Ecologically or Biologically Significant Areas (EBSAs)
published: 12 Jun 2015
Ob-Enisei River Mouth
The Ob and Enisei gulfs form the largest estuarine area in the Arctic. The continental outflow here is the greatest recorded in the Arctic seas. A large amount of fresh, warm river discharge causes an unstable saline regime in the upper layer of the largest part of the Kara Sea. Primary production in the frontal areas is high, which supports large stocks of freshwater and semi-anadromous fishes, aquatic birds and waterfowl. Anadromous and semi-anadromous species perform seasonal migrations through the estuary, while fast ice in the outer part of the river mouth zone serves as an important spawning area for the polar cod. The coastal zone of the area is characterized by exceptionally high biological and landscape diversity (coastal systems of transient habitats from sandy beaches to tundra, or “laidas”). It is the area where most of the biological hotspots are observed. The area supports a variety of aquatic bird species. Most of them have closer relations to the marine habitats during non-breeding seasons. These include globally threatened species like Steller’s eider (Polysticta stelleri), velvet scoter (Melanitta fusca) and long-tailed duck (Clangula hyemalis), which breed in tundra but make extensive use of coastal waters during the non-breeding period. The estuary also provides moulting and feeding habitats for sea ducks, geese and swans, including king eider, long-tailed ducks, scoters, dark-bellied Brent goose and Bewick’s swan. The area also serves as an important summer feeding ground for beluga whales, and polar bears occur in the outer part of it.
The Ob and Einsei river mouth area is a globally unique feature of the Eurasian Arctic that exerts a tremendous impact on the oceanographical regime and ecosystems of the shelf seas. The AMSA IIc report (AMAP/CAFF/SDWG, 2013) identified this large estuarine system as an area meeting most of the EBSA criteria.
The area includes deltas and estuaries of the great Siberian rivers Ob and Enisei, along with their outer maritime zones. Ob Gulf is the largest estuary in the Russian Arctic, and is nearly 1000 km long from the Ob Delta to the opening to the south-central Kara Sea in north. The Enisei Gulf is the second-largest, after the Ob.
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Ob and Enisei are the largest rivers in Russia, accounting for 75% of the freshwater inflow to the Kara Sea. One of the specific features of the Kara Sea is a strong continental outflow, which is the greatest recorded in the Arctic seas. The annual river run-off to the sea averages 1.350 km³, which is 2.8 times higher than in the Barents Sea and constitutes almost half of the total river water discharge into the Russian Arctic seas. Receiving a great amount of fresh and warm river discharge, the Kara Sea is characterized by an unstable saline regime in the upper layer. Surface water outside the Ob and Enisei river estuarine zones has a salinity of 7–10‰ and a temperature of 5-8° C. Below the heated and desalinated surface layer, a drop in temperature and an increase in salinity are recorded in the entire Kara Sea. The influence of the desalinated surface layer can be followed fora distance of hundreds kilometres from the river mouths. River plume fronts are present at the interface between the outflow of the Ob and Enisei rivers and the adjacent Kara Sea waters, however, they are subject to great seasonal and inter-annual variability. The coastal zone of the area is a good example of the land – sea ecotone and is characterized by exceptionally high biological and landscape diversity (coastal systems of transient habitats from sandy beaches to tundra, or so-called laidas, are characteristic). It is the area where most of the biological hotspots are observed, and it is the area where sea oil spills may penetrate far inland due to well- developed water channel networks connected to the sea. A specific aquatic ecosystem exists in the brackish water zone developing under the influence of river runoff. The principal ecological factors affecting species composition, distribution patterns and functioning of marine and coastal biota of the area are the following: - Harsh climate conditions. - Seasonal ice cover (from October/November to June/July on average) with wide distribution of land-fast ice. - Shallow waters. - Soft bottom and coastal sediments, low coasts. - Strong impact of