Community dynamics and co-occurrence relationships of pelagic ciliates and their potential prey at a coastal and an offshore station in the ultra-oligotrophic Eastern Mediterranean Sea

Filomena Romano; Paraskevi Pitta; Uwe John

doi:10.3389/fgene.2023.1219085

Community dynamics and co-occurrence relationships of pelagic ciliates and their potential prey at a coastal and an offshore station in the ultra-oligotrophic Eastern Mediterranean Sea

Front Genet. 2023 Jul 20:14:1219085. doi: 10.3389/fgene.2023.1219085. eCollection 2023.

Authors

Filomena Romano^{1

2}, Paraskevi Pitta¹, Uwe John^{3

4}

Affiliations

¹ Marine Biological Section, University of Copenhagen, Helsingør, Denmark.
² Hellenic Centre for Marine Research, Institute of Oceanography, Heraklion, Greece.
³ Ecological Chemistry, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.
⁴ Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB), Oldenburg, Germany.

Abstract

Ciliates have been recognized as one of the major components of the microbial food web, especially in ultra-oligotrophic waters, such as the Eastern Mediterranean Sea, where nutrients are scarce and the microbial community is dominated by pico- and nano-sized organisms. For this reason, ciliates play an important role in these ecosystems since they are the main planktonic grazers. Regardless the importance of these organisms, little is known about the community structure of heterotrophic and mixotrophic ciliates and how they are associated to their potential prey. In this study, we used 18S V4 rRNA gene metabarcoding to analyze ciliate community dynamics and how the relationship with potential prey changes according to different seasons and depths. Samples were collected seasonally at two stations of the Eastern Mediterranean Sea (HCB: coastal, M3A: offshore) from the surface and deep chlorophyll maximum (DCM) layers. The ciliate community structure varied across depths in HCB and across seasons in M3A, and the network analysis showed that in both stations, mixotrophic oligotrichs were positively associated with diatoms and showed few negative associations with ASVs annotated as marine Stramenopiles (MAST). On the other hand, heterotrophic tintinnids showed negative relationships in both HCB and M3A stations, mostly with Ochrophyta and Chlorophyta. These results showed, in first place that, although the two stations are close to each other, the ciliate dynamics differed between them. Moreover, mixotrophic and heterotrophic ciliates may have different ecological niches since mixotrophic ciliates may be more selective compared to heterotrophic species regarding their prey. These findings are the first glimpse into an understanding of the dynamics between heterotrophic and mixotrophic ciliates and their role in microbial assemblages and dynamics of ultra-oligotrophic environments.

Keywords: DNA; barcoding; mixotrophy; network analysis; prey-predator; vertical/temporal distribution.

Grants and funding

EC MSCA-ITN 2019 funding to the project MixITiN (Grant Number 766327).