Abstract
Predators play a key role in the functioning of shallow lakes. Differences between the response of temperate and subtropical systems to fish predation have been proposed, but experimental evidence is scarce. To elucidate cascading effects produced by predators in contrasting climatic zones, we conducted a mesocosm experiment in three pairs of lakes in Uruguay and Denmark. We used two typical planktivorous-omnivorous fish species (Jenynsia multidentata + Cnesterodon decemmaculatus and Gasterosteus aculeatus + Perca fluviatilis) and one littoral omnivorous-predatory macroinvertebrate (Palaemonetes argentinus and Gammarus lacustris), alone and combined, in numbers resembling natural densities. Fish predation on zooplankton increased phytoplankton biomass in both climate zones, whereas the effects of predatory macroinvertebrates on zooplankton and phytoplankton were not significant in either climate zone. Macroinvertebrates (that freely colonized the sampling devices) were diminished by fish in both climate areas; however, periphyton biomass did not vary among treatments. Our experiments demonstrated that fish affected the structure of both planktonic and littoral herbivorous communities in both climate regions, with a visible positive cascading effect on phytoplankton biomass, but no effects on periphyton. Altogether, fish impacts appeared to be a strong driver of turbid water conditions in shallow lakes regardless of climatic zone by indirectly contributing to increasing phytoplankton biomass.
Highlights
Aquatic communities and food webs are typically structured by either available resources or fish predation [1], classically known as, respectively, bottom-up and top-down control [2]
Our experiment highlights the role of predators as a strong structuring factor in the food webs in shallow lakes, promoting phytoplankton development in both temperate and subtropical climates
During the course of the experiment, we found a significant decrease in phytoplankton biomass and an increase in zooplankton abundance and biomass only when fish were absent
Summary
Aquatic communities and food webs are typically structured by either available resources or fish predation [1], classically known as, respectively, bottom-up and top-down control [2]. Habitats and local food webs can be connected by diel or seasonal movements of fish, macroinvertebrates and zooplankton [3,4,5], in shallow lakes. The occurrence of planktivorous fish is known to induce major shifts in size distribution [6,7,8] and sometimes in the behavior of zooplankton [9,10,11,12,13], indirectly influencing phytoplankton. Experimental studies have elucidated the effect of planktivorous fish predation on zooplankton communities in subtropical and Mediterranean shallow lakes [24,25,26,27]. Other studies including field surveys have focused on the effects of fish predation on zooplankton structure [27,28] and behavioral shifts [25,29,30,31]
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