Aquatic ecosystem profile

This chapter considers the White Sea ecosystem, paying special attention to the food web connections that are continuously establishing between the main bird and mammal species. The White Sea ecosystem is complicated, as each of its levels is characterized by numerous trophic ties that vary in the annual cycle and depend on the current environmental settings in both the White and Barents Seas. The state of phytoplankton and zooplankton communities controls the living conditions at the upper trophic levels. Therefore, these entities are mandatory for the inclusion into any ecosystem models. Constituting the crowning constituent of the hierarchy of the ecosystem ties, sea birds and marine mammals are important in terms of attaining adequate estimates of the inherent aquatic resources, and sustainable development and nature protection. Section 5.1 details the structure and functional characteristics of the phytoplankton community in the White Sea. Section 5.2 describes the same for zooplankton. Section 5.3 describes sea birds and their role in the White Sea ecosystem, while the same is done for marine mammals in Section 5.4.

5.1 PHYTOPLANKTON

Diatomaceous algae are the most abundant phytoplankton and produce the highest biomass in spring and summer. In autumn, some species of peridinien algae increase. The pelagic zone of the White Sea is characterized by an extremely low level of development of phytocene in winter (Makarevich, 1998). In January and February, the quantitative characteristics of the phytoplanktonic community in ice-covered areas are significantly variable. Cell counts are in the range 10-1, 500 cells l-1,

whereas the biomass is confined within the limits 0.3-9.2 mg l-1.

The pelagic zone accommodates mainly diatoms and peridinien algae with a predominance in the community composition of pennant diatoms. Importantly, in the activation stage of the diatomic complex, its biomass is formed mainly by single

non-colonial forms. The only exception is the population of Nitzschia grunowii - although being a constant flora component, these algae are invariably at very low concentration levels. During this activation period, the pelagic algae populations remain in the water column in a dispersed state.

Intensive development of phytoplankton in the White Sea starts in the first-half of April with the prevalent proliferation of cryophilic algae in water with a tempera- ture close to 0oC, the required nutrients being abundant in the water column at that time. The spring outburst of algae biomass and cell counts starts under the ice and right after ice-cover break-up.

At the beginning of May, the phytoplankton cell counts are maximal (3.8 mill cells l-1) while the algal biomass is 1.5g m-3(Kokin and Koltsova, 1971; Fedorov et al., 1982). This is due to the development in the pelagic zone of an early spring diatom algae complex, dominated by Nitzschia grunowii, Navicula septentrionalis,

N. vanhoefenii, and Thalassiosira cf. gravida. The most common species is N. grunowii.

The photic layer accommodates about 86% of the phytoplankton total biomass, which is maximal compared to other vegetation periods.

Grazing of algae by zooplankton during this period leads to a rapid decrease in the algal biomass and brings about some weakening of food competition for nutrients (Konoplya, 1973).

Maximal rates of primary production (302 mgC m-2day-1) accompanied by

high values of algal biomass (17.9 g m-2) across the entire vegetation season con- stitute the so-called vernal peak (Fedorov and Bobrov, 1977).

With the end of spring, in the first-half of June, algal species development slows down significantly: typical cell counts observed during this time period attain some hundreds of cells per litre. At the same time, a pronounced differentiation in the vertical distribution of phytoplankton ecological groups takes place - vernal species with high biomasses (50 mg m-3) are found at a 25-m depth, where low water temperature is still retained. At a 5-m depth, a biomass peak of similar height - generated by the growth of peridinean algae - is registered. During the transitional spring-summer period (when the temperature jump in the surface layer is estab- lished), summer phytoplankton species develop in insignificant amounts.

In July, with the increase in the water column temperature, an intensive growth of small-size Skeletonema costatum algae and species of genus Chaetoceros result in a considerable enhancement of phytoplankton cell counts: in some areas they are as high as 1.2 mill cells l-1. A biomass maximum (0.46 g m-3) and high rates of primary production (117 mgC m-2day-1) are observed at a 2.5-m depth.

In August, the growth of micro-algae typical of summertime slows down, and the cell counts decrease to tens of thousands of cells per litre. In the second-half of August, the phytoplankton biomass starts to increase again owing to the develop- ment of some larger species of the inherent summer-autumnal complex.

The first summer maximum of phytoplankton growth is mostly due to the intensive vegetation of diatoms. The second summer maximum is due to the proliferation of peridiniens. Skeletonema costatum and species of genus Chaetoceros become the predominant algae during the biological summer.

The autumnal plankton community is mostly composed of peridinien algae with a predominance of species belonging to the genera Protoperidinium, Ceratium, Dino- physis, and also some diatoms (e.g., Thalassionema nitzschioides).

The autumnal maximum of phytoplankton is observed between late August and mid-September. It is not necessarily characterized by a well-developed algal biomass peak, as it is influenced by the declining water temperature. This results in a sig- nificant reduction of algal growth, although the nutrients might remain fairly abundant during autumn.

During the entire vegetation period, the indigenous phytoplankton is mostly confined to the upper 10-m layer. Maximal cell counts in spring and autumn are registered at a 0.5-m depth, while in summer this depth increases up to 2.5 m.

