Ecological characterisation of dredge islands for the conservation of salt-marsh beetle fauna. The lagoon of Venice (Italy): a case study
2017
Zanella, Lorenzo | Scarton, F. (Francesco)
Salt marshes are wet environments at the transition between land and sea, which are inhabited by species that are adapted to stressing environmental factors, such as frequent tidal inundations and highly variable salinity. The rapid and global disappearance of these ecosystems results in the loss of those species that here have their typical habitat. In the lagoon of Venice, a programme for the protection of the surviving salt marshes was initiated by building dredge islands in the framework of more comprehensive restoration work. The ecological characterisation of these man-made habitats was studied through analysing the beetle fauna established on six dredge islands with different topographical traits. Beetle assemblages were evaluated by analysing species richness and abundance. The observed species were arranged in ecological groups and within sub-habitats, delimited according to the zonation of halophytes and ruderal vegetation. Both the composition and distribution of the beetle assemblages were strongly affected by the soil elevation, which determines the salinity gradient and the flooding rate. Hygrophilous and halobious taxa were dominant; however, many generalist taxa were present on some higher islands characterised by areas with a height greater than 60 cm above the mean sea level. Notably, these rarely submerged soils hosted some uncommon halophilous species, as well as thermophilous taxa typical of Mediterranean habitats that were not present on the surrounding mainland. Overall, although the dredge islands possessed some topographical traits that differed significantly from those of the natural salt marsh, they proved to host the biotic communities typical of these latter habitats, as well as other saline soil specialists.
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