Previously Extinct Population of the Brackish-Water Crustacean Calanipeda aquaedulcis (Copepoda, Calanoida) in the Middle Caspian

In the spring of 2024, the mass development of the copepod Calanipeda aquaedulcis Kritchagin, 1873, which had been absent here for almost 20 years, was observed in the Middle Caspian Sea off the coast of the Republic of Dagestan from the city of Makhachkala to the city of Kaspiysk. It again entered the group of dominant species and formed on average 92% of the total biomass of zooplankton. Mature males (45% of the total abundance), females (47%), and immature crustaceans of copepodite stages of development (8%) were recorded in the population. In the early 2000s, C. aquaedulcis was severely affected by the introduction of the copepod Acartia tonsa and the ctenophore Mnemiopsis leidyi into the sea. Currently, there is hope for the restoration of the C. aquaedulcis population in the Middle Caspian.