Abstract
Microbial eukaryotes are key components of the marine food web, but their distribution in deep-sea chemosynthetic ecosystems has not been well studied. Here, high-throughput sequencing of the 18S rRNA gene and network analysis were applied to investigate the diversity, distribution and potential relationships between microbial eukaryotes in samples collected from two cold seeps and one trough in the northern South China Sea. SAR (i.e., Stramenopiles, Alveolata, and Rhizaria) was the predominant group in all the samples, and it was highly affiliated to genotypes with potential symbiotic and parasitic strategies identified from other deep-sea extreme environments (e.g., oxygen deficient zones, bathypelagic waters, and hydrothermal vents). Our findings indicated that specialized lineages of deep-sea microbial eukaryotes exist in chemosynthetic cold seeps, where microbial eukaryotes affiliated with parasitic/symbiotic taxa were prevalent in the community. The biogeographic pattern of the total community was best represented by the intermediate operational taxonomic unit (OTU) category, whose relative abundance ranged 0.01–1% within a sample, and the communities of the two cold seeps were distinct from the trough, which suggests that geographical proximity has no critical impact on the distribution of deep-sea microbial eukaryotes. Overall, this study has laid the foundations for future investigations regarding the ecological function and in situ trophic relationships of microbial eukaryotes in deep-sea ecosystems.
Highlights
Marine microbial eukaryotes are fundamental for maintaining the functional stability of marine ecosystems (Caron et al, 2009), and they serve as important links to higher trophic levels as primary producers and consumers (Sherr and Sherr, 2002)
It has been shown that sulfidic and anoxic zones in the deep-sea harbor a great diversity of unclassified ciliates (Coyne et al, 2013) and Stramenopiles (Wylezich and Jürgens, 2011) with unknown ecological functions, and hydrothermal vents has been suggested as oases for parasitic protists (Moreira and López-Garcia, 2003)
Considering cold seeps to be typically chemosynthetic ecosystems, it is reasonable to assume that specialized microbial eukaryotic assemblages with possible parasitic or symbiotic trophic status exist in the microbial niches of cold seep sediments
Summary
Marine microbial eukaryotes are fundamental for maintaining the functional stability of marine ecosystems (Caron et al, 2009), and they serve as important links to higher trophic levels as primary producers and consumers (Sherr and Sherr, 2002). They graze on prokaryotic prey and in this way, they integrate the microbial loop into classical marine food webs (Massana et al, 2004a). Microbial eukaryotes with specialized assemblages and trophic status have been recovered from different deep-sea habitats. Considering cold seeps to be typically chemosynthetic ecosystems, it is reasonable to assume that specialized microbial eukaryotic assemblages with possible parasitic or symbiotic trophic status exist in the microbial niches of cold seep sediments
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