A couple of years ago, Mnemiopsis entered the Black Sea, which conquered the lion's share of the food supply for planktivorous fish and destroys their eggs and larvae. The most affected party in this ecological catastrophe was anchovy - one of the main commercial fish of the Black Sea - its number has sharply decreased. “Aliens” enter the Black Sea with ballast waters and on the bottoms of dry cargo ships from other seas and oceans of the world. And the sea, warm in winter, promotes their reproduction.
The comb jelly is not a jellyfish, they do not even have family ties with them, although they cannot be called otherwise. Outwardly, mnemiopsis are light, transparent, with skirts-blades and rowing plates. They have no brain, heart, skeleton, but they have a nervous system, an organ of balance and the ability to luminescence. According to the latest data from scientists, the comb jelly is one of the first living creatures on planet Earth. Previously, it was believed that this title belongs to sea sponges - much more primitive creatures.
But because of them there is also a terrible threat to the Caspian …
Scientifically, this is called "biological invasion". Plants or animals take root in a foreign environment and begin to master there thousands of kilometers from their homeland. In a new place, they acclimatize and displace the "indigenous people".
The problem of alien species has reached planetary proportions. “As an unwanted byproduct of globalization, alien species have a detrimental effect on ecosystems, human lives and the economic situation around the world,” the UN Secretary General said in a message.
Mnemiopsis leidyi (lat.) Is a comb jelly that lives in sea water in warm regions and resembles a jellyfish. Outwardly, mnemiopsis are light, transparent, with skirts-blades and rowing plates. They have no brain, heart, skeleton, but they have a nervous system, an organ of balance and the ability to luminescence. Mnemiopsis is a predator that feeds on zooplankton, eggs, fish and shellfish larvae. In the light, it shimmers with bright colors, at night gives the sea waves a yellowish luminescent glow. According to the latest data from scientists, the comb jelly may be one of the oldest living creatures on planet Earth.
The homeland of Mnemiopsis leidyi is the waters of the Atlantic Ocean, washing Florida, where they lived until recently. However, in our century of developed communications, the moment has come when Mnemiopsis set out to conquer other water areas.
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In 1987, Mnemiopsis entered the Black Sea waters with the ballast waters of ships. In 2006, Mnemiopsis leidyi was first seen in the North and Baltic Seas.
Mnemiopsis has many of the characteristics of an ideal invader. He is simultaneously a self-fertile hermaphrodite; he is omnivorous - consuming a wide range of feed; it survives in a wide range of environmental conditions with salinity ranging from 3.4 to 75 ppm and temperatures from 1.3 ° C to 32 ° C; at an optimal temperature (above 20 ° C), it develops very quickly, reaching its sexual maturity in 12 days; it also responds to increased nutrient concentration by rapid growth and reproduction.
Moreover, there is a high resistance and low sensitivity of Mnemiopsis to various pollutants. This invader was found even in the water area of ports, in the anchorage of ships, where the water environment was polluted with gasoline and oil. Individuals of the comb jelly of different ages and sizes felt great in a mixture of water and oil products.
In the Black Sea, Mnemiopsis did not have natural predators and they began to multiply rapidly, devouring plankton, eggs and fish fry. In favorable conditions, the comb jelly can eat ten times its own weight per day. Depending on the amount of food, it can double in size per day and lay 8 thousand eggs per day. By 1989, the amount of food for fish was reduced by 30 times compared to the period 1978-1988.
Gradually increasing, the total biomass of the ctenophore population in the Black Sea reached about 1 billion tons in 1989, and its density in the southwestern part of the Black Sea was 4000-5000 grams per cubic meter of water. There was a time when this species accounted for 90% of the mass of all living organisms in the Black Sea.
The transparency of the water sharply decreased, since the destroyed zooplankton no longer ate small algae, in addition, this comb jelly in the process of its vital activity secretes a colossal amount of mucus. The Black Sea has become like a muddy comb jelly soup. The number of fish feeding on plankton has dropped by dozens of times: anchovy, horse mackerel and sprat. Fisheries lost several hundred million dollars. The Black Sea dolphins also found themselves on a starvation diet.
As already indicated, the reason for the massive development of these "invaders" was the absence of predators capable of controlling their numbers: no one ate Mnemiopsis. Ctenophores are considered to be “dead ends” in food chains: low nutrient content makes them unattractive for effective nutrition.
It would seem that the Black Sea is threatened with complete biological collapse. But in 1997 - 1999. there is an invasion of the Black Sea by a new comb jelly - Beroe ovata. Unlike Mnemiopsis, Beroe cannot digest zooplankton, eggs, jellyfish and fish fry and feeds exclusively on … the ctenophore Mnemiopsis! Beroe is not confused by large specimens of the victim. It has no tentacles, but almost all of its body is one continuous throat. Beroe either pulls Mnemiopsis into itself gradually, or swallows it immediately through the wide-open mouth opening, while the entire body of the predator swells. After 3-5 hours, Beroe digests the victim and can immediately swallow the next one. In light, beroe has a yellowish-pink color, in the dark it becomes milky white.
