Phytoplankton community structure in five subtropical shallow lakes with different trophic status (Uruguay): a morphology-based approach

Abstract

Phytoplankton abundance and biomass can be explained as a result of spatial and temporal changes in physical and biological variables, and also by the externally imposed or self-generated spatial segregation. In the present study, we analyzed contrasting-season changes in the phytoplankton communities of five subtropical shallow lakes, covering a nutrient gradient from oligo-mesotrophy to hypereutrophy, using a morphologically based functional approach to cluster the species. Six environmental variables accounted for 46% of the total phytoplankton morphological groups variance, i.e., turbidity (Secchi disk), conductivity, total phosphorus, total nitrogen, total zooplankton abundance, and herbivorous meso:microzooplankton density ratio. The differences in resource availability and zooplankton abundance among the systems were related with important changes in phytoplankton composition and structure. Within phytoplankton assemblages, adaptations to improve both light and phosphorus/nitrogen uptake were important in nutrient-poor systems; while grazing-avoidance mechanisms, such as colonial forms or bigger individuals, seemed relatively important only in eutrophic Lake Blanca, where light was not a limiting factor. However, this was not observed in the nutrient-rich Lake Cisne, where low light availability (due to clay resuspension and dark water color) was identified as the main structuring factor. Our results suggest that the composition of phytoplankton morphologically based functional groups appear to reliably describe the trophic sate of the lakes. However, other factors, such as nonbiological turbid condition, or zooplankton composition, may interact rendering interpretations difficult, and therefore, deserve further studies and evaluation.

Fish but Not Macroinvertebrates Promote Trophic Cascading Effects in High Density Submersed Plant Experimental Lake Food Webs in Two Contrasting Climate Regions

“…Conversely, long-term effective control of phytoplankton biomass by zooplankton is rarely seen in similar lakes in the subtropics in whole-lake studies with the presence of natural fish communities [39,70,71] and has mainly been reported when fish disappear (e.g., with summer fish kills [33,60]). However, the three-level food web tested displayed the typical trophic cascade effects produced by planktivorous fish, resulting in enhanced phytoplankton biomass.…”

Morphology-based classification of functional groups for potamoplankton

“…Studies applying MBFG (Pacheco et al, 2010;Segura et al, 2013) and those compared MBFG with FG and (Gallego et al, 2012;Izaguirre et al, 2012;Hu et al, 2013) in a range of lentic water (lakes, ponds, and reservoirs) commended the high simplification and practicality of MBFG. Given that the MBFG was initially proposed for lakes, only a few researches have used it to investigate and compare the phytoplankton assemblages in riverine ecosystems and have concluded low sensitivity (Centis et al, 2010;Stanković et al, 2012;Mihaljević et al, 2015).…”

High chlorophyll a concentration in a low nutrient context: discussions in a subtropical lake dominated by Cyanobacteria

“…Water bodies with Chl-a concentration similar to Peri Lake usually have much higher P concentration. in a study in five subtropical shallow lakes in uruguay (characteristics similar to Peri Lake), tP concentration were considerably higher than Chl-a (Pacheco et al, 2010) in comparison with the concentration observed in Peri Lake. Fragoso et al (2011) also found Chl-a values similar to our study lake, but in much higher dissolved P concentration in a subtropical shallow lake in southern Brazil.…”