An inner shelf foraminiferal fauna and its respone to environmental changes

From February 1991 to January 1995, 25 samples of sea bottom sediment were collected at a depth of 16 m from a station located on the Adriatic inner shelf, to study the temporal changes of benthic foraminifera association. During the sampling, 24-hour recordings of sea bottom hydrological parameters were performed and one water sample was taken to evaluate nutrient, organic carbon and iron content. The inner continental shelf environment studied here is subject to vertical mixing with river waters. The main feature of the hydrological parameters is their marked lack of seasonality. The living assemblage (stained with Rose Bengal) is composed of 64 taxa. The number of living individuals remains yearly constant, although the dynamics are complex, with irregular and discontinuous time behavior for single populations. In confirmation of this, the H values of the Shannon's index of species diversity, calculated on each sampling interval, in spite of their variability, do not show any trend or seasonality. The dead assemblage, composed of 88 species, shows systematic differences with the living assemblage: Rotaliina dominate in the living assemblage and Textulariina and Miliolina dominate in the dead one. To obtain an overall view of the complex system, both univariate and multivariate statistical analyses of living taxa and environmental parameters were used. The results indicate that the occasional availability of phytoplankton is the main factor influencing the productivity of benthic foraminifera in this shallow water basin with deltaic influence. Fluctuations in dominant and subdominant taxa are linked to biotic interactions.