ALGAL RECRUITMENT AND THE MAINTENANCE OF A PLANT MOSAIC IN THE LOW INTERTIDAL REGION ON THE OREGON COAST

The role of recruitment of turf-forming algae in maintaining a low roc ky intertidal plant mosaic on the central Oregon coast was investigate d. Monthly samples suggested that spore release by one of the most abu ndant turf-forming red algae at wave-exposed sites (Constantinea simpl ex Setchell) occurred only in spring. In contrast, spore release by th e two most abundant wave-sheltered red algae [Odonthalia floccosa (Esp er) Falkenberg, Neorhodomela larix (Turner) Masuda] occurred at all ti mes but winter. At wave-exposed sites, the turf-dominant colonized cle arances frequently. At wave-sheltered sites, one dominant colonized fr equently and the other turf-dominant colonized clearances infrequently . Experiments evaluated the rates of recruitment of these algae to man ually cleared plots with respect to distance and direction from spore source, species of colonist, presence or absence of early colonists, w ave turbulence (wave-exposed or wave-sheltered), and location. We also tested the effect of grazing at wave-exposed but not at wave-sheltere d sites (where grazers were scarce). At one wave-exposed site, but not the other, recruitment of Constantinea within 1 x 2 m cleared areas r esponded differently to distance depending on its direction from the p ropagule source. Significant variation also occurred between clearance s and sites. The effects of preemptive competition and grazing were no t significant. At wave-protected sites, recruitment of Odonthalia but not Neorhodomela varied significantly with several factors. These incl uded presence of early colonists, blocks (one site only), and sites. H owever, no variation in recruitment of either species occurred with re spect to direction or distance from propagule source. Compared to Odon thalia, recruitment of Neorhodomela was extremely low suggesting that the high abundance of the latter depends on vegetative growth and long persistence. We conclude that recruitment processes can contribute to the maintenance of a high diversity mosaic at wave-exposed sites, but are of minor importance at wave-sheltered sites.