Effect of Glacier Melting on Polar Plankton Ecology and Physiology

SCHLOSS, I. R.; HERNANDO, M.; ALMANDOZ G. O.; HOFFMEYER, M.; MALANGA, G.; FERREYRA, G. A.

Montreal

Conferencia; IPY 2012 Conference; 2012

The increase in glacier melting observed at the Western Antarctic Peninsula diminishes surface salinity in the coastal ocean. Changes in salinity may, in turn, trigger ecological and physiologicalbiochemical responses in plankton organisms. In austral summer 2010 different aspects of plankton community were studied both in situ and experimentally in two contrasting environments, with more (E1) or less (E2) influence of glacier melting. Salinity, temperature and turbidity were measured; chlorophyll-a was considered a proxy for phytoplankton biomass. Its composition was additionally determined by microscopy and flow cytometry. An intense diatom bloom was observed during that summer, composed mainly of Porosira glacialis and Thalassiosira antarctica in January, with a secondary peak of cryptophytes by the end of February, which was only evident in E2. The diatom bloom decayed earlier in E1 than in E2, in coincidence with a large fresh water input and a high grazing pressure by small copepods. The presence of unidentified small organisms instead of cryptophytes in E1 might be related to the continuous fresh water inputs entering the area. Biochemical responses were studied in microcosmes by determining primary production, respiration, growth and by means of the formation of reactive oxygen species (ROS) as a function of low and high salinity (30 and 34 PSU, respectively). Oxygen production and growth were higher at 34 than at 30 PSU, while ROS concentrations and respiration were higher under low salinity conditions. However, after 48 hs, no significant differences were evident between salinity treatments in respirations. Grazing results were confirmed experimentally. Filtration (F) and ingestion (I) rates were estimated for the copepod Calanus propinquus with high and low concentrations of the blooming Porosira under normal and low salinity conditions (corresponding to the values observed in situ). In a first set of experiments, F and I were significantly lower under low salinity and low phytoplankton concentrations. A second set showed opposite results, indicating that copepods might acclimate to low salinity conditions. In general, while differences in community composition were evident in the field, our experimental results evidenced some degree of acclimation to low salinity, which was evident in the different physiological processes studied.