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The allocation of some pelagic larvae of bivalve mollusks in the western part of chukchi sea and the influence of abiotic factors on It

Delik Gabaev*, Natalya Kolotukhina

National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia

Abstract: For definition of spatial distribution of pelagic larvae of the bivalve mollusk in the Russian zone of Chukchi Sea in September-October 2016 in the 48th cruise of SRS "Academician Oparin" with the assistance of Norpac net with the cell of 150 μm at 30 stations in the horizon 15-0 m are took of planktonic samples. At once after catching samples were preserve in 4% solution of buffering formaldehyde, and in 2018, before the tests contents research they were washed out and fixed in 90% - m ethanol. The biggest quantity of pelagic larvae of the bivalve mollusk was found in the period from the 22nd of September until the 1st of October. The most yield area was situated on the opposite side of the Bering Strait (sum: 12,400 ind./m³) and on Bank Gerald (sum: 4,987 ind./m³). the most valuable factors influencing on the spatial allocation of the researched larvae are the water surface temperature and the water depth. The high abundance of larvae of the large bivalve molluscs allows to assume their successful cultivation in cold waters of Chukchi Sea.

Keywords: Chukchi Sea, pelagic larvae of bivalve mollusks, environment factors

Received July 04, 2019; Revised August 14, 2019; Accepted August 28, 2019

Citation: Delik Gabaev, Natalya Kolotukhina, The allocation of some pelagic larvae of bivalve mollusks in the western part of chukchi sea and the influence of abiotic factors on It. American Journal of Marine Science, 7 (1). 7-26. January 2019. doi:10.12691/marine-7-1-2

1. Introduction

The Chukchi Sea researching by the multi national collective of scientists was separated from the East-Siberian Sea not only due to its particular qualities of hydrological conditions but also in consequence of the peculiar content of the bottom dwellers [1]. There are significant stocks of oil, natural gas, coal, gold, tin, tungsten and mercury [2] on the coast and the global warming which is being observed during long years already [3,4] makes attractive the researching of the arctic seas where the Chukchi Sea is one of the most productive in the world [5,6]. The climate warming makes favor not only for the North marine way and the excavation of natural resources but also for the cognition and using of the arctic seas animal world. It is important to observe the Chukchi peninsula ecological conditions and its washing seas before the starting of its industrial development and it is important for the identification of the eco system changes after oil and gas production and commercial fishing [7,8]. After the short term of the Chukchi Sea researches conducted in the first part of last century the silent period has come but at the end of the last century and at the beginning of the new century stimulating by the shipping opportunities and oil production the interest to this Sea has arisen again. This Sea represents itself the unique region which is located at the edge of two oceans the Pacific and the Arctic. The Bering sea water [9] at estimate of 85 м³/per second comes to the Chukchi Sea in the significant degree through the Bering Strait together with the intensive stream system and the zooplankton [10] in estimate amount of 1.8 millions of metric tons annually comes together with this water. The warm Bering Sea water and the phytoplankton influx provide high productivity of the Chukchi Sea comparing to adjacent areas of the Arctic Ocean [11]. The water masses coming into the Chukchi Sea are represented by the coastal Alaska Sea water, coastal Bering Sea water and Anadyr Sea water (Figure 1), each one with its unique zooplankton community and quantity [10,12,13]. The local Chukchi Sea water was found only on the North of the Chukchi Sea and it was separated from the Alaska Sea water by the semi constant front which covers all the depth up to 70-71°N [14].

Some hydrographic peculiarities observing in the Chukchi Sea are the constant meanwhile the other peculiarities are changing and this way they become the very important determinatives of plankton and fishes allocation [15]. In summer the Bering Sea water (independently from the synoptic situation) are covering southern, eastern and partly central (until the Herald Strait) Sea areas [16]. Though in particular years, for example in 2007, almost all of the Chukchi Sea was filled with the Bering Sea water [17]. Taking into consideration the long years of observations the saltiness increases from west to east at estimate from 28 to 30-32 psu, near the ice edges it reduces till 24 psu and near the mouths of the rivers it reduces up to 3-5 psu [2]. The Winter water is very cold and salty under the cover of the water mass in the western Herald Canyon [18,19], leaving from the previous winter [20]. The winter temperature and the saltiness at the Chukchi seacoast have the inter annual differences nevertheless together with it they don’t have the same three-dimensional space during the time [21].

In summer 2004 the four underground waters and three water masses of the Chukchi Sea united by the depth were similar to other observations in the field of physical oceanography [14,18,19,21]. That summer the highest concentration of the chlorophyll-а was indicated in Herald Canyon area (200-300 mg chl-a/м²), in Bering Strait and near the Diomid Islangs the indications were (200-400 mg chl-a/м²) and the highest indications were in the area of cyclonic circulation between the Heart-Stone and Hope capes (200-500 mg chl-a/м²) [16]. In addition to the obvious changes in temperature, saltiness and the coastal sediment, the ecosystem of the Chukchi Sea probably will be able to switch from the benthic-dominant to marine dominant [22]. As the result of the meeting of the Bering Sea water stream and the Chukchi Sea water stream in the southern and middle parts of the Chukchi Sea the several circles of the cyclonic type [1,20,23] are being established, the biggest one from them is situated to the north and north-east from the cape Heart-Stone and Kolyuchinskaya Bay [24] and due to the low depth of the sea the autumn cycle increases the vertical flow of the material [25]. The impact of the Bering Sea warm waters with the Chukchi Sea cold waters leads to the mass death of south zooplankton and together with phytoplankton it enriches the benthos with the organic material [26].

