Fig 1.
Location of sampling station in Panzano Bay, north-western Gulf of Trieste, Adriatic Sea.
Roman numerals I–V along the coast between Grado and Monfalcone indicate Isonzo River mouth migration stages from Roman times up to the present, according to Brambati [56]: I: 313- ~600 AD, II: ~600–1589 AD, III: 1589–1896 AD, IV: 1896–1937 AD, V: after 1937 AD. The Gulf of Trieste features a layered gyre-type circulation pattern with a permanent cyclonic current in the bottom layer and an alternating cyclonic/anticyclonic flow on the surface [57].
Table 1.
Functional groups.
Fig 2.
Total mollusc abundance, species richness, and diversity.
Down-core trends in abundance, species richness, and diversity of bivalves, gastropods and scaphopods in the Panzano Bay sediment core. Species richness is given as observed number of species, and diversity as the exponent of the Shannon index, exp(H) (effective number of species). Overall down-core abundance (left graph) is plotted together with sedimentation rates as derived from median C. gibba shell ages of dated sediment layers.
Fig 3.
Grain size analysis and concentrations of several metals, nutrients and organic pollutants.
Dashed lines indicate threshold values for potential environmental effects according to NOAA sediment quality guidelines and to the Italian Ministerial Decree 26/2010 (ERL: Effects Range-Low; ERM: Effects Range-Median; TEL: Threshold Effects Level). For PAHs, no thresholds are plotted because measured concentrations are considerably lower.
Fig 4.
PCA of the investigated metal, nutrient and organic pollutant concentrations.
Fig 5.
Absolute (>10 individuals) and relative (>2.5%) abundances of the most common mollusc species.
Species are sorted according to their weighted average occurrence along the cores, from top (left side) to bottom (right side). Exceptions: maximum occurrence of Weinkauffia turgidula: 5; relative abundance of Pitar rudis: 2.5%, and of Anomia ephippium: 1.9%. For some species, the 0-value of the x-axis has been omitted for better readability.
Table 2.
Differences between consecutive temporal bins with regard to species composition and functional groups, based on PERMANOVA.
Fig 6.
Relative abundance of dominant mollusc species in six temporal bins.
Species are sorted according to their abundance rank in the deepest core section.
Fig 7.
Relative and absolute abundances of molluscs for each functional group.
Only main categories are shown (see Table 1), and categories with low abundances are omitted for better readability. Percentages of epifaunal molluscs (left column), scavengers (middle column), and echinoderm commensals (right column) increase while infauna and ascidian commensals decline towards the 20th century. Absolute abundances of infauna also increase towards the 20th century, in contrast to relative abundances.
Fig 8.
NMDS ordinations of the molluscan community.
Ordinations are based on down-core species abundances (A), feeding guilds (B), organism-substrate relations (C), and host associations (D). Greyscale shadings of dots mark the four main molluscan community phases as listed in panel C.
Table 3.
Correlations (Pearson’s r) between NMDS axis-1 and axis-2 scores and the investigated environmental variables.
Table 4.
Results of individual RDAs.
Fig 9.
Redundancy analysis for down-core community changes in relation to environmental variables.
Total nitrogen separates the topmost core intervals from the rest of the core and explains a significant amount of variation in relative abundance of species (A), feeding guilds (B), organism-substrate relations (C), and host associations (D). The second axis represent the first principal component in A-C because the stepwise selection selected one environmental variable only.