The First Record of Larval Crassostrea gigas (Thunberg 1793) (Bivalvia, Ostreidae) from the Black Sea

Larvae of the Crassostrea gigas oyster (Thunberg 1793) were found in the plankton of the Black Sea for the first time. The studies were carried out in 2014–2023 along the Sevastopol coast. Samples were taken monthly with a Jeddy plankton net (an inlet diameter 36 cm, mill gas mesh 135 µm). A water layer of 10 to 0 m was investigated. The live material was processed by total counting the larvae in the Bogorov chamber using MBS-9 and Mikmed-5 light microscopes. Oyster larvae were recorded in August 2020 and observed in the plankton from the end of August to the beginning of October. They were also found in the waters at Miskhor, the southern coast of Crimea in August 2023. The density of larvae amounted to 1–3 ind./m³. Larvae were found at the minimum water temperature of 19.7°C (September 2021) and maximum, of 26.6°C (August 2022). In August C. gigas larvae were at the veliconcha stage, their sizes ranging 275–340 µm. The oyster larvae in September and October were 380 µm in size being already in the late stages of development. Deposition of C. gigas larvae can be expected in the coastal waters of the northern part of the Black Sea from late August to mid-October.