Though often suggested in seagrass literature, interactions between abundant rhizophytic macroalgae and coexisting tropical seagrasses have not been directly examined. Based on a competitive interaction hypothesis, I first tested for negative correlations between species densities over large and small spatial scales. After finding negative correlations, I tested experimentally for a competitive interaction by manipulating the relative densities of the locally dominant seagrass and a representative macroalga. Based on significant growth responses to density manipulations, I demonstrated that these species are likely competing for some limiting resource, possibly nitrogen. This study contributes to a better understanding of processes that dictate community composition in these systems.