river runoff (including dominance of katabatic currents, desalination of seawater, complicated inter-annual, seasonal and diurnal dynamics of salinity, warming effect, huge sediment runoff). - Specific oxygen rate regime and winterkill phenomenon in the Ob River and Ob Gulf. Estuarine ecosystems differ considerably from both marine and fresh water ecosystems by species composition and food web structure; biological productivity of estuarine ecosystems is often high. Euryhaline species, which are adapted to wide fluctuation in salinity play important roles in the estuarine ecosystems, however the overall biodiversity is low compared to open-sea areas. Hydrobiology The pelagic ecosystem is strongly governed by oceanographical fronts. The estuarine front is located in the mouth of the gulf and extends to a distance of about 100 km. This front separates nutrient-rich waters discharged by the Ob, which fuel a high level of activity of brackish water phytoplankton, the productivity of which is not affected much by the turbidity and low transparency of the waters (figure 2). The maximum productivity of the brackish water phytoplankton in the frontal zone is reached in summer time (figure 2) when turnover of nutrients coming from dying off phytoplankton cells is particularly high, while the production of freshwater phytoplankton is limited by pre-vegetational nutrient reserves (Lapin, 2012). At the inshore periphery of the estuarine front, enhanced biomass of estuarine zooplankton (dominated by copepods: Senecella sibirica, Jaschnovia tolli, Limnocalanus grimaldii, Drepanopus bungei and mysids – Mysis oculata) (Vinogradov et al. 1994) is several times higher than in the adjacent waters (P.P. Shirshov Institute of Oceanology RAS unpublished data). Plankton abundance rapidly decreases both downstream and upstream. Quantitative distribution patterns of the plankton in the Ob Bay as a whole prove its enhanced biological productivity, which is, for example, considerably higher than the productivity observed in the Enisei Gulf. Freshwater and brackish water zooplankton die and sink to the bottom as soon as they occur in the saline zone, thus increasing the flux of organic matter to the benthic communities. In summary, the food web of the area functions primarily by detritus but not by pastoral succession type. Calanus spp. dominates plant-eating marine zooplankton while carnivorous zooplankton consists principally of Coelenterata and Chaetognatha (Kulakov et al., 2004). The benthic biodiversity of the Ob River decreases as the river meets the bay (Kuzikova 1988a,b, Kuzikova et al. 1989); however, within the Ob Gulf, benthic diversity and biomasses increase northwards following the increase in water salinity, in the following manner: in the inner segment of the Bay, the number of benthic species in a sample does not exceed 20, being as low as 3 to 4 in some samples, while maximal values – over 70 species in a benthic sample – are observed in the seaside segment of the Gulf. The total biomass and density of zoobenthos are exceptionally low in the freshwater portion of Ob Bay, being 2.5 g/m2 and 1500 ind./m2 respectively. In waters with salinity 6–10‰ these parameters vary within the limits of 7.4–12.4 and 700–1200 respectively. The benthic biomass reaches 100 g/m2, and abundance ca. 300 ind./m2 in the mouth segment of the Ob Gulf with dominance of bivalves and polychaets, the proportion of which exceeds 50% of the total biomass (Denisenko et al., 1999). There are remarkable gradients of alpha and beta diversity increasing from the brackish water zone towards offshore areas north of Yamal Peninsula; the distribution of benthic communities appears to follow the estuarine front climatology (Kozlovsky, 2012). Fishes The estuarine ichthyofauna numbers approximately 40 fish and fish-like (Siberian lamprey Lethenteron kessleri) species of 13 families. By their present status the fish populations of the Ob estuary can be divided into two major groups: permanent inhabitants and migrants. Non-migrating species (cyprinids, pike, and ruffe), immature and adult cohorts of sturgeon and semi-anadromous coregonids, which use the area for fattening, comprise the first group. The migrant group consists of anadromous and semianadromous species (Acipenseridae, Salmonidae, Coregonidae, and Osmeridae) performing seasonal (wintering, spawning, fattening) migrations through the estuary. Fast ice in the outer part of river mouth zone is an important