A new bioindex for the macrofouling biocoenosis of hard substratum in the lagoon of Venice

INTRODUCTION. The coastal fouling of hard substratum is characterised by higher biodiversity and biomass than that of open sea. In unstable habitats, biocoenoses do not reach a fully climax status since their ecological successions are interrupted by various factors. In the evaluation of the ecological status of a lagoon, the use of bioindexes, which summarise data about various environmental parameters, records both normal cycles and the occurrence of persisting environmental crisis. METHODS. We monthly collected data on wood and steel panels constantly immersed for one year in two stations, located in the southern Lagoon of Venice and characterised by different bathymetric and hydrodynamic features and anthropic impact. RESULTS. We propose a new environmental quality index for the macrofouling biocoenosis of hard substratum. It considers species richness, area occupied by the species and quality values attributed to chemical-physical parameters: Log10 ( R · A · IpH · IT · IS ) where: R = species richness A = area of the surface monthly recorded for each species IpH = pH quality index IT = temperature quality index IS = salinity quality index. DISCUSSION. The examined stations revealed overall a good state of health. Physico-chemical parameters seem the factors which mostly influence this fragile ecosystem, prevailing on biotic factors. In particular, salinity represented the most influential factor in the period considered. The bioindex resulted a valid tool, useful and sensitive, to evaluate the health condition of the lagoon of Venice. It furnishes an immediate value in logarithmic scale from 1 to 10 of the state of health and its seasonal variations can give information on environmental changes, since it registers the moment of the crisis and its long-term effects. Moreover, it allows a qualitative comparison of various lagoon zones by evaluating the temporal trend of changes.