Though the differences in time of ice melting, water temperature, water masses transportation, nutritions and chlorophyll-a make influence for the inter annual peculiarities of plankton communities [27]. In 2011 the plenty of the pelagic larvae of bivalve mollusk was higher in September/October and it reached 1,100 ind./м3 and if to compare the years of 2008, 2009, 2010 and 2011 its the biggest quantity was in Klondike in September (more than 30,000 ind./м³) and even bigger in Statoil in October (around 48,000 ind./м³) [27]. The stream directed to the North dominates in a year that’s why the inter annual changes of balanus larvae and larvae of bivalve mollusk plenty (which were not met during the summer 2012) were called by the water masses in summer 2012 came from Canadian bays which waters due to the high depths consist of a little amount of benthos animals [28,29]. In 2007-2010 the grade of ice coverage of the Chukchi Sea showed the 40% reduction in September comparing with the measuring made 20-30 years ago [30], and in 2012 the samples of zoo plankton community were strongly connected with the temperature in water depth [27]. The temperature of natural water lay and the bay depth make the determining influence on the quality and quantity content of the benthos [31], geomorphology biocenosis allocation, hydrodynamics, type and granulometric content of bottom sediments [32], and also as geochemical content of sediments as of bottom water [33]. The benthos biomass mainly is controlled by the food coming produced from the water surface and which was reached the bottom through pelagic-benthos connecting processes [32]. The same way the space models in macrofauna biomasses of the Chukchi Sea are connected with the variations in pelagic primary production and carbon flow to the ocean bottom under the different masses [22,34]. Due to the low depth of the Chukchi sea the part of phytodetritus coming on to the bottom from the surface waters is the highest one that’s why with the almost three times less square then the Barintsev Sea square the Chukchi Sea zoobenthos bio resources are less then the Barents Sea one’s only for one and half times [4]. Though the sediment carbon and the integrated chlorophyll-a concentration give no explanations the biomasses differences of the epifauna as the variation of food plenty doesn’t correlate with macro fauna biomass [22]. The highest benthos biomass is peculiar for the south-east part of the Sea to the north of Bering Strait which reaches up to 4,231 g/м² with the average biomass of ~1,500 g/м² in this area and the lowest biomass is peculiar for its northern and deeper part [35]. In the estuarys of the rivers the benthos biomass mainly is less then in the water area exclusively with sea waters [36].

In spite of the quite long research period of the bottom ecosystem of the Chukchi Sea started at the end of the 19th century and it is still not studied quite well [3] and for the studying of the sea bottom communities and the sea mammal animals the insignificant researches were made [6]. It is possible to make a conclusion that in the Barrow and Herald canyons (trenches) the quite high values of zoobenthos biomass are observed – up to 4,400 g/м² and up to 600 g/м² relevantly, unlikely from the Hanna and Herald Bays’ benthos biomasses which are characterized by rather low values – 10 –130 g/м² and 50–120 g/м² relevantly [8]. The species diversity (more then 1,435 species) of the Chukchi Sea bottom biocenosis is higher then in other east-arctic seas: 1,143 – in the Laptev Sea and 1,008 in the East-Siberian Sea [37]. Like every other Eurasia arctic seas the Chukchi Sea has invertebrates dominating groups inzone allocation [38], and the allocation of bivalve mollusk biomass reminds the allocation of common zoobenthos biomass [4]. On the south of central and south-east part of the Chukchi Sea it was noted the existence of significantly high productive benthos communities with extremely high biomass and biodiversity created most likely under the influence of the water circles rich with biogens that comes through the eastern part of Bering Strait [39]. On the slope of Herald’s bank, at estimate 10 to 25 km from its center, comparing to the top, the biodiversity in increasing and the bivalve mollusk and polychaete dominate in biocenosis [40,41]. The analysis of benthos data in Chukchi Sea doesn’t show any significant changes for the last 30 years, though the local penetration in it of quite warm water pacific species: crabs Telmessus cheiragomis and Oregonia grasilis and bivalve mollusk Pododesmus macrochisma indicate on its warming [3]. This way, the potential consequences of the climate change for the benthos of the Chukchi Sea there are moves in its species content and quantity to the north [42] and in warm years it is possible the reproduction conditions’ improvement among thermophilic invertebrates [42,43,44]. That’s why it is possible to assume that in future the movement direction of boreal species to the north will be saved with the replacement of trade arctic species [8,45].

Figure 1. The most recent scheme of the Chukchi Sea circulations and geographical place names. Adopted from Ref. [79]

The reproduction dynamics of the researched by us the two species of bivalve mollusk and the climatic factors demonstrate quasi two-year frequency [46]. The comparison of five year dynamics of zooplankton quantity in American part of Chukchi Sea (2008-2012) showed that many species including the larvae of bivalve mollusk favorably reproduced in 2010 with the intermediate temperatures [27,47]. The average global temperature of the Earth surface in 2016 was at 0.06 °С higher then in 2015 and became the highest since 1880 (like the ocean surface temperatures) [48]. That’s why many questions of meroplankton dynamics and also time and space allocation of larvae plankton need to have the modern researches called by the climate change [2,49].

The larvae of bivalve mollusk appearing starts in spring and summer and phytoplankton is considered as the spawning regulator [2]. Though the Far East coast global warming is characterized by severe winter and hot summer [46]. Due to high ice thermal capacity and marine water and also slow spring heating [50] the benthos animals spawning in Arctic can get late and lead to the spawning period narrowing [51,52], and the low temperatures which make the physiological processes slow lead to increasing of plankton period [53,54].

The available publications, as a rule, do not reveal the peculiarities of even mass species allocation, and in the tables characterizing structure of the meroplankton on explored water area the bivalve mollusk either are absent [55,56] or presented in the total quantity [13,47,57,58]. There of, the authors do not give the factors affecting abundance and area allocation of types and species. From the available literature regarding meroplankton of the polar seas it is known the only one work researching seasonal allocation of three species and one type of pelagic larvae of the bivalve mollusk [49]. That’s why our publication, partly, can help the researchers wishing to define types or species larvae of bivalve mollusk of the Chukchi Sea and to specify their area allocation and the defining factors. The research in abnormally warm 2016 represents close to the reality the picture of future changes of abundance and area allocation of some species and genus of the pelagic larvae of bivalve mollusks in the water area of the Chukchi Sea.

The aim of the present research is to identify the pelagic larvae of the bivalve mollusks of the Chukchi Sea and to study their allocation area and abundance in relation with the abiotic factors influencing on these processes.

2. Material and methods

The 48th cruise of the SRS “Academician Omarion” was 48 days since the 2nd of September till 19th of October 2016. Since 12th of September till 5th of October 2016 the researches made on the polygons of the Chukchi Sea. During the expedition to the 30st station in Chukchi Sea and Bering Sea the works on sea plankton collecting by the Norpak net with the diameter incoming hole of 39 cm and the cell 150 μm (Table 1). At all stations the Norpak net was lowered on the depth of 15 m, though in the Bering Strait and near the Ratmanov’s Island due to the strong stream it was not possible to lower the net deeper then 4 meters. Right after the meroplankton tests taking it was fixed in 4% solution of buffering formaldehyde, and in 2018, before the tests contents research they were washed out and fixed in 90% - m ethanol. The tests of plankton were researched with the help of Bogorov camera and binocular microscope MBS-10. At mass species of bivalve mollusks the shell length and height were measured. The coauthor of this message (Kolotukhina N.K.) has wide experience of work with the planktonic and recently settled larvae of bivalve mollusks [59,60,62,63,71], therefore the cosmopolitans were defined up to type and the Chukchi Sea autochthonic larvae up to a species. Together with the plankton catching by the means of Sigsbi trawl and Van-Vin's bottom scooper the benthos samples were taken and by the Sekki disk the water transparency was defined. The authors identified the species content larvae of bivalve mollusks on adult bivalve mollusks in the benthos tests. In order to get the material of the station which compares to the previous test researches, the sampling was located at the same coordinates as it was indicated in those publications.