The phytoplankton biomass at a 25-m depth varies mainly in the range 5-10 mg m-3. Below, at depths between 50 m and 75 m, the biomass does not exceed 1-2 mg m-3(with the exception of a short period when the biological spring terminates and the descending vernal species increase the algal biomass at these depths up to 60-170 mg m-3(Konoplya, 1973)).

The phytoplankton biomass spatial distribution in the White Sea is controlled by atmospheric cyclonic and anticyclonic circulation patterns (Fedorov et al., 1980). The spatial distribution of micro-algae within the upper 25-m layer is distinguished by the following specific features (Zhitina et al., 1988). Along the Terskiy and Kareleskiy coasts, there are zones with the concentration of algal wet matter reaching 10 g m-3. Further on to the center of the sea, the phytoplanktonic biomass increases up to 15g m-3. This zone extends over the whole central part of the White Sea. In the east, it nearly reaches the Zimniy coast. In the west it expands over the area approaching Kandalakshskiy Bay. Inside this enormous area there are two regions unequal in terms of the inherent algal biomass levels. The first area is located in the western part of the Bassein: the algal biomass there can be 17 g m-3and even higher (up to 20 g m-3). The second area is located in the eastern part of the Bassein at the exit from Dvinskiy Bay: the algal biomass there is less than 10 g m-3.

In the western part of the White Sea, the algal cell counts do not exceed

9.2 x 105cells l-1. The lowest cell abundance is registered in the central part, while the greatest one resides in the vicinity of the marine coasts.

In the eastern part of the sea, the greatest algal cell counts are found in the area s center (7 x 105cells l-1). Along the transect running from the area s center to the Letniy coast and the Gorlo, micro-algae cell counts are moderate (3-5 x 105cells l-1) and distributed notably non-uniformly.

In Dvinskiy Bay, algal cell counts vary in the range 4 x 105-106cells l-1with the

minimal levels restricted to the eastern part of the bay.

In the central area of Kandalakshskiy Bay, the largest algal cell counts (2.3 x 106cells l-1) are found within the 2.5-5.0-m depth range as well as in the inner part of the bay. Importantly, there is a tendency of persistent decreases of algal cell counts in the central part of the bay.

The phytoplankton chlorophyll distribution throughout the White Sea area has a patchy pattern. The observed maximal concentrations of chlorophyll-a in

surface layers of the White Sea are clearly associated with the waters subjected to re- freshening by the fluvial runoff. Consequently, high chlorophyll concentrations are restricted to the apexes of the sea bays.

The mean-weighted chlorophyll concentration in the photosynthetic layer within these re-freshened zones is approximately 1.5mg m-3. High chlorophyll concentra- tions (about 1.5mg m-3) are associated with the area of anticyclonic water movements in the central part of the Bassein. The Gorlo and the northern Bassein waters, driven by surface currents flowing along the Terskiy coast, are characterized by very low chlorophyll concentrations (less than 0.5mg m-3).

The spatial distribution of the chlorophyll content across the White Sea water column is conditioned by the water masses genesis. The highest chlorophyll concen- trations are restricted to the surface waters influenced by strong river runoff. Mean- weighted concentrations of chlorophyll in the upper part of the water column vary within the range 0.5-1.5 mg m-3. Exceptions are the waters in the Gorlo, where the chlorophyll concentrations do not exceed 0.5mg m-3. On average, the mean chlorophyll concentration in surface waters of the White Sea is 1 mg m-3.

The deep-water masses are characterized by rather low chlorophyll concentra- tions. The latter vary within the range 0.02-0.15mg m-3(on average they are about

0.1 mg m-3).

Anthropogenic eutrophication, which by definition is the enrichment of natural waters with nutrients (primarily phosphorus), leads to serious transformations of the structural and functional attributes of the indigenous algal communities. Increasing phosphorus concentration in the aquatic environment stimulates an enhanced pro- liferation of hydrobiota. Importantly, the alterations to the structure of the pelagic ecosystem occur at significantly greater rates than if happening under the influence of natural eutrophication.

The seasonal dynamics of phytoplankton growth are determined mainly by hydrophysical processes, first and foremost by the rate of water mass warming.

With the onset, and in the course of regular hydrological seasons, the thermal structure of water masses depends on the actual climatic conditions. Each hydro- logical season is characterized by a suite of algal species, determining the structure of algocenosis. In the case of anthropogenic eutrophication, the algal species composi- tion, pertaining to concrete seasonal complexes, changes due to broadening of the spectrum of dominant species. This is also accompanied by a loss of some forms of the most common species as well as by a transfer of some species into the planktonic complexes of adjacent seasons.

However, the vernal phytoplankton always develops with the start of ice break- up and the increase in insolation. Further on, this algal complex turns into the summer one, and its development is promoted by the increase in the water column temperature. Nutrients (of anthropogenic origin) accessible for the algae provoke a fast increase in algal concentration and thus are capable of reducing the pause between vernal and summertime peaks of micro-algae development.

