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Stable carbon and nitrogen isotope analysis was used to investigate the host-parasite trophic relationship between the parasitic isopod Ichthyoxenus japonensis and one of its freshwater fish host Carassius auratus auratus from Lake Fuxian, China. No significant differences in δ13C and δ15N were observed between the heterosexual pairs of I. japonensis in the same host. δ13C and δ15N of I. japonensis were significantly lower than those of its host fish, and the isotopic ratios of the isopod increased with the increase of host fish isotopic signatures. Unlike isotopic fractionation patterns generally observed among consumers and their diets, isopod parasite was 13C and 15N depleted relative to the muscle tissue of this host fish. Differential isotopic fractionation patterns in the isopod parasite and the fish may be attributed to differences in parasite and host metabolism. [ABSTRACT FROM AUTHOR]

The effect of darkness on the cyanobacterium Microcystis aeruginosa and the green alga Chlorella pyrenoidosa were observed. Cell growth, metabolic activity, chlorophyll a fluorescence, cell size, and maximum quantum yield (Fv : Fm) were determined. M aeruginosa and C. pyrenoidosa both maintained their initial cell abundances while in the dark, but they showed distinctly different physiological responses to darkness. During the dark period metabolic activity decreased slightly, cell size and Fv : Fm decreased significantly, and chlorophyll a increased markedly in M. aeruginosa cells. However, metabolic activity, cell size, and Fv : Fm decreased dramatically, and chlorophyll a decreased trivially in C. pyrenoidosa cells. After re-illumination, metabolic activity, cell size, and Fv : Fm of M aeruginosa and metabolic activity, chlorophyll a, and Fv : Fm of C. pyrenoidosa recovered significantly. No recovery was found in either chlorophyll a of M aeruginosa or cell size of C. pyrenoidosa. Compared with C. pyrenoidosa, M. aeruginosa is more capable of withstanding the dark circumstances, which are unfavorable to the growth of alga but usually exists in water and sediment of eutrophic lakes. Its greater tolerance of darkness may be one of the reasons that M. aeruginosa is commonly the dominant species in eutrophic lakes. [ABSTRACT FROM AUTHOR]

We collected sediment from Lake Taihu in winter, placed it in BG-11 medium, and then observed the recruitment of phytoplankton to the water column as incubation temperature was increased stepwise in eight increments from 5.5°C at the start of incubation to 30°C after 70 days. Recruitment of chlorophytes and diatoms was observed above 9°C, but recruitment of cyanobacteria was not detected until 12.5°C. Subsequently, cyanobacteria established dominance above 19.5°C. [ABSTRACT FROM AUTHOR]

We assessed the response of Chiorella pyrenoidosa to substance(s) from the rotifer Brachionus calyciflorus using flow cytometry and PHYTO-PAM fluorometry. The cell density of C. pyrenoidosa in the rotifer water treatment was significantly higher than that in the control, suggesting that substance(s) from the rotifer stimulated the alga to grow faster. Additionally, the cell size of C. pyrenoidosa in the rotifer water treatment was consistently smaller than that in the control. Esterase activity and chlorophyll fluorescence of C. pyrenoidosa cells in the rotifer water treatment increased and were higher than those in the control but were not significantly different. The maximal efficiency of PSII (Fv/Fm) and the effective quantum yield of PSII (ΦPSII) of C. pyrenoidosa in the rotifer water were also consistently higher than those in the control, although these differences also were not significant. The pattern, however, does seem to support the idea that C. pyrenoidosa responded to infochemical produced by the rotifer. [ABSTRACT FROM AUTHOR]

The effects of pyrophosphate and polyphosphate on the growth of Microcystis aeruginosa and Chiorella pyrenoidosa were studied in unialgal cultures and in cultures separated by a dialysis membrane. M. aeruginosa and C. pyrenoidosa were able to similarly utilize pyrophosphate and polyphosphate, but their growth rates and cell densities were low in comparison with those in the orthophosphate controls. C. pyrenoidosa had a higher growth rate than M. aeruginosa in both unialgal and the separated cultures; moreover, C. pyrenoidosa had a greater ability to utilize phosphorus than M. qeruginosa. But because the C. pyrenoidosa population developed early but then declined, M. aeruginosa eventually became dominant in the separated cultures. Therefore, the interaction between M aeruginosa and C. aeruginosa might be complex because of an allelopathy effect, and nutrient competition is not the only factor determining species dominance in the phytoplankton assemblage. [ABSTRACT FROM AUTHOR]

Variations of bacterioplankton community composition were monitored during Microcystis spp. blooms in Lake Taihu using denaturing gradient gel electrophoresis (DGGE) of amplified DNA fragments from April through November in 2005. Two sampling sites were selected—one in Meiliang Bay and the other in the center of the western region of the lake. The average abundance of Microcystis spp. was higher in Meiliang Bay than in the lake center, while the bacterioplankton community diversity of Meiliang Bay was significantly lower than that of the lake center (P < 0.05). Comparison of DGGE profiles indicated that in Meiliang Bay bacterioplankton communities decreased in band richness and species diversity as Microcystis spp. abundance increased. In the lake center, DGGE band number and Shannon index reached their peaks when Microcystis spp. blooms declined. The Shannon diversity index for the bacterioplankton community was negatively correlated with the Microcystis spp. abundance (r = -0.53, P = 0.10). Changes in composition and biodiversity of the bacterioplankton community in the two regions of the lake were moderately correlated with Microcystis spp. bloom formations, which suggested a possible linkage between bacterioplankton community variations and phytoplankton blooms events. [ABSTRACT FROM AUTHOR]