The materials on mineral forms of biogenous elements including phosphorus, several forms of nitrogen (nitrates, nitrites, ammonia), silicon and also oxygen, the contents of phytopigments (chlorophyll a) and also surface and bottom water temperature at the 26st station were provided by the authors of Propp L.N. The main parameters of the water environment were received by the means of profilograf SEACAT Profiler CTD model SBE 19plus V2 Sea-Birds Electronics Inc. production intended for the continuous automatic measurement of the sea water number of parameters: pressure, depths, temperatures, salinity, firmness of water, oxygen concentration, the saturation degree of oxygen in the water, the content of chlorophyll-a, turbidity, photosynthetic active radiation (PAR), pH, sound speed, descent and rise speed. Some parameters – surface and bottom water, surface and bottom oxygen concentration and also biogenius elements and chlorophyll – a concentration were researched by Propp L.N., Odintsov V.S. and it was sounding the same time. The water tests for the researches were taken by the Niskin’s batometers.

The statistical material processing was executed with the help of the program STATISTICA 6 [64] and tested at the level of α = 0.05. The graphic material for the publication was made by the means of the probe – the profilograph SEACAT Profiler CTD, Serfer 7 Golden Software, and Excel 2007.

Table 1. Information of ship-board experiments on the west the Chukchi Sea during September-October 2016

3. Results

3.1. abiotic factors of environment

Figure 2. Distribution of temperature of water and salinity at some stations at the Chukchi Sea, received with the help sound - profilograph

On the researched water area which the ice was removed only in August the data showed with the probe – profilograph the existence of a thermocline and halocline on many stations of the Chukchi Sea excluding coastal stations and the stations close to Bering Strait (Figure 2(a), Table 1). The water near the Vrangel and Herald Islangs is characterized as intermediate warm layer and negative temperatures in depth (Figure 2(a,b), Table 1). The profiles of salinity at the stations with one thermocline are almost the mirror reflection of the temperature profiles (Figure 2 (b,c)). Within this the profilograph data let to see the zones of water mixtures various in characteristics. So, on the same horizons of St. 10 and 11 they are observed both on the temperature and salinity profiles (Figure 2 (b, c)).

The hydrochemical mode of the Chukchi Sea is caused by difficult and active hydrodynamics of multidirectional streams of the Pacific water masses coming from the South through the Bering Strait and pushed from the North cold waters of the Arctic basin (Figure 1). In South Stream penetration to Herald island process, his speed decreases and it is possible to consider from water transparency increase from 2 to 18 m which is observed by the means of Sekki disk. In the areas with depths up to 50 m located to the west of the main core stream there is an intensive sedimentation. The layer of temperature jump at these stations (17 and 18) falls up to 30 m where below as a result of organic material destruction the oxygen absorption happens and it leads to its sharp decrease at a bottom by 2-3 times in comparison with a surface which is 2.9 ml/l (Table 1). These stations differ in abundance of benthos vital forms including bivalve mollusks. At shallow stations (4, 5, 7, 13) the favorable conditions for development of phytoplankton are created. As a result, due to seaweed active blossoming, the oxygen concentration at a bottom 3-10% exceeds then at a surface (Table 1). The micro seaweed abundance can be visually observed in the samples taken by planktonic net (Figure 3).

Figure 3. Two tests of water taken by planktonic network Norpac, on productive and not productive stations

The allocation of biogenies elements followed the processes going in vertical water column and their absorption in seaweed development process unites the biogens concentration at a surface (Table 2). For example, the phosphate content at the surface waters at the stations with the depth of 50 m in average was about 1 μM, and at a bottom – 2.8 μM (Table 2). On the same time at the station 10 with the depth of 95 m (Herald canyon), the phosphate content at a bottom was 5.5 and at a surface – 9.8 μM relevantly. Within this the surface waters of more southern stations (15-24) were less rich with biogenies elements and the phosphate content in those districts did not reach 1.0 μM, and the nitrite concentration did not reach 3.0 μM (Table 2). The nitrite concentration at surface tests at many station was various from analytical 0 and rises with the depth. The same tendency observed and in relation to ammonia: at average it increased from 0.61 to 5.0 μM relevantly. It’s maximum definitions 16.6 and 11.1 μM were related to low horizons at the stations, where the abundance of benthos organisms producing metabolism (st. 0 and 18 relevantly) products was noted. Moreover at the St. 18 the difference of biogenies elements content between the surface and bottom reached of maximum reading (Table 2).

The closest Euclidean distance was noted in salinity indications received by the means of analytic methods and probe between the oxygen content at a bottom and the carbon at a surface, between the oxygen concentration at a surface and environment pH, also the concentrations of chlorophyll-a at a surface and N-NO₃ (Figure 4(a)). The nonparametric multidimensional analysis of the environment showed that the water temperature at a surface and at a bottom, the concentration of chlorophyll-a and water salinity were the closest to the area latitude (Figure 4(b).

Figure 4. clustered analysis, none-metric multidimensional scalling (MDS) relationships and the diagramme of contents of planktonic tests at stations in the Chukchi Sea. a- relationship of abiotical factors at stations, b - relationship abiotical factors with latitude region, c - percentage of composition of species in planktonic tests, d - relationship between stations on structure of larvae, e - relationship between stations on abiotical factors, f - relationship between species at stations

Table 2. Some abiotic parametres observed in September-October 2016 on the west the Chukchi Sea

3.2. The Allocation of pelagic larvae of the bivalve mollusks

3.2.1. Zirfaea spp.

The quantity of Zirfaea spp. larvae (Figure 5 (a)) in our tests was low, and the maximum value (18 ind./m³) was revealed at the st. 15 (69 °01’N; 169 °16’W) (Figure 6(a)) where the depth was 50 m (Figure 7(a), Table 1). Water temperature at a surface reached 5.9 °C and at a bottom decreased to 1.1°C (Figure 7 (b, c), Table 1). Zirfaea spp. larvae abundance mostly depends on water temperature at a surface and water area depth (Figure 8(a) and between the number of this species and the water temperature on a surface there is a reliable interrelation (r = 0.46) (Table 3). The largest frequency of Zirfaea spp. larvae occurrence was observed from Provideniye Bay to the Heart-Stone cape (Figure 4 (c) and Figure 7(d)). Total larvae quantity in our tests was 0.38%. The average shell length was 302.5 34.4 μм, and the height - 285.0 50.1 μм.