Analyses of phytoplankton taxonomic composition dynamics during the period of plankton phytocenoses reconstruction driven by anthropogenic eutrophication

fails to confidently establish total species composition enrichment of the phytoplank- ton community. Evidently, the total number of micro-algae species and the ratio of systematic taxons during anthropogenic eutrophication are not significant. This is due to the fact that of the total number of the oceanographic factors affecting the plankton community, changes in the content of a single nutrient have been registered.

Sufficient availability of nutrients resulting from anthropogenic eutrophication is favorable for all micro-algae taxons, and increases the productivity to the phyto- plankton community as a whole. However, some separate species might exhibit even higher rates of development than others (including such parameters as cell number counts, biomass, and primary production).

Investigations of the impact produced by heavy metals on phytoplankton com- munities showed that in natural phytoplankton assemblages the inherent functional and structural characteristics become altered. For instance, marine unicellular algae prove to be sensitive to the input of such a type of pollutants. Their reaction to the contamination is traced most clearly when analyzing the dynamics in the phyto- plankton species composition.

The impact of enhanced concentrations of sub-lethal toxic compounds on the phytoplankton community might lead not only to a dramatic fall or rise of primary production, but also to a change in the community structure. This in turn might result in problems of energy transfer along the trophic chains.

Experiments dedicated to the littoral benthic diatoms in the White Sea (Bondarchuk, 1980, 1991) revealed a dependence of community structure change on the level of contamination. At the present (moderate) level of contamination, the number of dominating species has diminished. Apparently, in the case of very heavy contamination only one species will remain dominating.

Numerous field investigations indicate that sub-lethal concentrations of heavy metals while affecting the plankton do not cause changes to either primary produc- tivity or photosynthesis activity, although some changes in species composition and impoverishment of taxonomic diversity were observed under such conditions. Algal species resistant or immune to water intoxication become prevalent in the phyto- plankton community.

Results of experimental investigations of the effect of the sub-lethal concentra- tions of the most common pollutants and their combinations on the natural phyto- plankton populations carried out in Kandalakshskiy Bay in the period 1979-1983 (Kapkov et al., 1991) showed that all levels of heavy metal concentrations inhibited the formation of organic matter at sea. The degree of their effect varied during the whole vegetation period. Summer phytoplankton turned out to be more sensitive to increased pollutant concentrations. Thus, contamination with heavy metals in con- ditions of anthropogenic forcing will cause most undesirable changes in the natural phytoplankton community during the period of spring-summer bloom.

The joint action of different metals did not cause additive interaction between toxicants investigated - and vice versa, their joint presence in water impacted the biota to a lesser degree than each of them would separately.

5.2 ZOOPLANKTON

The number of zooplankton species inhabiting the White Sea is estimated to be

133. Analyses of species composition indicate that, by and large, the White Sea zooplankton is an impoverished fauna of the Barents Sea.

The zooplankton community in the White Sea consists in different seasons of marine eurythermous and euryhaline species: Pseudocalanus elongatus Boeck, Acartia longiremis Ailliebord, Temora longicornis Muller, Centropages hamatus Aill- ieborg, Oithona similis Claus, Oncaea borealis Sars, Microsetella norvegica Boeck, Evadne nordmanni Aoven, Podon leuckarti Sars, and larvae Cirripedia.

In coastal waters subjected to river runoff, there is an increase in the neritic plankton forms, such as A. longiremis, Acartia biElosa Giesbrecht, larva Cirripedia, and Acartia Aamellibranciata.

In the near-bottom layers such typical Arctic and Arctic-boreal species as Calanus glacialis Jaschnov, Metridia longa Aubbock, P. elongatus, Sagitta elegans Verril, and Oikopeleura vanhofeni Aohman consitute the major planktonic popula- tion. The most common species residing in the White Sea is P. elongatus. This zooplankton plays an important role in the diet of the White Sea herring and its juveniles.

The zooplankton concentration depends on the content of micro-algae in water. The availability of micro-algae is controlled in turn by the hydrological regime of the water and primarily by water temperature. The diversity of environmental con- ditions in different parts of the White Sea is the major reason for a non-uniform distribution of zooplankton.

In the Kandalakshskiy and Dvinskiy Bays, the zooplankton biomass is higher than in the Voronka and the Onezhskiy and Mezenskiy Bays. A high zooplankton biomass in both Kandalakshskiy Bay and the Bassein was also reported earlier.

In the Onezhskiy and Mezenskiy Bays as well as in the Voronka, the indigenous zooplankton species composition is represented mainly by small eurythermous and neritic zooplankton species, whereas in the areas with a strongly pronounced tem- perature stratification of water, large cold-water forms of zooplanktons also amply develop.

The biomass distribution of P. elongatus generally accounts for the total zoo- plankton biomass distribution in the White Sea because this species prevails nearly everywhere in terms of both its concentration and biomass. The concentration of P. elongatus in the Bassein is typically lower than it is in the Kandalakshskiy and Dvinskiy Bays.

The zooplankton distribution in the White Sea is influenced by cyclonic and anticyclonic circulations. Within the Bassein, in near-surface waters, maximal and minimal amounts of plankton in the so-called pole of warmth and pole of cold were observed from 1930-1970. However, fairly detailed investigations of the spatial distribution of zooplankton organisms carried out in the 1970s gave quite different results for these areas.

