The mechanism by which the surfgrass Phyllospadix scouleri Hook. (Potamogetonaceae), a dominant late successional plant, replaces algae during secondary succession was investigated in a rocky intertidal community on the Oregon coast. Experiments suggest some, but not all, middle successional species are necessary for surfgrass recruitment. The barbed form of surfgrass seeds allows them to become attached to algal species with a central axis approximately 1 mm in diameter, such as erect coralline algae and the red algae Rhodomela larix and Odonthalia floccosa, but not to algae with other forms. Observations suggest this interaction is obligate facilitation (sensu Connell and Slatyer 1977).