Rare earth elements (REE) are a class of increasingly used high-tech product components and new emerging environmental pollutants, which are accumulated, in particular, in marine biota. In this study, REE contents were estimated in shells of several molluscs common in the Black Sea. The summed REE contents in mollusc shells decreased in the following order of species: Magallana gigas = Anadara kagoshimensis > Flexopecten glaber ponticus ≥ Rapana venosa > Mytilus galloprovincialis, ranging from 0.46 to 1.9 mg·kg⁻¹. Canonical analysis of principal coordinates allowed for the correct identification of species based on the REE composition in no fewer than 67% of the samples. The mollusc shells were anomalously enriched in Sc, Y, La, Eu and Tb, most likely due to anthropogenic contamination. The Y/Ho ratios in all samples were represented by two fit values: 23.2 (chondritic) and 67.6 (superchondritic, mainly associated with A. kagoshimensis). A new universal relationship linking the contents of three light and heavy REE in Black Sea mollusc shells was proposed: Ce^0.3 Er^0.7/Yb = 2.00 ± 0.46 (mean ± standard deviation).

Among the commercial mollusks from the Black Sea, the ark clam Anadara kagoshimensis, the oyster Crassostrea gigas, the mussel Mytilus galloprovincialis, the scallop Flexopecten glaber ponticus, and the gastropod Rapana venosa hold the top positions in terms of cultivation and harvesting volumes. Mollusk shells are attracting attention due to their potential use in various biotechnological applications, including nutraceutical production. In the present study, using inductively coupled plasma mass spectrometry, concentrations of essential trace elements (Cr, Mn, Fe, Co, Cu, Zn, Se, Mo, and I) were measured in shells of the five mollusks sampled from the same biotope. The essential element concentrations in the mollusk shells differed significantly. The highest concentrations of Cr, Mn, and I were found in Anadara shells; Fe and Co in Crassostrea shells; Zn in Mytilus shells; and Cu and Se in Rapana shells. Principal component analyses demonstrated the overall accumulation of all elements as the main cause of the total data variance and the species-specific accumulation of certain elements as the second most important source of the data dispersion. Matrices of element concentration correlations showed considerable dissimilarity, which suggested species specificity in the concerted or competing element accumulation. Powdered shells of Anadara, Crassostrea, and Rapana are most suitable to fulfill the daily human requirements for many essential elements, and the consumption of these powders in amounts of less than a few tens of grams appears to be sufficient for this purpose.

Mollusc shells serve as valuable biogeochemical archives of natural or anthropogenic processes occurring in the aquatic environment throughout the life of the molluscs. One such process is trace element pollution, which can be assessed by analyzing the elemental composition of mollusc shells. However, different mollusc species accumulate elements in their shells from the aquatic environment at varying concentrations, and specific patterns of this accumulation remain largely unknown. In the present study, we measured the concentrations of 33 elements in the shells of five commercially important Black Sea molluscs, all collected from the same site, using inductively coupled plasma mass spectrometry. The species were ranked according to the number of elements with the highest concentrations in their shells as follows: Crassostrea gigas (9) = Rapana venosa (9) = Anadara kagoshimensis (9) > Flexopecten glaber ponticus (4) > Mytilus galloprovincialis (2). Cluster analysis of Pearson’s coefficients of correlation of elemental concentrations in the molluscan shells revealed significant separation of C. gigas, F. glaber ponticus, and M. galloprovincialis. Multivariate ordination analyses allowed the accurate classification of >92.3% of shell samples using as few as four elements (Fe, As, Sr, and I). Linear discriminant analysis revealed the probability of separation of all species based on the concentrations of these elements in their shells being not lower than 79%. The applied multivariate approach based on the analysis of four base elements in shells can help not only in the taxonomic identification of molluscs, but also, upon appropriate calibration, in monitoring medium-term dynamics of trace elements in the aquatic environment.

For the first time, the dimensional and weight characteristics of the bivalve mollusk Anadara kagoshimensis (Tokunaga, 1906), an alien species in the Sea of Azov, were examined. The relationships between allometric parameters of the mollusk (dimensions and weight) were approximated by power functions. The maximum coefficient of determination was noted for the power-law correlation between shell width and total weight of Anadara; the minimum one was noted for the correlation between its shell height and total weight. Also, the maximum coefficient of determination was noted for the power-law correlation between shell length and wet weight of Anadara soft tissues; the minimum one was noted for the correlation between its shell width and wet weight of soft tissues. The ratio between dry and wet weight of soft tissues was 0.16. A comparison of different Anadara habitats in the Black Sea, Sea of Azov, and Aegean Sea showed that cage farming of these mollusks in moderately saline waters ensures the most favorable conditions for their maximum growth.