CONICET | Buscador de Institutos y Recursos Humanos

Bacterioplankton is a relevant component of coastal marine food webs. In Antarctica, environmental conditions strongly limit the growth rates and metabolic activity of the biota. Macroalgae, as the large perennial brown algae Desmarestia anceps Montagne (Fig. 1), are one of the main primary producers in this environment and the organic matter released as a result of dying and decomposition of this macroalgae is considered a key event in the supply of nutrients to the other components of the Antarctic marine biota4, 5. Some bacteria associate to algal debris and directly obtain from it inorganic and organic nutrients for their own growth. During this activity, significant amounts of organic molecules (proteins, carbohydrates and organic acids) are released to the marine environment, constituting the dissolved organic matter (DOM) stock, which is unavailable to most marine organisms but can be used by a fraction of the bacterioplankton as carbon and energy source3. This trophic pathway is known as the ?microbial loop? and allows the dissolved organic carbon (DOC) to return to the higher trophic levels via its incorporation into bacterial biomass1. The microbial loop is coupled to the classic food chain formed by phytoplankton-zooplankton-nekton. ea ca In Antarctic marine environments, the time for decomposition and the physical mechanisms required for an effective biodegradation of algae debris is not fully understood. However, the association of marine bacteria to D. anceps thallus can be clearly appreciated in SEM images (Fig. a 2) obtained from initial studies on bacteria-related algae degradation in the Potter Cove ecosystem. Preliminary results showed that heterotrophic viable bacterial numbers increased with time during algae degradation. Nevertheless, the time required for a significant microbial-mediated damage of the thallus is extremely long at the typical sea water temperatures of the Cove (~1-2 ºC) and its effectiveness closely depends on the prior mechanical break-down mediated by icebergs and stones, which are driven by strong winds, currents and tides2.