The Kornati National Park (KNP) is usually considered an unpolluted reference area in environmental and ecological studies, but with the growth of tourism and a higher exposure to anthropogenic inputs, some parts of it are deteriorating into increasingly hazardous environments. The factors that contribute the most to the environmental risks are the fishing industry, chemical pollution and eutrophication, physical changes of the ecosystem, invasions of exotic species, and global climate changes [1
Stable isotopes of carbon (C) and nitrogen (N) are commonly used to decipher the environmental conditions and trophic relations in ecosystems [2
]. Stable isotope compositions of organisms are used to identify the biochemical processes and sources of the pollution, as they are mainly influenced by the isotopic ratios of diet, metabolic pathways, and fractionating processes [4
]. With the isotopic analysis, it is also possible to determine the source of sedimentary organic matter (marine, terrestrial) and thus to assess the anthropogenic impacts on the observed area [6
The isotopic composition of carbon (δ13
C) in organisms is typically influenced by food source, type of environment (marine, terrestrial), distance from the shore, vegetation type, and seasonal and environmental changes, while the isotopic composition of nitrogen (δ15
N) reflects the position of the organisms in the food web [3
]. The enrichment of the consumers regarding their food source is on average about 3.4‰ per trophic level for δ15
N and about 1‰ for δ13
]. The areas with a minimal anthropogenic input usually show relatively low δ15
N and δ13
C values, while ecosystems and organisms found within more anthropogenically impacted regions show increased δ15
N and δ13
C values as a consequence of the utilization of 15
N- and 13
C-enriched N and C [5
The isotopic measurements in this research were focused on the banded dye-murex Hexaplex trunculus
(Linne, 1758), which is a 4 to 10 cm-long mollusc and one of the most common organisms in the Adriatic Sea [9
]. The molluscs are simple to sample and are an excellent biomarker of seawater pollution, as they are present in polluted as well as in unpolluted areas [10
]. They mainly occur in rocky and muddy parts of the sublittoral zone, at depths between 1 m and 100 m [9
]. They are relatively immobile and, therefore, are representative for the area of study [11
]. The banded dye-murex are predators and resistant to hypoxia and anoxia, as they close their shells under hypoxic conditions [12
]. Today, they are mainly used because of fishing demands, whereas, in the past, they were mainly used because of their purple color [9
]. The color is the consequence of the pigments indirubin (C16
), indigotin, and other brominated derivatives, which are formed in the glands of H. trunculus
]. Many previous studies were focused on the effect of TBT (tributyltin) and the development of imposex, whereas, unfortunately, only a few studies on isotope fingerprints of H. trunculus
have been published to make a comparison.
The aim of this research was to compare individual sampling sites considering their different exposures to anthropogenic pollution and to assess if the Kornati National Park is an acceptable reference area. To determine this, the isotopic composition of organic carbon in the sediment as well as the isotopic composition of organic carbon and nitrogen in the muscle tissues of the banded dye murex were measured.
The main purpose of this research was to assess the adequacy of the Kornati National Park as an acceptable reference area for environmental studies. For this purpose, we compared different locations and evaluated the possible anthropogenic influence at the locations of Klobučar, Mana, Lojena, Piškera, and Vrulje.
On the basis of the isotopic analysis, the analyzed sites were divided into two subgroups: (a) Klobučar, Lojena, and Mana, where the anthropogenic influence on the environment is negligible, and (b) Piškera and Vrulje, where the anthropogenic influence on the environment is slightly elevated.
Even though some parts of the Kornati National Park are still preserved and intact, there are some areas where human activity has already made an evident impact and has consequently contributed to changes of the environment. Our pilot study shows that the areas closer to marinas and villages are more likely to be under the influence of anthropogenic pollution, yet, more distant areas remain anthropogenically unaltered. To extrapolate these results to the entire Kornati National Park, the analysis of more sampling sites is necessary, and the entire food web, including the dissolved and particulate load of the seawater, should be taken into consideration, so as to acquire a complete set of environmental data.