In July 1972, the greatest biomass was found in the southern Gorlo, in the area neighboring the Bassein. Areas relatively rich in zooplankton were also observed in

some parts of the Bassein adjacent to Dvinskiy Bay (the area of the pole of cold ) and partially within a cold spot located within the boundary area separating the Bassein and Onezhskiy Bay. The central part of the Bassein, particularly the pole of warmth , was poor in zooplankton. Major planktonic accumulations were found within the upper 25-m layer. With depth, the zooplankton biomass diminished. This is generally typical of the spring and summer distribution. Such cold-water species as

C. glacialis, M. longa, O. similis, P. elongatus, O. borealis, M. norvegica, S. elegans, and O. vanhofeni constituted the major biomass in the Bassein. The predominance of cold-water species qualitatively and quantitatively determines the zooplankton community composition in the White Sea.

O. similis and M. norvegica were distributed relatively uniformly in the upper layers of the White Sea, achieving maximal concentrations in the central part of the Bassein. In the upper layers, the juveniles P. elongatus and C. glacialis dominated, whereas at depths in excess of 25m, a significant portion of the zooplankton community was represented by older age groups of the two latter species and by M. longa and O. vanhofeni, which were generally found beneath the thermocline.

The water stratification in summer in the central Bassein develops due to a complete lack of convection and weak mixing produced by constant and drift currents. In this period, three water masses, viz. surface, intermediate, and bottom are clearly distinguishable. The core of the intermediate water mass has a negative temperature (-1.0oC) and is characterized by somewhat increased water salinity (28.50).

In contrast to spring, the distribution of zooplankton during summer in the Bassein exhibits different patterns. The observed decline in biomass in the upper layers is conditioned by the descent of elder colanoid juveniles to depths in the range 25-50 m. The greatest biomass (388 mg m-3) in this period is registered at depths within the range 50-100 m. At the same time in the intermediate layer (25- 50 m) extremely low biomass levels were registered. In summer, Calanus Enmarchicus Gunner dominated at all stations.

In autumn, as the surface waters in the Bassein cool, a general decline in the zooplankton biomass was observed. An exceptionally low biomass was registered in the upper water layers, whereas near the bottom, it proved to be slightly higher.

The best site for investigating zooplankton is Kandalakshskiy Bay. This area is characterized by clearly expressed water stratification. The presence of cold-water zooplankton is associated with near-bottom cold water. Boreal species mainly inhabit surface layers and/or shallow-water areas.

The zooplankton community in Kandalakshskiy Bay is subject to significant seasonal variations. In winter, the number of species is not significant and accounts for about 30-40% of all zooplankton species residing there.

In spring, the species diversity increases and reaches its maximum. In summer, the zooplankton species composition remains practically unchanged. The only exception here is the disappearance of neritic species, snake-necked tortoises (Hydromedusa genus) in particular. A drastic impoverishment of zooplankton species composition takes place during autumn.

In spring, the upper layers of the water column and shallow water areas are rich in zooplankton. Of the latter, the most abundant assemblages occur in the outer part of the bay where the zooplankton biomass in different years exceeded 500 mg m-3. The surface layer (0-25m) in the coastal areas of the White Sea is richer in zoo- plankton than the pelagic surface waters.

Planktonic organisms perform diurnal vertical migrations. These migrations are especially intensive in summer due to the ascension of living organisms to the water surface. During night hours, the biomass increases in the upper 25-m water layer. The high biomass of spring zooplankton in shallow waters and in the surface waters of Kandalakshskiy Bay is due to P. elongatus, which dominates during this time period and may account for about 70% of the total biomass. A significant

portion of it is comprised of A. longiremis and O. similis.

The plankton biomass in pelagic areas arises mainly from some copepod species:

P. elongatus, C. glacialis, O. similis, and O. borealis. 50% of the total biomass is provided by P. elongatus. In spring, C. glacialis resides at depths exceeding 25m. In the upper 10-m layer, this crustacean is not readily found.

The spatial distribution of zooplankton in Kandalakshskiy Bay in summer retains the features typical of the spring pattern. The biomass diminishes both with depth and in the offshore direction. In the outer part of the bay, the zooplank- ton biomass is higher than it is in the offshore area. In summer, the zooplankton biomass in Kandalakshskiy Bay is composed of the neritic plankton species of boreal origin: T. longicornis, C. Hamatus, and A. longiremis. Everywhere at all depths,

O. Similis and M. norvegica can be found. At depths exceeding 25m, C. glacialis,

M. longa, O. borealis, and P. elongatus become most abundant. During this period, the distribution of zooplankton is patchy. Patches with high concentrations of animals are formed due to their diurnal vertical migrations.

The total zooplankton biomass increases during night-time in the upper water layers. During daytime, the biomass increases at some middle depths.

The patchy distribution of zooplankton biomass in Kandalakshskiy Bay is controlled by the water circulation processes. Patches with zooplankton biomass higher than 500 mg m-3are fairly extensive constituting a few tens of square meters. Changes occurring in the zooplankton composition are of great significance in terms of formation of zooplankton accumulations in different years and various areas of Kandalakshskiy Bay.

