Correspondence: Bo-Ping Han, Institute of Hydrobiology, Jinan University, Guangzhou 510632, China. .... become a major water quality problem (Han, Li & Lin,.
Freshwater Biology (2013) 58, 100–113
doi:10.1111/fwb.12042
Effects of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community of a deep, tropical reservoir: an enclosure experiment SHUAI-YING ZHAO, YU-PING SUN, QIU-QI LIN AND BO-PING HAN Institute of Hydrobiology, Jinan University, Guangzhou, China
SUMMARY 1. An in situ enclosure experiment was conducted in a deep reservoir of southern China to examine (i) the effects of a low biomass (4 g wet weight m)3) of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community and (ii) the response of Daphnia to eutrophication. 2. In the absence of fish, Daphnia galeata dominated the zooplankton community, whereas calanoids were dominant in the fish treatments, followed by D. galeata. Silver carp stocking significantly reduced total zooplankton biomass, and that of D. galeata and Leptodora richardi, but markedly increased the biomass of smaller cladocerans, copepod nauplii and rotifers. In contrast, nutrient enrichment had no significant effect on the plankton community except for cyclopoids. 3. Chlorophyta, Cryptophyta and Bacillariophyta were dominant phytoplankton groups during the experiment. Chlorophyta with high growth rates (mainly Chlorella vulgaris in the fish enclosures and Ankyra sp. in the fishless enclosures) eventually dominated the phytoplankton community. Total phytoplankton biomass and the biomass of edible phytoplankton [greatest axial linear dimension (GALD) < 30 lm], Chlorophyta, Cryptophyta, Bacillariophyta and Cyanobacteria showed positive responses to fish stocking, while inedible phytoplankton (GALD ‡ 30 lm) was significantly reduced in the fish enclosures. However, there was no significant effect on the plankton community from the interaction of fish and nutrients. 4. Overall, the impact of fish on the plankton community was much greater than that of nutrients. High total phosphorus concentrations in the control treatment and relatively low temperatures may reduce the importance of nutrient enrichment. These results suggest it is not appropriate to use a low biomass of silver carp to control phytoplankton biomass in warmer, eutrophic fresh waters containing large herbivorous cladocerans. Keywords: Daphnia, enclosure experiment, nutrients, omnivorous fish, plankton, tropical limnology
Introduction Silver carp (Hypophthalmichthys molitrix), which is an omnivorous filter-feeding fish and able to suppress nuisance blue-green algae (e.g. Starling, 1993; Datta & Jana, 1998; Zhang et al., 2006), has often been considered to be effective in improving water quality in eutrophic lakes and reservoirs (Starling, 1993; Zhang, Xie & Huang, 2008). However, controversies remain about using this fish to control algal biomass (Radke & Kahl, 2002); for
instance, several studies have shown that stocking silver carp fails to reduce phytoplankton biomass in the presence of large herbivorous cladocerans (Domaizon & Devaux, 1999a; Fukushima et al., 1999; Radke & Kahl, 2002; Tang et al., 2002). One major reason for this failure is that grazing pressure on phytoplankton by zooplankton is reduced as a result of fish predation (Starling, 1993). After release from zooplankton grazing pressure, small phytoplankton, which cannot be effectively filtered by silver carp (
