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Macrobenthic communities of the Pechora Sea: the past and the present on the threshhold of the prirazlomnoye oil-field exploitation
Pergamon eII: S0025-326X(97)00114-2
Marine Pollution Bulletht, Vol. 35, Nos 7-12, pp. 287-295, 1997 ~) 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/97 $17.()0+1).0()
Macrobenthic Communities of the Pechora Sea: the Past and the Present on the Threshhold of the Prirazlomnoye Oil-field Exploitation V. B. POGREBOV*, G. I. IVANOVt and N. N. NEKRASOVA* *State Research Institute for Nature Conservation of the Arctic and the North (RINCAN), Post Box 288, Cheliyev Street, 13, St Petersburg 193224, Russia tAll-Russia Research Institute for Geology and Mineral Resources of the Worm Ocean VNIIOKEANGEOLOGIYA, Angliyskiy Avenue, 1, St Petersburg 190121, Russia
On data of bottom sampling, carried out by means of grab, trawl and underwater photography in AugustSeptember of 1993 in the area of the Pechora Sea, quantitative regularities of macrobenthos distribution are described for the ecological monitoring purposes. Maps of ~-biodiversity and biomass indices, bottom communities and trophic zones, singled out by dominant method, are presented. Assessment of structure changes of the investigated area bottom communities during the last 60-70 years is fulfilled. It is shown that the described communities on the whole are of natural undisturbed character and that the revealed changes are within the natural fluctuations in the abundance of benthic populations or may be interpreted in terms of methodical differences in the data analysis and generalization by different authors. © 1997 Elsevier Science Ltd. All rights reserved Keywords: Russian Arctic; Prirazlomnoye oil-field; ecological monitoring and assessment; benthic communities.
Exhaustion of Russia's continental oil and gas deposits forces us to pay attention to their search and exploitation on the marginal sea shelves and specifically - in the Arctic. During the last decade, 70 oil and gasbearing structures are revealed in the Barents Sea (20 of them are tested by drilling); nine deposits with a total reserve of 140 million tons of oil and condensate and 9 billions of gas are discovered (The Arctic Seas, 1993). The largest of them are the Prirazlomoye oil-field and Shtokmanovskoye gasocondesate-field. Supposed exploitation of these deposits needs some nature protection arrangements and, initially, assessment of the upto-date state of marine ecosystems for the purpose of
their posterior ecological monitoring. As a reliable indices of environmental impacts of human activities for marine ecosystems, changes of benthic community composition and structure may be regarded. The first priority of their usage is conditioned by benthos stability in time, its ability to characterize local situation in space and possibility to represent ecosystem changes in retrospective (Pogrebov, 1994). The goals of our researches in the Pechora Sea as a whole are: i) to analyse bottom dweller composition, structure and distribution in order to create a base for long-term monitoring of the Prirazlomnoye oil-field; ii) to reveal biological indices mostly sensitive for indication of man-induced changes in the environment; iii) to assess possible negative consequences caused by deposit exploitation and oil transportation for marine organisms. Materials presented below are answering only some of the questions raised, dealing only with macrobenthos, and of preliminary character. Later on, by obtaining the results of all hydrological, lithological and geochemical analyses as well as the results of analyses of meio- and microbenthic samples, detailed mathematical data processing will be accomplished. As for the objectives of this paper they are: i) to describe the contemporary state of the Pechora Sea bottom communities by the use of traditional Russian marine biology methods of classification (for comparison of the obtained data with that already published); ii) to assess the probable changes in benthic communities during the last 60-70 years, and to analyse their origin. The area of the Prirazlomnoye oil-field, investigated in the regional program of VNIIOKEANGEOLOGIYA, from the biological interest, was previously studied (Kiyko and Pogrebov, 1996). Also, it was an area of the Murmansk Marine Biological Institute investigations. The greater part of the results of this study remain unpublished. 287
Marine Pollution Bulletin
Methods and Materials
nomic point) are identified to orders, classes and sometimes even types level (e.g. Amphipoda, Bryozoa, Nemertini). Part of them is still in the process of identification at the Zoological Institute of RAS (St. Petersburg). It may be expected that after identification, the resulting list of macrobenthic species will be considerably longer (> 200 species). Up to date main types of macrophytes and invertebrates includes the number of species presented in Table 1. As noted, the most diverse groups are those of higher worms (mainly polychaetes, 63 species) and molluscs (chiefly gastropods, 30 species, and 28 species of bivalves).
Biological samples from the area of the Prirazlomnoye oil-field were collected in the July-September cruise of 1993 (as the Pechora Sea, where Prirazlomnoye oil-field is located, the south-eastern part of the Barents Sea is understood; Fig. 1). One hundred and twelve benthic stations were researched on the ecological survey at a depth of from 11 to 187 m (Fig. 1). Complete set of investigations on each of them included quantitative sampling, dredging and underwater photography (Kiyko and Pogrebov, 1997). Quantitative sampling was accomplished on 70 biological stations; qualitative, on 28. The number of analysed photographs was 124. On 22 stations, bottom organisms were collected in three size-weight categories: macro-, meioand microbenthos. Below are discussed the results, concerning the first of the mentioned groups only. Statistical data analysis (if needed) was fulfilled in a routine way (Maksimovich and Pogrebov, 1986).
TABLE 1 Number of benthic species found out on the area of the Prirazlomnoye oil-field during the ecological cruise of 1993 (preliminary underestimated data). Number of species
Group Phaeophyta Rhodophyta Protozoa Spongia Coelenterata Nemertini
Results and Discussion Total area of investigated bottom communities makes up 83.1 thousand km 2. During taxonomic analysis of collected samples 183 macrobenthic species and groups are identified. Some groups (difficult from the t a x • -
Number of species
Group
1 5 1 2 6 1
Annelida Arthropoda Mollusca Tentaculata Echinodermata Tunicata
Total 183
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Fig. 1 Map of benthic stations, investigated on the area of the Prirazlomnoye oil-field during the ecological cruise of 1993: 1, sites of macro-, meio- and microbenthos quantitative sampling; 2, sites of macrobenthos quantitative sampling; 3, sites of macrobenthos qualitative sampling.
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Fig. 2 Macrobenthic species a-diversity (species number per single quantitative sample; preliminary underestimated values) on the area of the Prirazlomnoye oil-field according to the results of ecological cruise of 1993: 1, less than 5; 2, 5-10; 3, 10-15; 4, 1520; 5, 20-25; 6, more than 25.
