The invention pertains to an antifouling coating composition including 20-100% by weight, calculated on the total amount of film-forming components, of a film-forming polymer (A) having an acrylic backbone bearing at least one terminal group of the formula: wherein X represents M is a metal of Group Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, VIa, VIb, VIIa, and VIII of the Periodic Table with a valency of 2 or more and a degree of ionisation less than that of the alkali metals metal; n is an integer of 1 to 2; R represents an organic residue selected from and R1 is a monovalent organic residue, and 80-0% by weight, calculated of polymer (B) a copper-based biocide for aquatic organisms wherein the antifouling coating composition is substantially free of any biocidal zinc compounds and substantially free of rosin, and in that the copper-based biocide has a metallic copper content below 2% by weight, based on the total weight of the copper-based biocide. The antifouling composition of the present invention combines a high storage stability with good performance under all aquatic conditions, irrespective of salinity.