Bacterial activity in the sea-surface microlayer: in situ investigations in the Baltic Sea and the influence of sampling devices

Abstract

The sea-surface microlayer (SML) is considered to be an 'extreme' environment. However, it is still unclear how bacteria that inhabit the SML (bacterioneuston) react to conditions within this interface. This deficiency is partly caused by the difficulty in obtaining representative samples. Our aim was to examine different sampling devices and characterize bacterioneuston activity in the Baltic Sea. Initial in situ studies revealed a decreased incorporation of 3 H-thymidine ( 3 H-TdR) by up to 90% in both glass-plate and metal-screen samples compared to the underlying bulk water. However, a series of tank experiments showed selective inhibition of bacterial productivity with either of these sampling devices, although bacterial cell counts and community composition were unaltered. The inhibition introduced by the glass plate could not be nullified by different cleaning treatments, but by the wiping technique used to scrape off the sample. Even with this modified, unbiased glassplate technique, 3 H-TdR incorporation of the bacterioneuston was still reduced by 50 to 80% compared to that in the underlying water, whereas the abundance of 5-cyano-2, 3-ditolyl tetrazolium chloride (CTC)-positive cells was not affected. Our in situ study thus revealed that in the Baltic Sea the presence of a pronounced bacterioneuston community different from that in the underlying water is unlikely. Reduced bacterial activities within the SML support the concept of a demanding habitat. Additionally, this study emphasizes the need to carefully evaluate the sampling devices used when measuring bacterial parameters. Furthermore, it supports the view that caution is required in comparisons of results from different studies.

The organic sea-surface microlayer in the upwelling region off the coast of Peru and potential implications for air–sea exchange processes

“…The observed accumulation of FAA and DHAA in the SML may therefore be related to a reduced activity of bacteria. For different coastal Baltic Sea sites, Stolle et al (2009) determined a lowered bacterial biomass production in the SML, despite bacterial cell numbers being similar to those in the ULW. During M91 bacteria were mostly depleted in the SML compared to the ULW supporting the idea of the SML being an "extreme environment" for bacteria.…”

“…Yellow-green latex beads (Polysciences, 0.5 µm) were used as internal standard. Sampling bacterioneuston with a glass plate does not bias cell abundance measurements (Stolle et al, 2009). …”

Bubble Transport Mechanism: Indications for a gas bubble-mediated inoculation of benthic methanotrophs into the water column

“…The sea-surface microlayer was sampled using a glass plate sampling technique with a framed wiper (Stolle et al, 2009). This technique collects water samples and particles therein of up to a 50 µm thick film of the sea-surface microlayer.…”

Bacterioneuston Community Structure in the Southern Baltic Sea and Its Dependence on Meteorological Conditions

“…First, the various SML sampling techniques differ in their operating modes and therefore result in the collection of SML samples from layers of different thicknesses (24). Recent studies have highlighted this problem, emphasizing that SML studies carried out with different sampling methods must be compared with caution (2,10,48). Second, particulate organic material is consistently enriched in the SML (25), which might result in strong differences between particle-attached and nonattached bacterion-euston communities, as is known from estuaries (9).…”

“…Still, despite high concentrations of potential organic substrates, bacterial growth efficiencies in the SML are generally low (43), and the reduced bacterioneuston productivity suggests that the SML is a stressful habitat (36,48). Conditions inhibitory to the bacterioneuston might include its increased exposure to organic pollutants, heavy metals, and UV radiation (34,54).…”