Eleven years monitoring of Lesina lagoon (South Italy) using a biotic index (Λ)

Abstract

1 - The scope of our work was to assess the ecological status of Lesina lagoon on the South Adriatic coast of Italy according to the biological priorities expressed by the directives of the government, priorities which can be summed up in the key words of bionomics, biomass and biodiversity. 2 - Our method was based on the characteristics of the sessile benthic macrofauna considered to be indicative of environmental status. We developed a biotic index (Λ) that grades from 1 to 10 the rising quality of the environment. The data required for applying the index, i.e. spatial distribution (Zonation), biomass (g ww/m2) and number of species of the benthic macrofauna, were obtained from samples of sediment taken at systematically distributed stations over the entire surface of the lagoon. Samples were taken in spring and again in autumn. 3 - Our first assessment in Jan. 1993 gave 8.48, a high value. No samples were taken in 1994 but quality probably remained high because in Nov. 1995 the index gave 7.86. In 1996 quality must have begun to decline because although we took no sample in that year, in May 1997 the index was 6.14, which is very low for spring, when quality is normally high. The situation did not improve until August 1998 when the index rose to 7.59. From then on till our last assessment in Oct. 2003 the environmental quality of Lesina was at a stable high, the index registering values above 7.00 with a peak of 8.15 in Aug. 1999. 4 - The index values that we registered closely coincided with the opinion on the state of the environment given by experienced fishermen whose livelihood depends on the quality of the lagoon.