A threat or a new species occupying an empty spot? Study on the Magallana gigas (Crassostrea gigas-the pacific oyster) populations in natural habitats from the Black Sea, Romania

Native to the Far East Pacific Crassostrea gigas is being used worldwide in aquaculture, being already in many areas an alien species. In August 2017, we found two populations of Crassostrea gigas in rocky substrate area from the Agigea harbor. We conducted therefore quantitative and qualitative studies. In 2018 we found another two groups along the same dam, suggesting that the area occupied by this species could be much bigger.

-preliminary quantitative survey of the macrozoobenthos using the samples procedures method.

-we used a metal quadrate with the side of 1 meter, in order to determinate the Magallana gigas density in the two groups

-we measure the entire surface occupied by the Pacific oyster in the studied locations using a graded rope

-we used the DNA barcoding method

The depth range varied between 4-10 meters. The entire surface covered by the Pacific oyster populations is over 350 m2. The density is relatively low, for both populations with an average of 1.16 oyster individuals/1m2. The smallest size was 5.2 cm, the largest size was 18.6 cm and the average size was 10.35. The relative small number of Pacific oyster individuals and their relative small average size suggests that this populations are young, around 5 years old, taking in count that a Pacific oyster individual grows in the first year of life around 4-5 cm. 

To confirm the morphological identification of the oyster species present in the Black Sea at the Romanian littoral, we used the DNA barcoding method. The specimens were sequenced for the COI (Cytochrome Oxidase subunit I) mitochondrial marker. Two 638 bp sequences were obtained and compared to COI sequences present in the GenBank database. We obtained an identity of 99-100% to sequences of Crassostrea gigas specimens from the native area of the species (Pacific Ocean - China and Japan). During this study no Black Sea native oyster species were found.



We need to conduct further studies in order to determine whether Crassostrea gigas will manage to reproduce and develop larger populations under the Black Sea special conditions and the ecological implications. Do we need to take action or just enjoy it?




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