Pelagic Sargassum and floating marine debris were collected in the Sargasso Sea (subtropical NW Atlantic) during the cruise MSM41 of the German research vessel Maria S. Merian in April 2015. Flotsam items were collected with a dip net (mesh size: 1 mm) from the rescue boat of the research vessel at 19 stations distributed in coordination with the other sampling activities of the cruise. Few, mostly larger, debris samples were taken from aboard the research vessel using a dip net with a mesh size of 9 cm. The exact sampling position of each floating item was recorded by a handheld GPS. All mobile epifaunal organisms were carefully washed down from the flotsam items with freshwater and retrieved in a sieve with a mesh size of 250 µm. The species were identified and the individuals counted. Each Sargassum thallus was inspected under a stereo microscope to identify the attached sessile epifaunal species. Sessile species were not quantified. The marine debris items or sub-samples thereof (in case of large bulky items) were preserved in buffered formalin-seawater solution. The sessile epifauna on the debris items was analyzed after the cruise in the laboratories of the Alfred Wegener Institute in Bremerhaven, Germany. Each Sargassum clump was blotted on tissue paper to remove adherent seawater and weighed. The sizes of the debris items were measured to calculate the surface area.