Seaweed invasions: conclusions and future directions

In the introduction of this special issue of Botanica Marina, we established the scope of this topic around a series of questions, which also provided a framework for integrating the different contributions and a means of highlighting deficiencies in knowledge and understanding (Johnson and Chapman 2007). In defining challenges for the future and suggesting how those challenges might best be tackled to optimize returns on research investment, it is useful to revisit those questions under four main headings dealing with species introductions per se, the invasion process, consequences of invasions and human responses to the threat and occurrence of invasion.