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The substrate of extensive areas of Oregon's bays and estuaries consists of shrimp-infested (Upogebia pugettensis [Dana, 1852]) mud that is unsuitable for the aquaculture of the Manila clam (Tapes philippinarum [Adams and Reeve 1850]).Substrate modification (addition of epibenthic oyster shell) and predator exclusion devices (Vexar() netting or cages) were used in combination to improve conditions for culture of Manila clam seed (7.4 mm and 10 mm) on intertidal shrimp-infested mudflats.Application of a 20 cm layer of oyster shell to the substratum in June 1994, significantly reduced recruitment and survival of young-of the year mud shrimp, but resulted in no significant reduction in subsequent juvenile shrimp concentrations.Survival of clam seed was poor in unprotected and Vexar() covered treatments.In contrast, cage treatments resulted in greater than 95% survival of planted clams.Growth rates were similar in all treatments (1.8-2.1 mm/mo during summer). Adult Hairy shore crabs (Hemigrapsus oregonensis [Dana 1851]) appeared to be important predators of Manila clam seed at the Yaquina Bay site.Laboratory predator-prey studies were conducted with both juvenile Dungeness crabs (Cancer magister Dana 1852-stage 2, 3, and 4 instars) and adult Hairy shore crabs (size 9-12 and 17-22 mm carapace widths).Juvenile Dungeness crabs consumed 1.5-2.5 times more Manila clams than adult Hairy shore crabs with similar carapace widths; however, Dungeness crabs occurred at about an order of magnitude lower densities than Hairy shore crabs at the Yaquina Bay site.High densities and high predation rates of Hairy shore crabs on Manila clams provided a possible explanation for poor survival of Manila clams in treatments without cage protection