Figure 5. Appearance investigated of pelagian larvae of the bivalve molluscs. a - Zirfaea spp., b - Kellia spp., c - Macoma spp., d - Mactra spp., e - Mya spp., f - S. groenlandicus, g - Chlamys spp., h - H. arctica

3.2.2. Kellia spp.

In allocation of Kellia spp. larvae (Figure 5 (b)) it is observed the one obvious larvae top number (163ind./м3 ) at st. 12, situated near the Herald Bank, over the depth of 42 m (70°32' N; 173°05’W) (Figure 6(b); 7(a)) and the positive temperature at a bottom and at a surface 1.5 and 3.8°С relevantly (Figure 7 (b,c), Table 1). Taking into consideration our observations, mainly the abundance of this specis larvae depends on environment рН at a surface and in depth of water area (Figure 8 (b)). The abundance of this type larvae from the total quantity of all bivalvia larvae in our tests was 2.5%. The average length of Kellia spp. larvae shell was 378.3 ± 20.7 μм, and the shell heigh - 309.2 ± 18.2 μм.

3.2.3. Macoma spp.

In allocation of Macoma spp. larvae (Figure 5 (с)) it was observed two water areas with maximum quantity. The first one, with the quantity of 420 ind./м3 – st. 6, was situated near the Herald Bank (Figure 6c) (70°31’N; 177°26’W) over the depth of 50 m with the negative water temperature at a bottom – 1.6°С, and at a surface 2.3°С. (Figure 7(a, b, c), Table 1). The second one with the biggest quantity – st. 19 (520 ind./м³) was situated over the depth of 48 m (67°27'N; 172°33’W) and was close to the Heart-Stone cape (Figure 6 (c), Figure 7(a), Table 1). At that station the water temperature at a surface and at a bottom was positive (4.6 and 3.1°С relevantly) (Figure 7 (b,c), Table 1). The highest frequency of this species of larvae was observed near the Bering and Herald Islangs. (Figure 4 (c); Figure 7(d)). The Macoma spp. larvae abundance mainly depends on environment рН at a surface and in depth of the water area (Figure 8 (с)). Total quantity of Macoma spp. larvae from the total quantity of bivalve larvae in our test was 14.0 %.

3.2.4. Mactra spp.

The Mactra spp. (Figure 5 (d)) larvae were met only at three stations (st. 6, 15 and 25). The maximum quantity of the larvae was observed at the st. 25 (Figure 6 (d), Table 1) (67°39'N; 173°24’W) (227 ind./м³) and almost one time less they were at the st. 15 (Figure 6(d), Table 1) (69°01' N; 169°16’W) (24 ind./м³), and at the st. 6 (Table 1) (70°31’N; 177°26’W) in four times less then at the st. 15 (6 ind./м³) (Figure 6(d)). At the st. 6 and 15 the depth was similar - 50 m (Figure 7(a)). The water temperature at the st. 15 at a bottom and at a surface was positive (1.1°С and 5.9°C relatively), and at the st. 6 at a bottom it was decreased down to negative points (-1.6°С) and at a surface it reached only 2.3°С (Table 1). At the st. 25 with the big quantity of larvae the depth and the latitude were less then at the previous stations and the temperature at a bottom was maximum (1.5°С), and at a surface it reached intermediate points between the comparable stations (4.2°С) (Table 1). Mainly the chlorophyll-a concentration at a surface and water area depth influence positively for the Mactra spp. larvae abundance (Figure 8 (d)). At the stations with the maximum quantity of the larvae the high concentration of chlorophyll - a was observed (Figure 7(e)). The Mactra spp. larvae authentically negatively correlate with environment pH (r = - 0.95) and authentically positively with the concentration of chlorophyll-a at a surface (r = 0.65) (Table 3). In our tests this species was represented in the smallest quantity (0.22%).

Figure 6. Spatial distribution of investigated larvae. a - Zirfaea spp., b - Kellia spp., c - Macoma spp., d - Mactra spp. e - Mya spp., f – S. groenlandicus, g - Chlamys spp., h – H. arctica, i – M. trossulus

Table 3. Pearson correlation coefficient between abiotic parametres and the abundance of pelagian larvae of bivalve molluscs in September - October 2016 on the west the Chukchi Sea. The bold print are dedicated reliable coefficient of correlation

Figure 7. Spatial distribution of some abiotical parametres and contents of planktonic tests. a - depth of investigated of water area, b - temperature of water at a bottom, c - temperature of water at a surface, d - variability in space of contents of planktonic tests, e - concentration of chlorophyll - a at a water surface, f - total distribution of investigated larvae of bivalve mollusks

Figure 8a-h.

Figure 8. none-metric multidimensional scalling (MDS) relationships spatial distribution of investigated larvae and factors of environment. a - Zirfaea spp., b - Kellia spp., c - Macoma spp., d - Mactra spp., e - Mya spp., f - S. groenlandicus, g - Chlamys spp., h - H. arctica, i – M. trossulus, j- relationship of summarized quantity of the investigated larvae at station with factors of environment, k- relationship of spatial distribution of the investigated species with factors of environment, l- similarity of spatial distribution between the investigated species

3.2.5. Mya spp.

In the allocation of Mya spp. (Figure 5(e)) larvae the significant gathering was observed at four stations (Figure 6(e)). At two closely situated stations in the area of Herald Bank (st. 12 and 13) with the depth 42 and 20 m (70°32'N; 173°05’W; and 70°32’N; 172°05’W relatively) the larvae quantity was quite close (275 and 203 ind./м³ relatively) (Figure 7(e), Table 1). The water temperature at a surface of those stations was similar (3.8 and 3.9 relatively), though at a bottom there were significant differences in water temperature (1.5 and 5.0°С relatively) (Table 1). The second larvae gathering with little less quantity (200 ind./м³) (Figure 6(e)) was found at the st. 17 (67°26' N; 169°37’ W) with the depth of 50 m and the bottom temperature 2.6°С, and surface temperature 5.1°С (Table 1). At the st. 25 (67°39’N; 173°24’W) with the maximum larvae quantity (480 ind./м³) (Figure 6(e)) water temperature at bottom, as at the st. 12 was (1.5°С), and at a surface reached (4.2°С) (Table 1). The hugest abundance of Mya spp. larvae was represented at the stations closed to the north-east coast of the Chukchi peninsula (Figure 4(c), Figure 6(e), Figure 7(d)), and the most important factors, determining their abundance were depth and chlorophyll concentration at the seawater surface (Figure 8(e)). At the seawater area with such quantity of larvae it was observed the high concentration of chlorophyll-a (Figure 7(e)). The abundance of Mya spp. larvae authentically positively correlates with chlorophyll-a concentration (r = 0.42) and authentically negatively with environment рН (r = - 0.65) (Table 3). Total quantity of Mya spp. larvae in tests was 8.0%.

