| Zoobenthos monitoring in areas of Stockman project influence |
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LYUBINA O.S., FROLOVA E.A., DIKAEVA D.R., FROLOV A.A., ARTYUKH O.L., GARBUL E.A., AHMETCHINA O.YU., NEHAEV I.O. Zoobenthos laboratory of Murmansk marine biological institute takes an active part in systematical investigation of the Barents Sea bottom communities in areas of Stockman field development of energy resources.Since 2002 zoobenthos sampling was annual in the area chosen for commercial activity gas-condensate field and on a varying pattern of stations along prospective pipeline route. In connection with changes in pipeline project the area of zoobenthos investigation in coastal zone was considerably extended. Currently it includes the following gulfs of the Kola Peninsula: Malaya Volokovaya of Varanger Fjord, Ura Bay and Teriberskaya Bay. During execution of these works in sum more than 400 samples from 131 stations were gathered and analyzed. Sampling, data-processing operation and statistical analysis of materials was made using standard methods. Collected during Stockman project fulfillment data array on bottom invertebrates allows to estimate biodiversity and quantitative zoobenthos distribution in different bottom landscapes of the central part of the Barents Sea and its coastal side. As a result of carried out investigations in definite areas of the Barents Sea 820 taxons of bottom and littoral invertebrates (693 species rank) belonging to 14 species, 32 classes, 87 orders, 227 families were defined. Nemerteans (82% frequency of occurrence), polychaete Heteromastus filiformis (68%), Galathowenia oculata (65%), Maldane sarsi (65%), Spiochaetopterus typicus (61%) and bivalves Thyasira gouldi (63%), Yoldiella nana (60 %), Mendicula ferruginosa (57%) are widely spread in the investigated area. Cluster analysis of obtained during long-term investigations data array on zoobenthos allowed us to zone (divide into districts) the central part of the Barents Sea in the areas of Stockman gas-condensate field impact according species affinity. Integral index of relative metabolism activity was used as a measure of organisms abundance: M=kN0.25B0.75, N – magnitude of organisms, B – biomass, k – taxon-specific coefficient of specific metabolism rate (Alimov, 1979, Golikov et al., 1990). For species affinity estimation S?rensen affinity coefficient (S?rensen, 1948) was used, clustering was made using weighted-mean method. As a result of analysis three large species complexes were defined in the central part of the Barents Sea. The first one is one-type and extensive deep-water complex. The second one is compositionally various in bottom communities and is characteristic of bottom uplands, slopes and littoral shoal, and of central part of Ura Bay as well. Third complex includes littoral communities of the Kola Peninsula bays. Bottom communities of the Barents Sea deep-water complex (230-380 m) are characterized by polychaete Spiochaetopterus typicus predominance.These invertebrates take up more than 60% of total energy consumption and about the same total biomass (60%). Besides dominating species polychaete Maldane sarsi and Aglaophamus malmgreni and bivalve Bathyarca glacialis frequently occur here and have noticeable part in relative metabolism intensity. Starfish Ctenodiscus crispatus, sipunculoidea Golphingia margaritacea and sea-cucumber Molpadia borealis make a considerable input in general biomass of communities. Polychaete Galathowenia oculata is of high importance in population density except dominant species. In deep-water communities where Spiochaetopterus typicus dominates invertebrates biomass remains on average level 96±5 gr/m2, population density - 2170±220 specimen /m2. Average species quantity per station constitutes 58±3. In areas of shallow depth in the southern part of the Barents Sea central trough Spiochaetopterus typicus communities have a number of transition forms with less dominant species’ rates. Communities from less deep areas of the Sea between 73° northern latitude and the Kola Peninsula constitute a further complex. Domination structure and quantitative indexes are diverse here. Six community types propagate on underwater slopes of 150 – 250 meters depth with oozy-sandy ground with stones impure where polychaete Maldane sarsi dominates or subdominanates. Besides this type polychaete Nephtys ciliata, Galathowenia oculata, Praxillela gracilis, or irregular sea-urchin Brisaster fragilis and bivalve Astarta crenata play an important role in different bottom areas. Quantitative indexes of these communities are similar, biomass of bottom organisms reaches on average 41±6 gr/m2, quantity is 2200±600 specimen /m2, species quantity in stations is 79±8. It should be noted that species diversity level in mentioned above communities rises with depth decrease and increase of rock material and shell rock in bottom sediments. Maximum species quantity in stations was detected in community where mollusc Astarta crenata (108 species / station) dominates on depth 66-135 meters. Considerable increase of species resources in shoal stations is most likely connected with abundance in this area of motionless sestonophage which are organisms that form ecological niches. Another type of bottom communities with Maldane sarsi domination evolves in central deep-water areas of Ura Bay at depths of 177-277 metres on soft oozy grounds. Biomass of this community reaches 93±6 gr/m2, density habitation is very high and reaches 5200±800 specimen/m2, species resources is on the contrary decreased (45±4 species per station) in comparison to similar communities from open sea areas. Variability of bottom communities in the upper sublittoral (depth of 2-25 metres) is considerably higher than in deep-water sea areas. In investigated bays of the Kola Peninsula integration of stations according to species composition affinity is not significant (affinity coefficient is 30% on average). Bivalves Macoma calcarea, Astarte borealis (on sandy ground), Modiolus modiolus, Chlamys islandica, Hyatella arctica (on solid substrates) often dominate in the coastal area. Sea urchins and basket stars, acorn shells and decapods locally dominate in bottom sediments of the coastal area. Biomass of the upper sublittoral bottom sediments varies from 8 to 370 gr/m2 (average 220±62 gr/m2), quantity varies from 250 to 5600 specimen/m2 (average 2100±500 specimen/m2) as well. Species resources of bottom invertebrates constitutes here on average 45±5 species per station. The third large complex consists of littoral communities. Stations similarity here according to species composition is considerably higher (similarity index 65+7%). On stony ground littoral in invertebrates habitation bivalves Mytilus edulis and barnacle Semibalanus balanoides dominate in level of energy consumption. On sandy ground bivalves Macoma balthica dominate. Biomass of bottom invertebrates of littoral complexes exceeds 900 gr/m2 and constitutes on average 600±200 gr/m2. Population density of organisms reaches on average 38000±2000 specimen/m2. Species resources on the contrary are quite lower than under water (22±3 species per station on average). Long-termed zoobenthos investigations have shown that habitations of underwater plains, coastal slopes and uplands, upper shelf sections of coastal zone have their own level of spatial variability and quantitative characteristics. Probably bottom communities’ distribution from deep-water plains up to upper sublittoral and littoral can be theoretically characterized as fractal distribution (Azovsky et al., 2007). Therefore different scale of observations and different density of stations is necessary for investigation of every area and for valid assessment of bottom communities inhabiting here. Influence assessment gas-extractive complex objects should be carried out differentiately and in different scales for different types of bottom communities.References |