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Bivalve Glycymeris pilosa – an archive of environmental change in the Adriatic Sea – case study of the Neretva channel

Bivalves have a wide geographic distribution and can therefore provide information about the environment for the most diverse marine habitats. Sclerochronological analyses are based on growth patterns preserved in the shell, which help to create a continuous decadal to centennial data time series on the growth and variability in the marine environment. Long lived species of bivalves are ideal paleoclimatic archives, because they provide insight into the conditions and variability in the environment for periods with different anthropogenic impacts. By studying the shells of long-living bivalves, scientists are trying to comprehend the historical range of environmental changes in order to understand the past climate changes as well as to forecast future ones. Due to its longevity and clarity of growth lines in shell sections, dog cockle Glycymeris pilosa was recently identified as a species with great potential for sclerochronological research in the Mediterranean. Data on the distribution and biology of this species in the Adriatic, as well as in other parts of the Mediterranean Sea, have long been limited since species was often misidentified as G. glycymeris. In this study we analyzed 49 large sized (> 60 mm) G. pilosa shells live collected by SCUBA in the south Adriatic Sea. Shells were collected on two occasions, in July 2015 and July 2016, near village Drače, northern side of the Pelješac peninsula. Samples of the umbo region were embed in the epoxy resin, cut through the maximal growth axis, grinded, polished and etched and acetate peel replicas were prepared from them. Growth increments were measured using Image-Pro software, and statistical analysis was conducted in dendrochronological software packages COFECHA and ARSTAN. Growth increments were clearly visible on 29 shells, with age ranging from 31 to 98 years, and those were used for chronology construction. Data series covered period between 1924 and 2015, and was statistically robust (EPS~0.85) from 1982 to 2015. Presence of marker years was discussed and chronology was related to available measured and modelled environmental parameters, including the influence of the Neretva River.

bivalve, sclerochronology, Glycymeris pilosa, Neretva, Mali Ston bay, Adriati

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