The better knowledge about the influence of biotic factors on the growth of Hypnea musciformis (Wulfen in Jacqu.) J. V. Lamour., a species of commercial interest, is necessary to the orientation of its management and conservation. Since the specimens of Sargassum C. Agardh are considered an important substrate for the fixation of H. musciformis, destructive sampling were done during eighteen months in natural population of H. musciformis growing on Sargassum spp. in three deepths on the rocky shore at Rio de Janeiro. A positive correlation was obtained for the biomass of both genus and the preference for subtidal habitat was observed. Amphipods are usually found in their frond so the impact of mesograzers (amphipods) in H. musciformis and S. cymosum var. nanum were tested in experiments in vitro.The amphipods grazing was confirmed for both species and H. musciformis, that has higher growth rate, favored the growth of S. cymosum var.nanum, reducing the mesograzers attack by being available food. So, we recommend that commercial harvest of H. musciformis growing on Sargassum spp. should be managed to avoid damage to the marine ecosystem.
Hypnea musciformis; Sargassum spp.; Amphypoda; herbivore