spawning area for the polar cod. Largest stocks of different coregonid white fish species as well as threatened Ob stock of Siberian sturgeon have feeding and wintering grounds in this area, or pass it during anadromous migration to their spawning grounds in the rivers. The oxygen content of the Ob River and Gulf also varies seasonally, with attendant impacts on winterkills. Formation of winterkill zones strongly affects distribution of wintering ground of fishes, including valuable species of Coregonids and Sturgeon. This natural feature accounts for sensitivity of the area to additional human pollution and disturbances to hydrological and sedimentation regimes. Birds The area supports a variety of aquatic bird species. Most of the regional waterbirds have closer relations to the marine habitats during non-breeding seasons. Gulls, terns, skuas and divers nesting on coastal tundra forage in marine areas. The following are typical breeding species in marine coastal habitats on mainland and inshore islands: West-Siberian gull Larus hueglini and Glaucous gull Larus hyperboreus, Arctic terns Sterna paradisaea. The following water birds are the most common and in some places are abundant breeders on coastal tundra: divers Gavia spp., swans Cygnus spp., bean goose Anser fabalis, greater white-fronted goose .albifrons, Brent goose Branta bernicla bernicla, sea ducks including king eider Somateria spectabilis; greater scaup Aythya marila, and common scoter M. nigra, Skuas Stercorarius spp., as well as diverse waders. Among globally threatened species, the Steller’s eider Polysticta stelleri, velvet scoter Melanitta fusca and long-tailed duck Clangula hyemalis breed on tundra but make extensive use of coastal waters during the non-breeding period. The Ob Delta is recognized as an important ground for moulting and autumn-staging dabbling and diving ducks, geese and waders. The estuary also provides moulting and feeding habitats for sea ducks, geese and swans, including king eider, long-tailed ducks, scoters, dark-bellied Brent goose and Bewick’s swan (figures 3 and 4). Mammals Among pinnipeds, ringed seal is the most abundant in the Kara Sea, and bearded seal is common as well. They occur almost everywhere in the Kara Sea during the ice-covered period. Vast land-fast ice formation in the south-western Kara Sea provides a favourable environment for ringed seal reproduction, whose principal breeding grounds adjust to the Yamal-Gydan coasts, including Ob Gulf and further east to the Enisei Gulf. The beluga whale (IUCN VU) is a characteristic and seasonally abundant cetacean in the area, and is considered to be possibly separated stock. Belugas make intensive use of the area, where they prey on polar cod and coregonids. Principal late summer feeding grounds of belugas are located along the mainland coasts of the Kara Sea, including Ob Gulf and Enisei Gulf.
The study area is considered the most developed coastal region of the Russian Arctic. Rich natural resources, both biological and mineral, of the Yamal Peninsula and adjacent shelf have been extensively explored for decades. The major human activities in the region are as follows: extraction and transportation of hydrocarbons, shipping and fisheries. The cumulative effect of local activities and long-range transportation of pollutants gathered on the vast drainage basin of the Ob River have resulted in remarkable changes in some biological components and their environment. Thus, major negative factors related to previous and modern human activities in the study area and affecting local biological systems are pollution and unsustainable exploitation of biological resources (primarily unsustainable fishing). Industrial exploration and development of petroleum activity in the study region peaked from 1976 to 1981. Since that time, hydrocarbon extraction has been spreading along the different coastal segments, followed by transport infrastructure. In particular, it is the westernmost segment of the Northern Sea Route including Ob Gulf and south-western Kara Sea that was first opened for year-round navigation in the 1970s. Extensive disturbance of ice cover in coastal areas, especially in fast ice zone, apparently impacted seal-breeding grounds in the region (Wiig et al. 1996). In Ob Gulf, in spite of the outflow of pollutants from its watershed, the water quality is evaluated as being slightly or moderate polluted according to its ecology-sanitary and hydrobiological