MEIOFAUNAL RECOLONIZATION OF AZOIC SEDIMENT IN A PO-DELTA LAGOON (SACCA-DI-GORO)

A recolonization experiment of azoic sand by meiofauna was carried out in the Sacca di Goro, a brackish water environment of the Po Delta, in order to describe the recovery dynamics of meiobenthic communities after simulated small and large scale disturbance (defaunation). Two trays of azoic sand were placed in two different sites (Fig. 1). The first tray was laid directly on the bottom of a site (NS) close to the control (CR) from which the sand was originally drawn. The second tray was located at a site (FS) 2 km from CR and suspended 0.5 m above a mudflat zone. Recolonization was very fast at both experimental sites. At NS, average densities of major taxa became similar to those of CR after one day, with nematodes dominating as at CR. On the contrary, at FS, mean abundances were always lower than those both at CR and at NS and the dominant group was represented by harpacticoids and nauplii together, which showed themselves to be good wide range colonizers. Whereas the NS community seems to reach a state of equilibrium similar to that of the CR in the long term, recolonization at FS is probably maintained by protracted immigration and emigration of individuals throughout the study period. The greater distance between potential colonizers and the epicentre of a large scale disturbance influences recolonization patterns in different ways according to whether the dispersal mode of the different organisms is a passive process or an active migration.