Genetic diversity has emerged as an important source of variation in the ecological properties of populations, but there are few studies of genetic diversity effects on colonisation processes. This relative scarcity of studies is surprising given the influence of colonisation on species coexistence, invasion, and population persistence. Here, we manipulated relatedness in experimental populations of colonising larvae in four sessile marine invertebrates. We then examined the influence of coloniser relatedness on the number, spatial arrangement and phenotype of colonisers following permanent settlement. Overall, relatedness influenced colonisation in all four species, but the effects of relatedness on colonisation differed among species. The variable responses of species to manipulations of relatedness likely reflect differences in intensity of inter- and intra-specific competition among adults, as well as the differential consequences of larval behaviours for each species. Relatedness appears to play an underappreciated role in the colonisation process, and we recommend that future studies of genetic diversity effects consider not only adult stages – the focus of most work to date – but also the importance of genetic diversity in early life history stages.