Fig. 3 Distribution of the total benthic biomass (g m -2) on the area of the Prirazlomnoye oil-field according to the results of ecological cruise of 1993: 1, less than 10; 2, 10-25; 3, 25-50; 4, 50-100; 5, 100-300; 6, 300-500; 7, more than 500. 289
Marine Pollution Bulletin
Analysis of macrobenthic ~-biodiversity variation over the studied area (Fig. 2) shows that the sites with a small number of species per station ( < 5) are located in the southern coastal part of the Pechora shoal. Stations with poor species composition correspond to areas with dense bottom and large-grainy sand; their biomass is low or they are characterized by strongly pronounced domination of one species (e.g. Serripes groenlandicus). A number of stations with low biodiversity are located in the zone of the Pechora River discharge, apparently testifying to an impact of fresh water on marine biota. Minimum species number (1) is registered in 'community' Oligochaeta var., located on dense silt. In the centre of the studied area from the west towards east zone of heightened biodiversity (more than 20 species) is observed. For benthic stations with more than 25 species per single sample, soft bottom (silty sand, sandy silt), high benthic biomass and bivalves prevailing are typical. Maximum number of species registered in a single sample is 36 (community Tridonta borealis on sandy silt). Rich species diversity is
noted also on stations located on poorly sorted sandy silt with gravel, pebbles and barnacles predominating (such stations are typical for the north-eastern part o f the Pechora Sea). Macrobenthic biomass over the Prirazlomnoye oilfield averages 298.5 g m -2. This allows to relate it to high productive regions of the Barents Sea shelf. Distribution of bottom organism total biomass (Fig. 3) is heterogeneous (per sample biomass varies here from 0.01 g m -2 to 3 kg m-2). Sites with low biomass (< 25 g m -2) are concentrated mainly in the southern coastal part of the Pechora Sea. Sites with high biomass are located between Kolguev Island and Novaya Zemlya coast (754.0 g m -2) and in the north-eastern part of the sea (572.6 g m-2). When comparing the map of biomass with the map of bottom sediments, one may see that decrease in biomass corresponds to a sandy bottom, whereas with an increase, to soft silt. The latter is favourable for development of infauna, which forms in the studied area as the basic part of total biomass. Any noticeable influence of depth on total biomass
50,
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55* Fig. 4 Macrobenthic communities, singled out on the area of the
Prifazlomnoye oil-field on base of species dominating in total biomass principle, according to the results of ecological cruise of 1993: 1, Hydroidea var.; 2, Actiniaria var.; 3, Nephthys
ciliata; 4, Scolelepis foliosa; 5, Maldane sarsi; 6, Pectinaria hyperborea; 7, Oligochaeta var.; 8, Echiurus echiurus; 9, Golfingia sp.; 10, Balanus balanus; 11, Balanus crenatus; 12, Gammaridae var.; 13, Cryptonatica clausa; 14, Yoldia amigdalea hyperborea; 15, Tridonta borealis; 16, Hiatella arctica; 17, Serripes groenlandicus; 18, Ciliatocardium ciliatum; 19, Macoma calearea; 20, Macoma torelli; 21, Mya truncata; 22, Ctenodiscus crispatus; 23, Stegophiura nodosa; 24, Cucumaria calcigera; 25, Styela rustica; 26, Pelonaia corrugata.
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Volume 35/Numbers 7-12/July-December 1997
distribution on the Pechora shoal is not revealed, but most likely it is connected with the researched area high turbidity, providing more or less even distribution of temperature, salinity and food material along the depth gradient. Basic share in total benthic biomass of studied area (54%) is formed by bivalves. Classification of sampling sites based on species dominating in biomass principle allows to single out 26 bottom communities (Fig. 4). The resulting scheme of their distribution seems to be unnecessarily fractional, and hampers revealing any general regularities. There are 12-26 communities registered on one station, 7 on two stations. These small communities are not discussed below because of the risk of errors arising in random sampling, detailed characteristics are given only
to communities representing three stations or more (Table 2; Figs 5 and 6). Analysis of meeting frequency for the most abundant species in communities, shows that peculiar species composition is characteristic only for a few of them (Fig. 6). To a greater extent it is displayed in comm. Serripes groenlandicus, which distinctive features are: i) pronounced prevailing of the dominating species which is almost absent in other communities; ii) absence of sipunculides Golfingia sp., species which is widely spread over other areas; iii) presence of specific accompanying species: Myriotrochus rinkii, Cucumaria calcigera, Alcionidium disciforme. Species structure of the rest communities to a certain degree reveals similarity. Especially bright it may be seen for comm. Tridonta
TABLE 2 Quantitative characteristics of main bottom biocenoses and the resources of human consumed (potentially human consumed) invertebrates on the area of the Prirazlomnoye oil-field according to the results of ecological cruise of 1993.
Typical biotopes depth, m, sediments
Number of species
Average biomass, g m2
Maldane sarsi (B-5)
50-150 sandy and clayey silt
33
154.0
Balanus ba/anus (B-10)
30-65 boulders, gravel, pebbles, sandy silt
62
Tridonta borealis (B-15)
20-100 sandy silt, silt, silty sand
87
Serripes groenlandicus (B-17)
I t 49 sand
69
Ciliatocardium ciliatum (B-18)
30-70 silt, silty sand
68
Macoma calcarea (B-19)
15-20 sand 170-185 sandy silt
53
Ctenodiscus crispatus (B-22)
120-180 silt, clayey silt
42
Biocenoses
Others
Occupied area (above the line), thous, km 2, share in the studied area (below, the line), % 4.2
Object
Resources thous, t
Bivalves
86.1
Shrimp, crabs Whelk Scallop Other bivalves Sea urchins
5.0 26.2 1 ! 1.7 131.1 55.6
Shrimp, crabs Whelk Bivalves
73.7 10.6 509.0
Bivalves
! 323.7
Bivalves Sea urchins
1330.0 97.0
Bivalves Whelk
104.1 0. I
Bivalves Whelk
34.2 4.5
5 902.7
2.8 3
415.0
19.5 24
213.5
9.8 12
352.2
9.4 11
219.4
4.3 5
152.5
3.4 4
128
29.7 36
TOTAL
Human consumed (potentially human consumed) invertebrates
183
298.5
83.1 100
Shrimp, crabs Whelk Scallop Other bivalves Sea urchins
6.9 0.3 42.6 1113.1 245.8
Shrimp, crabs Whelk Scallop Other bivalves Sea urchins Total:
85.6 41.7 154.3 4631.3 399.2 5312.1
291
Marine Pollution Bulletin B-5
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Fig. 5 Quantitative characteristics of main macrobenthic commu-
nities, singled out on the area of the Prirazlomnoye oil-field, according to the results of ecologicalcruise of 1993. B-5 - B-22 - communities, presented on Fig. 4 and in Table 2. Area of a circle is proportional to the average total biomass of the community. Circle sectors corresponds to the species with biomass more t h a n 5 % o f total: 1, Maldane sarsi; 2, Lumbriconereisfragilis; 3, Golfingia sp.; 4, Balanus balanus; 5, Tridonta borealis; 6, Serripes groenlandicus; 7, Ciliatocardium ciliatum; 8, Macoma calcarea; 9, Macoma torelli; 10, Ctenodiscus crispatus; 11, Pelonaia corrugata; 12, others. Sectors of the circle B-A corresponds to the area, occupied by communities B-5 - B-22.
