Chemical composition and net production of cultured bivalves and seaweed (the kelp Laminaria japonica) , and fouling organism in the Sishili Bay , were determined. The investigated cultured bivalve species involved the scallop Chlamys f arreri , the mussel Mytilus edulis , the oyster Grassostrea gigas , the clam Ruditapes philippinarum and Mactra chinensis , and the Ark shell Scapharca suberenata. The investigated fouling animals involved the clam Trapezium liratum , the ascidian Styela clava , Ciona intestinalis , Cnemidocarpa chinensis , Molgula manhattensis and Botrylloides violacens , and the seaweed Ulva pertusa. Samples were collected from different farming zones in the Sishili Bay in late May , 2000. All the investigated cultured bivalves and seaweed had reached commercial size. C content of soft tissue of bivalve species was similar , with the range 42. 2 to 46.0%ofsofttissuedryweight;whileNcontentwassignificantlydifferent. TheNcontentofthesofttissueof C. f arreri was the highest (12. 36 %) , while that of G. gigas was much lower (8. 19 %) . Chemical composition of shells varied with different bivalves. N content of M. edulis and R. philippinarum shells was the highest, 0.55 %and 0.56 %dryweightrespectively. C, H, NandPinmusselshellsaccountedfor 30.4%, 30.2%, 31.8% and 29.6% of the total C, H, N and P respectively. In contrast, the shells of C. f arreri contained only 0. 1 % N , and C , N and P in the scallop shells accounted for only f ascita were relatively high , possibly suggesting deficient N origin. 6. 2 % , 2. 5 % and 6. 9 % of thetotalC,H,NandPrespectively. Indifferentpartofkelp,Ncontentwasalsosignificantlydifferent. TheC/ N atomic ratios in L . japonica and U. In different farming zones , the C/ N ratios in the kelp were also different , indicating different nutrient conditions of the farming zones. In the Sishili Bay, about a 850t N and 78t P were removed every year just through the harvest the ecosystem. Because of the cultured bivalves and seaweed , and the lost of fouling organisms , indicating the effect of aquaculture on considerable amount of N and P was apportioned in mussel and oyster shells , it is suggested that large quantities of mussels and oysters should not be cultivated in oligotrophic coastal region.