parameters (Semenova et al. 1997, 2000). According to the analyses carried out in 1994–1996, the bottom sediments of Ob and Taz Gulfs are slightly polluted with oil products and polluted with heavy metals. In the Ob River mouth, Ob and Taz Gulfs, the threshold limit values (TLV) of heavy metals, phenols, pesticides, and detergents, established for fishery waters, are exceeded(Semenova et al. 1997, 2000). Despite the presence of heavily polluted local areas, the ecosystems of the Ob Gulf as a whole are able to resist the current anthropogenic load. Diverse aquatic biota, relatively low average values of saprobity and stable structure of plankton and zoobenthos communities prove this evaluation. No reliable changes in species composition, relative abundance and share of major ecological groups of zoobenthos were found while comparing with corresponding parameters observed from 1930 to the 1950s. Thus, the general status of the entire ecosystem is considered satisfactory. According to their hydrobiological parameters the waters of Ob Gulf are evaluated as being clean or moderately polluted (Leshchinskaya 1962, Kuzikova et al. 1989, Kuzikova 1995, Semenova et al. 2000). The ecological status of the Ob Gulf itself is more satisfactory than that of the lower and especially middle reaches of the river. The Ob Gulf, along with its tributaries, is home to the most important fishery both in the Yamalo-Nenetsk Autonomous Region (YaNAO) and in the entire Russian Arctic. Fish resource status is one of the region’s key ecological indicators. At present, fish resources and catches have considerably decreased due to bad environmental conditions as well as to changes in fishery management. Extensive pollution of the Ob-Irtysh River basin resulted in remarkable degradation of breeding and feeding habitats of fishes and corresponding catch reduction of most fish species (Andrienko et al. 1997). For example, the decline of Siberian sturgeon resources has been observed since the late 1980s. This decline is a combined result of unsustainable fishery, hydroplant construction, water pollution from human activities, destruction of spawning grounds by hydroplants, gravel extraction, wood rafting, and others. Multiple pathologies, including female sterility, were observed in this species. Recently, Siberian Sturgeon populations have been heavily affected by illegal fishing. The status of coregonid fish populations is more sustainable. Resources of most whitefishes and ciscoes are stable but undergo periodic fluctuations.
AMAP/CAFF/SDWG, 2013. Identification of Arctic marine areas of heightened ecological and cultural significance: Arctic Marine Shipping Assessment (AMSA) IIc. Arctic Monitoring and Assessment Programme (AMAP), Oslo. 114 pp. Andrienko E.K. Current status of resources and fishery of the Least Cisco in the Ob and Taz Gulfs basins. Resources of wildlife of Siberia. Fishes // Collection of scientific papers. Novosibirsk: Nauka, Siberian Department, 1990. – Pp. 39–41. Andriyashev A.P., Chernova N.V. Annotated list of fish-like and fishes of the Arctic Seas and adjacent waters // Voprosy ihtiologii. 1994. Vol. 34, Iss. 4. Pp. 435–456. Antonov S.G., Chernova N.V. Ichthyofauna composition // Matishov et al. (Eds.) Ecology and biological resources of the Kara Sea. Apatity, 1989. – Pp. 95–99. Brusynina I.N., Krokhalevsky E.K. Current status of the ecosystem of Ob River and its tributaries under conditions of anthropogenic impact // Collection of the scientific proceedings of GosNIORKH. - 1989. - Iss. 305. - Pp. 3–22. Bryzgalo V.A., Ivanov V.V. Ecological effects of anthropogenic impacts upon mouth zones of the rivers of basins of the Russian Arctic seas. // Ecological chemistry. – 1999. – Kudersky L.A. Fish resources of the great Siberian rivers and exploration of the Arctic natural resources. Biological resources of the Russian Arctic. Materials to the symposium. Moscow: 2000. Bustnes J.O., Mosbech M., Sonne C.,· Systad, G.H. 2010. Migration patterns, breeding and moulting locations of king eiders wintering in north-eastern Norway. Polar Biol (2010) 33:1379–1385 Decker M.