engleski

Growth, longevity and stable isotope composition of European date mussels Lithophaga lithophaga from eastern Adriatic

Bivalve mollusc shells are widely used as archives of past variability in aquatic environments. Longlived species are particularly useful for long-term reconstructions of climatic and environmental signals over decades to centuries. However, most of these species are living in cool marine waters under temperate settings. No equivalent of northern quahogs Arctica islandica (>500 years old) or dog cockles Glycymeris glycymeris (>200 years old) has ever been found in the Mediterranean. The European date mussel Lithophaga lithophaga (Mytilidae) is an endolithic bivalve species boring into calcareous substrates all around the Mediterranean coasts. Although under-investigated, this protected species (listed in the CITES Appendix II) has been suggested to live more than 50 years in the Aegan Sea, and therefore appears as a good candidate for paleo-ecological and paleoenvironmental studies. Here, we analyzed shell growth of 71 specimens collected in July 2013 off Split (Croatia) by counting ridges on the external shell surface. High variations in growth rates between individuals were noted and age of analyzed shells (based on the assumption of an annual periodicity of formation of external ridges) varied from 10 to 54 years (for a shell length of 30.6 to 93.6 mm). According to results of growth modelling using a generalized von Bertalanffy growth function, asymptotic shell length was 107.6 mm while growth coefficient was 0.03 year-1. Both parameters were used to calculate an overall growth performance index that was found to be similar to the one previously calculated in a Greek date mussel population (2.54 vs. 2.42, respectively). In addition, we analysed the oxygen and carbon isotope composition of one shell, randomly selected amongst medium-sized shells. A total of 147 discrete carbonate samples were collected on the shell surface using a micromilling device (2-8 samples per growth increment). Obtained δ18O results strongly suggest that growth ridges visible on the external shell surface of L. lithophaga are formed annually as we counted as many growth increments as δ18O cycles. The δ18O values ranged from -0.2 to 2.7 ‰, which equates to a temperature range of 13°C. The reconstructed seawater temperatures varied from 12 to 25ºC, a range in good agreement with measured temperature. Stable carbon isotope values decreased through ontogeny and ranged between -2.05 and 2.32‰. Results of this study provide first stable isotope data for Lithophaga lithophaga shells and show potential of this species as geochemical sclerochronological archive.

bivalve ; longevity ; stable isotopes ; oxygen ; Adriatic ; Lithophaga ; date mussel

nije evidentirano