Estimation of freshwater influx along the eastern Adriatic coast as a possible source of stress for marine organisms

Abstract

       Seawater salinity changes and thermal stress have been considered to be among the most important determinants of rocky intertidal zone organism distribution. The aim of present study was to determine the freshwater influx and evaluate the mussel Mytilus galloprovincialis shells as indicators of natural environmental conditions by comparing δ¹³C of shell carbonate layers with seawater salinity and tem- perature values measured over the 1998-2007 period. Our results show that the salinity was relatively constant in the open sea, with typical values of the northern and southern Adriatic being 37.65 ± 0.40 and 38.37 ± 0.19 respectively. It varied in intertidal zones, estuaries, locations close to under-sea freshwa- ter springs and during rainy days in closed lagoons on different locations along eastern Adriatic coast. Sa- linity and temperature variations at investigated sites showed freshwater influx which was also reflected in lower δ¹³C values of mussel M. galloprovincialis shell carbonates. Based on the measured parameters, three groups of locations in the investigated area (25 locations) can be defined: locations with strong to medium freshwater influence (9), with minor freshwater influence (6) and marine environment locations (10). Our results confirm that mussel M. galloprovincialis responds sensitively to subtle changes in the environmental conditions. Results of the isotopic analyses presented in this study support the hypothesis that the δ¹³C in mussel’s shell might be used as an indicator of environmental salinity conditions and hypo-osmotic stress. Therefore such investigations might represent an additional tool for waste water management and environmental protection.