Sanja Puljas

Using bivalve chronologies for quantifying environmental drivers in a semi-enclosed temperate sea

Annual growth increments formed in bivalve shells are increasingly used as proxies of environmental variability and change in marine ecosystems, especially at higher latitudes. Here, we document that well-replicated and exactly dated chronologies can also be developed to capture oceanographic processes in temperate and semi-enclosed seas, such as the Mediterranean. A chronology is constructed for Glycymeris pilosa from a shallow embayment of the northern Adriatic and extends from 1979 to 2016. The chronology significantly (p < 0.05) and positively correlates to winter sea surface temperatures, but negatively correlates to summer temperatures, which suggests that extreme winter lows and extreme summer highs may be limiting to growth. However, the strongest and most consistent relationships are negative correlations with an index of the Adriatic-Ionian Bimodal Oscillating System (BiOS) for which positive values indicate the inflow of the ultraoligotrophic Eastern Mediterranean waters to the Adriatic. In contrast, the substantial freshwater flows that discharge into the Adriatic do not correlate to the bivalve chronology, emphasizing the importance of remote oceanographic processes to growth at this highly coastal site. Overall, this study underscores the potential of bivalve chronologies to capture biologically relevant, local- to regional-scale patterns of ocean circulation in mid-latitude, temperate systems.

Growth and Longevity of the „Living fossil” Congeria kusceri (Bivalvia: Dreissenidae) from the Subterranean Dinaric Karst of Croatia

ABSTRACT The present study analyzed growth and longevity of the endemic cave dwelling bivalve Congeria kusceri obtained from the pit Jama u Predolcu, Croatia. A water temperature of 13–14°C constituted the lower limit for shell growth of C. kusceri. Obtained data also indicated that enhanced calcium uptake by C. kusceri during its summer growth and reproductive phases coincided with a decrease in alkalinity of the pit water. An analysis of shell growth rings in C. kusceri has identified an impressive longevity of 53 years. Calculations of growth rate suggested maximum theoretical shell lengths (L∞) of 16.7 mm for males and 18.7 mm for females and a growth constant of 0.04 year-1 for both sexes. Congeria kusceri can, however, grow to a shell length of > 24 mm, suggesting that longevity of this species could be greater than that identified in this study. The obtained results add to our understanding of how colonisation and continued and successful occupation of a subterranean freshwater habitat has been achieved.