The introduction and reproduction of Beroe led to a sharp decrease in the biomass of Mnemiopsis and, as a consequence, to the growth of zooplankton and fish larvae, and later the fish stocks of the Black Sea.
In 1999, Mnemiopsis leidyi made its way into the Caspian Sea. The alarm about a sharp decline in the population, first of the sprat, and then of the sturgeon, was sounded in all the Caspian states.
Scientists believe that Mnemiopsis was introduced, most likely, through the Volga-Don Canal, through the ballast water of ships, or on uncleaned bottoms. During the Soviet era, all transit ships were subjected to strict sanitary inspection in Astrakhan. With the fall of the general standards of control, the obstacles to "illegal" penetration into the alien water area of an uninvited alien were essentially removed.
The first information about the appearance of Mnemiopsis leidyi in the Turkmen waters of the Caspian Sea was obtained by chance in the second half of September 1999, during the period of collecting material on the biology and ecology of Karabogazgol. From the oral communication of the fishermen, it was noted that “jellyfish” appeared in the Caspian Sea, in the area of the bay, which they had never seen here before.
During 1999-2000, a wide distribution of Mnemiopsis in the waters of the Middle and South Caspian began to be noted. Having found suitable ecological and forage conditions here, the comb jelly not only mastered almost the entire water area of the Caspian, creating a powerful population with a high abundance, but also began to influence the entire ecosystem of the sea. During the expeditionary work in the Caspian in October 2000, a wide distribution of Mnemiopsis and its highest abundance along the western coast of the Caspian were noted. Ctenophores of different ages and sizes were caught in the trawl and cone net for catching sprat, and the fish required for analysis was practically not caught at these stations.
In February 2003, in the southern part of the Caspian, the concentration of Mnemiopsis reached up to 320 specimens per cubic meter of water. For three years, its livestock has grown so much that on moonlit nights the sea phosphoresizes.
Scientists associate the mass death of the Caspian sprat in the summer of 2001 with the vital activity of the ctenophore. According to specialists from the Dagestan branch of the Caspian Research Institute of Fisheries, about 200 thousand tons of sprat died then, which was one fifth of its total amount in the Caspian basin. According to other sources, not 40%, but almost the entire sprat (at least 80% of the population) died in the Caspian. The reason for the mass death of sprat was not a disease, but a real hunger.
Further along the food chain, there was a massive death of the Caspian seal. At the same time, in the first place, the population lost all the expected offspring (animals that did not fatten up either did not enter reproduction, or gave birth to weakened cubs, which soon died).
At this time, the sprat population has decreased by an order of magnitude, followed by a decrease in the number of sturgeon fish. In addition, Mnemiopsis devours their eggs, giving no chance of reproduction. It is predicted that sturgeon fishing will soon amount to only hundreds.
Scientists of the Caspian states have been looking for ways to combat Mnemiopsis for several years. In the laboratories of Russia and Iran, a number of experiments with the reproduction of Beroe were carried out. It was found that with an increase in water temperature, the feeding intensity of Beroe increases sharply. In the Caspian water, Beroe still needs to adapt, since the Caspian water has a different ionic composition and salinity than the Azov-Black Sea.
Studies have shown that beroe can live and grow intensively in the south of the Caspian, with a salinity of 12-13 ppm. The rate of beroe feeding was quite high (100 percent or more of its own body weight per day) at 21-26 degrees Celsius. The daily diet and growth rate at 12.8 ppm were close to those of the Black Sea (where salinity reaches 18 ppm). On the basis of physiological data, it was confident that the beroe can, as in the Black Sea, intensively feed on Mnemiopsis and sharply reduce its number in the Caspian Sea.
For the first time in the world, Russian scientists have succeeded in adapting beroe. The adaptation period takes 6-7 days. Beroe otava is caught in the Black Sea and delivered to the Caspian coast by road or aviation. During the adaptation period, individuals are brought to a sexually mature state and give birth to offspring. The resulting offspring live practically in the Caspian water. The adaptation method is patented.
However, scientists disagree on the possibility of using beroe in the Caspian. Someone considers the expansion of the range of release of adapted individuals of Beroe ovata into the waters of the Caspian Sea and the need for all the Caspian states to join this struggle. Others believe such activities are futile. It remains to hope that due to the differences in natural conditions in the Caspian, the harmful invader will not be able to enslave him completely and lead to a total catastrophe.