Predicting the impact of introduced marine species: Lessons from the multiple invasions of the European green crab Carcinus maenas

We compared ecological characteristics of three spatially independent invasions of the European green crab Carcinus maenas to determine which characteristics were most consistent across invasions, and hence would be most predictable in future invasions. For invasions in western North America (WNA), eastern North America (ENA), and South Africa (SAF), we compared five characteristics: (1) habitat usage, (2) diet preferences, (3) size of individuals, (4) rate of range expansion, and (5) demonstrated and potential impacts. We found that two characteristics, diet preference and ecological impact were relatively similar across the three invasions. Diet preference was particularly consistent with the rank order of taxa being virtually identical at the three sites. In contrast, habitat usage, individual size, and rate of range expansion were more variable. Differences in habitat usage and size were particularly evident in the WNA invasion, where C. maenas have failed to colonize protected and exposed rocky shores used elsewhere and have grown much larger than at other sites. We suggest that the degree of similarity of these characteristics across invasions provides a valuable measure of how predictable they will be in future invasions.