Foraminifera as ecological indicators in the Lagoon of Venice, Italy

Coastal environments, such as the Lagoon of Venice, are subject daily to a wide range of variability. In these environments benthic foraminifera, a class of marine Protista, can be used as bioindicators. These organisms, through the structure of their assemblage (their presence–absence–relative dominance) define the extent of similar environmental conditions (biotopes). Sampling carried out in 1983, based on the quantitative analysis of 559 bottom samples, has delineated the extent of the various biotopes for the entire Lagoon and it has indicated the parameters that control the distribution of the various biofacies, which are the exchange time with the sea, pollution, fresh water input and the presence of intertidal morphologies. In 2001, 52 new samples were collected using the same methodology as 1983 sampling. The new samples were then compared with the previous faunas using the Kolmogorov–Smirnov index. The results obtained through the comparison of foraminiferal associations from the samples taken in 1983 and 2001 from the sector of the Lagoon of Venice north of the Malamocco inlet indicate unchanged conditions for about 50% of the area. These results show the effect of the purification plant operating since 1986 in that area where industrial and urban stresses predominated. The results also indicate a collapse of some intertidal morphologies related to the increase of tidal energy following the deepening and straightening of the main channels. More stable conditions appear to predominate in the southern basin of the Lagoon where the main modifications are related to the collapse of the salt marshes due to the subsidence. These results show the capacity of the benthic foraminifera to monitor the changes occurring in unstable environments and to indicate the evolutionary trends of transition environments.