2015). At depth, the protist community closely tracked mesoscale events (eddies), where the communities followed the hydrographic uplift, raising the deeper communities for hundreds of meters, and compressing the communities above. The results suggest a dynamic partitioning of the water column, where the niche vertical position for each community changes throughout the year in the epipelagic, likely depending on nutrient availability, the mixed layer depth, and other hydrographic features. Below the photic zone, the community, dominated by Rhizaria, is depth-stratified and relatively constant throughout the year, although they followed local hydrographic and biological features such as the oxygen minimum zone. However, autotrophs bloomed during the rapid transition between the winter mixing and the stratified summer, and heterotrophs had their peak at the end of summer, when the base of the thermocline reaches its deepest depth. Mixotrophic lineages dominated throughout the year. The protist community showed a dynamic seasonality in the epipelagic, responding to hydrographic yearly cycles. ![]() The present study applies V4 18S rDNA metabarcoding to samples collected over three years in conjunction with the BATS time-series to assess marine protist communities in the epipelagic and mesopelagic zones (0-1000 m). While the available data is rich in horizontal and temporal coverage, little is known on their vertical structuring, particularly below the photic zone. They have different functions in the marine food web, playing essential roles in the biogeochemical cycles. Protists represent the majority of the eukaryotic diversity in the oceans. ![]()
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