Benthic foraminifera in a coastal marine area of the eastern Ligurian Sea (Italy): Response to environmental stress

摘要

Benthic foraminiferal assemblages from 19 superficial marine sediment samples of a coastal area in the Ligurian Sea were analysed for benthic foraminifera in order to recognize changes in assemblage composition and structure, decrease of faunal density, increased morphological abnormalities and inclusion of heavy metals in carbonate tests as possible evidences of environmental stress. Also grain size was determined as a main factor conditioning foraminifer’s distribution.The generalized low faunal density was considered as indicative of environmental stress, attributable to the well-known natural Cr and Ni enrichment, which characterizes marine sediments of the region. The cluster analysis highlighted distinct foraminiferal assemblages with decreasing species diversity approaching to the coast. This distribution was interpreted as the result of local source of environmental stress, probably due to the stream contribution. Deformed foraminifera more abundant than background levels of unstressed environments were also recorded in 39% of samples.Energy Dispersive Spectroscopy (EDS) analyses were carried out on carbonate tests of 55 specimens to investigate the role of the incorporation of heavy metals in the development of morphological abnormalities. Foraminifera showed the inclusion of heavy metals, not present in control specimens, indicating that environmental stress, due to metal sediment enrichment, plays a role in this phenomenon. Although anomalous elements were detected both in normal and deformed specimens and chambers, it was supposed that deformities develop as a result of the toxic effect of heavy metals on cytological activities because, contrarily to the normal specimens, all the deformed ones included anomalous elements. Higher occurrence of deformities in porcelaneous tests, typically enriched in Mg, is associated to the higher number of incorporated elements (Mn, Fe, Cu and Zn).