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

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 portrayed by intense reoccurring patterns in plankton succession with blooms of the Haptophyte Phaeocystis globosa and abundant populations of colonial diatoms and dinoflagellate grazers before and after the bloom. The study 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 percent of the identified OTUs belonged to symbionts, decomposers or other putative parasitic taxa belonging mainly to 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 robust to abiotic variations, but more exposed to the removal of highly associated 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 (O 2 , N, T, and N/P) were strongly connected with only 11 OTUs, while correlations between microbes dominated the network.

Protist Interactions and Seasonal Dynamics in the Coast of Yantai, Northern Yellow Sea of China as Revealed by Metabarcoding

“…Syndiniales is a group comprised exclusively of parasitic species that infect tintinnid ciliates, crustaceans, dinoflagellates and fish (Guillou et al, 2008). The high abundance of Syndiniales detected in this study corresponds well to the previous findings in several metabarcoding studies on planktonic microeukaryotes (Georges et al, 2014;Christaki et al, 2017), and supports the hypothesis that parasitic interactions could dominate plankton networks (De Vargas et al, 2015;Lima-Mendez et al, 2015). Otherwise, it should be aware that potentially high rRNA gene copy numbers and inactive spores could lead to overestimation on the proportion of Syndiniales (Not et al, 2009;Sassenhagen et al, 2019).…”

Diversity and potential activity patterns of planktonic eukaryotic microbes in a mesoeutrophic coastal area (eastern English Channel)

“…globosa bloom period, but gradually increased to reach its highest in fall-winter. Symbionts and degraders accounted for more than one third of the OTU diversity in fall-winter [ 67 ]. Microbial eukaryote community structure and seasonal succession were similar between surveys and years for the most abundant taxonomic groups, representing the majority of reads (>90).…”

“…However, other biases due to random sampling, sequencing methods, PCR and sequencing errors might have also contributed to this disparity [ 68 ]. In addition, previous studies in the area have suggested that inter-taxa relations, rather than environmental variables, were the main drivers of microbial community structure and temporal succession [ 45 , 67 ]. These studies showed that environmental variables could explain only around 30% of microbial eukaryote succession [ 45 ], and few correlations were observed, through network analysis, between OTUs and environmental variables while correlations between microbes dominated the network [ 67 ].…”

Variability and Community Composition of Marine Unicellular Eukaryote Assemblages in a Eutrophic Mediterranean Urban Coastal Area with Marked Plankton Blooms and Red Tides

“…Christaki et al [3] reported "new players in the succession scene" of the coast of eastern English Channel, and were associated with MALVs, MAST, and Cercozoa, which were also detected in our study. These new players were suggested to participate in complex interactions [7,15], shaping the spatial [7] and temporal unicellular eukaryote assemblages in the area [9]. Especially the rare microbial fraction of these assemblages appeared to be particularly active and play significant ecological roles [57].…”

“…In a recent study, Ramond et al [14] have attempted to link the taxonomic diversity of protistan taxa detected with HTS with 30 different traits in samples from ecosystems across the coasts of North Atlantic Ocean, suggesting that small taxa are characterized by broader taxonomic and functional diversity. Furthermore, previously underestimated trophic strategies, such as parasitism and decomposition, have been recognized as central to marine planktonic assemblage structure and ecosystem function [9,15]. In addition, the environmental effects [9,16] and biotic relationships in unicellular eukaryotic communities have been explored, using classical and modern ecological tools [17,18].…”