BIOCENOSES OF BENTHIC FORAMINIFERA OF THE AVEIRO CONTINENTAL SHELF (PORTUGAL): INFLUENCE OF THE UPWELLING EVENTS AND OTHER SHELF PROCESSES

Abstract

This work aims to compare the dimensions and composition of benthic foraminiferal biocenoses (living specimens) during two summer sampling events. Forty-four sediment samples were collected on the Aveiro Continental Shelf (Center of Portugal) (latitude of 40º30'N-40º50'N, longitude of 8º46'W-9º20'W) for granulometry, total organic matter (TOM) and living foraminiferal analyses.

The sediment samples were collected during summers of 1994 and 1995, on stations located along transects (east-west direction) and between the bathymetries of 10-200 m. During the sampling campaigns, measurements of salinity, temperature and density data were recorded in the water column.

The results showed that the living assemblages were mainly found in stations located between 20-80 m depth. The abundance of living foraminifera was generally reduced at depths <20 m in the so-called “coastal deposits”, where the sediments are frequently remobilized and transported by the littoral drift. Living benthic foraminiferal densities were also reduced in stations at 80-200 m depth, despite the high sedimentary TOM contents. Results obtained in this work indicate that, in this marine setting, the most determinant factors for the dimension and composition of living foraminifera are not the sediments’ granulometry and organic matter content. In fact, the coastal dynamics, sediment stability, availability of quality food, among other factors, such as the bottom salinity oscillations and their combination, should better explain the abundance of living foraminifera and the biocenoses composition.