borealis and Ciliatocardium ciliatum. In both cases their kernel is formed by three species: T. borealis, C. ciliatum and Golfingia sp. Their accompanying species list is very similar. Spatially these two communities border and may be considered as the extention of each other. Both of them are typical for the same habitat. By more largescale description these communities may be reduced to one T. borealis and C. ciliatum. Communities with different predominating species do not change with each other abruptly but turn one into another continuously, revealing ecotone zones (comm. Echiurus, Cryptonatica, Hiatella and some others may be considered as such ecotones). The same species ordinarily meets in different communities. Among such widely spread species for the region of the Prirazlomnoye oil-field are T. borealis (meeting frequency 60%), Macoma calcarea (57%), Stegophiura nodosa (50%), Maldane sarsi (47%), C. ciliatum (33%), Pectinaria hyperborea and Macoma torelli (31%), Golfingia sp. (30%), etc. m a y be mentioned. It is supposed that the 292
concluding classification for ecological monitoring purposes should be based on the results of multivariate (cluster) analysis. Trophic groups distribution in the studied region is mainly patchy (Fig. 7). The greatest share, up to 40% of total, occupies the zone o f motile filter-feeders (MFF). It is formed basically by communities of bivalve molluscs, T. borealis, Serripes groenlandicus, C. ciliatum. On the whole this zone corresponds with the middle depths of eastern and central parts of the Pechora Sea. On coastal sites with poorly sorted and boulder-gravel bottom, zones of sessile filter-feeders (SFF) prevailing are locally dispersed. As usual they are formed by communities of barnacles, hydroids and ascidians. On sites with the most fine-grainy bottom sediments surface deposit-feeders (SDF) and subsurface deposit-feeders (burrowing; BDF) zones are discovered. The largest part of the SDF zone is formed by comm. M. calcarea, Yoldia amigdalea hyperborea and S. nodosa, which are disposed primary near the coasts. B D F zone is located
Volume 35/Numbers 7-12/July-December 1997 13-22
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Fig. 6 Species structure of main maerobenthic communities, singled
out on the area of the Prirazlomnoyeoil-field, accordingto the results of ecologicalcruise of 1993. B-5 - B-22 - communities, presented on Fig. 4 and 5. Species numeration corresponds to their alphabetical sequence in data matrix: 4, Alcionidium dis'ciforme; 21, Balanus balanus; 22, Balanus crenatus; 38. Ciliatocarditun ciliatum; 41, Cryptonatica clausa; 42, Ctenodiscus crispatus; 43, Cucumaria calcigera; 51, Elliptica elliptica; 62. Golfingia sp.; 67, Hiatella arctica; 79, Lumbriconereis fragilis; 83, Macoma calcarea; 84, Macoma torelli; 86, Maldane sarsi; 90, Saduria sabini; 98, Myriotrochus rinkii; 106, Nicania montagui: 132. Pectinaria hyperborea; 133. Pelonaia corrugata; 161. Serripes groenh:ndicus; 167. Stegophium nodosa; 181, TrMonta borealis; 182. Yolidia I~vperhorea. Roman numerals corresponds to the biomass, g m ~: I - less than 0.1" II 0.1-1; Ili - 1-10; IV- 10-100: V - more than 100.
mainly far from coasts at a comparatively large depth. It is formed by comm. Ctenodiscus erispatus, M. sarsi and other BDF Annelida. The zone of carnivores and herbivores (C&H) prevailing is noted near the coasts of Kolguev and Dolgiy Islands. On the former site this zone is singled out because of high abundance of predatory mollusc C. clausa and on the latter - of polychaetes of subclass Errantia. Assessment of bottom communities changes in the area of Prirazlomnoye oil-field during the last 60-70 years shows that total benthic biomass does not differ from ones registered here in 1920-1930s (Brotskaya and Zenkevich, 1939). Negligible differences observed for the studied region (not more than 14% of 1920-1930s average biomass), are most likely connected with natural fluctuations of benthic populations abundance (or may be the result of possible errors of random sampling). Structure of bottom communities, described for the studied area in 1920-1930s, and o f ones, singled out in our work (Table 3), according to Sorensen index is similar by 72-84%. These are very high values - they are 2-8 times as high as usually used for uniting stations
into one community in standard hydrobiologicat investigations. Share of many abundant invertebrates in total benthic biomass of 1920-1930s and 1993 differs from each other by not more than 3% (Spongia, Coelenterata, Nemertini, Polychaeta, Bryozoa, Brachiopoda, Tunicata). Some groups reveal more sizable differences (Bivalvia and Crustacea in complex IV up to 20% and 15% respectively, Gephyrea in complexes III and IV - 5-11%, Echinodermata in complex I I I - 5%). However, noted differences may be fully defined by the fact that complexes of V. A. Brotskaya and L. A. Zenkevich envelopes almost all the eastern part of the Barents Sea (to Zhelaniya Cape in the North), not only the Pechora shoal. In other words these differences may be explained by data averaging through a considerably larger area. Analysing distribution of communities on the studied area (V. A. Brotskaya and L. A. Zenkevich as the base), we revealed that on the whole our descriptive units are located in the same boundaries and do not coincide only on some stations. Thus, by the main biocenotic indices (abundance, structure and distribution), the Pechora Sea bottom communities do not differ significantly from 293
Marine Pollution Bulletin
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Fig. 7 Trophic zones, singled out on the area of the Prirazlomnoye oil-field, according to the results of ecological cruise of 1993: 1, sessile filter-feeders; 2, motile filter-feeders; 3, surface depositfeeders; 4, subsurface deposit-feeders; 5, carnivores and herbivores.
