In 1999 the author reported for the first time on the occurrence of Corbula gibba and Acanthocardia paucicostata on the Maasvlakte-beach, south of the port entrance of Rotterdam (province of Zuid-Holland, the Netherlands). This report explored the assumption that ballast water from ships had introduced those species in this area. During the year 2000, a big supply of sand was deposited to fight erosion of the latter beach. Since that time the beach finds of both species has dramatically decreased.