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

Abstract

Acantharians are important contributors to surface primary production and to carbon flux 10 to the deep sea, but are often underestimated because their delicate structures are destroyed by plankton nets or dissolved by preservatives. As a result, relatively little is known about acantharian biology, especially regarding their life cycles. Here, we take a paired approach, bringing together high-throughput, in-situ imaging and high-throughput sequencing, to investigate acantharian abundance, vertical distribution, and life-history 15 in the western North Pacific. Observed concentrations of acantharian cells correlated well with sequence abundances from acantharians with known, recognizable morphologies, but not to sequences from those without known morphology (basal environmental clades). These results suggest basal clades may lack characteristic starshaped skeletons or are much smaller than known acantharians. The decreased size-20 range of acantharians imaged at depth supports current hypotheses regarding asymbiotic acantharian life cycles: cysts or vegetative cells release reproductive swarmer cells at depth and juvenile cells grow as they ascend towards the surface. Moreover, sequencing data present the possibility that photosymbiotic acantharians also reproduce at depth, like their asymbiotic, encysting relatives, which is counter to 25 previous hypotheses. Finally, in-situ imaging captured a new acantharian behavior that may be a previously undescribed predation strategy.

Recommendations for interpreting zooplankton metabarcoding and integrating molecular methods with morphological analyses

“…It remains difficult to link molecular estimates of diversity and community structure with morphological richness and abundance (Laakmann et al, 2020), and the lack of standardization in metabarcoding methods makes it difficult to compare molecular richness across studies (Santoferrara, 2019). A better understanding of the relationship between metabarcoding and morphological analyses can help optimize methodological choices for studying zooplankton ecology (Bucklin et al, 2019;Brisbin et al, 2020). Here, we provide recommendations for best practices regarding subsampling, replication, and ethanol preserva-tion.…”

Diversity and ecology of Radiolaria in modern oceans

“…Prey (or sometime predators aiming to prey on Collodaria) swimming near the pseudopodial network get glued on it and will be slowly be digested in specific vacuoles. Prey capture by Acantharia is still an unresolved process, despite a recent study (Mars Brisbin et al, 2020) reporting that acantharians in the near-surface layer consistently displayed long pseudopodial extensions terminating in dropshaped structures, which could serve as a fishing apparatus similar to those observed in polycystine radiolarians. Oroscenids feeding behaviour is primarily unknown.…”

“…mostly ciliates and tintinnids) or even multicellular heterotrophs (e.g. copepods, large mollusc larvae; Anderson, 1977; Sugiyama and Anderson, 1998; Bernstein et al ., 1999; Matsuoka, 2007; Sugiyama et al ., 2008; Suzuki and Not, 2015; Mars Brisbin et al ., 2020). A few reports, however, indicate that some radiolarians could be detritivores (Anderson, 1983).…”

“…Therefore, the existence of a deep‐sea and diverse acantharian population should be considered and deserves further attention. However, given the evolutionary history of acantharian skeleton (Decelle et al ., 2012a; Decelle and Not, 2015), with basal clades represented by rudimentary skeletons (see above), we cannot rule out that this environmental clade I, never morphologically characterized, lack the typical acantharian strontium sulfate skeleton (Mars Brisbin et al ., 2020). At broader geographical scales, despite a lack of detailed annotation and pattern analyses, DNA metabarcoding of surface waters suggested that Acantharia are one of the 11 most diverse eukaryotic lineages (de Vargas et al ., 2015), with 1043 operational taxonomic units (can be considered a proxy for species richness to some extent; Caron and Hu, 2018).…”

“…high-throughput sequencing of a constrained DNA region, often for marine protist communities the small-subunit ribosomal RNA gene) has allowed much more extensive exploration of diversity patterns (Caron et al, 2004(Caron et al, , 2012. Surveys of acantharian metabarcodes retrieved in the surface and deep-sea (>200 m) zones suggested higher acantharian diversity (mainly dominated by Clades E and F) in surface waters (Decelle et al, 2013;Mars Brisbin et al, 2020). Similar to clone library surveys (see above), DNA metabarcoding systematically highlighted an overwhelming dominance of the environmental Clade I in deep waters, regardless of the sampling location (i.e.…”