A fuzzy logic model to recognise ecological sectors in the lagoon of Venice based on the bentic community.

The lagoon of Venice is a mosaic resulting from the interaction of several biotic and abiotic factors. A qualitative scheme of such a mosaic was proposed in literature; it subdivided the lagoon into six ecological sectors (“lagoon mouths”, “vivified lagoon”, “rough eutrophic”, “calm eutrophic”, “urban”, “estuarine”), related with current velocity, salinity, eutrophication and pollution, and expressed by means of the sessile macrobenthos living on wooden piles. In this paper, we present the conversion of that scheme into a fuzzy logic model, which considers four input variables: abundance of marine species; abundance of lagoon species; abundance of oligohaline species and total abundance of the sessile macrozoobenthos. Three fuzzy sets describe abundance levels (low, medium, high) for each one of the four variables; the 81 (34) resulting combinations have been associated to the six ecological sectors, for a total of 486 “if … then” rules. We have used two different interpretations of the inference process, and combined their results with the “crisp weighting” technique to obtain the fuzzy membership grades to the six ecological sectors. The model, built on data from the lagoon of Venice in 1993–1994, has been validated with more recent data from the same stations and from the nearby lagoon of Grado-Marano; the results are in agreement with the literature information.