3.2.6. Serripes groenlandicus

The Serripes groenlandicus larvae (Figure 5 (f)) the maximum abundance was noted at the st. 17 (880 ind./м³) (67°26’N; 169°37’W) (Figure 6 (f) with the seawater depth 50 m (Figure 7(a), Table 1), at the st. 18 (67°31'N; 171°22'W) with the reducing of the depth till 48 m the larvae abundance reduced almost twice (460 ind./м³) (Figure 6(f), Figure 7(a)). The water temperature at water surface at the st. 17 and 18 reached 5.1 и 5.3°С relevantly. And at the st. 17 from the surface to the bottom it was reducing almost in two times (till 2.6°С), at the st. 18 – more then two times (till 2.3°С) (Table 1). As many other types researched by us the most valuable factors influencing for the S. groenlandicus larvae abundance were the depth and the water temperature at the sea surface (Figure 8(f)). The S. groenlandicus larvae spatial allocation authentically negatively correlates as with bottom oxygen concentration (r = -0.50), as with silicon concentration at water surface (r = -0.41) (Table 1). The highest frequency of that species was noted at shallow water – near the Herald Bank and near the Vrangel and Herald Islands (Figure 4(c), Figure 7(d)). The quantity of S. groenlandicus larvae in our tests was 15.3% from total quantity of bivalvia larvae. The average shell length reached to 262.0 ± 8.9 μm, and height - 225.5 ± 9.8 μm.

3.2.7. Chlamys spp.

The allocation of Chlamys spp. (Figure 5(g)) larvae was found only one gathering in two closely situated stations near the cape Point-Hope (Alaska): st. 15 (69°01’N; 169°16’W) and st. 16 (68°11' N; 169°1’ W) (Figure 6(g)) with the bottom temperature 1.1°С and 2.7°С, at the surface 5.9 and 6.7°С relatively (Table 1). At the station 15 the Chlamys spp. abundance was 15 ind./м³, at the station 16 - 38 ind./м³. The strongest influence on the larvae quantity of that type makes the dissolved organic carbon at a water surface and environment рН (Figure 8 (g)). Also the Zirfaea spp. larvae the quantity of Chlamys spp. larvae in plankton authentically positively correlates with the temperature at the water surface (r = 0.46) (Table 3). The total quantity of Chlamys spp. larvae in our tests was 0.52%. The middle length of their shell was 261.5± 5.4 μм, and the height - 238.1 ± 5.4 μм.

3.2.8. Hiatella arctica

The Hiatella arctica (Figure 5 (h)) larvae showed the highest abundance in our test. Three stations with the maximum quantity of larvae (st.16, 17 and 18) (867, 2,000 and 4,120 ind./м³ relatively) were situated at closed latitude: (68°11'N; 67°26’ N and 67°31' N ). But the longitude of the stations was more different (169°1'N; 169°37’N and 171°22'N relatively)(Table 1) Those stations were situated north-east from Dezhnev cape, opposite Bering Strait (Figure 6(h)). The highest frequency of that species larvae was noted from the Ratmanov island till Kolyuchinskaya Bay (Figure 4(c), Figure 7(d)). The H. arctica larvae abundance was increasing significantly with the depth reducing (58 m, 50 m and 48 m relatively)(Figure 4 (c), 7(a, d)). Though the water temperature as at the bottom (2.7°С, 2.6°С and 2.3°С relatively), as at the water surface was reducing (6.7°С; 5.1°С and 5.3°С relatively) (Table 1). As for many previous types the most valuable factors defining the H. arctica larvae quantity were the water area depth and the temperature at the seawater surface (Figure8(h)). As Mya spp. and Mactra spp. the abundance of H. arctica larvae authentically positively correlates with chlorophyll-a at the water surface (r = 0.47), also as S. groenlandicus authentically negatively correlates with the oxygen concentration at the bottom (r = -0.56) and with the silicon concentration at the seawater surface (r = - 0.40) (Table 3). The total quantity of H. arctica larvae in our tests was 58.7%. The average shell length was 312.6 ± 4.7 μм, and height - 295.0 ± 5.5μм.

3.2.9. Mytilus trossulus

M. trossulus (Figure 5(i)) larvae was in small quantity in our tests. A number up to 13 ind./м³ was found only at two nearly situated stations 12 and 13 in the district of Herald Bank (Figure 6(i)). The latitude of those stations was the same (70°32' N) and only longitude at the station 12 one degree western, then at the station 13 (173°05' W and 172°05' W relatively) (Table 1). The depth at the station 12 was deeper at the station 13 more then two times, and the differences in water temperature at the bottom were more significant (1.5 and 5°С relatively) (Table 1). At the same time the water temperature at the seawater surface at those stations was similar (3.8 and 3.9°С relatively) (Table 1). The water area depth and the water temperature at the surface (Figure 8(i)) made significant influence on M. trossulus larvae density and its total quantity was 0.43% in our tests.

The biggest quantity larvae of bivalve mollusks were observed by us at the stations 17 and 18 (Figure 7(f)), situated in the zone of water circle, appearing during the collision of Anadyr seawater directed to the north-west of Chukchi Sea and coming from the west of Siberian Coastal Stream (Figure 1). During the removing from the Bering Strait the abundance of the H. arctica and Zirfaea spp. larvae was reducing and S. groenlandicus and Macoma spp. was increasing and at the Islangs of Vrangel and Herald those species demonstrated the highest frequency (Figure 4 (c); Figure 7(d)). Also at the bottom the huge quantity of up mentioned bivalve mollusks were found. The larvae of five most numerous species such as H. arctica, S. groenlandicus, Macoma spp., Mactra spp. and Mya spp., were met in its abundance at those stations where the highest temperatures at a bottom and at a surface and maximum chlorophyll-a concentration were noted (Figure 6 (c,d,e,f,h); Figure 7(b,c,e)). The comparison of researched larvae types spatial allocation with abiotic factors shows that mainly the larvae abundance weakly depends on environment, as the larvae allocation at the stations often doesn’t match to the parameter indicators of the environment (Figure 4(d, e), Table 3).

