Abstract
Abstract. The sea surface microlayer (SML) represents the boundary layer at the air–sea interface. Microbial eukaryotes in the SML potentially influence air–sea gas exchange directly by taking up and producing gases and indirectly by excreting and degrading organic matter, which may modify the viscoelastic properties of the SML. However, little is known about the distribution of microbial eukaryotes in the SML. We studied the composition of the microbial community, transparent exopolymer particles and polysaccharides in the SML during the PEACETIME cruise along a west–east transect in the Mediterranean Sea, covering the western basin, Tyrrhenian Sea and Ionian Sea. At the stations located in the Ionian Sea, fungi – likely of continental origin and delivered by atmospheric deposition – were found in high relative abundances, making up a significant proportion of the sequences recovered. Concomitantly, bacterial and picophytoplankton counts decreased from west to east, while transparent exopolymer particle (TEP) abundance and total carbohydrate (TCHO) concentrations remained constant in all basins. Our results suggest that the presence of substrates for fungi, such as Cladosporium, known to take up phytoplankton-derived polysaccharides, in combination with decreased substrate competition by bacteria, might favor fungal dominance in the neuston of the Ionian Sea and other low-nutrient, low-chlorophyll (LNLC) regions.
Highlights
The sea surface microlayer (SML) constitutes a 1 to 100 μm thick boundary layer between the ocean and the atmosphere (Cunliffe and Murrell, 2010; Liss and Duce, 2005; Zhang et al, 2003) with distinct physical and chemical properties compared to the underlying water (Cunliffe et al, 2013; Zhang et al, 2003)
The present study focuses on transparent exopolymer particle (TEP) as important structural components of the SML and their precursors, carbohydrates, and microbial eukaryotes distribution, focusing on the myconeuston community composition in the SML using samples collected during the PEACETIME cruise in the Mediterranean Sea during May and June 2017
ANOSIM showed that the differences in the eukaryotic community composition were slightly larger across basins than between SML and underlying water (ULW) (p = 0.0025, R = 0.2263)
Summary
The sea surface microlayer (SML) constitutes a 1 to 100 μm thick boundary layer between the ocean and the atmosphere (Cunliffe and Murrell, 2010; Liss and Duce, 2005; Zhang et al, 2003) with distinct physical and chemical properties compared to the underlying water (Cunliffe et al, 2013; Zhang et al, 2003). While phytoplankton throughout the water column play an important role in the ocean as primary producers, phytoneuston in the SML (Apts, 1989; Hardy and Apts, 1984; Naumann, 1917) might have an additional crucial role by impacting air–sea gas exchange (Ploug, 2008; Upstill-Goddard et al, 2003). More recent studies using 18S rRNA gene sequencing found a decreased protist diversity in the SML compared to underlying water with chrysophytes and diatoms enriched in the SML (Cunliffe and Murrell, 2010; Taylor and Cunliffe, 2014)
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