Abstract
This study aims to analyze the effects of nutrients and predation by zooplankton on phytoplankton biomass (chlorophyll a) in a eutrophic reservoir in Brazil (Apipucos Reservoir, State of Pernambuco), through experiments in microcosms. For this, samples of water were placed in 1 L Erlenmeyer flasks and kept for seven days. Treatments included the addition of nutrients (nitrogen combined with phosphorus and isolated additions of nitrogen and phosphorus), with presence and absence of zooplankton and a control which contained the reservoir water without any manipulation. The addition of nutrients did not stimulate phytoplankton growth. However, zooplankton significantly decreased phytoplankton biomass in the treatments it was added to (p < 0.05). The results of this study showed that for the reservoir studied, predation by zooplankton is the most significant factor in the regulation of phytoplankton, contradicting several studies which show that phytoplankton biomass is more strongly controlled by nutrients (bottom-up control) than by predation (top-down control).
Highlights
Top-down and bottom-up controls have received considerable attention in recent years, mainly due to disputes about which one is more effective in regulating the phytoplankton community
This study aims to analyze the effects of nutrients and predation by zooplankton on phytoplankton biomass in a eutrophic reservoir in Brazil (Apipucos Reservoir, State of Pernambuco), through experiments in microcosms
The results of this study showed that for the reservoir studied, predation by zooplankton is the most significant factor in the regulation of phytoplankton, contradicting several studies which show that phytoplankton biomass is more strongly controlled by nutrients than by predation
Summary
Top-down (predation) and bottom-up (nutrients) controls have received considerable attention in recent years, mainly due to disputes about which one is more effective in regulating the phytoplankton community. It is believed that the phytoplankton biomass is more strongly controlled by nutrients (bottom-up) than predation (top-down). Many studies have demonstrated that the addition of nutrients, especially nitrogen (N) and phosphorus (P), can significantly increase the growth of phytoplankton, and influence the taxonomic composition and size class distribution of these organisms [2,9,10,11,12]. Zooplankton can have both direct and indirect effects on the phytoplankton community, through predation and by the re-
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