Joint P.P.Shirshov`s Cruise
In accordance with the recommendations of SCC Meeting (Istanbul, 16-17 May, 2000) in August-November 2000, a multi ship joint cruise was realized for field observations in order to full fill the Project Tasks objectives. Four ships (one from Turkey, two from Russia and one from Bulgaria) participated to this survey.
The main goals of P.P.Shirshov`s Cruise were;
|to study the mesoscale hydrological structures and their influence on ecosystem of the Black Sea,|
|to study the interactions between shelf and deep sea water masses,|
|to study the state of Black sea ecosystem under unusual warm climatic conditions of year 2000,|
|to study the
long-term changes of the Black Sea ecosystem,
including the behavior of exotic species. such
as Mnemiopsis and Beroe .
During this expedition, two research vessels R/V Akvanavt and R/V Kvant - explored the ecosystem of the Black Sea in August-November. These studies includes the regular field observations as well as the special investigations on important processes taking place in the Black Sea ecosystem. Field works involved physical, chemical and biological studies.
Along with the field studies the set of experiments and measurements was done in land laboratories: growth rate and respiration rate experiments with ctenophores, processing of samples of phyto-, zoo- and bacterioplankton, analysis of satellite images of surface temperature distribution and others.
Observations were carried out during one day cruises in the shelf waters in the vicinity of town Gelendhjik in the northern-eastern part of the Black Sea; two cruises in August: 11 and 17; and two cruises in September: 23 and 28. Every cruise included a transect from a shore with 5 stations at a bottom depths of 10, 20, 40, 130 and 300 m. The following measurements were fulfilled in every cruise: bacterioplankton, microheterotrophes, ptytoplankton, zooplankton, macrozooplankton. The collection of jelly-fish organisms were done by net tows. Simultaneously, divers observed the vertical distribution and counted the numbers.
Ammount of bacterioplankton varied about 1000000 cell/ml and from 105 to 119 mg/m3 in outer shelf. In inner shelf the ammount of bacterioplankton was 1.5 times higher. This corresponds to the low mesotrophic level. Numbers of microzooplankton were low. Their total biomass varied from 50-60 mg/m3 in outer shelf and 70-100 mg/m3 in near shore waters. In subsurface layer these values were equal to 154-184 mg/m3 and to 227-257 mg/m3, respectively.
Among phytoplankton, pico-, nano- and microphytoplankton were represented in equal proportion (ca 30% by numbers) in subsurface water. By biomass, cyanobacteria dominated in outer waters, while cryptomonades, green and small peridinea prevaluated in inner shelf. In microphytoplankton the following species had principal meaning: Prorocentrum sp., Ceratium spp, Rhizosolenia spp., Nitzschia spp., Navicula spp., Chaetoceros spp. Vertical distribution of phytoplankton had a pronounced maximum at a depths of 30-50 m. It was formed by diatoms species Rhizosolenia spp. and Nitzschia spp. Their biomass was 10 times higher than that near the surface and reached 200-250 mg/m3. Thus, the main part of phytoplankton community was located near bottom of photic zone and was not under favorable growth conditions.
In spite of the large range of data it is seen that the numbers of Mnemiopsis in the bay and in the outer shelf waters were approximately of the same values. Only at station with 40 m depth the numbers of Mnemiopsis were lower than that at other depths. At this station the high ammount of medusa Aurelia aurita with the organism sizes from 20 to 100 mm were observed.
Average numbers (m3) and range (in brackets) of Mnemiopsis leidyi
|Pier (7 m)||500 (450-570)||145|
Analysis of age structure of population Mnemiopsis leidyi shows that it was rather similar on all sampling sites with the exception of station at 40 m depth. The most young part of population was more numerous in the bay, where the reproduction is taking place. At all stations more than one half of population was made up of young specimen from 10 to 20 mm. Only at 40m depth the population was more "oldest" . The latter and special features of this station mentioned above could be caused by intrusion of open waters to shelf. High numbers of Aurelia and high average size of Mnemiopsis are typical for open water.
In conclusion, it could be postulated that the structure and the quantitative level of population of Mnemiopsis leidyi did not varied broadly in shelf area. This permit to investigate the seasonal dynamics of this species in shelf waters based on regular observations which were took place in the Blue bay in 1998-2000.
In summer 1999 invasion of Mediterranean ctenophore Beroe ovata led to diminishing of Mnemiopsis leidyi. Nevertheless Beroe ovata was not observed in summer 2000. First specimen were registered in the Blue Bay only in September.
During the Black sea expedition in September 2000 the investigations of physiology of the ctenophore Beroe ovata were continued. 8 experiments were performed to estimate the digestion time of Beroe ovata of different size feeding on Mnemiopsis ledyii. It was found that this parameter strongly depended on the predator/prey size varying from 1.3 to 9.75 h. The egg production rate was evaluated for the ctenophore incubated for 24h after collection from the sea. In 3 sets of experiments the respiration rate of small sized ctenophores was measured. The obtained relationship described by the equation R=0.1W0.96 r2 =0.90, where R respiration rate, ÁlO2/ind/h, W dry weight, mg/ind.
The expedition started at November 1 and planed to be finished at November 30. It includes the field observations in three cruises. 1-st cruise focused on mesoscale hydrological structures and their influence on ecosystem of the Black Sea. This structure with the divergence zone in the central part of the sea was observed from satellite images in October. Field observations were carried out from November 1 to November 7. In cruise the physical, chemical and biological data were collected. Participation of Ukrainian scientist Dr. Stanichny in Russia expedition during November was funded by the ODBMS NATO Project. Second cruise was conducted from November 17 to November 23. The main task of the cruise was to study the interactions between shelf and deep sea ecosystems. Physical, chemical and biological data were collected. Finally the third cruise is planed from November 25 to November 30. This cruise will devoted to standard studies of the Black Sea ecosystem on transects from the shore to center of the sea. Special attention will be paid to chemical and hydrological measurements.