Taking into consideration the similarities of spatial allocation of the researched species of pelagic larvae mollusk divide in three groups (Figure 8 (l)). The first group consists of two the most massive species (H. arctica and S. groenlandicus). The second group consists of two species with low quantity (Chlamys spp. and Zirfaea spp.), and the third group consists of five species (Kellia spp., Macoma spp., Mactra spp., Mya spp. and Mytilus trossulus) with the average numbers of larvae quantity (Figure 8 (l)). The seven of nine researched species have the spatial allocation peculiarity. Their abundance is increasing in south-west or in north-east of the Chukchi Sea. In another words those species like more cold and find for them the optimal temperature in cold stream from the East-Siberian sea (south-west part of the Chukchi Sea) or in the north-east of the Chukchi Sea where the warm waters of Bering Sea are driven out by the cold sea waters (Figure 9 (b, c, e, f, g, h, i); Figure 1). And only in two species of Zirfaea spp. and Mactra spp. are observed the obvious abundance increasing in the north-west Russian part of the Chukchi Sea where the warm waters of Atlantic are reaching (Figure 1), or in south-east, where the warm waters of Bering Sea are reaching. (Figure 7 (b,с); Figure 9(a, d)).

Figure 9. Dependence of spatial distribution of investigated larvae from the longitude and latitude of stations. a - Zirfaea spp., b - Kellia spp., c - Macoma spp., d - Mactra spp. e - Mya spp., f – S. groenlandicus, g - Chlamys spp., h – H. arctica, i – M. trossulus

The high similarity between the stations in spatial allocation of pelagic larvae is observing near the north-east coast of Chukchi peninsula and in water area closed to the Islangs of Vrangel and Herald (Figure 4(c), Figure 7(d)). The comparison of bivalve larvae species abundance in Russian waters of the Chukchi Sea and the environment factors influencing on its quantity showed at the stations with the maximum quantity of larvae (st. 16, 17 and 18) as in factors as in larvae it is is observed close Euclidean distance (Figure 4 (d, e)). Meanwhile at the stations with less quantity of larvae the environment factors influence on its allocation is not so significant (Figure 4 (d, e)). The cluster analysis of spatial allocation of researched species observed the maximum close distance between M. trossulus, Zirfaea spp., and Chlamys spp., and the maximum far distance was with H. arctica (Figure 4 (f)).

Nonparametric multidimension scaling showed that the total amount of larvae on researched territory mainly depend on station depth and the water temperature at a surface (Figure 8 (j)). Total quantity of larvae spatial allocation demonstrates three top character with the highest population number opposite the Bering Strait and less number near the Herald Bank and the lowest one at the Kolyuchinskaya Bay (Figure 7(f)). At least in two water areas with the highest total amount of larvae there were observed the high concentrations of chlorophyll-a (Figure 7(е)). Though the research of percentage correlation of the species at the stations showed the abundance of H. arctica, Zirfaea spp., Mya spp., M. trossulus, Chlamys spp., and also Mactra spp. closer to the north reduces and at Macoma spp. and S. groenlandicus increases (Figure 7 (d)). It is characteristic that at the stations with maximum larvae density caused by high density of H. arctica larvae, the other larvae species are significantly less (Figure 4(c); Figure 7(d)).

The stations depth where the total quantity of the larvae exceeded 3,000 ind./м³ was 42-58 m (Figure 7(a), Table 1). At those stations the water temperature at a surface was 4,0°С higher, and at the bottom it reduced less then 1,5°С (st. 12, 16, 17, 18, 25) (Table 1); Figure 7(b, с)). At the same time at the stations with low larvae abundance the water temperature was as a rule less then 4°С (st. 4, 8, 11, 14 and 21) and at the bottom it reduced usually till negative amounts (Table 1; Figure 2).

4. Discussion

The research of the abiotic parameters of the environment in russian sea waters of Chukchi Sea in autumn 2016 showed that significant influence on the water mass allocation, temperature at a bottom and at a surface makes warm water of the Bering Sea which is coming through the Bering Strait. Directed to the north the streams make significant influence as on physical properties as on entire ecosystem of all Arctic Ocean [65]. This is very huge source of non salty water [66], warm and biogens for Arctica [67], helping to the ice melting [18] and stimulating primary production in the region [3,11,22,26,62,69,70,71,72]. Many researches confirm the positive influence of Bering Sea to the productivity and biodiversity of Chukchi Sea [11,16,17,55,71,72,73]. Especially it is visible the influence of Bering Sea from the eastern part of researched by us area where the summer water comes appeared by the mixture of rich with biogens Anadyr sea water with non salty water of Bering shall [20,72]. That’s why the observed by us isotherms shows not but meridional allocation: to the east of researched water area bottom waters are with the temperature of + 2°С and the surface waters with the temperature of + 4°С penetrate easily far away to the north in “tongue” shape (Figure 7(b,c)). Probably such isotherms allocation is the result of the Anadyr seawater is colder then Bering Sea shall water [20,72].

The collision of several streams in the district of Herald Bank leads to the convergence about what the hydrological data approves in particular sharp changes of oceanic characteristics [69]. The probe of prophylograf data also revealed zones of mixture of different in characteristics waters where on the same horizons at st. 10 and 11 it is visible the change as per temperature as per saltiness (Figure 2(b,c)). Especially there is strong influence of Bering Sea to the south of Chukchi Sea [20,74]. The southern and especially south-east water areas are characterized by the average annual deficiency of silicates caused by high primary products in these areas [16].

