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, i n order to describe the recovery dynamics of meiobenthic communities a fter simulated small and large scale disturbance (defaunation). Two tr ays of azoic sand were placed in two different sites (Fig. 1). The fir st tray was laid directly on the bottom of a site (NS) close to the co ntrol (CR) from which the sand was originally drawn. The second tray w as located at a site (FS) 2 km from CR and suspended 0.5 m above a mud flat zone. Recolonization was very fast at both experimental sites. At NS, average densities of major taxa became similar to those of CR aft er 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 an d the dominant group was represented by harpacticoids and nauplii toge ther, which showed themselves to be good wide range colonizers. Wherea s the NS community seems to reach a state of equilibrium similar to th at of the CR in the long term, recolonization at FS is probably mainta ined by protracted immigration and emigration of individuals throughou t the study period. The greater distance between potential colonizers and the epicentre of a large scale disturbance influences recolonizati on patterns in different ways according to whether the dispersal mode of the different organisms is a passive process or an active migration .