In autumn, with the onset of seasonal migrations, different zooplankton species accumulate at different depths. During this period, the zooplankton biomass in deep water rises most significantly. The abundance of neretic species in this period rapidly declines. The zooplankton species diversity in the upper layers is appreciably impo- verished. In the lower part of the bay the concentrations of planktonic organisms remain quite high. Migrating along the vertical, O. similis, P. elongatus, and O. borealis constitute the background species in this autumnal period.

Spatial distributions of the total biomass of zooplankton in the Bassein and in Kandalakshskiy Bay follow the pattern characteristic of copepod species in these areas, as their part in the total biomass exceeds 80%.

In different seasons of the year, M. longa and C. glacialis move down to deep-

water areas where negative water temperatures remain. In summer, such boreal species as P. elongatus, C. hamatus, T. longicornis, and A. longiremis mostly reside in surface waters, which are fairly warm.

Throughout an annual cycle, significant variations are registered in the distribu- tion of zooplankton species. This is conditioned by the change in the species age composition and is connected with the specific features of life cycle characteristics of separate species.

Diurnal and seasonal migrations are typical of all species. M. longa, C. glacialis, and P. elongatus migrate throughout the whole water column. C. hamatus,

T. longicornis, and A. longiremis move up and down within the surface and transi- tional water layers.

The greatest intensity and amplitude of diurnal vertical migrations of different zooplankton species is registered in August with the termination of the white nights period. The coefficient of intensity of diurnal vertical migrations during this period is in the range 14-78%. Later in autumn and further into winter, during the period of homogenous temperatures, the sky illumination is minimal and the intensity of the zooplankton migration intensity is rather low.

Seasonal variations in the vertical distribution of zooplankton species arise mostly from some specific features of their biology. Phytophagues C. glacialis and

P. elongatus move up to the water surface in spring during vegetation. In the autumn-winter period, the upper layers are inhabited by euryphagous M. longa even if there is a lack of phytoplankton. Other species are practically invariably located in the 20-30-m upper layers. Inside this layer, but deeper than in other months, the crustaceans remain during the most intensive warming up of the White Sea (i.e., July-August).

Relatively high zooplankton biomass and concentration are typical of Dvinskiy Bay. Significant variations of indices characterizing the zooplankton biomass and concentration over a sequence of years are revealed. For the 1976-1985 period the zooplankton concentration varied within the range 2,400-28,700 specimens m-3, the biomass fluctuating between 102-434 mg m-3. Such variability is inherent in some specific features of the annual hydrological regime. Its impact expands not only upon the state of the zooplankton community per se, but upon its temporal and spatial distributions.

During spring and summer, the warming of the White Sea water was very intensive in 1973-1975, 1977, 1980, 1983, and 1984. A moderate level of warming

was observed in 1970, 1972, 1976, 1979, and 1981. In 1971, 1978, and 1985, the water temperature was fairly low. All of these changes affected the zooplankton state and produced the most crucial variations in the content of zooplankton in the outer part of the Dvinskiy Bay (the coefficient of correlation r = 0.88 at P = 0.99). During the spring period, the correlation coefficient related to the content of zooplankton in Dvinskiy Bay was 0.92 at P = 0.95.

The vernal spatial distribution of zooplankton biomass in Dvinskiy Bay is very heterogeneous. Areas with increased levels of biomass are more stable in the south- eastern part of the bay. A pronounced vertical stratification of water, constant currents directed to the south-east along the Letniy coast, and cyclonic eddies in

the bay area favor a significant enhancement of the concentration of planktonic organisms. Large amounts of zooplankton in this area were reported for 1976, 1979, 1982, and 1984. High concentrations of the zooplankton are observed in the south-western areas of the bay. The densest zooplankton accumulations were found in the upper 25-m layer, but with depth the biomass proved to be abating. The characteristic Arctic and Arctic-boreal species are mainly the organisms which in spring constitute the total zooplankton biomass in Dvinskiy Bay. This can probably be explained by the impact exerted by the closely located pole of cold . If in the inner part of the bay the zooplankton community encompassed P. elongatus in prevailing amounts, then in off-coastal areas neighboring the Bassein such species as S. elegans, C. glacialis, and M. longa developed in large quantities.

Due to a pronounced temperature stratification of water, the biomass and species composition of zooplankton vary noticeably with depth. In surface water,

P. elongatus, O. similis, and M. norvegica prevail. At depths in excess of 10 m the above-mentioned species are joined by M. longa and O. vanhofeni. Warming of surface water in summer is accompanied by intensive growth of boreal species in the Dvinskiy Bay. The indigenous zooplankton background is composed of small copepods (Copepoda): O. similis, A. longiremis, P. elongatus and T. longicornis. The most numerous in the plankton of this period are O. similis and P. elongatus. The O. similis species is predominant in the upper 10-m layer, where its content is generally more than a half of the total concentration of the zooplankton there.

In contrast, the concentration of P. elongatus increases with depth. Even at significant depths its biomass might exceed 40% of the total zooplankton biomass. In some years, other zooplankton organisms also contribute to the zooplankton community in summer. Thus, in August 1976, a very intensive growth of A. digitale was observed in Dvinskiy Bay, where this species was predominant in the upper 25-m layer.

