Microscopy images of a Baltic Sea surface slick

Biomass was collected from a Baltic Sea surface slick collected on a 100 µm mesh size plankton sieve for microscopic analysis. For logistical reasons, the sample remained uncooled for two weeks before fixation with acidic Lugol’s iodine solution at a final concentration of 1% and subsequent storage in the dark at 4 °C. Microscopic analysis was performed using an inverted light microscope (CK X 41, Olympus, Evident, Tokyo, Japan) at 200 - 400 x magnification. For community composition analysis, particles, cells and organisms in 820 µL were enumerated.