Heterotrophic bacterial communities are major drivers of organic matter remineralization in the World’s Oceans. As much of organic matter consists of polymers, investigating the hydrolytic potential among marine bacteria is crucial for the understanding of marine nutrient cycles and their linkages with bacterial community structure. The present study characterized the response of bacterioplankton communities to polymeric carbohydrates at four locations in the Southern and Atlantic Oceans using natural seawater microcosms amended with chitin, alginate, and agarose. Cell numbers as determined by flow cytrometry increased markedly in temperate water microcosms (Patagonian Shelf), yielding almost double cell numbers with alginate and chitin compared to the control regime (3 × 106 cells mL-1). In warm water microcosms (Mauritanian Upwelling), only alginate distinctly stimulated bacterial growth, yielding almost double cell numbers (2.3 × 106 cells mL-1). Cell numbers remained almost unchanged in polar water microcosms (Polar Front, Antarctic Ice Shelf). 454 pyrosequencing as well as CARD-FISH revealed that Gammaproteobacteria were significantly stimulated across all locations and regimes (p < 0.05). Agarose and alginate strongly stimulated Alteromonadaceae in temperate waters, reaching relative abundances of 63 and 78%, respectively. This was largely due to single OTUs related to Pseudoalteromonas atlantica and Alteromonas macleodii, respectively. The response of Colwellia was determined by both location and substrate, being stimulated by agarose and alginate in polar waters and by chitin at all locations except the Antarctic Ice Shelf. The latter instead featured a significant stimulation of Fibrobacteres (reaching 28%). Chitin strongly stimulated Reichenbachiella (Cytophagales) in polar and temperate waters, with relative abundances increasing by 300- to 1500-fold (p < 0.005). At present, several alginate-degrading strains from the Gammaproteobacteria and Bacteroidetes are investigated by physiological and whole-genome analyses, indicating that closely related strains have distinct alginate utilization modes. In conclusions, this study presents a comprehensive picture of bacterial polysaccharide degradation in different oceanic regions and contributes to the understanding of fundamental marine nutrient cycles across wide geographical scales.