Abstract: Oyster reef ecosystem is a natural decontamination plant of estuarine environment. This paper analyzed the bioaccumulation of heavy metals by Crassostrea sp. population at the dams of Yangtze River estuary, with its purification capacity and ecological services value assessed. The results indicated that Crassostrea sp. had a high capacity in bio-accumulating Cu, Zn and Cd, with the bio-concentration factor (BCF) and biota-sediment accumulation factor (BSAF) being (14.28±2.41)×10³, (12.75±2.02)×10³ and (14.51±3.71)×10³, and 26.78±4.53, 23.24±3.69 and 16.62±4.25, respectively. The bioaccumulation capacity decreased in the order of Cu>Zn>Cd>As>Pb>Hg. The total weight and fresh meat weight of the oyster at the dams of Yangtze River estuary were about 1.07×10⁶ t and 1.75×10⁵ t, respectively, and the total storage of nutrients and heavy metals were 1.462×10⁶ kg N, 1×10⁵ kg P, 24 745 kg Cu, 58 257 kg Zn, 609 kg Pb, 254 kg Cd, 0.18 kg Hg and 329 kg As. The total ecological services value of the oyster reef was estimated at about 8.27×10⁶ RMB·a^-1, including habitat value of about 5.10 ×10⁶ RMB·a^-1 and environmental value of about 3.17×10⁶ RMB·a^-1. Such an environmental value was equivalent to the value of treating about 7.31×10⁶ t combined sewage each year, and corresponded to a large municipal sewage plant with a treatment capacity about 20 000 t·d^-1.

Key words: hemispherical photograph, Markov matrix., canopy openness, Leaf area index, thinning