We present the first direct assessment of marine reservoir effects in the Moreton Bay region using radiocarbon dating of known-age, pre-AD 1950, shell samples from the east coast of Stradbroke Island and archaeological shell/charcoal pairs from Peel Island in Moreton Bay. The resulting ΔR value of 9±19 ¹⁴C years for the open ocean conforms to regional values established for northeast Australia of 12±10 ¹⁴C years. Negative ΔR values of -65±61 ¹⁴C years and -216±94 ¹⁴C years for southern Moreton Bay highlight the potential for larger offsets over the last ~900 years. These may be linked to changing terrestrial inputs and local circulation patterns.