A proposed integrated bioindex for the macrofouling biocoenosis of hard substrata in the lagoon of Venice

Bioindices are often employed to evaluate the ecological status of an unstable habitat such as a lagoon. However, no bioindex to date has considered the macrofouling biocoenosis of hard substrata, which is characterised by a higher biodiversity than that of the benthic communities of soft substrata. We analysed the progression of the hard-substratum biocoenosis at two stations located in the southern basin of the lagoon of Venice using data collected monthly from artificial panels that were immersed continually for a period of one year. Our goal was to develop an integrated specific bioindex, according to the objectives of the Water Framework Directive (WFD) in Europe, that is easy to calculate and provides a useful and immediate value for the ecological status on a logarithmic scale from 1 to 10. The bioindex proposed here takes into account species richness, covering area, and the Q-values of important physico-chemical parameters (e.g., pH, salinity, temperature). To validate the bioindex, our sampling campaign was repeated for an additional year at the two previous stations and a third station in the central basin that had different hydrodynamic features and was subject to greater anthropogenic impact. The ecological status of the third station was "poor-to-moderate", in contrast to the "good" status of the two stations in the southern basin. Seasonal changes in the bioindex values provide useful information on environmental changes because they indicate the moment of an ecological crisis as well as its causes and long-term effects.