Littoral epilithon of lentic water bodies at Hope Bay,Antarctic Peninsula:biomass variables in relation to environmental conditions

摘要

We studied the structural characteristics of the littoral epilithon in nine lentic water bodies at Hope Bay,Antarctic Peninsula,during summer 2002.At each site we measured the main physical and chemical variables and took epilithic samples for the analysis of dry weigh,ash,ash-free dry weight and chlorophyll a concentration.Distance from the sea of each water body was also considered.One site was selected for sampling lakes and ponds,except for Boeckella lake,where two sampling sites (A and B) were selected due to the heterogeneity of its littoral zone.Three stones for chlorophyll a analysis and another three to estimate dry weight,ash and ash-free dry weight,were taken randomly about 1 m away from the shore-line of each sampling site.Measurements of physical and chemical characteristics were obtained similarly.Water samples for chemical analysis were taken sub-superficially.Lakatos's system of classification and the Autotrophic Index were used to make functional inferences about the epilithic communities.Two PC A analyses were made to classify the water bodies according to environmental features and epilithic variables.In the latter,major patterns in data of epilithon were subsequently interpreted based on environmental data using external validation.Pingui pond,located in the middle of the penguin rookery,was considered as a passive sample in both PCA analyses due to its extreme characteristics.Limnological features of the studied water bodies were similar to those of other Maritime Antarctic lakes.According to the Lakatos's index,60% of the sampled lakes had high epilithic mass and a same proportion showed an inorganic type of epilithon The fact that 40% of the water bodies were autotrophic confirmed the importance of benthos as primary producer.According to environmental features,the well-defined groups of lakes emerged from the PCA were mainly determined by distance from the sea,pH,conductivity and salinity,and corresponded to the principal hydrological basins found in the region.Based on the results of the second PCA,littoral epilithon was affected by nitrate concentration and conductivity.In this ordination,water bodies from the same hydrological basin were separated probably as a result of a very complex inter-play of factors with a site-specific response to particular microhabitat characteristics.