Relationship between Microcystis blooms and crustacean zooplankton in the subtropical lake in China Feizhou Chen Nanjing Institute of Geography and Limnology, CAS

Cyanobacteria (i.e. Microcystis aeruginosa) blooms are frequently associated with changes of zooplankton community. Few zooplankton can use bloom-forming cyanobacteria directly because of its poor nutrition (Arnold 1971), inedibility (Webster & Peters 1978) and toxin production (Lampent 1982, Fulton & Paerl 1987). Some zooplankton can use decomposed cyanobacteria. Some feed other edible algae with less inhibition of bloom.

Some species have certain physiological and behavioral adaptations to coexist with cyanobacteria bloom in natural lakes (DeMott et al. 1991) which to some extent showed difference with the results of experiments in the laboratory.

Colonial Microcy stis Population Predation Competition Planktivorous Fish Behavior Crustacean Plankton Crustacean plankton

Laboratory experiments (Enclosure experiments) Field investigations

Toxicity (unicellar and destroyed colony) +green alga Survival rate (%) ◇ Population Daphnia carinata

1 ×10 5 S 1 ×10 4 S 1 ×10 5 S+1 ×10 4 M 1 ×10 4 S+1 ×10 4 M 1 ×10 5 S+5 ×10 4 M 1 ×10 4 S+5 ×10 4 M 1 ×10 5 M+1 ×10 4 S 1 ×10 4 M+1 ×10 4 S 1 ×10 5 M+1 ×10 5 S 1 ×10 4 M+1 ×10 5 S

1 mg/l Scenedes mus Biomass of colonial Microcystis (mg L -1 ) ( μm) Growth rate (ind.d -1 ) Mixture (colony+green alga)

50 mg/l Microcysti s Growth rate (ind.d -1 ) Biomass of Scenedesmus (mg L -1 )

Change in mean brood size of egg-bearing females of Moina micrura and Diaphanosoma brachyurum before and after the occurrence of Microcystis bloom. The different letters show significant difference between the two periods (M. micrura: P<0.01; D. brachyurum: P<0.05). brood size (enclosure experiment) a b A B

Significnatly negative correlations were shown between the biomass of Microcystis and densities of the herbivorous cladocerans during the bloom period. (Enclosure experiment)

◇ Predation Biomass of Microcystis （ mg L -1 ） Mean feeding rate C. cornuta: FR= B, r=0.9254, p<0.05 D. carinata: FR= B, r=0.9657, p<0.01

◇ Competition 50 mg/L colonial Microcystis +1 mg/L Scenedesmus 10 mg/L colonial Microcystis +1 mg/L Scenedesmus

50 mg/L colonial Microcystis +1 mg/L Scenedesmus 10 mg/L colonial Microcystis +1 mg/L Scenedesmus

◇ Lake Taihu Microcystis

in Meiliang Bay

Microcystis density （ ×10 6 cells/L ） Density of crustacean plankton (ind./l) Biomass of crustacean plankton (μg/l)

◇ Metazoan zooplankton Dominant: Rotifera: Polyathra trigla 、 Rotaria rotatoria 、 Brachionus angularis Brachionus calyciflorus 、 Keratella cochlearis 、 Keratella quadrata 、 Filinia spp. 、 Trichocera spp. Cladocera: Daphina spp. Ceriodaphima cornuta 、 Moina spp. 、 Bosmina spp. 、 Diaphanosoma brachyurum Copepoda: Sinocalanus dorrii 、 Limnothora sinensis 、 Schmackeria imopinus 、 Cyclops vicinus 、 Microcyclops spp. 、 Mesocyclops spp. 、 Thermocyclops spp

1.Meiliang Bay 2.Gonghu Bay 3.East shore area 4.East Lake Bay 5.Southwest area 6.Northwest area 7.Middle area 8.Wuli Lake

Cyanobacteria Green algae Annual average of densities of cyanobacteria and green algae in Lake Taihu ( )

Annual average of zooplankton densities in Lake Taihu ( )