Abstract: The vertical distribution of ephippia (or resting eggs) of Daphnia species and its correlation with the concentrations of total nitrogen and total phosphorus in the sediments (25-1 cm) of Meiliang Bay in Lake Taihu were studied. The results showed that the ephippia of threeDaphnia species (D. galeata, D. pulex and D. similoides sinensis) in the sediments of Meiliang Bay were identified, with D. galeata being the dominant species. The ranges of average ephippial density and the density of ephippia containing resting eggs of Daphnia species were 0.03-2.01 and 0-0.33 ind·g^-1 dw, respectively. The average densities of ephippia containing resting eggs of three Daphnia species at the T₁ and T₂ sampling points were higher than that at the T₃ sampling point. In the sediment layers of 16-1 cm, the concentration of total nitrogen (TN) at the T₁ sampling point and that of total phosphorus (TP) at the T₂ sampling point showed obvious increasing trends, while their changes at the T₃ sampling point were limited. There was a significant relationship between ephippial densities of D. pulex and TP content at the T₁ sampling point (P<0.05), while the ephippial densities of D. similoides sinensis at the T₃ sampling point and the density of ephippia containing resting eggs of D. galeata at the T₂ sampling point were significantly correlated with both TN and TP contents (P<0.05). The vertical distribution of the ephippial (or resting eggs) density ofDaphnia species in the sediments could recur the historical succession of Daphnia species in lakes, which was related to the levels of total nitrogen and total phosphorus.

Key words: shade tolerance, germination, light gradient, seedling, adaptation.