The Concept of Hierarchical Structure of Large Marine Ecosystems in the Zoning of Russian Arctic Shelf Seas

Main features of biogeographical regionalization were developed in previous notes of authors. In this chapter a review on the new information on large marine ecosystems is given based on strong theoretical and empirical material including own research. The originality of method of a research consists that at the description of the sea basin (ecoregion) the three-rank system of units considering zonal, vertical and azonal distinctions of the environment which influence the distribution of marine inhabitants is used. The principles of the regionalization of hierarchical structure are discussed on the example of the Barents Sea.


Introduction
The system of the Global Ocean bioregionalization developed by Spalding et al. (2007) includes 12 realms, 62 provinces and 232 ecoregions (large marine systems). In the Arctic realm whole marine basins (seas) are treated as ecoregions. Their biogeographical features are determined by the degree of their isolation, surface and deep water circulation system, river runoff, tides, thermohaline regime, waving condition of formation and dynamics of ice cover, bottom relief and geological features, ground deposits, types of shore and coast line configuration. The essential role in the formation of oceanographic regime of water area is coupling the interaction between the sea and atmosphere. As a solution to detailed biogeographical division of large marine ecosystems, a landscape and bionomic approach was suggested (Petrov 2004(Petrov , 2012, where the patterns of marine organisms distribution are related to the conditions of their habitat. According to this approach sea bottom organisms which are usually called benthos are consistently found in the combination of relief and types of sea sediments with a specific set of hydrological and hydrochemical factors forming in the whole the large marine ecosystem consisting of local ecoregions. A detailed regionalization of such large marine ecosystems in range of sea basins is necessary for carrying out monitoring, rational use and protection of marine biological resources at different hierarchical levels. Experience of authors of present paper on biogeographical regionalization of the sea basins is based on rich theoretical and empirical material, including on own researches executed earlier summarized in works of Petrov (2009Petrov ( , 2012, Bobkov and Petrov (2013).

Methodical Approach
The biogeographical heterogeneity of the Global Ocean can be treated from landscape and bionomic positions. This approach is based on statement that the specificity of biotic composition is determined by natural conditions. The formation of a bionomic structure in a marine ecoregion is influenced by oceanographic processes which cover water masses, the bottom and boundary layers of the atmosphere (Petrov 2004, Spalding et al. 2007). The landscape-bionomic differentiation of large marine ecosystems reflects three directions of these processes: zonal (latitudinal), vertical (deep) and azonal (geomorphological). In a multicomponent scheme of interactions, two main functional links are distinguished: hydrological and geologogeomorphological (Petrov 2004). Water masses serve as the main ecological factor of biogeographical regionalization. Warm Atlantic waters are delivered into the Barents Sea by Norwegian, West Spitsbergen, Nordcape and West Greenland currents. Cold waters and ice are taken away from the Arctic with East Greenland and Labrador currents. The influence of a hydrological factor is manifested in zonal differentiation of the sea basins. The geological structure and bottom relief constitute a lithogenic basis on which underwater landscapes are formed. Relief and Fig. 4.1 Three-rank system of units of landscape-bionomic regionalization (Petrov 2004) types of ground define the geomorphological subdivision of the bottom which can be used as the basis for studying benthic organisms distributions. The geologogeomorphological structure of the sea floor serves as a framework for defining a system of azonal units regionalization which are not connected with system of zonal units. The both above mentioned feedback loops bear certain environmental pressure affecting to third connection -the bionomic one. Thus, a three-rank system of units at regional level was earlier proposed by Petrov (2004) the essence of which is given in Fig. 4.1. It can be seen that the underwater landscape connects all three units of differentiation. It is characterized by a common geological structure, relief and homogeneous hydroclimate with a corresponding set of bottom organisms and is accepted as an initial unit in hierarchical structure of marine ecoregion.

Units of Zonal Differentiation
The Arctic Ocean and its seas belong to the Arctic geographical belt subdivided into Polar and Arctic nature zones. In the Arctic zone change of environmental conditions occurs in both latitudinal and longitudinal (sectors) directions. Four climatic sectors may be distinguished in the North Polar area: Atlantic, Siberian, Canadian and Pacific (Korotkevich 1985). The Barents Sea belongs to the Atlantic coastal sector.
The division of the Barents Sea Arctic zone into arctic and subarctic provinces is determined by the influence of warm and cold currents forming a stable water mass transfer with characteristic zonal groups of plankton and benthos (  The central part of the basin is situated in the subarctic province. The south-western part of the sea is the most warm area heated by Atlantic waters and belongs to boreal zone. The Barents Sea extrazonal province (Petrov 2009). Located at the intersection of warm and cold waters, the Barents Sea contains a biota which constantly experiences changes with either the onset of warm-water forms or their replacement with cold-water forms. Therefore, the zonal boundaries are vague and encapsulate the arctic and boreal zones through narrow dynamic transitions.

Units of Vertical Differentiation
The prevails. In the second (Ib) -community of Alaria esculenta. In the middle floor (II) the community of Chorda tomentosa + Odonthalia dentata dominates; in the ground floor -community of Balanus balanus (Propp 1971). The upper (surface) stage is located on the border between the atmosphere and sea surface, it is subject to the seasonal fluctuations depending mainly on the budget of solar radiation. On the bottom of the Barents Sea the thermal regime is defined distribution of arctic, subarctic and boreal water masses. In underwater landscapes, where the temperature near the sea floor is below freezing all year round, high arctic fauna dominates. A diver moving from the littoral to the sublittoral zone will find changes in fauna distribution from boreal to high arctic one, even in the same area that confirms its dependence on the water temperature.

