Modern diatoms of the Black Sea: invaders or indigenes?

The Black Sea basin became closed several times, which led to significant desalination, then was salted, having received a connection with the ocean. The marine fauna and flora was replaced by freshwater and vice versa. The last cardinal transformation took place at the turn of about 7–8 thousand years ago, when the Bosporus and Dardanelles strains opened, and salt water began to flow into the Black Sea basin from the Mediterranean Sea. The main issue under discussion concerns speciation and its speed – did the diatoms that penetrated the Black Sea from the Mediterranean retained genetic unity, or did their evolution lead to the formation of new (now native) species?