We studied spatial patterns in assemblages of epiphytic microalgae on the leaves of two seagrass species with different morphologies and longevity,Cymodocea nodosaandPosidonia oceanica, which cooccur in Chebba in Eastern Tunisia. Epiphyte assemblages were described for each species in summer. Epiphyte microalgal assemblages were more abundant on the leaves ofC. nodosabut more diversified on the leaves ofP. oceanica. We suggest that the differences in species composition and abundance between those seagrass species may reflect an interaction of timescales of seagrass longevity with timescales of algal reproductive biology. Short-livedC. nodosawas dominated by fast growing species such as the cyanobacteria speciesOscillatoriasp., whileP. oceanicaleaves were colonized by more mature and diversified species such as Prorocentrales. Local environmental conditions (hydrodynamics, light penetration), host characteristics (meadow type, shapes forms of leaves, life span, and growth rate), and grazing effect seem also to be responsible for these dissimilarities in epiphytic microalgae communities.