In 1976, in the vicinity of the Vepreyevsky station, the species Deriuginia tolli Ainco was found - rare for the White Sea Arctic crustaceans. As the temperature of surface water rises, C. glacialis and M. longa start to migrate to deeper layers of the water column.

The growth of summertime zooplankton in Dvinskiy Bay is relatively homo- geneous in comparison to the spring period. Increased biomass levels are still typical of the inner part of the bay. In pelagic areas there is a total decline of quantitative indices. The upper 50-m layer proves to be richest in zooplankton throughout the bay.

In autumn, the Bassein-like regularities in zooplankton distribution remain intact. During this period, the development of zooplankton in Dvinskiy Bay abates and its biomass at all depths noticeably declines. Warm-water forms of zooplankton disappear and the number of eurybionte species diminishes. However, against the background of a homogeneous distribution of planktonic organisms in the upper 10-m layer, some small areas occur with increased concentra- tions of M. longa and S. elegans. A slight increase of the zooplankton biomass at depth presumably originates owing to the development cold-water species.

For the late autumnal period, a reverse water mass stratification is typical of

Dvinskiy Bay. During this period, oceanic and Arctic species are the major com- ponents of the zooplankton community. Onezhskiy Bay is the shallowest and, con- sequently, warmest area of the White Sea. Sixty-one zooplankton species are found in Onezhskiy Bay and its composition includes both pelagic forms and benthic (bottom) animals.

The specific features of the hydrological regime in Onezhskiy Bay create special living conditions for the indigenous organisms. This affects the zooplankton compo- sition and distribution. Significant summer warming and strong winter cooling of the whole water column are favorable for the existence of eurybionte forms. Widely represented in all Nordic Seas, such forms as A. longiremis and P. elongatus prevail significantly in the local zooplankton community. In addition, O. similis, which is distributed everywhere, also contributes to the zooplankton community in Onezhskiy Bay. In Onezhskiy Bay, such Arctic copepod forms as M. longa and mollusks such as Aimacina helicina, as well as some other planktonic organisms characteristic of the Nordic Seas, are practically absent.

The basis of the plankton community to the south of the Solovetskiy Archipe- lago is composed of boreal neritic species. In the upper layers of the northern part of Onezhskiy Bay, eurythermic species of zooplankton, which are widely distributed in the Bassein, develop in large amounts. In pelagic areas, the Arctic and Arctic-boreal species prevail in the plankton composition.

In the northern area of Onezhskiy Bay, where water temperatures are lower, such warm-water boreal species as T. longicornis, C. hamatus, E. nordmanni, and P. leuckarti, become less numerous, whereas the role of the Arctic species, such as

C. glacialis and M. longa in the plankton community become more important as the depth increases. Early stages of development of the Arctic species M. longa in June are found there and constitute the basis of the zooplankton community. But in July, as the water temperature increases, the above species move down in search of cold-water layers. During this period, in the upper layers of the inner part of Onezhskiy Bay, species typical of the pelagic area of the White Sea, such as O. similis, M. norvegica, S. elegans, and A. digitale, are found in large amounts. Their concentration decreases toward the inner part of the bay since these species are intolerant to freshened water conditions. In surface waters to the south of the Solovetskiy Archipelago the basis of the plankton community everywhere is almost composed of A. longiremis and larvae of Cirripedia. In the bottom layers, it is C. glacialis that dominates most frequently.

The distribution of the total biomass of zooplankton across Onezhskiy Bay is very inhomogeneous. Areas with high zooplankton concentrations are located in the neighborhood of areas nearly devoid of zooplankton. Patches with high biomass are observed in the outer part of the bay in spring and in summer. In summer, analogous patches are observed in the vicinity of the Pomorskiy coast. In the outer part of the bay P. elongatus, A. longiremis, Cladocera, larvae of Cirripedia, and Aamellibran- chiata prevail in terms of the biomass. Nearer thr coast, high levels of biomass are formed owing to P. elongatus, A. longiremis, and larvae of Cirripedi.

The interannual variability of small-size zooplankton concentrations in Onezhskiy and Dvinskiy Bays depends on the water temperature variations. The

correlation between the water temperature in spring and zooplankton concentration in the inner part of Onezhskiy Bay is r = 0.80 at P = 0.99.

Seasonal studies of zooplankton development in Onezhskiy Bay have shown that during spring and summer the average level of the zooplankton biomass for the whole bay is not high. Indeed, it is significantly lower in comparison to Dvinskiy Bay.

In autumn, in Onezhskiy Bay, especially within the areas of shallow water, the water temperature falls sharply. This is accompanied by either a disappearance or significant decrease of some warm-water forms such as Cladocera and larvae of Cirripedia. The basis of the autumnal zooplankton is constituted by P. elongatus,

A. longiremis, and M. norvegica. During this period, a very significant biomass decrease occurs at all depths, although in some years (1974 and 1975) there was an increase in the zooplankton biomass throughout the entire water column. This resulted from the development of some new, non-indigenous planktonic species. In 1974 such high concentrations of tunicate larvae were registered in the upper 10-m layer within the southern, and central parts of the bay, whereas in the inner parts it occurred at depth, 25-50 m above the bottom. To the south of the Solovetskiy Archipelago, near the Pomorskiy coast, zooplankton biomass growth (302 mg m-3) occurred due to the presence of the cold-water tunicate O. vanhofeni. Near the Onezhskiy coast, a similar phenomenon was produced by the boreal F. borealis. During autumn 1975, the zooplankton biomass in near bottom waters in the outer part of Onezhskiy Bay increased owing to thriving C. glacialis.

