Ana Sola

Influence of environmental characteristics on the distribution of ciliates in the River Henares (Central Spain)

We studied the composition, distribution and dynamics of ciliated protozoan communities as well as their relationships with the physical-chemical characteristics of their environment in the River Henares (Central Spain).A total of 67 species belonging to 54 genera were identified. Thirty-four species were subjected to statistical treatment using absence-presence data. Principal component analysis reduced the number of variables to two factors which accounted for 84.73% of total variance. The first axis grouped non-conservative variables, which strongly depended on biological activity. This axis was identified with ‘nutrient status and pollution level’. In contrast, the second factor included conservative variables, poorly influenced by the activity of organisms. This axis was identified with the ‘water mineral content’. From the arrangement of different species of ciliates with regard to these two factors, and using non-hierarchic cluster analysis, we established three different groups with respect to each factor.The saprobiological characterization of the different sampling points indicated that three different stretches can be distinguished in all seasons, and we propose some tentative relationshps between chemical and biological variables which characterize the different levels of saprobity in this river.