Distribution and Conservation Status of Pylaiella littoralis (L.) Kjellm., nom. cons. (Ectocarpales, Heterokontophyta) in the Northern Black Sea Region

A new locality of <i>Pylaiella littoralis</i> has been identified in the coastal marine waters off the Cape Martyan Reserve (Southern Coast of Crimea, the Black Sea). In the Northern Black Sea region, which covers the coastal area from the Danube Delta to the Northern Caucasus, this species is considered a rare element of the natural flora with decreasing populations. However, in the Mediterranean Sea, <i>P. littoralis</i>, first recorded in 1960, is categorized as an alien species. Since the Black Sea regional conservation documents emphasize the Caspian-Mediterranean range of <i>P. littoralis,</i> we analyzed original publications for a period of more than two hundred years. Together with the results of our own observations, it showed that the species does not usually form abundant growths and thickets in the Northern Black Sea region, but it is widespread enough. <i>Pylaiella littoralis</i> was first identified in the Northern Black Sea (and in the Black Sea in general) in the early 1930s in Odesa Bay as an alien species, which was later overlooked. The erroneous idea about the occurrence of <i>P. littoralis</i> in the Caspian Sea before the launch of the Volga-Don Canal (1952) arose due to an inaccuracy made in the 1950s in the succession of citations that began with a publication from 1800. We believe that this multizonal eurybiont was introduced by sea transport through the straits into the Mediterranean and Black Seas almost simultaneously - around the early 1930s. After the end of the lag-phase of invasion, a rapid expansion of the species occurred. This could have been triggered by the intensification of marine traffic, climatic changes or progressive eutrophication of waters. By the 1960s, <i>P. littoralis </i>had colonized the coastal areas of both seas, and through the canal, it penetrated into the previously isolated Caspian Sea, where it had also spread widely by the early 1970s. Thus, <i>P. littoralis</i> is also a naturalized alien species in the Northern Black Sea region as well as in the entire Black Sea and the Caspian Sea. Its introduction, and rapid, widespread distribution did not result in a transformation of the native phytocenoses and biotopes of the Northern Black Sea region. However, the erroneous inclusion of <i>P. littoralis</i> in the rarity fraction of the natural flora of the region and the unreasonable conservation measures are obvious. KEY WORDS: Northern Black Sea region, macrophytobenthos, <i>Pylaiella littoralis</i>, distribution, conservation, biological invasion, alien species