IADO   05364
INSTITUTO ARGENTINO DE OCEANOGRAFIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Effect of glacier melting on polar plankton ecology and physiology
Autor/es:
HERNANDO, M.P.; ALMANDOZ, G; BARRÍA DE CAO, M. S; CHAZARRETA, C J; DUTTO, M. S.; FERRARIO, M.; FERREYRA, G.; GARCÍA, M. D.; GIAMPORTONE, A.; HOFFMEYER, M. S.; LÓPEZ ABBATE, M. C.; MALANGA, G.; PETTIGROSSO, R.; SCHLOSS, I.R.
Lugar:
Buenos Aires
Reunión:
Workshop; 4th IMCOAST; 2012
Resumen:
The increase in glacier melting observed at the Western Antarctic Peninsula as a direct response to global warming, produces saline dilution of coastal oceanic waters. Changes in salinity may, in turn, trigger ecological and physiological/biochemical responses in plankton organisms. In order to evaluate the effect of the decrease in salinity on phyto- and zooplankton in Antarctica, in summers 2009/2010 and 2010/2011 different aspects of plankton community were studied. Two contrasting conditions were analized both in situ and experimentally, with more (E1) or less (E2) influence of glacier melting in Potter Cove, King-George/25 de Mayo Island (62°14´S, 58°38´W). 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 2010 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 probably a high grazing pressure by small copepods such as Oithona similis. The presence of unidentified small organisms in E1 phytoplankton could be related to the presence of particulate feeders such as salps and appendicularians grazing selectively. The oxidative stress (i.e, the physiological response to stress, measured as the concentration of reactive oxygen species, ROS) showed no differences between areas during the bloom period. However during the post-bloom ROS concentrations were significantly higher in low salinity waters than far from glacier influence (0.53 and 0.3 UA.Chl-1.h-1 respectively). This aspects were further studied during summer 2011, when  biochemical responses were evaluated in microcosms, determining primary production, respiration, growth and the formation of 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 community respiration. After 8 days of exposition, phytoplankton biomass was significantly higher under high salinity conditions (35 µg L-1) than under low salinity (8.5 µg L-1). The taxonomic composition showed contrasting results under both salinity conditions. Althoug both environments were dominated by diatoms, in low salinity waters high abundance of small pennate cells was found, while large central chain-forming diatoms were found under high salinity conditions. Microzooplankton, mainly formed by tintinnids, aloricate ciliates and small copepods nauplii larvae, showed a decrease in abundance all along the experiments. Grazing responses of large copepods on phytoplankton were experimentally confirmed. Filtration (F) and ingestion (I) rates were estimated for the copepod Calanus propinquus (advanced copepodites) 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 so far evidenced some degree of acclimation to low salinity, which was evident in the different physiological processes studied.   Our results would indicate that planktonic associations formed by small diatoms, Oithona spp and tunicates would be more tolerant to glacier melting than the classical microphytoplankton and bigger zooplankton such as Calanus propinquus and euphausiids.