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Mnemiopsis Leydyi in the Azov Sea

S. Volovik

When considering comb-jelly as a new though serious factor with an impact on the state of the marine ecosystem and fish stock of the sea, Azerbaijan Scientific Research Institute on Fishery carried out periodic studies on its biology, distribution, population dynamics, relationships with other components of biota as well as on the assessment of the invasive species’ impact on ecosystem.

The fact should be stressed that those studies were implemented simultaneously and as an addition to traditional ecological and fishery studies having been done in the Azov basin during 1927-1952 (based on individual components and parameters) and in the Black sea (since 1993).

In total the institute undertakes 18-22 tours in the Azov Sea and 4-5 – in the Black Sea on an annual basis with field materials on vessels and onshore stations collected by the institute employees additionally to the tours. Thus, the institute possesses sufficient information to provide real status of the ecosystem of the Azov Sea and Russian parts of the Black Sea while comparing the data with retrospective materials.

Works implemented enabled to gather extensive information, but the point I would like to draw your attention to is that there exists no single parameter of the state of ecosystem (its biota and fish stock included) not having been influenced by the consequences of the comb-jelly’s introduction. Part of the information obtained was provided in the book published in 2000 – “Comb-jelly Mnemiopsis Leydyi (A.Agassiz) in the Azov Sea and Black Sea: its biology and consequences of introduction”.

At this point, I would like to briefly exemplify the fact that influenced as a result of the impact of Mnemiopsis is the state of the entire marine ecosystem; there are no reasons to state the influence of any single ecological factor by the invasive species. At the same time it should be re-stressed the damage alone due to the loss of the haul in the Black Sea and Azov Sea (totaling accordingly to 240-340 and 40-43 mln US Dollars on an annual basis or 400-600 and up to 120 thousand tons) is tremendous and with social, ecological and other associated losses to be added to the list the amount gets even more enormous.

Some biological features of the invasive species. The species cannot live in the Azov Sea in winter time and therefore it dies. Every year Mnemiopsis enters the sea, behaving as an invasive species with all the ensuing consequences. Depending on the abundance of the comb-jelly in the Black Sea region, regime state of isolated parts of the sea, weather pattern in the region, zooplankton community status, intensity of the comb-jelly’s penetration and distribution, the population tend to change, though two scenarios could be actually highlighted. During the years with early entrance of the invasive species (April-May) before the comb-jelly acclimatizes in the entire water area of the sea, Black Sea khamsa and other pelagofile fish manage to finish spawning with their productivity and stock state significantly improving and during these years fishery of Black Sea khamsa and sardelle is deemed possible and realistic. During the years with early entrance there exist no conditions either for formation of productive posterity, stock growth or satisfactory fattening, those - compulsory for favorable migration, hibernation, further maturing of the producers as well as any fishery of Black Sea khamsa and sardelle. Biomass of the population during late entrance reaches 12-18 mln tons with that during early entrance amounting to 25-33 mln tons.

Here are some individual factors of the ecosystem having undergone changes due to the impact of the comb-jelly prior to and following introduction of the species:

  • turnover of biogenic elements (number of cycles) increased by 1.5 times;
  • increased number of carotinoids, organic substance in the bottom sediments; increased oxygen consumption rate by surface layer of soil almost by 1.5 times;
  • increased production of primary organic substance; varying rate of production and destruction processes;
  • increased production of microbial community in water column and sediments, varying structure of the community based on number and biomass of the dominating groups;
  • specific features in production of phytoplankton including changes in biomass of the community as a whole and its individual groups with those changes being both temporal and spatial;
  • slight changes in the zooplankton community: during July-August the biomass of the community reduced by 2-3 times. Enormous changes in the specific structure of the community;
  • in case of entrance during intensive reproduction of bottom organisms, the invasive species ate away meroplankton influencing in this way settling of young organisms of zoobenthos, replenishment level, structure and biomass of organisms in biocenoses;
  • influence of Mnemiopsis on pelagofile and planktonofile fish was extremely negative (over 11 year period their fishery in 8 cases was actually non-existent) through the mechanisms of reproduction, fattening, hibernation; influence on fish feeding on benthos;
  • the only positive effect recorded was that introduction of Mnemiopsis caused some increase in survival of the larvae of zander, though the effect was obtained due to its indirect impact.

Modern knowledge on biology and consequences of the comb-jellies introduction in the Azov-Black sea basin gave way to the following conclusions:

  1. Consequences of the introduction of comb-jelly in the Caspian will turn out even graver as compared to those in the Azov-Black sea region due to specific structure of biota of the Caspian ecosystem.
  2. There is no simple escape from Mnemiopsis: to mitigate its negative consequences specific measures are required.
  3. Experience of the Azov-Black Sea region testifies that distribution control of the invasive species is realistic and could be implemented as a result of practical measures. There exist some ideas on that point.
  4. Consequences of Mnemiopsis in terms of scope and negative pattern are comparable (if not exceeding) based on damage as a result of registration of outflow, pollution, damping and other types of anthropogenic impact.
  5. The fact that CEP has undertaken studies on the comb-jelly immediately following its introduction without waiting for this invasive species to change biota of the Caspian Sea is highly commendable.

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