The first record of larval Crassostrea gigas (Thunberg 1793) (Bivalvia, Ostreidae) from the Black Sea

Larvae of the oyster, Crassostrea gigas (Thunberg 1793) are being 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 (inlet diameter 36 cm, mill gas mesh 135 µm). A water layer of 10–0 m was investigated. 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, southern coast of Crimea in August 2023. The density of larvae amounted to 1–3 ind./m³. Larvae were found at the following water temperatures: minimum, 19.7 °C (September 2021), maximum, 26.6 °C (August 2022). In August, the larvae of C. gigas were at the stage of veliconch, their sizes ranging 275–340 mkm. The sizes of oyster larvae in September and October were 380 mkm, being already in the late stages of development. In the coastal waters of the northern part of the Black Sea, C. gigas larvae can settle on substrates from late August to mid-October.