Thus, the zooplankton biomass in the White Sea is formed by the following species: P. elongatus, Calanus glacialis, Metridia longa, A. longiremis, T. logicornis,

O. similis, O. borealis, M. norvegica, S. elegans, O. vanhofeni, and F. borealis, as well as bottom zooplankton larvae.

When estimating the nutrition basis for the pelagic fish species, it is more important to reveal the specific features of their spatial and temporal distribution across the sea. In order to solve these problems, simultaneous samplings of zoo- plankton were carried out in different parts of the White Sea.

The Arctic species C. glacialis constitutes a significant biomass in the Dvinskiy and Kandalakshskiy Bays. In small amounts this zooplankton species is present in the outer part of Onezhskiy Bay. In the Gorlo it is rather rare. Along the Terskiy and Pomorskiy coasts, the maximum abundance of this crustacean is registered at depths exceeding 10 m, while in Dvinskiy Bay it is more frequent in the surface water. In the outer part of Onezhskiy Bay, C. glacialis is distributed uniformly throughout the water column.

The Arctic species M. longa is mostly abundant in the central Bassein. The most significant concentrations of this species are reported from Dvinskiy Bay. Metridia was found neither in Mezeskiy Bay nor in the Voronka, although it is present in insignificant amounts in the northern part of Onezhskiy Bay. M. longa, as a rule, does not reside in layers located closer than 10 m to the water surface. This regularity is observed everywhere throughout the White Sea, except for Dvinskiy Bay.

The boreal-Arctic species Sagitta elegans is distributed in the White Sea within the areas where water stratification is well pronounced. The highest biomass of this

species is found in the transitional area between Dvinskiy Bay and the Bassein, near the Pomorskiy and the Terskiy coasts. S. elegans also occurs in the outer part of Onezhskiy Bay.

Young Sagitta generally reside in the upper 25m. At depths in excess of 50 m only adult specimens are observed. Sagitta dimensions increase with depth in the Gorlo, in Kandalakshskiy Bay, and near the Pomorskiy coast. In Dvinskiy Bay, exclusively large specimens are found in the upper layers, while in Onezhskiy Bay, only small forms are observed mainly throughout the entire water column.

The Arctic-boreal species Pseudocalanus elongatus is well adapted to the White Sea habitats. This is one of the most numerous species of the zooplankton community in the White Sea. It is found nearly everywhere and generally at all depths.

The boreal species Temora longicomis inhabits predominantly surface waters. Temora resides mainly in shallow, well-aerated coastal waters. It is widely distributed over the entire White Sea, but does not form large agglomerations. This species is also found in the well-warmed coastal zone of the Gorlo. Areas with pronounced thermal stratification accommodate Temora in the upper 10-m layer, whereas in marine areas characterized by strong mixing and more homogeneous temperatures, Temora inhabits the upper 25-m layer.

During summer, larvae of Cirripedia are the predominant species in zooplankton samples both in terms of their biomass and concentration. They are an invariable component of zooplankton residing in the Mezenskiy and Onezhskiy Bays as well as in the Voronka. In the northern part of Onezhskiy Bay and near the Pomorskiy and Terskiy coasts, the concentration of the Cirripedia larvae is significantly lower. There is a specific feature in the distribution of the Cirripedia larvae - the tendency to inhabit areas with hydrological regimes resembling that of the Gorlo.

5.3 SEA BIRDS OF THE WHITE SEA: CONCISE CHARACTERIZATION OF THE CONTEMPORARY STATUS

In terms of ornithology, the White Sea is one of the most studied seas in Russia. The first research addressing birds in this region dates back to the late 18th century. At the same time, historically most attention was paid to ornithological studies during nesting periods in the areas of mass reproduction. These are relatively shallow-water areas with a large number of islands located in the Onezhskiy and Kandalakshskiy Bays.

Connected to the Barents Sea, the White Sea can be considered part of the greater Arctic Ocean. However, both quantitative and qualitative analyses of the White Sea nesting avifauna differ noticeably from avifauna in other parts of the region. In contrast to the Barents Sea, sea birds, and birds whose habitat is close to the coastline are more widely distributed. The number of typical sea birds (residing on land only during reproduction) is limited in comparison to other regions.

