Abstract
The sea surface microlayer (SML) is located at the air-sea interface, with microorganisms and organic matter in the SML influencing air-sea exchange processes. Yet understanding of the SML bacterial (bacterioneuston) community composition and assembly remains limited. Availability of organic matter, UV radiation and wind speed have previously been suggested to influence the community composition of bacterioneuston. Another mechanism potentially controlling bacterioneuston dynamics is bacterioplankton attached to gel-like particles that ascend through the water column into the SML. We analyzed the bacterial community composition, Transparent Exopolymer Particles (TEP) abundance and nutrient concentrations in the surface waters of the Peruvian upwelling region. The bacterioneuston and bacterioplankton communities were similar, suggesting a close spatial coupling. Four Bacteroidetes families were significantly enriched in the SML, two of them, the Flavobacteriaceae and Cryomorphaceae, were found to comprise the majority of SML-enriched operational taxonomic units (OTUs). The enrichment of these families was controlled by a variety of environmental factors. The SML-enriched bacterial families were negatively correlated with water temperature and wind speed in the SML and positively correlated with nutrient concentrations, salinity and TEP in the underlying water (ULW). The correlations with nutrient concentrations and salinity suggest that the enriched bacterial families were more abundant at the upwelling stations.
Highlights
The sea surface microlayer (SML) constitutes the uppermost layer of the ocean, only 1– 1000 μm thick, with unique chemical and biological properties that distinguish it from the underlying water (ULW) (Zhang et al, 2003; Liss and Duce, 2005)
Transparent Exopolymer Particles (TEP) were found in abundances ranging from 5.78 × 105 to 1.09 × 107 particles l−1 in the SML compared to 6.58 × 105 to 1.18 × 107 particles l−1 in the ULW
The total bacterial numbers determined by flow cytometry were not significantly different between the SML and the ULW (p = 0.89, t-test) and were strongly correlated
Summary
The sea surface microlayer (SML) constitutes the uppermost layer of the ocean, only 1– 1000 μm thick, with unique chemical and biological properties that distinguish it from the underlying water (ULW) (Zhang et al, 2003; Liss and Duce, 2005). Bacterioneuston community composition of the SML has been analyzed and compared to the underlying water in different habitats with varying results, and has primarily focused on coastal waters and shelf seas, with limited study of the open ocean (Agogué et al, 2005a; Franklin et al, 2005; Cunliffe et al, 2009c). In the North Sea, a distinct bacterial community was found in the SML with Vibrio spp. and Pseudoalteromonas spp. dominating the bacterioneuston (Franklin et al, 2005). Found little or no differences in the bacterial community composition of the SML and the ULW (Agogué et al, 2005a; Obernosterer et al, 2008). Difficulties in direct comparisons between studies can arise because of the different methods used to sample the SML, which result in varied sampling depths (Agogué et al, 2004; Cunliffe et al, 2009a, 2011)
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