In this work, we analyzed for the first time the role of bacterial communities in the biodegradation process of two fundamental biomass sources in temperate and subanctarctic coastal sediments: the kelps Macrocystis pyrifera and Undaria pinnatifida. Experimental systems were setup as simplified versions of a coastal environment. M. pyrifera was placed in sediments from a subantarctic environment (Ushuaia Bay) and U. pinnatifida in sediments from a site in northern Patagonia (Nuevo Gulf), sites where these two species is a major source of biomass respectively is regularly deposited.