An experimental test of the occurrence of competitive interactions among SE Asian seagrasses

The occurrence of competitive interactions among the seagrass species prese nt in a multispecific SE Asian seagrass meadow was tested by the cumulative removal of shoots of an increasing number of seagrass species from the mea dow in order of decreasing and increasing resource requirements for plant g rowth. The removal of shoots of the dominant species Thalassia hemprichii h ad very few effects on shoot size, shoot density and leaf area index of the extant seagrass species. The shoot density of Enhalus acoroides decreased when T. hemprichii shoots were removed, but that of Syringodium isoetifoliu m increased when the shoots of all the species with higher resource require ments than itself were removed from the experimental plots. The size of Hal ophila ovalis shoots decreased by 30 % when both T. hemprichii and E. acoro ides shoots were removed from the plots. The shoot density of T. hemprichii increased. only when the shoots of all the accompanying species were remov ed from the plots. The results show that species interactions in this multi specific seagrass meadow are asymmetric. The elucidation of the nature of t he interactions among seagrass species provides a key to understanding the maintenance of the high biodiversity and production that characterizes pris tine SE Asian coastal ecosystems.