Changes and recover of macrozoobenthic communities after restoration measures of the Orbetello Lagoon (Tyrrhenian coast, Italy)

1. This paper describes the long-term dynamics of the macrozoobenthic communities in the Orbetello Lagoon, one of the largest Western Mediterranean lagoons. which was affected by eutrophication processes that began in the 1980s and peaked with two severe anoxic crises in 1992 and 1993. 2. The aim of the present research was first to establish the characteristics of this basin prior to the anoxic crises, and second to assess the recovery of the lagoon after various restoration measures were completed in 1996. Investigations were carried out by studying macrozoobenthic communities in 4 years (1976, 1988, 1994, 1999) that were representative of the different (eu)trophic status in the lagoon. 3. Results of multivariate analyses indicated that each year was significantly different from the others. The years 1976 and 1999 exhibited the highest number of species as compared with 1988 and 1994. The majority of species characterizing the 1976 communities were marine taxa whereas 1988 and 1994 showed a lower percentage of marine species and a higher percentage of opportunistic organisms in comparison with 1976. The species assemblage in 1999 showed an intermediate composition between 1976 and 1988-1994. 4. Eutrophication processes caused a clear impoverishment of the macrobenthic communities in 1988 and 1994. The increase in overall number of species during 1999 may have been due to improved environmental conditions of the lagoon. However, the composition of the community suggested that still there were signs of disturbance in the lagoon in 1999, 6 years after the last intense anoxic crises and even after completion of the environmental restoration measures. 5. It was hypothesized that secondary disturbance events, sustained by high seasonal release of nutrients from the sediments, could cause the deviations from the expected improvement in benthic conditions. Copyright (C) 2001 John Wiley & Sons, Ltd.