To date, marine boring organisms are not known for the whole Antarctic region, probably because of the scarcity of calcareous substrata. In Terra Nova Bay (Ross Sea), the study of some populations of the scallop Adamussium colbecki allowed us to record a bioerosive activity on carbonates due to a chlorophyte, belonging to the genus Phaeophyla. The same kind of infestation was also observed on the thick shells of the gastropod Neobuccinum eatoni. The algae actively bore the light-exposed portions of the shells showing, in A. colbecki, an infestation that is strongly size dependent; the ageing of the periostracum is among the most probable causes. The pattern of infestation is not homogeneous in different populations, probably in relation to irradiance intensity; depth, sedimentation rates and ice cover negatively affect the growth and distribution of Phaeophyla sp.