Species of the genus Jassa are an important element of marine fouling communities, several species often co-occurring on a wide range of hard substrates. At Helgoland (North Sea, German Bight), the cosmopolitan J. marmorata occurs associated with the NW European species J. falcata and J. herdmani. Field and laboratory experiments revealed some ecological differences among species which may facilitate their coexistence. Test panels in the field were instantly colonized by the complete spectrum of resident Jassa species, but J. marmorata proved clearly superior to its congeners in rapidly colonizing new habitats. Further differences among species relate to microhabitat selection (differential use of peripheral and central parts of algal thalli) and the behavioural response to mechanical disturbance. © 2012 Springer-Verlag.