-B., Gavrilo M., Mehlum F., Bakken V. 1998. Distribution and abundance of birds and marine mammals in the Eastern Barents Sea and the Kara Sea, late summer 1995. – Meddeleser No 155, Oslo, 83 pp. Denisenko, S., Sandler, H., Denisenko, N., and Rachor, E. 1999. Current state of zoobenthos in two estuarine bays of the Barents and Kara Seas. – ICES Journal of Marine Research, 56 Supplement: 187–193. Khlebovich V.V. Critical salinity of biological processes. - Leningrad: Nauka, 1974. - 235 pp. Kozlovsky V.V. 2012. Macrozoobenthos of the upper shelf of the southwestern Kara Sea. Moscow: P.P. Shirshov Institute of Oceanology, 25 p. (in Russian). Kulakov M.Yu., Pogrebov V.B., Timofeyev S.F., Chernova N.V., Kiyko O.A. Ecosystem of the Barents and Kara Seas coastal segment // The Global Coastal Ocean. Interdisciplinary Regional Studies and Syntheses / Edited by A.R. Robinson and K.H. Brink. The Sea: Ideas and Observations on Progress in the Study of the Seas. Vol. 14. Harvard University Press. Cambridge, MA, 2004. P. 1135-1172. Lapin S.A. 2012. Spatio-temporal variability of the hudrological and hydrochemical characteristics of the Ob Gulf as the basis of its bio-productivity. Ph.D. Thesis. Moscow: Moscow State University, Faculty of Geography, 25 p. (in Russian). Matishov G.G., Shparkovsky S.L. et al. (Eds.) 1989 Ecology and bioresourses of the Kara Sea. Apatity Kola Sci. Center of the RAS, 189 pp. (In Russian) Pavlov, V. K., L.A. Timokhov, G. A. Baskakov, M.Yu. Kulakov, V.K. Kurazhov, P.V.Pavlov, S.V. Pivovarov and V.V. Stanovoy. 1996. Hydrometeorological regime of the Kara, Laptev and East- Siberian seas. Technical Memorandum APL-UW TM 1-96. Seattle, Applied Physics Laboratory, University of Washington. 1996. 183 pp. Petersen M.R., Bustnes J.O., Systad GH. 2006. Breeding and moulting locations and migration patterns of the Atlantic population of Steller’s eiders Polysticta stelleri as determined from satellite telemetry. Journal of Avian Biology 37: 58-68. Ruban G.P. Population status of sturgeons of Siberian water bodies and perspectives of their commercial exploitation // Biological resources of the coastal zone of the Russian Arctic. Symposium materials. – Moscow: VNIRO, 2000. – pp. 123–129. Ruban, G. & Bin Zhu 2010. Acipenser baerii. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 7 March 2014.
Areas described as meeting EBSA criteria that were considered by the Conference of the Parties
C1: Uniqueness or rarity High
The area is the biggest estuary system in the Arctic, affecting the entire adjacent marine ecosystem of the Kara Sea. The huge river run-off has a great impact on the Arctic Ocean, influencing hydrology, ice regime and geochemistry. Some populations of semi-anadromous fish are particular to this area, i.e., Ob Sturgeon, but there are no endemic species of fish, seabirds or marine mammals.
C2: Special importance for life-history stages of species High
Estuaries are important staging areas for aquatic birds, important habitat for white fishes (feeding, migrating, wintering); the maritime zone, with fast-ice, is an important spawning area for polar cod, while the fast ice in the gulfs is a breeding ground for ringed seals.
C3: Importance for threatened, endangered or declining species and/or habitats Medium
Important summer feeding grounds for beluga whales (IUCN near threatened), important staging areas for long-tailed duck (IUCN, VU) and velvet scoters (IUCN, EN); Steller’s eiders (IUCN VU) make use of the area, and polar bears (UICN VU) occur in the outer part of the area.
C4: Vulnerability, fragility, sensitivity, or slow recovery Medium
The dynamic hydrological regime acts as a buffer for many external impacts; animals such sea ducks and white fishes have long life expectancy and low reproductive rates, thus slow recovery rate; sea ducks and polar cod fry are particularly vulnerable to oil spills, while the estuarine ecosystem in general may be vulnerable to changes in the salinity regime caused by large-scale bar dredging for port construction (Lapin, 2012).
C5: Biological productivity High
Owing to high primary production at the frontal zones (Lapin, 2012) the area supports large stocks of freshwater and semi-anadromous fishes, aquatic birds and waterfowl.
C6: Biological diversity Low
Biodiversity of the lower trophic levels is relatively low due to a variable hydrological regime and vast zone of brackish waters; however, there are remarkable gradients towards offshore areas (Kozlovsky, 2012) while waterfowl and shorebirds are relatively diverse.
C7: Naturalness Medium
The Enisei river estuary is rather pristine while Ob Gulf is already experiencing shipping traffic, geological explorations and onshore infrastructure construction in several points. Rivers bring considerable amounts of pollutants (on the Arctic scale) from their vast watersheds.