Ocean-wide comparisons of mesopelagic planktonic community structures

Abstract

Marine plankton mitigate anthropogenic greenhouse gases, modulate biogeochemical cycles, and provide fishery resources. Plankton is distributed across a stratified ecosystem of sunlit surface waters and a vast, though understudied, mesopelagic 'dark ocean'. In this study, we mapped viruses, prokaryotes, and pico-eukaryotes across 32 globally-distributed cross-depth samples collected during the Tara Oceans Expedition, and assessed their ecologies. Based on depth and O2 measurements, we divided the marine habitat into epipelagic, oxic mesopelagic, and oxygen minimum zone (OMZ) eco-regions. We identified specific communities associated with each marine habitat, and pinpoint environmental drivers of dark ocean communities. Our results indicate that water masses primarily control mesopelagic community composition. Through co-occurrence network inference and analysis, we identified signature communities strongly associated with OMZ eco-regions. Mesopelagic communities appear to be constrained by a combination of factors compared to epipelagic communities. Thus, variations in a given abiotic factor may cause different responses in sunlit and dark ocean communities. This study expands our knowledge about the ecology of planktonic organisms inhabiting the mesopelagic zone.

Global biogeography of the smallest plankton across ocean depths

“…Water masses may impact microbial communities in basically two ways: a) as a selective force – since they have different temperatures and salinity (54, 55) as well as organic matter composition (56–58) – or; b) as a physical barrier to dispersal due to sometimes strong differences in water density (14). We found significant positive correlations between prokaryotic community structure and water mass compositions in the open ocean, which is in line with previous studies that found bacterial communities associated with specific water masses (13, 14, 56, 59). This relationship is likely linked to the fact that each water mass has different types of organic matter (57, 61) that likely select for different prokaryotes (56, 58).…”

From the Sunlit to the Aphotic Zone: Assembly Mechanisms and Co-Occurrence Patterns of Protistan-Bacterial Microbiotas in the Western Pacific Ocean

“…Similar to the bacterial community, the protistan community in the present study was clearly stratified down the water column, demonstrating a large vertical difference between photic and aphotic protistan-bacterial microbiomes in the western Pacific. Recent studies, including those on protistan communities at station ALOHA in the North Pacific Subtropical Gyre ( 45 ), in the subtropical and subantarctic waters of the southwest Pacific ( 46 ), and in the tropical and subtropical global oceans ( 32 ), support this conclusion. The dichotomy in distribution of protists and bacteria along the water column observed in the present study and at both local and global scales likely underlies the heterogeneity of biotic, abiotic, and dispersal conditions encountered in photic and aphotic zones, and this variation in biotic, abiotic, and dispersal conditions may be a crucial factor that can directly influence community composition.…”

“…Clone libraries, fingerprints, high-throughput sequencing, and metagenomics have revealed differential patterns of bacterial communities that occur in photic versus aphotic zones in a vast array of marine environments ( 35 , 37 – 45 ). Observational data on the vertical distribution of FL and PA bacteria are abundant, whereas data on protists, particularly below the photic zone, are lacking ( 32 , 45 , 46 ). Similar to the bacterial community, the protistan community in the present study was clearly stratified down the water column, demonstrating a large vertical difference between photic and aphotic protistan-bacterial microbiomes in the western Pacific.…”

“…The community composition of predator, host, and nonpredatory microbial alliances (as determined by the exchange of important elements, such as vitamins) is apparently a significant underlying factor influencing the assembly of bacterial communities. However, protists and bacteria have rarely been investigated simultaneously as an organismal factor to reveal the role of biotic interactions in community assembly studies ( 29 , 30 ), especially in the marine aphotic zones ( 31 , 32 ).…”