Assessing the relevance of top-down and bottom-up effects as phytoplankton structure drivers in a subtropical hypereutrophic shallow lake

ALVARENGA, PATRICIO FRANCISCO; SINISTRO, RODRIGO; FRAU, DIEGO; SCARABOTTI, PABLO AUGUSTO; BATTAUZ, YAMILA; MAYORA, GISELA

AQUATIC ECOLOGY

SPRINGER

Lugar: Berlin; Año: 2019 vol. 53 p. 265 - 280

1386-2588

Despite several studies explain trophic cascade in water systems we have lack of knowledge referring to top down-bottom up effects on phytoplankton from eutrophic lakes. In this study, we tested the importance of trophic cascades on phytoplankton structure, predicting that environmental variations are the main drivers. We performed a monthly sampling during a year to measure environmental variables, phytoplankton and zooplankton, plus two samplings (winter and summer) to assess fish structure. Furthermore, we analyzed zooplanktivorous fish stomach-gut content, and completed a hatching zooplankton resting-eggs experiment to assess the effect of fish on dormant populations. We run a partial redundancy analysis (pRDA) for phytoplankton using zooplankton, nutrients availability and environmental variables as predictor variables. We finally calculated several ratios of zooplankton:phytoplankton biovolume to assess potential predation effects. Phytoplankton was correlated with variations in temperature and conductivity plus nutrients (pRDA: 63.4%, F= 4.6 P= 0.001), and was dominated alternatively by diatoms and cyanobacteria. Zooplankton was dominated by microphagous rotifers (>45% of total biovolume), and only the ratio microphagous rotifers:small chlorophytes was significant during summer and autumn (F= 10.6 P= 0.005). Fish community was dominated by insectivorous-planktivorous fish (>65% of total density), yet a negative selection of zooplankton items (Ivlev?s index