High contribution of Rhizaria (Radiolaria) to vertical export in the California Current Ecosystem revealed by DNA metabarcoding

Abstract

Passive sinking of particulate organic matter (POM) is the main mechanism through which the biological pump transports surface primary production to the ocean interior. However, the contribution and variability of different biological sources to vertical export is not fully understood. Here, we use DNA metabarcoding of the 18S rRNA gene and particle interceptor traps (PITs) to characterize the taxonomic composition of particles sinking out of the photic layer in the California Current Ecosystem (CCE), a productive system with high export potential. The PITs included formalin-fixed and 'live' traps to investigate eukaryotic communities involved in the export and remineralization of sinking particles. Sequences affiliated with Radiolaria dominated the eukaryotic assemblage in fixed traps (90%), with Dinophyta and Metazoa making minor contributions. The prominence of Radiolaria decreased drastically in live traps, possibly due to selective consumption by copepods, heterotrophic nanoflagellates, and phaeodarians that were heavily enriched in these traps. These patterns were consistent across the water masses surveyed extending from the coast to offshore, despite major differences in productivity and trophic structure of the epipelagic plankton community. Our findings identify Radiolaria as major actors in export fluxes in the CCE.

Eukaryotic influence on the oceanic biological carbon pump in the Scotia Sea as revealed by 18S rRNA gene sequencing of suspended and sinking particles

“…Parasitic Syndiniales sequences are commonly detected in 18S rRNA gene sequencing in high abundances (e.g., Sauvadet et al ; de Vargas et al ; Cleary and Durbin ; Gutierrez‐Rodriguez et al ). They affect a wide variety of hosts, ranging from diatoms (Berdjeb et al .…”

Estimating Biogenic Silica Production of Rhizaria in the Global Ocean

“…Diatoms are considered the world's largest contributors to the Si cycle, dominating both the standing stock of water column biogenic silica (bSi) and its production rate (Ragueneau et al, , ; Tréguer & De La Rocha, ). A number of studies ranging from sediment traps to environmental molecular surveys have emphasized the importance of rhizarians in biogeochemical cycles and export of C and bSi to the deep ocean (Biard et al, ; Guidi et al, ; Gutierrez‐Rodriguez et al, ; Lampitt et al, ). Moreover, recent studies combining genomic and in situ imaging approaches have shown that the contribution of large Rhizaria to the biomass of zooplankton has been largely underestimated (Biard et al, ), with their abundance correlating with carbon export fluxes at 150‐m depth in oligotrophic oceanic regions (Guidi et al, ).…”

Paired high-throughput, in-situ imaging and high-throughput sequencing illuminate acantharian abundance and vertical distribution

“…6B) are consistent with the idea that many acantharians sink to release swarmers with juveniles growing in size as they make their way up towards the surface. Adult cells sink quickly, whether for reproduction or as detritus (Gutierrez-Rodriguez et al, 2019), and both vegetative cells and cysts dissociate after releasing swarmers (Decelle et al, 2012a(Decelle et al, , 2013, making them less likely to be caught on 470 camera. A large number of swarmers released at depth would potentially produce many small juvenile cells that gradually increase in size as they slowly ascend.…”

“…The acantharian skeleton is composed of strontium sulfate, the densest known organic biomineral, causing acantharians to sink quickly after death (Decelle et al, 2013). In addition, their amoeboid cell structure with sticky cellular extensions (pseudopodia) 40 predisposes sinking acantharians to form aggregates, further enhancing sinking rate (Gutierrez-Rodriguez et al, 2019). The biogeochemical significance of acantharians has been historically underestimated, however, because traditional sampling methods often miss acantharians; plankton nets destroy delicate acantharian cell structures (Michaels, 1988) and common preservatives dissolve acantharian skeletons (Bernstein et al, 45 1992).…”

“…The biogeochemical significance of acantharians has been historically underestimated, however, because traditional sampling methods often miss acantharians; plankton nets destroy delicate acantharian cell structures (Michaels, 1988) and common preservatives dissolve acantharian skeletons (Bernstein et al, 45 1992). DNA sequencing surveys have revealed that acantharians account for large numbers of sequences from the water column and sediment traps in diverse ecosystems, including tropical and subtropical regions (Fontanez et al, 2015;Hu et al, 2018), polar regions (Martin et al, 2010;Decelle et al, 2013), and productive temperate coastal regions Gutierrez-Rodriguez et al, 2019). However, the 50 relationship between DNA sequence abundance and acantharian biomass or flux is not clear and is complicated by acantharians being multinucleated and having multiple life stages, including encystment and reproductive swarmer production.…”