In spite of the meridional distribution of water temperature in the sea and also saltiness and chlorophyll-a at the surface (Figure 7 (b,c,e), they mainly are connected with latitude of the station (Figure 4(b)). Probably it is explained that between latitude and longitude of our stations there is high correlation (r = 0.998, p = 0.00). The close distance between Chl – a, P-po₄ и N-NO₃ (Figure 4(a)) is possible to explain by the photosynthesis dependence from the concentration of nitrogen and phosphor mineral compounds and the correlation between water temperature at the bottom and ammonium nitrogen (Figure 4(a)), probably, it was called by the stimulating temperature influence on the activity of epi- and infauna, producing the base for the ammonia appearing. Close indicators between environment рН and oxygen content at the water surface (Figure 4(a)) it is possible to explain with global warming leading to the reduction of oxygen solubilities, increase of CO₂ concentration and the result of microbiological oxidation of diatomic seaweed huge biomass. Global warming and the changed ocean streams reduce subsurface oxygen concentrations, and the increasing atmospheric CO₂ leads to the oceanic oxidation [75]. The correlation of Corganics concentration at a surface with the O₂ concentration at a bottom (Figure4(a)) it is possible to explain with the abundance of the died-off cells falling on a bottom as a result of microseaweed blossoming on which destruction the oxygen at the bottom is absorbed. The spatial model of primary production well coincides with the distribution of rich organic material which can be the subject of denitrification [76]. The reliable negative correlation between the content of oxygen and saltiness at a surface (Table 3) can be explained with the coming of less salty enriched with oxygen Alaska water to the Chukchi Sea [16].

Our observations of nine species of pelagic larvae of the bivalve mollusks in the Chukchi Sea revealed the correlation of larvae allocation of four species (Zirfaea spp., S. groenlandicus, H. arctica, and M. trossulus) and also total larvae allocation quantity related with water temperature on a surface and water area depth (Figure 8 (a, f, h, i, j)). The settlement of pelagic invertebrates benthos larvae was stimulated with the highest temperature during the long period of time [77]. Therefore it was found in Bering Sea the independence of meroplankton total density from water temperature and geographic latitude [60], most likely it is possible to explain with a large number of the studied species of a meroplankton having various thermopathy. Water temperature influences to the sea invertebrates spawning beginning [78], the duration of the pelagic period [53,54] and the reducing of time that larvae spend in water column can increase their survival [2,79,80]. Indirect influence of water temperature is noticeable also when studying the correlations between the total number of larvae and the water area depth (Figure 8 (j)).

The positive temperatures at the bottom and at the surface, probably, affect positively on the microseaweed reproduction, mollusk spawning and the duration of pelagic stage. In warm water areas we registered the maximum of larvae quantity as per four species as per total quantity of all researched species of bivalve mollusks (Table 1). Those stations were situated near the Bering Strait where the collision of Bering sea warm waters happens with the cold waters of Arctic (Figure 1). The huge income of zooplankton from Bering sea together with the phytoplankton communities provide high productivity of Chukchi sea comparing to the intermediate sea areas of the North Arctic Ocean [11]. The biggest quantity of diatomic seaweed was observed in the central Chukchi hollow and in the central Chukchi gutter where the highly productive Bering shelf waters flow [81].

Inflow of these "rich" Pacific waters defines the reproductive success as per brought zooplankton as per local zooplankton communities [11,13]. The high authentic relation between allocation three species of bivalve mollusks - H. arctica, Mya spp. and Mactra spp. and the abundance of chlorophyll-a (Table 3, Figure 7 (e), Figure 8 (d,e)) can explain the high density of up mentioned species at the water areas with the high chlorophyll-a concentration (Figure 5 (d,e,h); Figure 7(e)). The spatial allocation of density and the content of meroplankton correlates with the temperature change, saltiness and the chlorophyll-a [56], and the high density of larvae is positively connected with the high chlorophyll-a concentration [3,49,56,68,82]. Probably, at the stations with obvious dominance of one species the reduction of another species quantity (Figure 4(c); Figure 7(d)) is also called by the trophic factor.

The changes of phytoplankton structure which is being the first link in trophic system will determine the quality content and the quantity accessible resources in Arctic region for higher trophic levels [83]. The cold temperatures in 2008 influenced very good for seaweed blossoming and the benthos got more nutrition then in 2009 [84]. This gives understanding that how much the reproduction success of Arctic species can change as a response to the seasonal changes related to the climate [49]. Though in winter the larvae don’t depend on high summer nutrition concentration and as exchange they find alternative sources [77], more over the temperature and the saltiness can suppress the importance to provide nutrition [85]. The lower Euclid distance between the spatial M. trossulus and Zirfaea spp. (Figure 4(f)) larvae allocation, probably, can be explained by their close thermopathy, the more favorable temperature regime for them observed in the south of Chukchi sea. In our benthos tests those species were not met, more over Zirfaea spp. was not noted by the other researches [86,87] and M. trossulus makes gathering only at shall waters of the Chukchi sea [88,89]. The differences in reproduction success between the species are connected with their biogeographical borders [90] and the highest density of H. arctica larvae in our tests, probably, is explained by the proximity gathering of producers situated on the stone soil of Bering Strait [88].

The pelagic larvae of cold waters species Kellia spp. and Mya spp. appear in very comfortable conditions in northern part of researched water area meanwhile the larvae of other species are boreal – Arctic and low – boreal types Zirfaea spp., Mactra spp. and H. arctica demonstrated the high density in the south of Chukchi sea (Figure6 (a, b, d, e, h)). Interspecies difference of spatial larvae allocation is visible also in percentage species correlation in plankton tests (Figure 4(c); Figure 7(d)). The different thermopathy among the aforecited species is also visible in volume figures which coordinates represent latitude and longitude of the station. The Zirfaea spp. and Mactra spp larvae density gets higher either in the north-west where the warm Atlantic waters come either in the south-east close to the Bering Strait through which the warm waters of the Bering Sea come (Figure 1; Figure 9 (a, d)). Other species population increases either in the south where the cold waters of the East-Siberian Sea come through the Long Strait, either in the russian north-east part of the Chukchi Sea closed to the cold waters of the North Arctic Ocean (Figure 1; 9(b, c, e, f, g, h, i). The similarity of spatial allocation between s. groenlandicus and H. arctica can be explained by their close reaction of the Si concentration at the water surface and the O₂ at the bottom, and at the Chlamys spp. and Zirfaea spp. (Figure 8 (l)) there was observed the authentic positive correlation with the temperature at the water surface (Table 3). Some representatives of their species are divided in same way by biogeographical factors [87].

