Seagrass restoration in Venice lagoon: integrate analysis of environmental parameters and ecological communities on transplanted sites.

Over the past few decades seagrass meadows have shown a wide regression worldwide due to multiple anthropogenic impacts. During that period Venice lagoon experienced asignificant decrease of Zostera marina and Zostera noltei, particularly in the central and Northern basins (Site of Community Importance IT3250031).At present, most of the local anthropogenic pressures which caused seagrass decline have significantly decreased, creating the ecological conditions for a new colonization. The LIFE SeResto project (LIFE12 NAT/IT/000331) started in 2014 with the aim to restoreand consolidate water habitats no. 1150* in the Northern basin of Venice lagoon through thetransplantation of seagrass local species(mainly Z.marina and Z. noltei) on 35 sites. An environmental monitoring was carried out on the transplantation sites, considering: seagrass transplantation success, abiotic parameters of waters and sediments, biological quality elements (BQEs) macrophyte, macrobenthos and fish fauna. Monitoring results were analyzed to investigate factors affecting transplant ssuccess and to assess changes inBQE secological status (sensu WFD)in the surrounding areas. In the 17 sites transplanted in spring 2014 the mean seagrass cover after 30 months was ca. 60% of the intervention areas (10x10m), while in the other 18 sites transplanted in spring 2015 the mean cover was ca. 44.5¯ter 18 months.Rooting success greatly varied among sites ,ranging from areas where seagrass did not root (cover 0%) to areas with a fast and full colonization rate (cover 100%). As expected, rooting success resultedstrictly relatedto nutrient concentration on water (DIN r= -0.71, TDP r=-0.76, TSS r=-0.85) and sediment (IP r= -0.86) and to low suspended solid concentration (TSS r=-0.88). Multivariate analysis indicates the presence of different clusters of sites identified on the basis of the environmental characteristics of water and sediment and reflects the coherence amongrooting success and the high ecological status of macrophyte (MaQI) and fish (HFBI) indexes. Macrophyte community showed a rapid increase of total number of species, with particular reference to the most sensitive, while changes in fish and macrobenthic communities were slower because seagrass meadows are not yet well-developed and the habitat recover is still in progress.