II
In the Kerguelen Region (Southern Ocean), there are two contrasting regimes in terms of productivity and carbon export: an iron fertilized area which produces annual blooms on the plateau, and high-nutrient-low-chlorophyll (HNLC) off the plateau. The total (DNA) and active (RNA) free-living and particle-attached prokaryotic communities, were described during the late Austral summer. Depth was a constraining factor, especially for free living prokaryotic communities. Above the surface mixed layer, prokaryotic communities on and off the plateau were different (ANOSIM p<0.05) with an overall lower diversity on plateau in comparison to off plateau. The community was dominated by Flavobacteriales on plateau (>50% relative abundance). The particle attached fraction showed lower alpha diversity compared to the free living one, in all sites. Main taxa contributing to the differences between regimes (SIMPER p<0.05) belongs to Flavobacteriales such as Aurantvirga and Ulvibacter on plateau, and Formosa off plateau. Cellvibrionalles and SAR11 also contributed to the differences between the two contrasting regimes. Overall, community composition changed among stations at both fractions, being more diverse in the free living one. Dominant groups as Flavobacteriales, could reflect the advantage over other community members, probably due to their polymer degradation capabilities.
