The spread of an alien (Musculista senhousia, Bivalvia) in the Sacca di Goro lagoon (Adriatic Sea, Italy)

The Asian date mussel, Musculista senhousia (Mytilidae), which is endemic in western Pacific, appeared and become very abundant in the Sacca di Goro, a brackish lagoon in the Po River Delta (northern Adriatic Sea, Italy) in the early 1990s. The course of the invasion was documented through a macrobenthic monitoring program at three sites in the Sacca. From 1994, when the new mussel was first collected, M. senhousia spread throughout the lagoon, and, within a few years, reached densities exceeding 10000 individuals m-2. Mussel effects on biodiversity was assessed by comparing the macrobenthic community structure and composition: over a five yr-period some changes in the macrobenthic community seem to be apparent, suggesting a positive effect of the mussel on the number of species and benthic richness. Considering trophic guilds, positive significant correlations were highlighted between M. senhousia and detritivores and herbivores, while suspension feeders probably suffered competition from the date mussel. M. senhousia was initially successful because it exploited a naturally disturbed, sparsely occupied environment. The closely-dated documentation of the first collections, increasing abundance, and spread of M. senhousia at our study sites provided an opportunity to observe in progress a biological invasion of a habitat