Developing a sclerochronology network in the Adriatic Sea: Growth synchrony among populations of Callista chione

Callista chone samples were live collected at three localities in the Adriatic Sea: Gulf of Venice, Italy, Pag Bay and Pašman Channel, Croatia. Acetate peel replicas were prepared and the Image Pro Primer program was used to measure increment widths in samples that had clear boundaries. Visual cross-dating of the images was performed using list-year method and validated using COFECHA, while the R package dplR was used to construct the chronologies. The age of analysed shells ranged from 15 to 46 years (N=32; 29,9 ± 8,8 years) at the Gulf of Venice, from 14 to 41 years (N=63; 26,0 ± 5,1 years) at Pag Bay, and from 14 to 41 years (N=33; 26,8 ± 4,8 years) at the Pašman Channel. Final statistically robust standard master chronologies spanned from 1986 to 2018 (Gulf of Venice), from 1994 to 2019 (Pag Bay) and from 1994 to 2015 (Pašman Channel). Statistically significant correlation was obtained only between the Gulf of Venice and Pag Bay residual master chronologies (1994–2018; r = 0.607; p <0.001). Although there are some coincidences between all three localities, suggesting a common signal among populations, the growth chronology in the Pašman Channel recorded a very different signal potentially linked to differing oceanographic influences. The Pašman Channel locality is more affected by the inflow of warmer and saline waters coming from the south than the two other sites which are located in geographically and hydrographically isolated Adriatic areas. No correlation was found between any shell master chronologies and surface seawater temperature. Also, no correlations between the shell C.chione master chronologies and parameters describing the Adriatic-Ionian Bimodal Oscillating System (BiOS) were observed. Correlation maps indicate different relationships between shell master chronology and chlorophyll a concentration in the region. Significant correlations were mostly limited to March and April and showed spatial variations.