## 5 Discussion
These results corroborate the TROX model [26], which suggests a decrease in infaunal percentages in oligotrophic environments, where nutrients are a limiting factor; this is represented by deeper stations in our study system. The TROX model also predicts an increase in infaunal percentages in relation to enhanced food supply at the seafloor and to limited oxygen penetration within it. This pattern is also related to the sediment grain-size (i.e., fine) enriched in OM. This is well supported in our Gf model; in fact, when the entire bathymetric range is considered, the two most important components shaping the foraminiferal assemblages are nutrients (i.e., OC) availability and grain-size (i.e., sand). Based on the SEM model, diversity (Hill) is positively, though weakly, related to depth. Variations in species diversity (i.e., species richness) along bathymetric gradients have been deeply documented in both the eastern and western Mediterranean Sea [66]. These authors revealed an optimum (maximum) in species richness between 200 and 1000 m water depth, followed by a steady decline towards depth. In our record, the increase of diversity at greater depths (\(\text{SPC}=0.19\)) matches well their finding only when the entire bathymetric range is considered. This implies that diversity might be affected by spatial heterogeneity of various physicochemical and hydrodynamic parameters, caused by geomorphological differences and relict sedimentary processes. At the 13-28 m depth interval, depth positively affected infauna (\(\text{SPC}=0.14\)) and negatively affected Hill (\(\text{SPC}=-0.24\)). In this bathymetric range, sand, PLI and N are strongly affected by depth, and sand negatively affects infauna but positively affects diversity. Here, sand content, indicative of stronger hydrodynamics, plays a major role in shaping the benthic foraminiferal assemblages as defined by infauna and diversity. Coarse sediments are commonly well-oxygenated and exhibit a lower organic matter availability compared to finer ones; shallow water sandy bottoms are frequently unstable moving substrates subject to immobilization by waves and transport by coastal drift currents; these substrates preferentially host epifaunal species. The increase in diversity with sand content could be due to more heterogeneous microhabitats and increased availability of nutrients and oxygen within the sediments. Total nitrogen (N) also contributes to shape the foraminiferal assemblages (i.e., infauna and diversity) but to a lesser extent than sand content. At the 59-215 m depth interval, depth caused decreases in organic matter (i.e., OC and N). The main food source for benthic organisms is available via the fraction of OC produced in surface water and can effectively reach the seafloor [67; 68; 69]. The organic matter degrades along the water column; therefore, the greater the distance between the surface and the bottom, the less labile nutrients reach the benthic communities. This explains the negative relation between OC and N with depth. At this bathymetric range, the only factor influencing infauna and diversity is nitrogen. Increases in nitrogen in marine sediment are commonly associated with the presence of phytoplankton with a higher protein content, which is preferentially used by benthic foraminifera as labile organic matter [70].