DNA fingerprinting: an effective tool for taxonomic identification of precious corals in jewelry

Abstract

Precious coral species have been used to produce jewelry and ornaments since antiquity. Due to the high value and demand for corals, some coral beds have been heavily fished over past centuries. Fishing and international trade regulations were put in place to regulate fishing practices in recent decades. To this date, the control of precious coral exploitation and enforcement of trade rules have been somewhat impaired by the fact that different species of worked coral samples can be extremely difficult to distinguish, even for trained experts. Here, we developed methods to use DNA recovered from precious coral samples worked for jewelry to identify their species. We evaluated purity and quantity of DNA extracted using five different techniques. Then, a minimally invasive sampling protocol was tested, which allowed genetic analysis without compromising the value of the worked coral objects.The best performing DNA extraction technique applies decalcification of the skeletal material with EDTA in the presence of laurylsarcosyl and proteinase, and purification of the DNA with a commercial silica membrane. This method yielded pure DNA in all cases using 100 mg coral material and in over half of the cases when using "quasi non-destructive" sampling with sampled material amounts as low as 2.3 mg. Sequence data of the recovered DNA gave an indication that the range of precious coral species present in the trade is broader than previously anticipated. Precious corals are among the most appreciated and oldest known gems. They are valued for their color, texture and workability (polishing, carving), and have thus been collected and used for adornment for millennia 1-3. Growing demand, particularly in Asia in recent years, has led to an increase in prices of precious corals used in jewelry 4-6. The most valuable precious coral species belong to the Coralliidae family within the Octocorallia subclass of the Anthozoa. The precious coral material used for jewelry is the worked (i.e. cut, carved and polished) hard coral skeletal axis, which is a biogenic material created by a biomineralization process 7. In this process, closely packed magnesium-rich calcite crystals are secreted by coral polyps (1-2 mm in size) to build up a skeleton over decades. The polyps can thrive on the surface of the skeleton as colonies connected and surrounded by a 0.5-1 mm thick surface tissue (coenenchyme) 8. The Coral Commission of The World Jewellery Confederation (CIBJO) lists eight Coralliidae species as significant in the precious coral jewelry industry 9,10. Precious coral products are sold worldwide, with production centers located in Italy, Japan and Taiwan and large-scale trade of raw material between these areas 5,6,11. Until recent decades, the populations of these highly coveted marine animals experienced exploitation in boom and bust cycles where the discovery of precious coral beds led to rushes by coral fishers and these beds were exploited as long as it remained economically feasible 12,13. Local and international regulations were put...

Coral-ID: A forensically validated genetic test to identify precious coral material and its application to objects seized from illegal traffic

“…The Coralliidae family contains 45 described species in the three genera, Corallium, Hemicorallium and Pleurocorallium [26,27]. Eleven species are estimated to be present in the commercial trade, however there is no consensus on the exact number of species used in jewelry [4,5,24]. The color of the skeletal axis of some species is known to be highly variable.…”

“…The recent study by Lendvay et al [24] has shown that the number of short mitochondrial DNA copies recovered following a minimally destructive sampling of precious coral objects spans over the range of 1-10 4 . We tested the sensitivity of the Coral-ID assay using DNA of C. rubrum, C. japonicum and P. elatius.…”

“…To adjust potential individual variations of DNA purity, a DNA cocktail was prepared for each of the three species by pooling DNA of 3-5 samples with known identical mtMutS sequences. Then, absolute quantification of a 172-198 bp long fragment of the mitochondrial ribosomal large subunit RNA gene was carried out using quantitative real-time PCR technology as in agreement with the MIQE guidelines [41] as described by Lendvay et al [24]. Following the quantification, each of the three DNA cocktails were serially diluted to 10 4 , 10 3 , 10 2 and 10 copies per 5 µl volume.…”

“…We assessed precision by analyzing each of 10 case-type precious coral jewelry samples 10 times with the Coral-ID assay. All 10 case-types test samples originated from the coral collection of the Swiss Gemmological Institute SSEF and were analyzed previously by Lendvay et al [24]. In their study, moderate levels of DNAranging from c. 250-750 mtDNA copies per µl of the 172-198 bp long fragment of the mitochondrial ribosomal large subunit RNA genewas measured in each of these samples.…”

“…The technical study of Lendvay et al [24] demonstrated the presence of DNA preserved in the internal skeletal axis of precious corals. These authors concluded that genetic testing of precious coral jewelry objects may be a powerful tool for taxonomic identification of coral jewelry when using optimized laboratory techniques combined with a "quasi non-destructive" sampling method that keeps the market value of the objects.…”