Parasitic Eukaryotes in a Meso-Eutrophic Coastal System with Marked Phaeocystis globosa Blooms

Urania Christaki,Elsa Breton,Savvas Genitsaris,Sara Rachik,Télesphore Sime-Ngando,Luen L Li,Sébastien Monchy

doi:10.3389/fmars.2017.00416

Abstract

This study explored the potential interactions and relations of the putative Symbiotic/Decomposer/Parasitic community (SymbDec) with other taxa and predominant environmental parameters in the eastern English Channel (EEC) over a 2.5 years period (32 sampling dates). The EEC is a meso-eutrophic coastal system characterized by strong repeating patterns in plankton succession with recurrent massive blooms of the Haptophyte Phaeocystis globosa preceded and followed by communities of colonial diatoms and dinoflagellate grazers. The metagenomic sequencing results of the V2-V3 hypervariable region of the 18S rRNA gene allowed an overview of the planktonic community, which consisted of 32 high-level taxonomic groups. Forty-two % of the detected OTUs belonged to potentially parasitic taxa or decomposers such as Syndiniales (MALV – MArine ALveolates), Fungi, Cercozoa, Perkinsea and others, most of which were plankton parasites. We examined the Local Similarity Analysis (LSA) network of lag delayed correlations on the 142 most abundant OTUs (> 0.1 % of the total number of reads). LSA showed that 99 OTUs had highly significant connections, involving 26 OTUs characterized as potential parasites, and 2 decomposers. The parasitic network had small world characteristics, rendering the assemblage more resilient to environmental change, but more susceptible to the removal of highly connected taxa. The majority of the highly connected OTUs belonged to MALV, which were mainly connected with dinoflagellates, suggesting that it might play an important role on dinoflagellate top-down control. The bloom forming P. globosa was not observed in connection with parasitic OTUs in the network. Four environmental parameters (O2, N, T, and N/P) were strongly connected with only 11 OTUs, while correlations between microbes dominated the network.

Highlights

Marine parasitic protists have been observed and described— along with other protists—from the early microbiologists over the last few centuries
The highest value recorded for PO4 was recorded during the P. globosa bloom in April 2012 (Figure 1)
It is noteworthy that the bloom forming P. globosa was not present in any of the networks constructed. These results have showed that the importance of Symbiotic/Decomposer/Parasitic community (SymbDec) Operational Taxonomic Units (OTUs) in the eastern English Channel (EEC) is extended throughout the whole year, as SymbDecs were found to comprise 42% of the total number

Summary

Introduction

Marine parasitic protists have been observed and described— along with other protists—from the early microbiologists over the last few centuries (see Caron et al, 2009; Skovgaard, 2014, for a review). During the last few decades, using the genetic diversity of the 18S rRNA gene, novel eukaryotic taxonomic groups have been revealed within the marine protistan plankton (e.g., López-García et al, 2001; López-García and Moreira, 2008) with great amount of them belonging to potential intracellular symbionts and parasites (e.g., Guillou et al, 2008; Bråte et al, 2012). Parasitism is without a doubt a relation, which enhances the density and extend foodwebs. This in turn enhances the connectivity between species and makes carbon transfers more efficient, because parasitic taxa have complex life cycles and infect organisms that belong at different trophic levels (e.g., Laferty et al, 2008; Niquil et al, 2011). In many microbial communities, recurrent organizational patterns cannot always associate with straightforward community roles and/or detailed dependencies between species owing to missing information on “overlooked” microbial interactions (for a review see Bik et al, 2012)

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