Biological impacts of oil on sandy shore ecosystems remain incompletely understood, especially following smaller spills on subtropical beaches. Here we quantified changes to benthic assemblages on a sandy beach following the 270-t spill of heavy fuel oil from the Pacific Adventurer that occurred in March 2009 off Moreton Island in Eastern Australia. Assessments of ecological impacts are based on spatial contrasts between multiple reference and impact sites sampled 1෥ek and 3୯nths after the spill. Benthic invertebrate assemblages exposed to oil had significantly fewer individuals of fewer species 1෥ek after the spill, markedly changing their ecological structure. Biological differences consistent with oil-related mortality were significant on the lower shore and in the swash and remained so 3୯nths after the spill. This signals a lack of recovery of these communities in the short term, despite the fairly rapid removal of oil. Results show that, despite the relatively small size of the spill, heavy fuel oil contamination can cause substantial impacts on sandy beach ecosystems, and that recovery may be prolonged.