Magnitude of within-patch variation in seagrass Halophila ovalis growth affected by adjacent Thalassia hemprichii vegetation

Seagrass beds in South-east Asia sometimes consist of a mosaic of different species in monospecific patches. We examined whether the magnitude of with in-patch variation in the seagrass Halophila ovalis is affected by the pres ence or absence of surrounding vegetation consisting of another seagrass sp ecies Thalassia hemprichii In an intertidal flat in Thailand waters. We mea sured biomass and growth rates of H. ovalis at. the edges and centers of tw o different types of patches: (i) H. ovalis patches adjoining T. hemprichii vegetation (HT patches), and (ii) H, ovalis patches adjoining unvegetated sand flats (HS patches). Furthermore, we examined the possible effects of i nterspecific interactions on the growth of H. ovalis by experimentally remo ving adjoining T. hemprichii at the edges of HT patches. The biomass of H, ovalis was greater at the patch centre than the parch edge in both types of patches. For the growth rate of H, ovalis, significant interactions were d etected between patch types and positions in patches. The difference in gro wth was significant and more than 4-fold between edges and centers of the H S patches, whereas the growth was not significantly different between edges and centers of the HT patches. The removal of T. hemprichii did not signif icantly affect the growth rate of H, ovalis at the edge of the HT patches. These findings demonstrate that the magnitude of within-patch variation in H, ovalis growth is affected by the conditions of adjoining habitats. Howev er, any effects of local competition with T. hemprichii on H. ovalis growth were not evident in this short-term manipulative experiment.