COUPLING OF SEAGRASS (CYMODOCEA-NODOSA) PATCH DYNAMICS TO SUBAQUEOUS DUNE MIGRATION

1 The coupling between patch dynamics - described by the patch growth (horizontal and vertical), patch mortality, and life-history of Cymono cea nodosa (Ucria) Aschers., and the disturbance caused by the migrati on of subaqueous dunes over the plants was examined in a shallow NW Me diterranean bay (Alfacs Bay) where this species maintains a patchy cov er. 2 C. nodosa shoots survived substantial burial rates (up to 2.4 mm day(-1)) by growing vertically at rates proportional to, albeit four- fold slower than, burial rates. Patch death was caused by erosion as l arge subaqueous dunes migrated pass the plant patch. 3 Patch growth wa s fastest over the progressing slope of the dunes (similar to 2.5 m ye ar(-1)) and flowering was also stimulated by sand accretion. 4 The tim e interval between the passage of consecutive dunes, which sets the ti me window available for patch development, ranged between 2 and 6 year s. This time interval allowed C. nodosa to recolonize bare substrata, with patch formation occurring about half a year after the disturbance , and also allowed established shoots to complete their life-cycle and produce seeds and thus enable subsequent recolonization. The time win dows available for patch development also set an upper limit to patch size of about 26 m. 5 Significant cross correlations between dune topo graphy and patch dynamics and plant flowering frequency provide eviden ce that the spatial heterogeneity in the vegetation is closely associa ted with the disturbance imposed by the migration of sand dunes. The m igration of subaqueous dunes maintains C. nodosa in a continuous state of colonization involving spatially asynchronous patch growth and sub sequent mortality, which is ultimately responsible for the characteris tic patchy landscape of this Bay.