Impacts of the grounding of the oil tanker Jessica off San Cristóbal island, Galápagos, included both effects of oil on biota and also mechanical effects associated with a shallow furrow 50 m x 30 m gouged across the rocky seafloor and wreckage strewn over 7500 m(2). The wreckage represented a minor but potentially chronic source of pollution to the surrounding environment through delayed releases of oil, antifouling compounds and other toxic chemicals, and a possible source of exotic marine taxa. Investigation at the wreck site indicated that impacts on subtidal plant and macro-invertebrate communities were largely confined within 100 m of the wreck site itself. Observed population effects included significant increases in cover of opportunistic algae (filamentous green algae, filamentous red algae and Ulva sp.) and the hydroid Ectopleura media adjacent to the wreck, while densities of the green sea urchin Lytechinus semituberculatus significantly decreased from 0.3 m(-2) adjacent to the wreck to 11 m(-2) at 100 m distance.