The South Pacific Gyre (SPG) covers 10% of the ocean's surface and is considered a marine biological desert. However, recent investigations have shown that primary production occurs throughout its deep euphotic zone and that this fuels the regeneration of nutrients and the recycling of organic matter. We set out to investigate the SPG's microbial communities' heterotrophic capability to utilize polysaccharides, an important marine organic matter component. Using fluorescently labeled polysaccharide (FLA-PS) incubations (Reintjes, et al., 2017), we analyzed the initial step of organic matter degradation by measuring both the rate of external hydrolysis and the rate of direct uptake of polysaccharides by marine microorganisms. Furthermore, we investigated the change in bacterial abundance and diversity during the FLA-PS incubations using direct cell counts and 16S rRNA sequencing. The presented dataset contains the microbial diversity, total cellular abundance, and direct FLA-PS uptake results generated during the FLA-PS incubations performed with six polysaccharides (laminarin, xylan, chondroitin sulfate, arabinogalactan, fucoidan, and pullulan) over 18 days. The incubations were performed with seawater from the epipelagic and bathypelagic (75 m, 160 m, 1250 m, and 2800 m) in the central gyre, and seawater from the epipelagic (75 m) at two stations adjacent to the gyre. Our study found that the SPG's microbial community showed remarkably high extracellular enzyme activities, and a considerable fraction of the microorganisms were capable of the direct uptake (selfish-uptake) of FLA-PS. Interestingly, a wide variety of bacteria were capable of cycling HMW organic matter using distinct polysaccharide processing mechanisms in the SPG. This research shows that the SPG features not only organisms capable of existing on the fine edge of minimal substrate concentrations but also those capable of taking advantage of abrupt changes in physical conditions and substrate availability

<0.01 = n.a.Hydrolysis rates were measured as the change in polysaccharide molecular weight as a function of time, as determined via gel permeation chromatography with fluorescence detection (Arnosti, 2003; doi:10.3389/fmicb.2020.583158). Unit: rate.x.nM.L.hr (x being the individual substrate, highlighted in column 11 - Substrate Type).