Today, the beginning of the 21st century the global shipping turnover has increased to the extent that almost 80 percent of all cargo shipments are implemented by long-distance vessels. In the context of a rapid development of navigation, some species of marine organisms are frequently transported to different parts of the World Ocean, in many cases located thousands of kilometers away from their original habitat. How do migration processes take place?

Suppose that an oil tanker arrives in a port of destination and discharges oil into an intake structures. After that the tanker becomes much lighter, the center of gravity is displaced, disturbing its seagoing characteristics. Even a small storm can lead to an emergency. To prevent this, each tanker has special ballast tanks filled with outside water. It is a "house" for many marine organisms. Some of them can turn into dangerous "aliens" and colonize new territories. Alexander Zvyagintsev, Dr. Sc. (Biol.), senior research officer of Ecology of Shelf Communities at the Laboratory, RAS FEB Institute of Marine Biology named after A. Zhirmunsky, discusses risks of these processes in an article published in the Far Eastern Scientist newspaper.

About 10 bln tons of ballast water containing over 700 species of aquatic organisms, many of which can become a serious threat to marine ecosystems, economy and even human health are carried annually in the tanks of cargo vessels. Some "alien" species are transported by way of the so-called ship's overgrowth, i.e. animals and plants settle on the underwater parts of the vessel, which is also a serious problem. No customs or quarantine service can stop or somehow limit the flow of underwater migrants. Total global damage by such growth is about USD 50 bln annually.

Dissemination and settlement of new species is one of the reasons of instability of marine ecosystems. If the population of aboriginal species reduces or even disappears, this is an indicator of changes in the environment. When they are replaced by alien species that never lived

Decapoda suborder (DIOGENES NITIDIMANUS)--an alien species in the Peter the Great Bay.

there before, we understand that the ecosystem has become unstable and "sick". Such unexpected occurrence of "alien" species in the ecosystem is called a "biological invasion" (invasion--a medical term referring to parasitology) or "biological contamination". In this case the invasion means dissemination of a species beyond the limits of its historical habitat induced (directly or indirectly) by human activities. At present transportation of alien species by way of marine growth and ballast waters of vessels has become global and absolutely unpredictable, which determined its name--the "environmental roulette".

Dissemination of species can be both deliberate and occasional. For example, to balance a drastic reduction of the population of game species, in the 1950s-1980s Kamchatka crab and humpback salmon from the Pacific Ocean were deliberately brought to the Barents Sea. The same way mullet was brought to the Caspian Sea. In 1939-1940 the Caspian Sea accepted another "alien"--a benthic polychaete clam worm: at present it is the basic food ration for Caspian sturgeons.

It is absolutely clear that the consequences of such large-scale experiments are ambiguous--numerous positive and negative results come together. New species often break the ecological balance. For example, in the early 1960s, the Far Eastern red-finned mullet was successfully acclimatized by Russian scientists in the Sea of Azov. But this experiment led to unpredictable consequences--due to the increased competition the world-famous sturgeons disappeared.

Here is another example. In 1952, after commissioning of the Volga-Don Canal, the fauna of the Caspian Sea changed drastically--about 70 species colonized this new territory for some decades. As for the "guests" that have changed the ecological situation in two seas, we can single out North American ctenophore--a planktonic invertebrate organism. It extirpated zooplankton that resulted in the extinction of many fishes in the Black Sea due to starvation. In 1999, it got through the Volga-Don Canal on ships to the Caspian Sea, which, finally, had a negative effect on the population of sturgeons.

According to Zvyagintsev, not every migration of alien organisms leads to critical negative ecological consequences. But they become more and more numerous due to a rapid development of water transport, and negative effects become more and more tangible. For example, the settlement of the North American ctenophore in the Black Sea resulted in economic losses amounting to

USD 240 mln annually due to the reduction of anchovy reserves. Or another example: the entire marine industry of New Zealand, focused on breeding mollusks and crustaceans, was closed because of "blooming" water caused by the profuse growth of toxic species of seaweeds.

A number of species, including game species (three species of crabs, giant oyster, red-finned mullet, humpback salmon) were transported to different parts of the World Ocean from the Peter the Great Bay (Primorye Territory). As a result, there have been observed some cases of changes in local ecosystems.

In its turn, the ecosystem of the Peter the Great Bay also suffers from an external pressure. It is located on the border of a moderate and subtropical zones and is characterized by a diversity of the hydrological regime and environmental conditions, which promotes acclimatization of alien warm-water species there. The author of the article states: over 16,000 vessels visit local ports annually, and almost half of them make long-distance trips and contribute to dissemination of "aliens". Moreover, the process of settlement of alien species is supported by warm waters discharged from cooling systems of local industrial enterprises. For instance, Vladivostok Thermal Electric Power Station-2 discharges millions of cubic meters of water to the Golden Horn Bay annually.

The estimated economic growth of the Primorye Territory will lead to a sharp increase of an anthropogenic effect on the costal ecosystems of the Peter the Great Bay. From December 2009, when the oil pipeline within the "Western Siberia--Pacific Ocean" system was put into operation, hundreds of supertankers have been exporting oil from Russia with an annual turnover of up to 15 mln tons. According to the scientist, the flow of alien species brought with ballast water and the marine growth on the supertankers is no less dangerous for marine ecosystems than possible oil spills. Acclimatization of these "guests" may result in unpredictable effects.

According to the specialists of the RAS FEB Institute of Marine Biology named after A. Zhirmunsky, in the last decades 66 subtropical species of marine invertebrates, namely ascidia, barnacles and marine bristle-worms, have been brought and are now acclimatizing in the Peter the Great Bay. The ascidia are in the list of dangerous species, as their overgrowth in breeding cages for cultivated bivalves make it impossible to breed them, which is proved by the situation in mariculture in coastal waters of Canada.

Acorn barnacles that settled in the bay in the last century are able to survive even on the operating ship screw. It causes reduction of the speed of the vessel and is resistant to toxic coatings designed to prevent growth.

Speaking of the contribution made by Far Eastern scientists to solve all these problems, Zvyagintsev pointed out: in 2007 experts of the Institute of Marine Biology within the framework of the RAS FEB special complex program "Biological Safety of Far Eastern Seas in the RF", initiated large-scale studies of "residents" of ballast waters, and in 2008 they established a special monitoring center that is now actively operating.

A. Zvyagintsev, Dangerous Aliens, the "Far Eastern Scientist" newspaper, No. 7, 2012