Colonization and distribution of the red algal epiphytes Melobesia mediocris and Smithora naiadum on the seagrass Phyllospadix torreyi

Abstract

The distribution of the red algal epiphytes Melobesia mediocris (Fosl.) Setch. and Mason and Smithora naiadum (Anders.) Hollenb. on the seagrass Phyllospadix torreyi Watson was surveyed around Mussel Point, Pacific Grove, California, where Melobesia was found to be dominant along the wave-exposed western side of the point while Smithora was dominant on the more protected eastern side. Colonization by the epiphytes of the new growth of Phyllospadix in the field occurred within 25 h with Melobesia colonizing young Phyllospadix blades more rapidly and in greater numbers than Smithora. Percent cover of Melobesia on Phyllospadix was lowest on the new growth, increasing on the older portions of the blade, and decreasing at the senescent ends of the lamina. Population structure showed male gametophytes to be rare and tetrasporophytes and female gametophytes in almost equal abundance. Mean diameters of the crustose tetrasporophytes were larger than those of the female gametophytes. These mature plants, however, showed no increase in size with age.