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Abstract
Abstract. Microbial eukaryotic community composition was examined by 18S rRNA gene tag pyrosequencing, during the early phase of spring phytoplankton blooms induced by natural iron fertilization, off Kerguelen Island in the Southern Ocean (KEOPS2 cruise). A total of 999 operational taxonomical units (OTUs), affiliated to 30 known high-level taxonomic groups, were retrieved from 16 samples collected in the upper 300 m water column. The alveolata group was the most abundant in terms of sequence number and diversity (696 OTUs). The majority of alveolata sequences were affiliated to Dinophyceae and to two major groups of marine alveolates (MALV-I and MALV-II). In the upper 180 m, only 13% of the OTUs were shared between of the fertilized stations and the reference site characterized by high-nutrient low-chlorophyll (HNLC) waters. Fungi and Cercozoa were present in iron-fertilized waters, but almost absent in the HNLC samples, while Haptophyta and Chlorophyta characterized the HNLC sample. Finally, the 300 m depth samples of all stations were differentiated by the presence of MALV-II and Radiolaria. Multivariate analysis, examining the level of similarity between different samples, showed that protistan assemblages differed significantly between the HNLC and iron-fertilized stations, but also between the diverse iron-fertilized blooms.
Highlights
Molecular investigations into the planktonic protists of natural microbial communities have revealed an astonishing diversity (e.g. Caron et al, 2012 and references therein) and a variety of novel and/or previously unobserved groups of saprophytes, parasites and intracellular symbionts (e.g Guillou et al, 2008; Massana and Pedrós-Alió, 2008; Bråte et al, 2012)
A series of molecular studies have examined spatial or temporal patterns in protistan community structure and diversity. These have indicated that the microbial community structure is generally highly responsive to environmental forcing, and that dominant protistan taxa can differ markedly over temporal and spatial scales associated with common oceanographic features (e.g Countway et al, 2007, 2010; Nolte et al, 2010; Gilbert et al, 2012; Mangot et al, 2013; Lie et al, 2013; Wolf et al, 2014; Christaki et al, 2014)
Taxonomic group) (Table 4); the most frequent operational taxonomical units (OTUs) belonged to Alveolata, followed by Stramenopiles, Hacrobia (Table 3)
Summary
Molecular investigations into the planktonic protists of natural microbial communities have revealed an astonishing diversity (e.g. Caron et al, 2012 and references therein) and a variety of novel and/or previously unobserved groups of saprophytes, parasites and intracellular symbionts (e.g Guillou et al, 2008; Massana and Pedrós-Alió, 2008; Bråte et al, 2012). A series of molecular studies have examined spatial or temporal patterns in protistan community structure and diversity These have indicated that the microbial community structure is generally highly responsive to environmental forcing, and that dominant protistan taxa can differ markedly over temporal and spatial scales associated with common oceanographic features (e.g Countway et al, 2007, 2010; Nolte et al, 2010; Gilbert et al, 2012; Mangot et al, 2013; Lie et al, 2013; Wolf et al, 2014; Christaki et al, 2014). The Southern Ocean has a unique geography with several large-scale water masses separated by oceanic fronts, and has major implications for the global ocean circulation and climate system It is the largest high-nutrient lowchlorophyll (HNLC) ocean, in which iron limits phytoplankton production, resulting in a large stock of major inorganic nutrients (Martin and Fitzwater, 1990).
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