In the marine environment, alien species are generally most abundant in harbors, marinas, and aquaculture areas, and more so in areas of high human activity. The threat of invasive species to biodiversity is thought to be second only to habitat loss, and in some ecosystems alien species already outnumber native species. 1 Species today are introduced rather rapidly through human activities of maritime trade and transport. There are more than 500 marine alien species identified to date on the coast of Turkey. All organisms, from the largest to the smallest, including fish, mussels, jellyfish, seaweeds and microscopic pathogens may be an invasive species. 2

1 https://tudav.org/calismalar/denizel-biyocesitlilik/biyolojik-yayilim/biyolojik-yayilim/
2 https://www.istilacilar.org/denizel-istilaci-yabanci-turler/