INVESTIGADORES
UNREIN Fernando
congresos y reuniones científicas
Título:
Microbial food web structure in antartic shallow lakes from Hope Bay, Antarctic Península
Autor/es:
UNREIN, F.; IZAGUIRRE, I.; MASSANA, R.; GASOL, J. M.
Lugar:
Punta del Este, Uruguay
Reunión:
Conferencia; Shallow Lakes Conference; 2008
Resumen:
Antarctic freshwater lakes are often considered to be relatively simple aquatic ecosystems, typically oligotrophic, with short food chains, dominated by the microbial food web, and with copepods as the top predators. In the Maritime Antarctica region, however, some coastal shallow lakes are exposed to natural eutrophication due to the activities of sea animals. Pico- and nanoplanktonic organisms largely dominate these lakes. Here we investigated the trophic structure of the pelagic microbial food web in Antarctic shallow lakes with different trophic status. Six lakes (4 oligotrophic, 1 mesotrophic, and 1 eutrophic) were sampled four times in two consecutive austral summers. Pico- and nanoplankton were analysed by flow cytometry and epifluorescence microscopy. Short-term grazing experiments were performed with FLB (fluorescently labeled bacteria). Main limnological features were also recorded.The biomasses and abundances of pico- and nanoplankton clearly increased from the oligotrophic to the eutrophic lakes.  Bacterioplankton ranged between 4 x 105 and 1 x 107 cell ml-1. Heterotrophic flagellates abundance was on average 350 cell ml-1 in the most oligrotrophic lakes and 6500  cell ml-1 in the most eutrophic one. The same pattern was observed in their average body size, which increased from ca. 5 (oligotrophic) to 10 μm3 (eutrophic). Photosynthetic picoplankton was most abundant in the mesotrophic lake. It was represented by a coccoid Chlorophyte, and by some Synechoccocus-like picocyanobacteria. Plastidic nanoplankton was represented almost exclusively by flagellated forms, belonging to Chlorophyte (Chlamydomonas spp.), Chrysophyceae (Ochromonas-like) and Dictyochophyceae (Pseudopedinella-like). Grazing experiments with FLBs confirmed that the latter two groups are mixotrophic.Among the nanoplanktonic fraction the mixotrophic mode of nutrition, which combines autotrophy and heterotrophy in the same organisms, widely dominates oligrotrophic lakes where nutrients are limiting. However, its importance decreases when increasing the trophic status. Eutrophic lakes are dominated either by obligated autotrophic or heterotrophic organisms.