MIGRATION OF LARGE-SCALE SUBAQUEOUS BEDFORMS MEASURED WITH SEAGRASSES(CYMODOCEA-NODOSA) AS TRACERS

The vertical growth of seagrasses in response to burial by migration o f bedforms is combined with dating techniques to provide precise and r apid estimates of the migration speed of subaqueous dunes over seagras s patches. Two methods to estimate the time interval between the passa ge of successive dunes and the motion of single dunes through seagrass patches are described. The second method is more precise. The applica tion of these methods to vegetated (Cymodocea nodosa) subaqueous dunes in the Alfacs Bay (NW Mediterranean) showed that the dunes traveled a t an average speed of 13.0 +/- 0.6 m yr-1 and demonstrated that the me thods can resolve migration speeds from 0.15 to 980 m yr-1 with this p articular seagrass species. In areas vegetated with different seagrass species, bedform migration can be estimated over different time scale s. The strong coupling between seagrass and sediment dynamics resemble s the coupling of vegetation and land dunes.