The dataset comprises abundances and lengths of the Pacific oyster Magellana gigas (formerly Crassostrea gigas). The data were collected at 14 sites along the pier system around the island of Helgoland in the German Bight, North Sea (54°11' N, 7°53' E). Ten replicate quadrats (0.25 m²) were placed at the vertical pier walls at each site by SCUBA divers. In each replicate quadrat, all oysters were counted and measured in 2005, 2006 and 2012.