Global biogeography of the smallest plankton across ocean depths

Abstract

Tiny ocean plankton (picoplankton) are fundamental for the functioning of the biosphere, but the ecological mechanisms shaping their biogeography are partially understood. Comprehending whether these microorganisms are structured by niche vs. neutral processes is highly relevant in the context of global change. The ecological drivers structuring picoplankton communities differ between prokaryotes and minute eukaryotes (picoeukaryotes) in the global surface ocean: while prokaryotic communities are shaped by a balanced combination of dispersal, selection, and drift, picoeukaryotic communities are mainly shaped by dispersal limitation. Yet, whether or not the relative importance of these processes in structuring picoplankton varies as we dive into the deep ocean was unknown. Here we investigate the mechanisms structuring picoplanktonic communities inhabiting different ocean depths. We analyzed 451 samples from the tropical and subtropical global ocean and the Mediterranean Sea covering the epi- (0-200m), meso- (200-1,000m), and bathypelagic (1,000-4,000m) depth zones. We found that selection decreased with depth possibly due to lower habitat heterogeneity. In turn, dispersal limitation increased with depth, possibly due to dispersal barriers such as water masses and bottom topography. Picoplankton β-diversity positively correlated with environmental heterogeneity and water mass variability in both the open-ocean and the Mediterranean Sea. However, this relationship tended to be weaker for picoeukaryotes than for prokaryotes. Community patterns were generally more pronounced in the Mediterranean Sea, probably because of its substantial cross-basin environmental heterogeneity and deep-water isolation. Altogether, we found that different combinations of ecological mechanisms shape the biogeography of the smallest members of the ocean microbiome across ocean depths.

A fungi hotspot deep down the ocean: explaining the presence ofGjaerumia minorin Equatorial Pacific bathypelagic waters

“…Information about the studied stations and sampling of Malaspina 2010 expedition could be found in previously published works. In particular, the methodology for bacterial abundance with flow-cytometry and prokaryotic biomass calculation is described in Pernice et al (2015) 24 ; DNA extraction, 454-pyrosequencing, and bioinformatic pipeline for samples belonging to the deep ocean are in Pernice et al (2016) 16 ; DNA extraction and Illumina sequencing for 12 vertical profiles (5 to 4000 m) are in Giner et al (2020) 17 ; Illumina sequencing from samples belonging to surface of the entire cruise are in Logares et al (2020) 25 ; and data for Illumina sequencing in bathypelagic samples are in Junger et al (2023) 26 . All the Illumina raw data (12 vertical profiles, global surface and global bathypelagic) has been newly analyzed here with DADA2 27 to define the distribution of the ASV of interest (363) in the different datasets.…”

The photic‐aphotic divide is a strong ecological and evolutionary force determining the distribution of ciliates (Alveolata, Ciliophora) in the ocean

“…richness) remain unclear given contradictory data in the literature (Canals et al, 2020; Sun et al, 2019; Zhao et al, 2017; see Discussion). Also, contemporary patterns of ciliate diversity and taxonomic composition in the vertical profile have not been reported in a phylogenetic context, even though depth can explain both community assembly and the evolutionary histories of other protists in the ocean (Junger et al, 2022; Weiner et al, 2012).…”