TABLE 3 Composition of bottom complexes, singled out on the area of the Prirazlomnoye oil-field in 1920-1930s (Brotskaya, Zenkevich, 1939) and according to the results of ecological cruise of 1993. Complex III Group Spongia Coelenterata Nemertini Gephyrea Polychaeta Crustacea Pantopoda Gastropoda Bivalvia Bryozoa Brachiopoda Echinodermata Tunicata Others Total
Complex IV
1920-1930
1993
1.4 f0.6 4.6 '2.6
2.1/0.8 1.6/0.6 0.2/0.1 40.2/15.1 25.8/9.8 16.1/6.1
4.0/2.7 1.2/0.8 3.0/2.0 3.1/2.0 0.2/0.2/0.1 0.1/7.2/4.5 10.0/6.5 10.5/6.6 24.0/15.6 1.5/1.0
2.5/1.0 133.7 '60.5 156.1/59.1 2•4 '1.1 1.1/0.4 !.8/0.7 0.3 '0.1 25.5/11.5 16.5/6.2 2•4/1.1 0.3/0.1 -220.8/100 264.3/100
11.5/7.5 2.7/1.7 79.0/51.3 112.2/70.7 4.0/2.7 1.8/1.1 0.1/-10.0/6.5 8.7/5.5 8.0/5.2 3.6/2.3 -5.9/3.7 153.8/100 158.6/100
1. I '0.4
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1920-1930
1993
Notes. Fractions numerator corresponds to biomass, g m 2, its denominator to share in total biomass, %. those observed here in 1920-1930s. So, they m a y be considered as c o r r e s p o n d i n g to b a c k g r o u n d (undisturbed) state. It allows us to regard the P r i r a z l o m n o y e oil-field benthos as unimpacted. 294
Summary
and Conclusions
The greatest patchiness b o t h of b o t t o m communities and trophic zones is observed in eastern and southern parts of the studied area (along the coasts)• These areas are characterized by the m o s t mosaic distribution o f biotopes what is caused by shallow depth, diversity of b o t t o m sediments and, probably, by a complicated h y d r o d y n a m i c regime. T h e latter is determined by: i) nearness of straits which provides the water exchange between the Barents and K a r a Seas; ii) ' c o r n e r ' location o f the Pechora Sea, what increases the role o f windinduced p h e n o m e n a on its area; and iii) the Pechora River discharge, which is exposed to considerable seasonal fluctuations• Influence o f the P e c h o r a River discharge is well observed when c o m p a r i n g the schemes o f b o t t o m communities and trophic zones distribution with the m a p of stations with detailed u n d e r w a t e r p h o t o g r a p h y . This c o m p a r i s o n shows that high patchiness o f b o t t o m communities in the southern p a r t of the Pechora Sea is caused just by this factor which provides distribution and redistribution of biogens, organic and inorganic suspended substances. On the contrary, the areas with m o r e stable e n v i r o n m e n t (e.g. on large depths and m o n o t o n o u s b o t t o m sediments of central and western parts of the Pechora Sea) revealed b o t t o m communities and trophic zones occupying the largest area.
Volume 35/Numbers 7-12/July-December 1997 High determination o f macrobenthos composition, abundance and structure by natural factors (depth, type of b o t t o m sediments, a m o u n t of suspended material in near-bottom water) allows to expect a marked affect on studied communities by human activity (disturbance of habitat, increase in contaminant concentrations in water and bottom sediments, etc.). Examples of that type of bottom communities responses on shelf oil-field exploitation are well known for the N o r t h and Norwegian Seas (Gray et al., 1990; Warwick and Clarke, 1993). In other words characteristics of benthos species, community, trophic and other structures, adapting to environmental changes, m a y be used as a reliable indices for ecological monitoring, organizing and conducting. All these conditions should be met when selecting biological parameters which should be registered in ecological monitoring on the exploitation area of the Prirazlomnoye oil-field. First, the list of registrated parameters should include m o s t general indices with clear ecological meaning such as biodiversity, total biomass and ratio of b o t t o m organisms with various characteristics (taxonomic, size, trophic, etc.). At the same time, taking into account high level of hydrodynamic, fine oxygen regime and prevailing sands on the Prirazlomnoye oil-field area, we are not expecting strong environmental impacts on its develop-
ment and oil transportation in the case of its accidentfree exploitation. It is quite clear that for the area under discussion natural environmental factors would be of first priority, in comparison with probable pollution of environment with oil-products if the a m o u n t of their disharge to the area of the Pechora Sea would not be catastrophically high. The Arctic Seas (1993) Bioindication of the environment state, biotesting and technology of pollutants destruction. Apatity. 182 p. (Russian). Brotskaya, V. A. and Zenkevich, L. A. (1939) Quantitative registration of the Barents Sea bottom fauna. Transact. of AllUnion Inst. for Fish. and Oceanogr. 4, pp. 5-126. (Russian). Gray, J. S., Clarke, K. R., Warwick, P. M. and Hobbs, G. (1990) Detection of initial effects of pollution on marine benthos: an example from the Ekofisk and Eldfisk oilfields, North Sea. Marine Ecological Progress Series 66, 285-299. Kiyko, O. A. and Pogrebov, V. B. (1997) Long-term benthic population changes (1920-1930s - present) in the Barents and Kara Seas. Marine Pollution Bulletin 35, 322-332. Maksimovieh, N. V. and Pogrebov, V. B. (1986) Quantitative hydrobiological data analysis. Leningrad State University Press, Leningrad. 97 pp. (Russian). Pogrebov, V. B. (1994) Biological evaluation of the environment quality in the course of Arctic offshore development. In Developm. of Rus. Arct. offshore. JUSTNV-PAINO OY AJACTOS AB, Helsinki, pp. 328-331. Warwick, R. M. and Clarke, K. R. (1993) Comparing the severity of disturbance: a meta-analysis of marine macrobenthic community data. Marine Ecological Progress Series 92, 221-331.
