The microbial food web structure of a hypertrophic warm-temperate shallow lake, as affected by contrasting zooplankton assemblages

FERMANI, PAULINA; DIOVISALVI, N; TORREMORELL, A.; LAGOMARSINO, L; ZAGARESE, H. E.; UNREIN, F.

HYDROBIOLOGIA

SPRINGER

Lugar: Berlin; Año: 2013 vol. 714 p. 115 - 130

0018-8158

The zooplankton of the hypertrophic Laguna Chascomús (Argentina) is generally dominated by small rotifers and highly evasive cyclopoids. An unusual dominance by small cladocerans was observed after a massive winter fish kill in 2007. The aim of this study was to investigate the structure of the microbial food web under two contrasting zooplankton assemblages. The lake was sampled every other week between 2007 and 2009. The abundances of heterotrophic bacteria (HB) and picocianobacteria (Pcy) rank among the highest values reported for aquatic systems (up to 1.1 x 108 and 2.7 x 107 cells mL-1, respectively). Pcy averaged 53% of the total picoplanktonic biomass. The abundance of ciliates displayed little varibility. HF were very abundant (>105 cells mL- 1) when small-cladocerans dominated, and decreased when rotifers dominated. Picoplankton showed the opposite pattern, while the proportion of grazing resistant morphologies (i.e. microaggregates of Pcy) was higher during the first summer. Our data are consistent with empirical models describing the relationship between HF and HB abundances. The HF-HB and HF-Pcy relationship was affected by changes in zooplankton dominance. Contrarily to our hypothesis, the present results suggest that large numbers of rotifers (>5000 ind. L-1) are more efficient than small-cladocerans at controlling HF populations.