Units of Azonal Differentiation
The azonal features of marine basin are presented to us as following: the size, depth and bottom hollow form, a relief of the shore and degree of isolation from the Global Ocean. In general, the distribution of life forms on the seabed is controlled by properties of geological structure, bottom relief and sea sediments and these items gives a reason to distinguish a system of azonal units shown in Fig. 4.1, namely: the marine basin, area, district, region (landscape).

Discussion
Landscape-bionomic concept characteristic of the Barents Sea as of the large marine system marked in scheme of ecoregions of Spalding et al. (2007) shown in Fig. 4.5 under # 18 was elaborated. Its structural elements became reason to discuss. The concept is based on the WWWF's Arctic Programme (Barents Sea …. 2003) visualized on a map in Fig. 4.6. The map was taken as a basis issue where ecoregions shown in Fig. 4.6, are correlated with features deriving from joint analysis of distributions of principal geomorphological elements and macrobenthos shown in Figs. 4.7 and 4.8 respectively. A brief description of these ecoregions is provided below.
1. Southwestern ecoregion in Fig. 4.6 (1 a, Norway near-shore areas, and 1b, the Kola Peninsula near-shore areas) corresponds to Southwestern geomorphological area in Fig. 4.7. The coastline with narrow shelf is washed by waters of the North Atlantic current. The boreal fauna with relic forms in deep fjords prevails.
Owing to the influence of warm Atlantic water, coastal sites have the greatest variety of benthos presented with brown and red algae, sessile and vagile sestonophagous -filtrators on a stony slope. The variety and productivity of benthos decreases with depth. Fig. 4.6 corresponds to Kanin-Pechora flat geomorphological area in Fig. 4.7. In shallow waters on sandy-mud grounds sessile and vagile organisms prevail: sestonophagous, detritivores and ground feeders inhabiting the seabed. The dominating communities are bivalve molluscs Ciliatocardium ciliatum, Macoma calcarea and Serripes groenlandicus. Fig. 4.6 corresponds to the southern part of the Central Barents rift in and the West Barents Sea tectonic and geomorphological areas in Fig. 4.7 and represents a wide transition zone between the Atlantic and Arctic waters. Deep-water communities of ground  Fig. 4.7. This is a zone of detritivores collecting detritus from a seabed. The deep-water community includes Ophiopleura borealis and foraminifer Hormosina globulifera, and also the community of bivalve molluscs of family Astartidae (Elliptica elliptica and Astarte crenata). 5. Ecoregion of the Novaya Zemlya shore in Fig. 4.6 corresponds to the Novaya Zemlya tectonic and geomorphological areas in Fig. 4.7. It is washed by the Arctic water mass with some influence of Atlantic water in the west. On sandymud bottom grounds the trophic groups comprise sessile and vagile sestonophagous-filtrators Hyatella arctica, Strongуlocentrotus sp., whereas Ophiura robusta, Balanus balanus are dominating in bentic community. 6. Ecoregion of the Svalbard Archipelago and the in banks of Spitsbergen in Fig. 4.6 is located inside the Spitsbergen highland geomorphological area in Fig. 4.7 filled by Arctic water mass but influenced by the North Atlantic. It is characterized by high biodiversity. Trophic groups include macrophytobenthos, sessile and vagile sestonophagous-filtrators. On stony bottom grounds, the community of brown algae dominates. The community of sessile sestonophagous is formed  (Kiyko et al. 2006 Fig. 4.6 occupies the North Barents-Kara tectonic and geomorphological areas in Fig. 4.7 and is washed by the Arctic waters. Despite of its northern location, the coastal zone is characterized by both high biodiversity and productivity. The group of inhabitants includes acrophytobenthos, and sessile and vagile sestonophagous-filtrators. Among ground feeders are the communities of polychaeta and sipunculida, as well as the community of holothurian. The slope community of the Saint Anna trench is formed by Ascidiacea var., Nephasoma minuta, Thenea muricata.

Conclusions
In this article the current literature and knowledge on the hierarchical structure of large marine ecosystems was reviewed and based on that it was presented how the Russian Arctic shelf seas fit to the system. The emphasis has been done on the Barents Sea. The following conclusions based on experience of authors on biogeographical regionalization of sea basins including their rich theoretical (bibliographical) sources and own empirical material executed earlier issues, are summarized below.
1. The principles of the hierarchical zoning system of units were discussed by using the large marine ecosystem of the Barents Sea as an example. 2. Landscape-bionomic differentiation reflects three components of the oceanographic process: zonal, vertical and azonal., and three-rank system of units at regional level was introduced. 3. The formation of the marine basin bionomic structure is controlled by the oceanographic processes. In a multicomponent scheme of interactions the following functional links are distinguished: hydrological and geologo-geomorphological ones. Both of them cause a certain environmental pressure, effecting the structure and functions of the third link -the bionomic one. 4. The regionalization unit system is essential for monitoring, rational use and protection of marine biological resources at different hierarchical levels.
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