295
Marine Pollution Bulletht, Vol. 35, Nos 7-12, pp. 287-295, 1997 ~) 1997 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/97 $17.()0+1).0()
Macrobenthic Communities of the Pechora Sea: the Past and the Present on the Threshhold of the Prirazlomnoye Oil-field Exploitation V. B. POGREBOV*, G. I. IVANOVt and N. N. NEKRASOVA* *State Research Institute for Nature Conservation of the Arctic and the North (RINCAN), Post Box 288, Cheliyev Street, 13, St Petersburg 193224, Russia tAll-Russia Research Institute for Geology and Mineral Resources of the Worm Ocean VNIIOKEANGEOLOGIYA, Angliyskiy Avenue, 1, St Petersburg 190121, Russia
On data of bottom sampling, carried out by means of grab, trawl and underwater photography in AugustSeptember of 1993 in the area of the Pechora Sea, quantitative regularities of macrobenthos distribution are described for the ecological monitoring purposes. Maps of ~-biodiversity and biomass indices, bottom communities and trophic zones, singled out by dominant method, are presented. Assessment of structure changes of the investigated area bottom communities during the last 60-70 years is fulfilled. It is shown that the described communities on the whole are of natural undisturbed character and that the revealed changes are within the natural fluctuations in the abundance of benthic populations or may be interpreted in terms of methodical differences in the data analysis and generalization by different authors. © 1997 Elsevier Science Ltd. All rights reserved Keywords: Russian Arctic; Prirazlomnoye oil-field; ecological monitoring and assessment; benthic communities.
Exhaustion of Russia's continental oil and gas deposits forces us to pay attention to their search and exploitation on the marginal sea shelves and specifically - in the Arctic. During the last decade, 70 oil and gasbearing structures are revealed in the Barents Sea (20 of them are tested by drilling); nine deposits with a total reserve of 140 million tons of oil and condensate and 9 billions of gas are discovered (The Arctic Seas, 1993). The largest of them are the Prirazlomoye oil-field and Shtokmanovskoye gasocondesate-field. Supposed exploitation of these deposits needs some nature protection arrangements and, initially, assessment of the upto-date state of marine ecosystems for the purpose of
their posterior ecological monitoring. As a reliable indices of environmental impacts of human activities for marine ecosystems, changes of benthic community composition and structure may be regarded. The first priority of their usage is conditioned by benthos stability in time, its ability to characterize local situation in space and possibility to represent ecosystem changes in retrospective (Pogrebov, 1994). The goals of our researches in the Pechora Sea as a whole are: i) to analyse bottom dweller composition, structure and distribution in order to create a base for long-term monitoring of the Prirazlomnoye oil-field; ii) to reveal biological indices mostly sensitive for indication of man-induced changes in the environment; iii) to assess possible negative consequences caused by deposit exploitation and oil transportation for marine organisms. Materials presented below are answering only some of the questions raised, dealing only with macrobenthos, and of preliminary character. Later on, by obtaining the results of all hydrological, lithological and geochemical analyses as well as the results of analyses of meio- and microbenthic samples, detailed mathematical data processing will be accomplished. As for the objectives of this paper they are: i) to describe the contemporary state of the Pechora Sea bottom communities by the use of traditional Russian marine biology methods of classification (for comparison of the obtained data with that already published); ii) to assess the probable changes in benthic communities during the last 60-70 years, and to analyse their origin. The area of the Prirazlomnoye oil-field, investigated in the regional program of VNIIOKEANGEOLOGIYA, from the biological interest, was previously studied (Kiyko and Pogrebov, 1996). Also, it was an area of the Murmansk Marine Biological Institute investigations. The greater part of the results of this study remain unpublished. 287
Marine Pollution Bulletin
Methods and Materials
nomic point) are identified to orders, classes and sometimes even types level (e.g. Amphipoda, Bryozoa, Nemertini). Part of them is still in the process of identification at the Zoological Institute of RAS (St. Petersburg). It may be expected that after identification, the resulting list of macrobenthic species will be considerably longer (> 200 species). Up to date main types of macrophytes and invertebrates includes the number of species presented in Table 1. As noted, the most diverse groups are those of higher worms (mainly polychaetes, 63 species) and molluscs (chiefly gastropods, 30 species, and 28 species of bivalves).
Biological samples from the area of the Prirazlomnoye oil-field were collected in the July-September cruise of 1993 (as the Pechora Sea, where Prirazlomnoye oil-field is located, the south-eastern part of the Barents Sea is understood; Fig. 1). One hundred and twelve benthic stations were researched on the ecological survey at a depth of from 11 to 187 m (Fig. 1). Complete set of investigations on each of them included quantitative sampling, dredging and underwater photography (Kiyko and Pogrebov, 1997). Quantitative sampling was accomplished on 70 biological stations; qualitative, on 28. The number of analysed photographs was 124. On 22 stations, bottom organisms were collected in three size-weight categories: macro-, meioand microbenthos. Below are discussed the results, concerning the first of the mentioned groups only. Statistical data analysis (if needed) was fulfilled in a routine way (Maksimovich and Pogrebov, 1986).
TABLE 1 Number of benthic species found out on the area of the Prirazlomnoye oil-field during the ecological cruise of 1993 (preliminary underestimated data). Number of species
Group Phaeophyta Rhodophyta Protozoa Spongia Coelenterata Nemertini
Results and Discussion Total area of investigated bottom communities makes up 83.1 thousand km 2. During taxonomic analysis of collected samples 183 macrobenthic species and groups are identified. Some groups (difficult from the t a x • -
Number of species
Group
1 5 1 2 6 1
Annelida Arthropoda Mollusca Tentaculata Echinodermata Tunicata
Total 183
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Fig. 2 Macrobenthic species a-diversity (species number per single quantitative sample; preliminary underestimated values) on the area of the Prirazlomnoye oil-field according to the results of ecological cruise of 1993: 1, less than 5; 2, 5-10; 3, 10-15; 4, 1520; 5, 20-25; 6, more than 25.
