Revista Chilena de Historia Natural 80 (3): 345-362, 2007
RESEARCH ARTICLE
Effect of macrophytes and food resources on the horizontal distribution of testate amoebae
and rotifers in an Andean-Patagonian lake
The presence of macrophytes in the littoral zone of lakes produces particular conditions
including higher resource availability for consumers. For this reason, the littoral zone is generally the area with the highest diversity of
lakes and rivers. In this work we studied the horizontal distribution of testate amoebae and rotifers in Lago Escondido (Argentina) in
relation to food resources availability. The study was carried out along a north-south transect that includes the littoral and the pelagic
zone of the lake. Phytoplankton and zooplankton were sampled during summer and spring (2001-2003) in five sampling stations: one
pelagic and four littoral. Rotifers and testate amoebae, as well as phytoplanktonic algae abundance and biomass were estimated. Food
resources were classified as nanoplankton (< 20 µm) and net phytoplankton (> 20 µm) and the biovolume of these fractions
varied significantly within the pelagic and littoral zones of the lake. Nanoplankon dominated the pelagic zone and was mainly composed
by nanoflagellates while net phytoplankton prevailed in the littoral zone and was composed by diatoms, cyanophytes and chlorophytes.
The highest number of species and diversity of testate amoebae and rotifers were observed in the littoral stations; nevertheless, no
significant differences between the zones colonized by different macrophytes were observed. The CCA analysis showed four different
groups. Keratella cochlearis, Synchaeta spp., Polyarthra vulgaris and Collotheca mutabilis
characterized the pelagic samples and were related with a high abundance of nanoplankton. On the other hand, rotifers like
Trichocerca spp., Lecane spp. and Euchlanis spp. and the testate amoebae Difflugia
pyriformis and Trinema enchelys associated with the littoral samples were related with high abundances of net
phytoplankton. Besides, a third group of species (Lecane spp. And Arcella spp.), presented in both zones,
was mainly related with a decrease in abundance of net phytoplankton. Finally, the rotifer Synchaeta spp. was associated
with the spring pelagic samples when the cyanophyte Coelosphaerium kuetzingianum increased its
abundance. Summarizing, in Lago Escondido, food resources could be an important factor driving testate amoeba and rotifer
distribution. Therefore the major role of macrophytes for this small-bodied zooplankton is food supply through an increment of net
phytoplankton.
Key words:
littoral zone, pelagic
zone, testate amoebae, rotifers, algal resources
