Use of stable isotope signatures (δ13C & δ15N) in the Black Sea Danubian area – new approach for understanding the influence of terrestrial discharge upon the marine ecosystem

Abstract. Coastal marine zones located in front of large rivers are of major biological interest. In these areas, the origin of the organic matter is complex and highly variable. The continental inputs, added to the nutrients already present in the marine environment, influence considerably the productivity and functioning of the ecosystems. Used for the first time in aquatic ecology on the Romanian coast, the proportion of stable isotopes of carbon (13C/12C) and nitrogen (15N/14N) allowed the identification of the organic material sources (terrestrial and marine) as well as the analysis of the food webs due to the predictable isotopic relation between consumers and their food. Preliminary analyses of stable isotopes of the particulate organic matter POM of the Danube water as well as marine POM, sediments and marine organisms were made on 186 samples collected at 10 stations in October 2004. The identification of the isotopic signatures of the main sources of organic material (terrestrial and marine) was achieved along with those of some groups of marine organisms present in this area (macrophytes, bivalves, polychaetes, amphipods, macrurans, brachyurans and fish). The results obtained in the Black Sea were compared with those of the Mediterranean Sea seawards the Rhone river and showed that the isotopic signatures of the two river POM were close to each other, whereas they largely differed in marine phytoplankton and macrophytes.