Comparative Metabarcoding and Metatranscriptomic Analysis of Microeukaryotes Within Coastal Surface Waters of West Greenland and Northwest Iceland

Stephanie Elferink,Uwe John,Stefan Neuhaus,Lars Harms,Allan Cembella,Sylke Wohlrab

doi:10.3389/fmars.2020.00439

Abstract

Climate change alters environmental conditions that are expected to have a profound effect on the biodiversity, community composition, and metabolic processes of microeukaryotic plankton in Arctic and Subarctic coastal waters. The molecular biodiversity [large subunit (LSU) rRNA gene] of three plankton size-fractions (micro-, nano-, and picoplankton) from coastal waters of ice-influenced west Greenland was compared with fractions from ice-free northwest Iceland within their summer environmental context. Putative metabolic functions were determined by differentially expressed mRNA (metatranscriptomics) of the microplankton. Temperature and salinity variations were more closely correlated than inorganic macronutrients with metabolic functions and community composition. Temperature explained much of the community variance, approximately 20% among micro- and nanoplankton, whereas other environmental factors accounted for rather low fractional variance (<7%). Species of smaller cell-size were more evenly distributed (Pielou’s evenness index J) across regions, with a higher diversity and total abundance, and thereby indicating high plasticity. The metatranscriptomic profiles in these respective microeukaryotic communities revealed that diatoms were more plastic in their gene expression than dinoflagellates, but dinoflagellates had a more diverse, albeit homogeneously expressed, gene pool. This could be interpreted as expression of alternative lifestyle strategies, whereby the functionally more conservative diatoms fill their niches primarily through variable resource use, whereas dinoflagellates apparently differentiate their niches through more diverse lifestyles. Patterns of microeukaryotic diversity are thus primarily associated with differences in metabolic function and activity of diatom- versus dinoflagellate-dominated communities in Arctic and Subarctic waters during summer.

Highlights

Total extant richness of marine eukaryotes is estimated at up to 2.2 million species (Mora et al, 2011), of which 226,000 are described (Appeltans et al, 2012); known taxa informally regarded as “algae” comprise around 32,500 distinct species from marine and freshwater systems (Guiry, 2012)
With respect to dispersal mechanisms and the importance of cell size, we identified diversity variation between the size-fractions but focused on how the community composition of diatoms versus dinoflagellates of each sizefraction was related to within- or between-region differences in ambient abiotic conditions
In this study we focused on the LSU rRNA D1/D2 region, which has a high taxonomic resolution to differentiate at the species level for many major microeukaryote groups, such as diatoms and dinoflagellates (Medlin et al, 1998; John et al, 2003; Sonnenberg et al, 2007; Moniz and Kaczmarska, 2009; Toebe et al, 2013; Kretschmann et al, 2015)

Summary

Introduction

Total extant richness of marine eukaryotes is estimated at up to 2.2 million species (Mora et al, 2011), of which 226,000 are described (Appeltans et al, 2012); known taxa informally regarded as “algae” (i.e., including cyanobacteria and eukaryotic macroalgae) comprise around 32,500 distinct species from marine and freshwater systems (Guiry, 2012). The high diversity among microeukaryotic plankton may be attributable to “contemporaneous disequilibrium” of patchy phytoplankton distribution (Richerson et al, 1970), reflected by differences in life history transitions (Huisman et al, 2001), species oscillations (Huisman and Weissing, 1999), environmental fluctuation (Roy and Chattopadhyay, 2007), cryptic intraspecific variation (Menden-Deuer and Rowlett, 2014), and differential niche partitioning (Connell, 1980) The resolution of this apparent plankton paradox involves defining the number and partitioning of ecological niches in the pelagic and determining to what extent species compete for limiting resources. Metatranscriptomic analysis already addresses key issues in plankton functional ecology, such as resource partitioning and functional variation between diatom communities (Alexander et al, 2015a; Pearson et al, 2015), profiling characteristics of a harmful algal bloom (Cooper et al, 2014), and responses of phytoplankton to varying iron availability (Marchetti et al, 2012)

Methods

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Discussion

Conclusion