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

Abstract

Suspended marine particles constitute most of the particulate organic matter pool in the oceans, thereby providing substantial substrates for heterotrophs, especially in the mesopelagic. Conversely, sinking particles are major contributors to carbon fluxes defining the strength of the biological carbon pump (BCP). This study is the first to investigate the differential influence of eukaryotic communities to suspended and sinking particles, using 18S rRNA gene sequencing on particles collected with a marine snow catcher in the mixed layer and upper mesopelagic of the Scotia Sea, Southern Ocean. In the upper mesopelagic, most eukaryotic phytoplankton sequences belonged to chain‐forming diatoms in sinking particles and to prymnesiophytes in suspended particles. This suggests that diatom‐enriched particles are more efficient in carbon transfer to the upper mesopelagic than those enriched in prymnesiophytes in the Scotia Sea, the latter more easily disintegrating into suspended particles. In the upper mesopelagic, copepods appeared most influential on sinking particles whereas soft‐tissue metazoan sequences contributed more to suspended particles. Heterotrophic protists and fungi communities were distinct between mixed layer and upper mesopelagic, implying that few protists ride along sinking particles. Furthermore, differences between predatory flagellates and radiolarians between suspended and sinking particles implied different ecological conditions between the two particles pools, and roles in the BCP. Molecular analyses of sinking and suspended particles constitute powerful diagnostic tools to study the eukaryotic influence on the BCP in a more holistic manner compared to classic carbon export studies focusing on sinking particles.

Diverse groups of fungi are associated with plastics in the surface waters of the Western South Atlantic and the Antarctic Peninsula

“…In our data set, Chytrids were detected, particularly from samples from the AP, but had a low frequency despite often having a high relative abundance in samples where they were present. In Arctic systems Chytrids have been reported as the most abundant fungi group in ice cores (Hassett, Ducluzeau, & Collins, 2017; Hassett & Gradinger, 2016) and seawater (Comeau, Vincent, Bernier, & Lovejoy, 2016), A diversity of Chytrids and other basal fungi have been found in lakes on the Antarctic continent (Rojas‐Jimenez et al., 2017), and in Antarctica soils (Cox, Newsham, & Robinson, 2019) as well as on organic particles in the Scotia sea (Duret et al., 2020). Our study demonstrated the benefit of using a combination of marker genes for epiplastic fungi.…”

“…Moreover, marine plastics are often covered in polysaccharide‐rich diatom biofilms (Lacerda et al., 2019), this could explain the attachment and association of fungi with biofilms on plastics (Kettner, Rojas‐Jimenez, Oberbeckmann, Labrenz, & Grossart, 2017; Oberbeckmann, Osborn, & Duhaime, 2016). Recent studies have directly linked fungi to the degradation of organic matter (Cunliffe, Hollingsworth, Bain, Sharma, & Taylor, 2017;Ortega‐Arbulú, Pichler, Vuillemin, & Orsi, 2019), and in the open ocean fungi may attach to marine snow particles (Bochdansky, Clouse, & Herndl, 2017; Duret, Lampitt, & Lam, 2020). Other marine debris such as wood also harbour fungi, suggesting that Fungi are well adapted to live on different types of floating marine substrates (Kettner, Oberbeckmann, Labrenz, & Grossart, 2019; Kettner et al., 2017).…”

Planktonic protist diversity across contrasting Subtropical and Subantarctic waters of the southwest Pacific

“…In our study, we found an opposite distribution between Acantharea and RAD-B, which showed preference for the upper (<500 m) and deeper (>500 m) mesopelagic samples, respectively (Figure 7). Among Acantharea, most sequences were assigned to the order Chaunchantida (Figure S9, Figure S14), which has been found in sinking particles collected in the Southern Ocean (Duret et al 2020) and the California Current (Gutierrez-Rodriguez et al 2019; Preston et al 2020). In a recent study conducted in the Southern Ocean, RAD B was reported to be enriched in small (<10 µ m) suspended particles relative to sinking particles (Duret et al 2020) while RAD-A were consistently found in sinking particles reaching abyssal depths in the California Current Ecosystem (Preston et al 2020).…”

Single-cell metabarcoding reveals biotic interactions of the Arctic calcifierNeogloboquadrina pachydermawith the eukaryotic pelagic community

“…Diatoms of the genus Chaetoceros generally from chain-like structures which in the presence of high levels of biomass, tend to cluster together into larger colonies forming aggregates and producing abundant exopolymeric gels that lead to high carbon export (Chamnansinp et al, 2013;Booth et al, 2002;Duret et al, 2020). This is particularly true in the Baffin Bay, where it has been estimated that in July, cells of C. gelidus can contribute up to 91 and 49% of total phytoplankton abundance and carbon respectively (Booth et al, 2002).…”

“…Crustaceans and soft-bodied Urochordata are also known to actively or passively participate in the formation of marine aggregates (Duret et al, 2020). By feeding indiscriminately on organic particles present in the aggregates, N. pachyderma diet could also contain these organisms, or their remains.…”