Fig. 3 Distribution of the total benthic biomass (g m -2) on the area of the Prirazlomnoye oil-field according to the results of ecological cruise of 1993: 1, less than 10; 2, 10-25; 3, 25-50; 4, 50-100; 5, 100-300; 6, 300-500; 7, more than 500. 289
Marine Pollution Bulletin
Analysis of macrobenthic ~-biodiversity variation over the studied area (Fig. 2) shows that the sites with a small number of species per station ( < 5) are located in the southern coastal part of the Pechora shoal. Stations with poor species composition correspond to areas with dense bottom and large-grainy sand; their biomass is low or they are characterized by strongly pronounced domination of one species (e.g. Serripes groenlandicus). A number of stations with low biodiversity are located in the zone of the Pechora River discharge, apparently testifying to an impact of fresh water on marine biota. Minimum species number (1) is registered in 'community' Oligochaeta var., located on dense silt. In the centre of the studied area from the west towards east zone of heightened biodiversity (more than 20 species) is observed. For benthic stations with more than 25 species per single sample, soft bottom (silty sand, sandy silt), high benthic biomass and bivalves prevailing are typical. Maximum number of species registered in a single sample is 36 (community Tridonta borealis on sandy silt). Rich species diversity is
noted also on stations located on poorly sorted sandy silt with gravel, pebbles and barnacles predominating (such stations are typical for the north-eastern part o f the Pechora Sea). Macrobenthic biomass over the Prirazlomnoye oilfield averages 298.5 g m -2. This allows to relate it to high productive regions of the Barents Sea shelf. Distribution of bottom organism total biomass (Fig. 3) is heterogeneous (per sample biomass varies here from 0.01 g m -2 to 3 kg m-2). Sites with low biomass (< 25 g m -2) are concentrated mainly in the southern coastal part of the Pechora Sea. Sites with high biomass are located between Kolguev Island and Novaya Zemlya coast (754.0 g m -2) and in the north-eastern part of the sea (572.6 g m-2). When comparing the map of biomass with the map of bottom sediments, one may see that decrease in biomass corresponds to a sandy bottom, whereas with an increase, to soft silt. The latter is favourable for development of infauna, which forms in the studied area as the basic part of total biomass. Any noticeable influence of depth on total biomass
50,
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22 15 18
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55* Fig. 4 Macrobenthic communities, singled out on the area of the
Prifazlomnoye oil-field on base of species dominating in total biomass principle, according to the results of ecological cruise of 1993: 1, Hydroidea var.; 2, Actiniaria var.; 3, Nephthys
ciliata; 4, Scolelepis foliosa; 5, Maldane sarsi; 6, Pectinaria hyperborea; 7, Oligochaeta var.; 8, Echiurus echiurus; 9, Golfingia sp.; 10, Balanus balanus; 11, Balanus crenatus; 12, Gammaridae var.; 13, Cryptonatica clausa; 14, Yoldia amigdalea hyperborea; 15, Tridonta borealis; 16, Hiatella arctica; 17, Serripes groenlandicus; 18, Ciliatocardium ciliatum; 19, Macoma calearea; 20, Macoma torelli; 21, Mya truncata; 22, Ctenodiscus crispatus; 23, Stegophiura nodosa; 24, Cucumaria calcigera; 25, Styela rustica; 26, Pelonaia corrugata.
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Volume 35/Numbers 7-12/July-December 1997
distribution on the Pechora shoal is not revealed, but most likely it is connected with the researched area high turbidity, providing more or less even distribution of temperature, salinity and food material along the depth gradient. Basic share in total benthic biomass of studied area (54%) is formed by bivalves. Classification of sampling sites based on species dominating in biomass principle allows to single out 26 bottom communities (Fig. 4). The resulting scheme of their distribution seems to be unnecessarily fractional, and hampers revealing any general regularities. There are 12-26 communities registered on one station, 7 on two stations. These small communities are not discussed below because of the risk of errors arising in random sampling, detailed characteristics are given only
to communities representing three stations or more (Table 2; Figs 5 and 6). Analysis of meeting frequency for the most abundant species in communities, shows that peculiar species composition is characteristic only for a few of them (Fig. 6). To a greater extent it is displayed in comm. Serripes groenlandicus, which distinctive features are: i) pronounced prevailing of the dominating species which is almost absent in other communities; ii) absence of sipunculides Golfingia sp., species which is widely spread over other areas; iii) presence of specific accompanying species: Myriotrochus rinkii, Cucumaria calcigera, Alcionidium disciforme. Species structure of the rest communities to a certain degree reveals similarity. Especially bright it may be seen for comm. Tridonta
TABLE 2 Quantitative characteristics of main bottom biocenoses and the resources of human consumed (potentially human consumed) invertebrates on the area of the Prirazlomnoye oil-field according to the results of ecological cruise of 1993.
Typical biotopes depth, m, sediments
Number of species
Average biomass, g m2
Maldane sarsi (B-5)
50-150 sandy and clayey silt
33
154.0
Balanus ba/anus (B-10)
30-65 boulders, gravel, pebbles, sandy silt
62
Tridonta borealis (B-15)
20-100 sandy silt, silt, silty sand
87
Serripes groenlandicus (B-17)
I t 49 sand
69
Ciliatocardium ciliatum (B-18)
30-70 silt, silty sand
68
Macoma calcarea (B-19)
15-20 sand 170-185 sandy silt
53
Ctenodiscus crispatus (B-22)
120-180 silt, clayey silt
42
Biocenoses
Others
Occupied area (above the line), thous, km 2, share in the studied area (below, the line), % 4.2
Object
Resources thous, t
Bivalves
86.1
Shrimp, crabs Whelk Scallop Other bivalves Sea urchins
5.0 26.2 1 ! 1.7 131.1 55.6
Shrimp, crabs Whelk Bivalves
73.7 10.6 509.0
Bivalves
! 323.7
Bivalves Sea urchins
1330.0 97.0
Bivalves Whelk
104.1 0. I
Bivalves Whelk
34.2 4.5
5 902.7
2.8 3
415.0
19.5 24
213.5
9.8 12
352.2
9.4 11
219.4
4.3 5
152.5
3.4 4
128
29.7 36
TOTAL
Human consumed (potentially human consumed) invertebrates
183
298.5
83.1 100
Shrimp, crabs Whelk Scallop Other bivalves Sea urchins
6.9 0.3 42.6 1113.1 245.8
Shrimp, crabs Whelk Scallop Other bivalves Sea urchins Total:
85.6 41.7 154.3 4631.3 399.2 5312.1
291
Marine Pollution Bulletin B-5
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Fig. 5 Quantitative characteristics of main macrobenthic commu-
nities, singled out on the area of the Prirazlomnoye oil-field, according to the results of ecologicalcruise of 1993. B-5 - B-22 - communities, presented on Fig. 4 and in Table 2. Area of a circle is proportional to the average total biomass of the community. Circle sectors corresponds to the species with biomass more t h a n 5 % o f total: 1, Maldane sarsi; 2, Lumbriconereisfragilis; 3, Golfingia sp.; 4, Balanus balanus; 5, Tridonta borealis; 6, Serripes groenlandicus; 7, Ciliatocardium ciliatum; 8, Macoma calcarea; 9, Macoma torelli; 10, Ctenodiscus crispatus; 11, Pelonaia corrugata; 12, others. Sectors of the circle B-A corresponds to the area, occupied by communities B-5 - B-22.
