Comparison of samplers for the biological characterization of the sea surface microlayer

The surface film of the hydrosphere covers more than 70% of the world's surface. The sea surface microlayer (SML) or "skin" of the ocean is a sink for natural and anthropogenic material originating from the atmosphere and the water column. Organisms living in this SML are called "neuston." Our knowledge of the biology of the SML is still in its infancy. Research of the sea surface microlayer requires the use of appropriate sampling techniques and strategies, and the question of what is the most suitable device has not yet been answered. In the present study, we have compared the efficiency of the Harvey glass plate ( GP) and the Garrett metal screen ( MS) to analyze a wide range of microbiological parameters in SML samples collected at two coastal stations in the NW Mediterranean Sea. Two types of membranes ( Teflon and polycarbonate) were also used to collect bacterioneuston. The MS was the most appropriate technique for most biological parameters providing higher enrichment factors as compared to the GP and, therefore, the highest enrichment factors compared with underlying waters (UW). Control experiments with UW demonstrated that the enrichment reported for the MS was not biased by any selectivity of the sampler itself. Therefore, we recommend the use of the MS when the aim is to compare different biological parameters. In contrast, there is clear evidence that hydrophobic and hydrophilic membranes have an important drawback and should not be used for quantification purposes.