Experimental evaluation of the effects 3 of siltation - derived changes in sediment conditions 4 on the Philippine seagrass

1 2 This study investigated if siltation-associated changes in the sediments are 3 detrimental to seagrasses. We chose Cymodocea rotundata as the test species because it 4 is considered one of the Southeast Asian seagrass species most sensitive to siltation. The 5 approach included the (1) evaluation of the effects of silted sediments on plant growth, 6 evaluation of the effects of in situ sulfide additions to the sediment on (2) the production 7 of shoots, rhizomes and roots, and on the elongation rate of the horizontal rhizomes of 8 plants located at the edge of a meadow, and on (3) leaf growth, mass allocation patterns 9 and shoot density in a well-developed seagrass meadow. The results showed that under 10 high light availability major changes in sediment conditions associated with siltation did 11 not negatively affect the plants but enhanced their growth likely by increasing the 12 availability of nutrients. Pore water sulfide concentrations of 1mM reduced by more 13 than half the production of shoots, rhizome and roots, and the elongation rates of 14 horizontal rhizomes of C. rotundata plants at the edge of the meadow, but had no 15 effects on leaf growth and shoot density in a well-developed C. rotundata meadow. 16 17