borealis and Ciliatocardium ciliatum. In both cases their kernel is formed by three species: T. borealis, C. ciliatum and Golfingia sp. Their accompanying species list is very similar. Spatially these two communities border and may be considered as the extention of each other. Both of them are typical for the same habitat. By more largescale description these communities may be reduced to one T. borealis and C. ciliatum. Communities with different predominating species do not change with each other abruptly but turn one into another continuously, revealing ecotone zones (comm. Echiurus, Cryptonatica, Hiatella and some others may be considered as such ecotones). The same species ordinarily meets in different communities. Among such widely spread species for the region of the Prirazlomnoye oil-field are T. borealis (meeting frequency 60%), Macoma calcarea (57%), Stegophiura nodosa (50%), Maldane sarsi (47%), C. ciliatum (33%), Pectinaria hyperborea and Macoma torelli (31%), Golfingia sp. (30%), etc. m a y be mentioned. It is supposed that the 292
concluding classification for ecological monitoring purposes should be based on the results of multivariate (cluster) analysis. Trophic groups distribution in the studied region is mainly patchy (Fig. 7). The greatest share, up to 40% of total, occupies the zone o f motile filter-feeders (MFF). It is formed basically by communities of bivalve molluscs, T. borealis, Serripes groenlandicus, C. ciliatum. On the whole this zone corresponds with the middle depths of eastern and central parts of the Pechora Sea. On coastal sites with poorly sorted and boulder-gravel bottom, zones of sessile filter-feeders (SFF) prevailing are locally dispersed. As usual they are formed by communities of barnacles, hydroids and ascidians. On sites with the most fine-grainy bottom sediments surface deposit-feeders (SDF) and subsurface deposit-feeders (burrowing; BDF) zones are discovered. The largest part of the SDF zone is formed by comm. M. calcarea, Yoldia amigdalea hyperborea and S. nodosa, which are disposed primary near the coasts. B D F zone is located
Volume 35/Numbers 7-12/July-December 1997 13-22
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out on the area of the Prirazlomnoyeoil-field, accordingto the results of ecologicalcruise of 1993. B-5 - B-22 - communities, presented on Fig. 4 and 5. Species numeration corresponds to their alphabetical sequence in data matrix: 4, Alcionidium dis'ciforme; 21, Balanus balanus; 22, Balanus crenatus; 38. Ciliatocarditun ciliatum; 41, Cryptonatica clausa; 42, Ctenodiscus crispatus; 43, Cucumaria calcigera; 51, Elliptica elliptica; 62. Golfingia sp.; 67, Hiatella arctica; 79, Lumbriconereis fragilis; 83, Macoma calcarea; 84, Macoma torelli; 86, Maldane sarsi; 90, Saduria sabini; 98, Myriotrochus rinkii; 106, Nicania montagui: 132. Pectinaria hyperborea; 133. Pelonaia corrugata; 161. Serripes groenh:ndicus; 167. Stegophium nodosa; 181, TrMonta borealis; 182. Yolidia I~vperhorea. Roman numerals corresponds to the biomass, g m ~: I - less than 0.1" II 0.1-1; Ili - 1-10; IV- 10-100: V - more than 100.
mainly far from coasts at a comparatively large depth. It is formed by comm. Ctenodiscus erispatus, M. sarsi and other BDF Annelida. The zone of carnivores and herbivores (C&H) prevailing is noted near the coasts of Kolguev and Dolgiy Islands. On the former site this zone is singled out because of high abundance of predatory mollusc C. clausa and on the latter - of polychaetes of subclass Errantia. Assessment of bottom communities changes in the area of Prirazlomnoye oil-field during the last 60-70 years shows that total benthic biomass does not differ from ones registered here in 1920-1930s (Brotskaya and Zenkevich, 1939). Negligible differences observed for the studied region (not more than 14% of 1920-1930s average biomass), are most likely connected with natural fluctuations of benthic populations abundance (or may be the result of possible errors of random sampling). Structure of bottom communities, described for the studied area in 1920-1930s, and o f ones, singled out in our work (Table 3), according to Sorensen index is similar by 72-84%. These are very high values - they are 2-8 times as high as usually used for uniting stations
into one community in standard hydrobiologicat investigations. Share of many abundant invertebrates in total benthic biomass of 1920-1930s and 1993 differs from each other by not more than 3% (Spongia, Coelenterata, Nemertini, Polychaeta, Bryozoa, Brachiopoda, Tunicata). Some groups reveal more sizable differences (Bivalvia and Crustacea in complex IV up to 20% and 15% respectively, Gephyrea in complexes III and IV - 5-11%, Echinodermata in complex I I I - 5%). However, noted differences may be fully defined by the fact that complexes of V. A. Brotskaya and L. A. Zenkevich envelopes almost all the eastern part of the Barents Sea (to Zhelaniya Cape in the North), not only the Pechora shoal. In other words these differences may be explained by data averaging through a considerably larger area. Analysing distribution of communities on the studied area (V. A. Brotskaya and L. A. Zenkevich as the base), we revealed that on the whole our descriptive units are located in the same boundaries and do not coincide only on some stations. Thus, by the main biocenotic indices (abundance, structure and distribution), the Pechora Sea bottom communities do not differ significantly from 293
Marine Pollution Bulletin
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Fig. 7 Trophic zones, singled out on the area of the Prirazlomnoye oil-field, according to the results of ecological cruise of 1993: 1, sessile filter-feeders; 2, motile filter-feeders; 3, surface depositfeeders; 4, subsurface deposit-feeders; 5, carnivores and herbivores.
