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Submerged macrophytes are regarded as being hardly assimilated by zooplankton for their lack of essential nutrients such as polyunsaturated fatty acids (PUFAs) thus serve as poor quality food, contrary to field stable isotopic investigations with observed macrophyte carbon contributions to zooplankton. However, periphyton growing on them produces the PUFAs and is thus a nutrient supplement. We hypothesize that with this supplement, zooplankton can be supported by macrophyte carbon. To test this hypothesis, we fed zooplankton with (1) 13C enriched Vallisneria natans detritus, (2) periphyton and (3) a mix of the two. We compared growth and reproduction of zooplankton under these three food treatments and calculated zooplankton assimilation of macrophyte carbon when fed a mixed diet, using a stable isotope-mixing model. The fatty acid profile of the two carbon resources was also analyzed. Our results demonstrate that Daphnia magna can grow and reproduce well, and use V. natans carbon when a supplement of periphyton is available.

Microcystins (MCs) have a toxic effect on crustacean zooplankton in the laboratory, but there is little or no unequivocal evidence in the literature of their lethal effects on crustacean zooplankton in the field. We used the natural microcystins extracted from Microcystis spp. to test if they could cause any negative effects on crustacean zooplankton. We conducted three experiments in enclosures with water from Lake Taihu, China, and microcystins derived by extraction from Microcystis spp. collected from the lake when the species was in bloom conditions. Initial concentrations of extracellular microcystins (EMCs = MC-RR + MC-LR + MC-YR) ranged from 9.7 to 44.9 μg/L in treatments with microcystin addition. Microcystin concentrations sharply decreased on second day in all the three experiments. EMCs at the end of the experiments varied from only 2.7 to 14.2 % of the levels at the start of the experiments. The dominant species of crustacean zooplankton in the lake were Bosmina longirotris, Ceriodaphnia cornuta, Mesocyclops spp., Limnoithona sinensis, Sinocalanus dorrii and Schmackeria inopinus. ANOVA analysis showed that the density and biomass of cladoceran and copepod did not significantly differ between treatments with microcystin addition and controls. Our results indicate that microcystins derived from lysing Microcystis do not cause any negative effects on crustacean zooplankton.

Many plants mitigate damage due to loss of tissues through compensatory growth, yet their compensatory abilities vary depending on physical and environmental conditions. We conducted an outdoor experiment using a 2 × 2 factorial experimental design (leaf damage and nutrient level), in order to evaluate the compensatory growth response of Vallisneria spiralis (a submerged macrophyte widely distributed in China) to partial leaf removal in two nutrient regimes. Our results reveal that under both high- and low-nutrient conditions, V. spiralis exhibited substantial compensatory growth response to partial leaf removal via accelerated growth rates, with significantly greater compensatory abilities observed in the high-nutrient sediments. These observations suggest that V. spiralis has a strong compensatory ability to partial leaf removal, providing arguably one of the major mechanisms for the coexistence of this plant with herbivores, in particular, in eutrophic freshwater ecosystems (e.g. Lake Taihu).

The composition of summer phytoplankton communities in two highly eutrophic areas of Lake Taihu, a large, shallow water body in China (area 2,338 km2; mean depth 2.0 m), was studied in relation to selected environmental variables. Both areas have multiple uses, including drinking water supply, fisheries, and recreation. The first area, Meiliang Bay, is much closer to central lake and subjected to wind-driven sediment resuspension, while the second, at Wuli Lake, is less affected by wave action but is considered more nutrient-rich due to its proximity to human inhabitation. By comparing two lake areas, we attempt to advance the understanding and management of different regions of shallow lakes, mainly differing in resuspension levels and eutrophication levels. A comparison of these two lake areas indicated a higher standing crop of phytoplankton in Wuli Lake than in Meiliang Bay. Canonic Correspondence Analysis indicated that nutrient status and sediment resuspension were the principal factors influencing phytoplankton composition in both areas. The dominant algal group in Meiliang Bay comprised immobile R-type strategists (Reynolds in Growth and reproductive strategies of freshwater phytoplankton, 1988), including filamentous diatoms and green algae (Aulacoseira granulate and Planctonema lauterbornii), and recruitment-beneficial RS-type strategists, mainly the colonial cyanobacteria (Microcystis spp.). The community of Wuli Lake was dominated by S-strategists, principally motile flagellates (Cryptomonas spp.) and C-strategists including small nonmotile centric diatoms and chlorococcal green algae.