*4.2. Preservation Regime and Size Variability*

The presence of pristine specimens of the tiny thin-walled species reinforces the recent character of the analyzed material and further indicates the excellent preservation of the samples, suggesting that the reported assemblages are not biased by dissolution. The absence of differential preservation of thin-walled specimens of the analyzed species along with the strong carbonate preservation potential of the study area [106] indicate minimized modifications on the size spectrum of the planktonic association.

The mean population size of the identified planktonic foraminifera along with the standard deviation values of species-specific sizes reflecting the overall variability per basin analyzed are summarized in Table 2, while the species-specific size variations along the study transect are shown in Figure 3. The number of individuals measured per species varied from 2 to 170, averaging 21 individuals per species per sample. Generally, the mean population size of the analyzed planktonic foraminiferal assemblages is skewed toward larger sizes from north to south. Our dataset reports a 4–16% increase (avg ~11%) for all species from Adriatic to Ionian settings, except for *G. ruber* (including both chromotypes and morphotypes) and *G. bulloides*, which support the opposite pattern (Table 2). The most consistent in size within the central Mediterranean sub-basins with the smallest standard deviation between analyzed samples are the populations of *G. bulloides*, *G. ruber* (s.s. and s.l.), and *G. rubescens* based on the number of specimens measured.


**Table 2.** Intraspecific ECD ranges and their average values (in µm) per basin analyzed. nd: not determined.

μ

**Figure 3.** Average population size of the planktonic foraminifera species identified together with their overall population size. The gray shaded areas denote one standard deviation. The labels in the vertical axis are representative of the core-top locations presented in Table 1.

*Orbulina universa* population is the largest one in both study basins, even more than *G. truncatulinoides* and *G. inflata* which are followed (Table 2). Spherical shells of *O. universa* reflected by their ultimate chamber that covers all the previous ones of the pre-adult trochospiral stages seem to be very voluminous in the Ionian as well as in Adriatic basins. Our results from the central Mediterranean show an inverse correlation between shell size and latitudinal occurrence since their average shell diameters increase from the Adriatic (414 µm) to the Ionian Sea (496 µm). A closer view of the central Mediterranean dataset, regarding this species, indicates an intra-basin latitudinal relationship to the shell size, with the smallest specimens (avg. = 414 µm) occurring in the south Adriatic basin, intermediate values (avg. = 491 µm) are recorded in the north Ionian sub-basin and the largest specimens (avg. = 503 µm) are found in the south Ionian sub-basin. Next in size is *G. ruber rosea*, which is significantly larger than the white variety of the same species, similar to what was found in the Aegean and Levantine sub-basins [24].

The oligotrophic, symbiont-bearing species *T. trilobus* and *G. siphonifera* present similar shell sizes, indicating that they thrive in the same water masses constrained mostly by the same productivity regime of the surface waters. Within *G ruber* (w) morphospace, the

sensu lato appears larger (by ~20%) than the sensu stricto populations. This seems reliable since the former includes the mixing of Platys and Elongate specimens (morphotypes B and C of Kontakiotis et al. [21]). *Neogloboquadrina pachyderma* and *G. bulloides* present quite similar intermediate-sized average values of about 220–230 µm, probably correlating with the same levels of primary productivity of the sub-surface waters. Finally, the species *T. quinqueloba*, *G. glutinata* and *G. rubescens* are the smallest ones recording ECD values less than 200 µm. Although the two first species are known from the literature as small-sized foraminifera, our results show that *G. rubescens* can also be added to this group confirming the previous observations of Al-Sabouni et al. [82] and Zarkogiannis et al. [24] from the Atlantic Ocean and the eastern Mediterranean Sea regarding its small size.
