An impact of non-native species invasions on the Caspian Sea biota.

The Caspian Sea is a large inland brackish basin, vulnerable to invaders due to its long isolation and considerable endemism among its native biota. A brief description of Caspian biota evolution until its modern state is given. The pathways and vectors of invasion and the ways of establishment of non-native species since the early 20th century are summarized. The newly established species are euryphilic, with high ecological plasticity, able to adapt to new environments and to affect their biodiversity. This review is based on unpublished field data, collected in 1999-2019 in the Northern, Middle and Southern Caspian, and on relevant published information. The arrival of non-native species occurred in three periods: (1) in the 1930s, deliberate introductions aimed at enriching commercial stocks and edible resources, (2) since 1952, the construction of the Volga-Don Canal led to the arrival of benthic foulers and macrophytes from ships; (3) since the early 1980s to present, ballast water tanks were mounted on ships, favoring the arrival of phyto- and zooplankton species. Most established non-native species reached the Caspian Sea via the Black Sea. They include both Black Sea native species and non-native species from the North Atlantic areas, which first arrived and established in the Black Sea. Few established non-native species came from brackish water; fresh water fishes were deliberately introduced to develop aquaculture. Though not numerous, these species became dominant in both benthos and plankton communities, where they replaced native Caspian species. Among them, the invading ctenophore Mnemiopsis leidyi, which had no predators, continues to thrive in the Caspian ecosystem, impoverishing its biodiversity and bio-resources. However, lately its natural predator, the ctenophore Beroe ovata, arrived and established in the Southern and Middle Caspian providing a chance for ecosystem recovery, as has already happened in the Black Sea.

Screening of antibacterial producing actinomycetes from sediments of the caspian sea.

Actinomycetes are interesting as a main producer of secondary metabolites and industrial antibiotics from marine environments. A total of 44 strains of actinomycetes were isolated from Caspian Sea sediments at a depth of 5-10 m. Preliminary screening was done using cross-streak method against 2 gram-positive and 4 gram-negative pathogen bacteria. The most potent strains MN2, MN3, MN38, MN39, MN40, MN41, and MN44 were used to extract the antibacterial substances. The antibacterial activities were performed using Kirby-Bauer disk diffusion method. Potent actinomycetes were screened for hydrolytic exoenzymatic activities (amylase and protease). All of the 24 isolates were active against at least to one of the test organisms. The MN38 strain showed activity against Staphylococcus aureus (20.0±0.5mm), Bacillus subtilis (27.0±0.2 mm), and Escherichia coli (20.0±0.3 mm). The MN39 strain was also active against E. coli (23.0±0.4mm), B. subtilis (23.0±0.2mm), Klebsiella pneumonia (24±0.1mm), whereas, the MN3 strain showed activity against Pseudomonas aeruginosa (20.0±0.2mm). The results of this investigation revealed that the marine actinomycetes of Caspian Sea sediments were potent source of novel antibiotics and bioactive compounds.