Seagrasses exhibit extensive clonal growth and kinship structure among neighbouring genets. Zipperle et al. demonstrate a predominantly outcrossing mating system and multiple paternity in the intertidal seagrass Zostera noltii. They find geitonogamy intrinsic to the clonal life-history of Z. noltii, whereas biparental inbreeding is negligible. Pollen dispersal distance matches average clone size; however, natural disturbance in the intertidal habitat potentially selects for small clone sizes and increased relative pollen dispersal distance, thereby indirectly affecting the mating system.