Experimental evaluation of the effects of siltation-derived changes in sediment conditions on the Philippine seagrass Cymodocea rotundata

Abstract

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