Experimental study of trophic cascade effect of silver carp (hypophthalmichthys molitrixon) in a subtropicallake,lake donghu:on plankton community and underlying mechanisms of changes of crustacean community

摘要

An eclosure experiment was carried out to test trophic cascade effect of filter-feeding fish on the ecosystem: growth of crustacean zooplankton,and possible mechanism of changes of crustacean community structure. Four fish biomass levels were set as follows;0,116,176 and 316 g m~(-2),and lake water 9containing ca. 190 g m~(-2) of filter-feeding fishes) was comparatively monitord. Nutrient levels were high in all treatments during the experiment. Lowest algal biomass were measured infishless treatment. Algalbiomass decreased during days 21-56 as a function of fish biomass in treatments of low (LF),medium(MF) and high9 HF) fish biomass. Crustaceans biomass decreased with incresing fish biomass. Small-bodied cladocerans,Moina micrura,Diaphanosoma branchyurum and Scapholeberis kingii survived when fish biomass Small-bodied cladocerans,Moina micrura,Diaphanosoma branchyurum and Scapholeberis kingii survived when fish biomass was high whilst,large-bodied cladocerans Daphnia spp. and the cyclopoids Theromcyclops taihokuensis,T.brevifuratus,Mescyclops notius and Cyclops vicinus were abundant only inNF enclosures. Evasive calanoid Sinodiaptomus sarsi was significantly enhanced in LF,but decreased significantly with further increase of fish biomass. Demographic data indicated that M.micrura was well developed inall tre4atments.Our study indicates that algalbiomass might be controlled by silver carp biomass in eutrophic environment. Changes of crustacean community are probably affected by the age of the first generation of species. Species with short generation time were dominant and species with long generation time survived less with high fish biomass.Evasive calanoids hardly developed intreatments with high fish biomass because of the (bottle neck) effect of nauplii. Species abundance were positively related to fish prediation avoidance. Other than direct predation,zooplankton might also be suppressed by filter-feeding fish via competition.