TABLE 3 Composition of bottom complexes, singled out on the area of the Prirazlomnoye oil-field in 1920-1930s (Brotskaya, Zenkevich, 1939) and according to the results of ecological cruise of 1993. Complex III Group Spongia Coelenterata Nemertini Gephyrea Polychaeta Crustacea Pantopoda Gastropoda Bivalvia Bryozoa Brachiopoda Echinodermata Tunicata Others Total
Complex IV
1920-1930
1993
1.4 f0.6 4.6 '2.6
2.1/0.8 1.6/0.6 0.2/0.1 40.2/15.1 25.8/9.8 16.1/6.1
4.0/2.7 1.2/0.8 3.0/2.0 3.1/2.0 0.2/0.2/0.1 0.1/7.2/4.5 10.0/6.5 10.5/6.6 24.0/15.6 1.5/1.0
2.5/1.0 133.7 '60.5 156.1/59.1 2•4 '1.1 1.1/0.4 !.8/0.7 0.3 '0.1 25.5/11.5 16.5/6.2 2•4/1.1 0.3/0.1 -220.8/100 264.3/100
11.5/7.5 2.7/1.7 79.0/51.3 112.2/70.7 4.0/2.7 1.8/1.1 0.1/-10.0/6.5 8.7/5.5 8.0/5.2 3.6/2.3 -5.9/3.7 153.8/100 158.6/100
1. I '0.4
9.6 '4.3 25.4'11.4 11.6'5.2 0.01 2.7 '1.2
1920-1930
1993
Notes. Fractions numerator corresponds to biomass, g m 2, its denominator to share in total biomass, %. those observed here in 1920-1930s. So, they m a y be considered as c o r r e s p o n d i n g to b a c k g r o u n d (undisturbed) state. It allows us to regard the P r i r a z l o m n o y e oil-field benthos as unimpacted. 294
Summary
and Conclusions
The greatest patchiness b o t h of b o t t o m communities and trophic zones is observed in eastern and southern parts of the studied area (along the coasts)• These areas are characterized by the m o s t mosaic distribution o f biotopes what is caused by shallow depth, diversity of b o t t o m sediments and, probably, by a complicated h y d r o d y n a m i c regime. T h e latter is determined by: i) nearness of straits which provides the water exchange between the Barents and K a r a Seas; ii) ' c o r n e r ' location o f the Pechora Sea, what increases the role o f windinduced p h e n o m e n a on its area; and iii) the Pechora River discharge, which is exposed to considerable seasonal fluctuations• Influence o f the P e c h o r a River discharge is well observed when c o m p a r i n g the schemes o f b o t t o m communities and trophic zones distribution with the m a p of stations with detailed u n d e r w a t e r p h o t o g r a p h y . This c o m p a r i s o n shows that high patchiness o f b o t t o m communities in the southern p a r t of the Pechora Sea is caused just by this factor which provides distribution and redistribution of biogens, organic and inorganic suspended substances. On the contrary, the areas with m o r e stable e n v i r o n m e n t (e.g. on large depths and m o n o t o n o u s b o t t o m sediments of central and western parts of the Pechora Sea) revealed b o t t o m communities and trophic zones occupying the largest area.
Volume 35/Numbers 7-12/July-December 1997 High determination o f macrobenthos composition, abundance and structure by natural factors (depth, type of b o t t o m sediments, a m o u n t of suspended material in near-bottom water) allows to expect a marked affect on studied communities by human activity (disturbance of habitat, increase in contaminant concentrations in water and bottom sediments, etc.). Examples of that type of bottom communities responses on shelf oil-field exploitation are well known for the N o r t h and Norwegian Seas (Gray et al., 1990; Warwick and Clarke, 1993). In other words characteristics of benthos species, community, trophic and other structures, adapting to environmental changes, m a y be used as a reliable indices for ecological monitoring, organizing and conducting. All these conditions should be met when selecting biological parameters which should be registered in ecological monitoring on the exploitation area of the Prirazlomnoye oil-field. First, the list of registrated parameters should include m o s t general indices with clear ecological meaning such as biodiversity, total biomass and ratio of b o t t o m organisms with various characteristics (taxonomic, size, trophic, etc.). At the same time, taking into account high level of hydrodynamic, fine oxygen regime and prevailing sands on the Prirazlomnoye oil-field area, we are not expecting strong environmental impacts on its develop-
ment and oil transportation in the case of its accidentfree exploitation. It is quite clear that for the area under discussion natural environmental factors would be of first priority, in comparison with probable pollution of environment with oil-products if the a m o u n t of their disharge to the area of the Pechora Sea would not be catastrophically high. The Arctic Seas (1993) Bioindication of the environment state, biotesting and technology of pollutants destruction. Apatity. 182 p. (Russian). Brotskaya, V. A. and Zenkevich, L. A. (1939) Quantitative registration of the Barents Sea bottom fauna. Transact. of AllUnion Inst. for Fish. and Oceanogr. 4, pp. 5-126. (Russian). Gray, J. S., Clarke, K. R., Warwick, P. M. and Hobbs, G. (1990) Detection of initial effects of pollution on marine benthos: an example from the Ekofisk and Eldfisk oilfields, North Sea. Marine Ecological Progress Series 66, 285-299. Kiyko, O. A. and Pogrebov, V. B. (1997) Long-term benthic population changes (1920-1930s - present) in the Barents and Kara Seas. Marine Pollution Bulletin 35, 322-332. Maksimovieh, N. V. and Pogrebov, V. B. (1986) Quantitative hydrobiological data analysis. Leningrad State University Press, Leningrad. 97 pp. (Russian). Pogrebov, V. B. (1994) Biological evaluation of the environment quality in the course of Arctic offshore development. In Developm. of Rus. Arct. offshore. JUSTNV-PAINO OY AJACTOS AB, Helsinki, pp. 328-331. Warwick, R. M. and Clarke, K. R. (1993) Comparing the severity of disturbance: a meta-analysis of marine macrobenthic community data. Marine Ecological Progress Series 92, 221-331.
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