3.2 INTRODUCTION

Ships have always had the potential to transfer marine-fouling organisms via their hulls. In contrast, the risk of organism transfer posed by ballast water is comparatively recent. The use of sea water for ballast came into practice in the 1870s; previously, solid materials such as chains and boulders had been used²³
Many common fouling species easily survived [on hulls during the slow] open sea voyages undertaken by early sailors²⁴ They can, however, also survive fast voyages over long distances with rapid changes in water conditions²⁵ Significantly, the appearance of many species of exotic fouling organisms worldwide has coincided with the great increase in the volume of shipping since the Second World War²⁶ Some of these species have very short larval periods and could not have survived a journey in ballast water. This suggests that they were transferred as adults on vessel hulls. Barnacles, for example, are testament to the effectiveness of hulls as a vector for transport around the world: they are now so widely distributed that it is almost impossible to trace the history and routes of their transport²⁷