Phytoplankton responses to experimental enhancement of grazing pressure and nutrient recycling in a small Andean lake

QUEIMALIÑOS, CP; MODENUTTI, BE; BALSEIRO, EG

FRESHWATER BIOLOGY (PRINT)

Blackwell Publishing

Lugar: Oxford; Año: 1998 vol. 40 p. 41 - 49

0046-5070

1. Three series of field experiments with different zooplankton species composition and biomass were performed in a small lake in the South Andes. We attempted to measure the responses of phytoplankton species resulting from grazing mortality and stimulation of growth by nutrient recycling. 2. Nanoflagellates contributed substantially to total phytoplankton cell abundance. Chrysochromulina parva represented 93.4%, 92.2% and 95.9% of total phytoplankton density in December, January and February, respectively. This fraction was depressed in all treatments with increasing zooplankton biomass. 3. We obtained a negative relationship between C. parva cell number and dissolved P increase. On the contrary, we observed an increased in cell abundance of the diatom Aulacoseira granulata and we obtained a significant positive relationship between Aulacoseira abundance and P concentration. These results indicate that the ungrazed diatom was able to capitalise on the increase in nutrient availability. 4. As a net result of the increase or decrease of algal species we observed a change in the nano:net phytoplankton relationship. The outcome of three-day incubations with increased zooplankton biomass was an increasing importance of net phytoplankton. 5. The results indicate the importance of the indirect effects of the zooplankton (through nutrient recycling) to explain the development of diatoms and the role of grazing as a growth limiting factor for the flagellate C. parva.