The observed maximum density of Macoma spp. and S. groenlandicus larvae in the south of Chukchi Sea (Figure 6 (c, f) and their the highest density in the north at the Islangs of Vrangel and Herald (Figure 4(c); Figure 7 (d)) can explain that the period of larvae catching started with the beginning of the pelagic period at least at S. groenlandicus. This type has circum-Arctic allocation which explains its late density comparing to the more thermophilic Mya truncata and Hiatella arctica [49]. The meroplankton showed the season connection, within this the larvae of the bivalve mollusks are available during August-November in the Chukchi Sea [4,58]. As other mollusks M. truncata and H. arctica start spawning from the south and there their larvae at the tests moment came more often in plankton net. Though the higher density of S. groenlandicus and Macoma spp. was near the north islangs (Figure 4 (c); Figure 7(d)), probably, it says about more favorable conditions for the producers. The streams existing system of local character as a rule contributes to hold the larvae near to the producers [91,92,93] and the larvae themselves possess behavior features interfering to carry them out on far distances [94,95].

To the negative influence of global warming on sea inhabitants it is possible to relate the CO₂ concentration in the air which dissolves good in the water and leads to the increasing of carbonic acid in the sea [70,75]. Our observations revealed its negative impact to the pelagic larvae of bivalve mollusks as three from nine researched species Kellia spp., Macoma spp., and Chlamys spp showed the dependence of the spatial allocation from the pH environment (Figure 8(b, c, g)), and Mya spp. and Mactra spp. authentically negatively correlate with this parameter (Table 3). Perhaps, this interrelation depends on thickness of a larval shell capable to be dissolved in the oxidized sea water [75,96]. And at some of those species the thin bivalves are noted even at adult mollusks [86].

The authentic, but weak interrelation of spatial allocation of the studied species with abiotic factors (Table 3; Figure 4 (d, e)), perhaps, is explained by the fact that the larvae often have broader tolerance to the surrounded parameters, than the adult individuals [97,98]. Therefore in spite of the fact that the temperature and chlorophyll-a have an impact on observed community structure the influence is still low [13,99]. However for M. balthica the sea water temperature increase is represented as unfavorable for the number of the produced larvae, shifting at the same time the spawning period [3]. The “highly productive” period in plankton comes to the series of cold years, and the "middle productive" to the normal and warm ones [100]. At the same time the water temperature increase in the sea can reduce the time of larval development that will increase both larvae survival, and the number of recruits influencing the structure of benthos community [80]. In addition to the obvious changes in temperature, salinity and a coastal sediment, the ecosystem of the Chukchi Sea can switch from the benthos-dominated to the sea-dominated [22], and the temperature conditions will favor to the reproduction of thermophilic species to the detriment of cold-loving.

Apparently, on the explored water area the benthos fauna is more represented by a warm-water complex of subarctic, Pacific origin [13] as at the stations with the maximum abundance of larvae (St. 12, 17, 18 and 25) at a bottom and at a surface the positive water temperatures (Table 1, Figure 2) were observed. somewhat the influence of warm Bering water is also visible on the chlorophyll-a allocation. Its maximum values were noted near the Bering Strait with the gradual decrease coming to the Vrangel and Herald Islangs (Figure 7 (e)) that confirms observations [101] about the decrease in primary production towards the North. Most likely, these important abiotic parameters also have led to the fact that the greatest abundance of the pelagic larvae bivalve mollusks met by us was observed at the Bering Strait (up to 12,400 ind./m³), near Herald Bank (up to 4,987 ind./m³) and near Kolyuchinskaya Bay (up to 4,052 ind./m³). Our materials confirm benthos tests in which the most highly productive area is located in a southeast part of the sea, just in the center of the cyclonic circulation noted even in 1933 [16,22]. Coincidence of meroplankton and benthos tests in the productive importance of water areas confirms the researches [91,92] about the existence of mechanisms holding the pelagic larvae near producers.

In spite of the strong impact of the Bering Sea waters on abiotic factors of the Chukchi Sea, the direct impact on benthos of the Chukchi Sea is still limited due to its low temperatures [13,102,103]. Almost all subarctic shelves Pacific species, coming through the Bering Strait, die at the shelf of the Chukchi Sea under the influence of the Arctic conditions, without penetrating into its oceanic areas [13]. However the penetration of allochthonous species into the Chukchi Sea on the “wave” of global warming happens sometimes [5]. The climate change can expand the penetration borders, a dimensional range and the communities efficiency of the Chukchi Sea and, therefore, to change structure, distribution, a stock, zooplankton production and predators that forms the basis for regular monitoring [13,27].

Many researchers of reproductive biology of invertebrates note its variability. The nutrition concentration and the temperature during a larval phase make influence on the reproduction success of sea bivalve mollusks by the influence on their growth and survival [104]. The sensitivity of the Bering Sea ecosystem to the climatic changes is found on the abnormal conditions of 1997 connected with recent arrival of ENSO and PDO [105]. The abundance larvae of bivalve mollusks and also as calanoids was much lower in 1999, than in previous years [106]. The abundance pelagic larvae of the bivalve mollusks in coastal waters of Alaska in August-September 2010 and 2011 and their absence in August-September 2012 is caused by the fact that in the summer of 2012 the water masses came from the Canadian pool [58] containing few benthos larvae [28,29]. In 2008 in the northwest of the Chukchi Sea the temperature on a water surface was colder, than in 2009 [55], and in connection with the climatic changes observed in this region, the production destruction on the shall can probably increase in the future [73]. Most likely, abnormally warm 2016 [48] was not the most fruitful for the pelagic larvae of the bivalve mollusks as five years' observations of zooplankton in the American part of the Chukchi Sea (2008-2012) showed 2010, optimum for reproduction of many species, a year with the intermediate values of water temperature [27,47,55]. In abnormally warm 2004 the pelagic larvae of the bivalve mollusks were much less in Chukchi Sea, than in cold 2009 and 2010 [57].

Many species of bivalve mollusks are the nutrition supply for numerous consumers of the Chukchi Sea such as whales, seals, walruses, fishes and large crabs [2]. Some species of the bivalve mollusks (Chlamys spp., Mya sp. M. trossulus and H. arctica) are the biofouling of the artificial substrates, including oil platforms which operation will depend on the abundance of the organisms which occupied them. The high larvae bivalve mollusks density of Serripes groenlandicus and also possible increase in number of M. trossulus and Chlamys sp. larvae in case of appearing during their reproduction season will create favorable conditions for the mariculture of this sea. The mollusks cultivated on plantations can become the good indicator of the environmental conditions, and the research of their tissues on toxins presence can become an exact indicator of the environment changes as a result of anthropogenic intervention.

Acknowledgements

This publication has been made at grant support FEB Ras № 15-I-6-059. Authors thank of the Propp L.N. and Odintsov V.S. for given some of abiotic parameters.

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