RESPONSE OF A MIXED PHILIPPINE SEAGRASS MEADOW TO EXPERIMENTAL BURIAL

The effect of burial due to sudden sediment loading was examined in a mixed Philippine seagrass meadow through the experimental deployment o f sediment (0, 2, 4, 8, and 16 cm deposited over the experimental plot s). The responses in shoot density, vertical growth, and branching of the species present were assessed 2, 4, and 10 mo following disturbanc e. Shoot density responses were strongly species-specific. The large E nhalus acoroides maintained shoot density at all burial treatments, an d only showed evidence of decline by the end of the experiment. Thalas sia hemprichii and, to a lesser extent, Cymodocea rotundata showed a s harp decline in shoot density even at moderate burial treatments, from which they failed to recover. The accompanying species (Halodule unin ervis, Syringodium isoetifolium, and Cymodocea serrulata) showed an in itial decline in shoot density followed by recovery. The small Halophi la ovalis showed an opportunistic growth in plots receiving intermedia te (buried by 4 and 8 cm sediment) disturbance, reaching shoot densiti es well in excess of those on control plots. The results suggest a pat tern of species loss following disturbance by sediment burial correspo nding to the sequence, T. hemprichii --> (C. rotundata, S. isoetifoliu m, H. uninervis) --> C. serrulata --> E. acoroides. Vertical growth in creased significantly for all species with differentiated vertical sho ots, except C. serrulata. The examination of the time course of vertic al growth imprinted on the shoots of the dominant species, T. hemprich ii, revealed a rapid response to burial through increased internodal l ength, which was maintained over 8 mo following the disturbance. The r esulting cumulative vertical growth along the experiment was Linearly correlated with the degree of burial imposed on the plants. Branching of vertical shoots also increased significantly (73 to 96%, depending on the species) with burial. Experimental burial induced changes in sh oot age distribution of some of the species, involving rearrangements, through selective mortality or recruitment, of the contribution of yo ung shoots to the populations. The results obtained show major differe nces in species response to small-scale disturbance, closely linked to predictions derived from consideration of species growth rate and siz e, and provide evidence of the importance of small-scale disturbance i n the maintenance of multispecific seagrass meadows.