Salp ingestion rates of microplastics, analyzed with Epifluorescence microscopy, collected aboard multiple cruises (SEAPLEX, SKrillEx I, and SKrillEx II)

Salps were collected on SKrillEx I and II during nightly transects in 202-μm mesh bongo tows, towed to approximately 200 m depth, and samples were preserved in 5% formaldehyde buffered with sodium tetraborate. We also used zooplankton samples collected on the August 2009 SEAPLEX cruise, where samples were collected using a manta net, 333-μm mesh, towed for 15 minutes at the surface, with samples preserved in 5% formaldehyde buffered with sodium tetraborate. Salps were identified to species, life history phase (oozooid or blastozooid), and measured for zooid length. The length of the stomach was measured, noted for degree of fullness, and dissected from each salp. Dissected salp stomachs were cut in half and placed in 15 mL of Milli-Q water for at least 24 hours to soften and release gut contents. The contents were then vacuum-filtered onto 5-μm pore polycarbonate filters with an additional 70 mL of Milli-Q water to aid in filtration. Those filters were analyzed with modified epifluoresecence microscopy techniques for microplastic particles. All microplastic particles were analyzed for plastic shape, length, surface area, and fluorescence. Ingestion rate of particles/hour for each salp was measured.