The first group is composed of divers (red-throated diver [Gavia stellata] and black-throated diver [Gavia arctica]), numerous species of river ducks (mallard duck [Anas plathyrhynchos], widgeon [Anas penelope], pintail [Anas acuta]), some species of sea gulls (common [Aarus canus] and black-headed [Aarus ridibundus], lesser black- backed gull [Aarus fuscus]), and charadriiforms (ringed plover [Charadrius hiaticula], oystercatcher [Haematopus ostralegus], red-necked phalarope [Phalaropus lobatus], and turn-stone [Arenaria interpres]). The second group consists of cormorant [Phalacrocorax carbo], common eider [Somateria mollissima], scaup [Aythya mania], common scoter [Melanitta fusca], common golden-eye [Bucephala clangtila], goosander [Mergus merganser], red-breasted merganser [Mergus serrator], arctic skua [Stercorarius parasiticus], herring gull [Aarus argentatiis], great black-backed gull [Aarus marinus], Arctic tern [Sterna paradisaea], black guillemot [Cepphus grylle], and razorbill [Aica torda]. Among these typical sea birds (in the White Sea), in some years there nested glaucous gull [Aarus hyperbor- eus], kittiwake [Rissa tridactyla] and puffin [Fratercula arctica].

5.3.1 Abundance

The major places of reproduction for sea and coastal zone birds are located in the Onezhskiy and Kandalakshskiy Bays. The total abundance of birds effecting their reproduction in the fjords of the White Sea is estimated at 110,000-130,000, of which 30,000-50,000 are ducks and 80,000 are ploverforms (Bianki, 1993).

Sea ducks are nearly represented by a single species, viz. common eider (endemic population). According to the estimations performed by Bianki et al. (1995), the total number of eiders in the White Sea is 40,000-60,000, of which 20,000-30,000 birds are mature specimens. Although undertaking seasonal migrations, the White Sea common eiders (in contrasts to other sea bird species) do not leave the White Sea Basin. The major places of molting of post-nuptial males are located in the shallow waters near the Solovetskiy Archipelago and the Terskiy coast.

In these very areas, populations of common eiders spend winters in stationary polynya. According to airborne surveillance conducted in 1977, about 37,800 common eiders spend winter in polynyas in the White Sea (Shklyarevich, 1979). A significantly fewer number of birds belonging to this species spend winter in polynya in the inner part of Kandalakshskiy Bay.

On the basis of the number of assessments carried out in the 1990s by Semashko and Cherenkov in Onezhskiy Bay (see Babkov, 1992), typical sea colonial bird species prevailed in the nesting areas. The basis of the marine avifauna is only constituted by five species, viz. the Arctic tern (15,000-20,000 pairs), herring gull (5,600-5,700 pairs), common eider (5,000-5,500 pairs), razorbill (3,000 pairs), and black guillemot (2,500 pairs). Other species of colonial sea birds were considerably less in number. Thus, the local cormorant population was only 300-400 pairs. The red-breasted merganser was represented by 250-300 pairs, the number of the Arctic skuas was 160-170 pairs, while the population of the great black-backed gulls and sheld ducks (Tadorna tadorna) was 111 pairs and 20-30 pairs, respectively.

Of semi-aquatic birds, gulls were the most abundant: 4,500 pairs of the common

gull, and 1,800-1,900 pairs of the black-backed gull. The population of charadrii- forms was noticeably lower. Of the latter, the most numerous species were oyster- catchers (1,000-1,100 pairs) and turn-stones (430-450 pairs). Ringed plovers were not numerous (30-35 pairs).

The majority of sea, aquatic, and semi-aquatic birds nest in Kandalakshskiy Bay, where the Kandalaksha State Natural Reserve is established. According to the State Reserve scientists, in 1997 approximately 12,000 pairs of birds belonging to 6 common species nested on the archipelago of the bay (Koryakin, 1997).

The basis of the Kandalaksha Bay avifauna is constituted by typical sea birds, primarily the common eider and herring gull. The number of the former species in 1997 significantly exceeded 6,000 pairs, while the population of the latter was only 2,000 pairs. Sea ducks are represented by such species as the scoter, greater scaup, and red-breasted merganser. The first two former species nest on islands in insignif- icant numbers, and their total population does not exceed 1,000. The red-breasted merganser uniformly nests in fjord areas and on islands of the archipelago of the western part of the sea, where the population of these birds rarely exceeds 1,000 pairs (Bianki et al., 1995).

In Kandalakshskiy Bay the Arctic tern was scarce in 1997 (only 887 pairs according to Koryakin, 1997). Of alciforms, the black guillemot was most numerous (361 pairs). However, based on other sources, the number of nesting alciforms increased in this region to 700-750 pairs in the mid-1980s (Bianki et al., 1995).

Seagulls nest regularly in Kandalakshskiy Bay, but their numbers do not exceed 100 birds (Bianki et al., 1995). Cormorants nest nearby as well. According to some previous reports, in the mid-1980s the population of cormorants did not exceed 200 birds.

The semi-aquatic birds were mainly represented by mainly two species, viz. the common gull and oystercatcher. The numbers of the former reached 1,215pairs, that of the latter - 906 pairs.

The population of river ducks, such as the mallard, widgeon, and pintail pre- dominantly nest on the islands of the White Sea. Their numbers are estimated at 200-300 pairs of each species (Bianki et al., 1995).

In addition, in the White Sea there are areas of residence, molting, and migration stops of mass males belonging to several sea duck species, and other aquatic birds. The inner part of Kandalakshskiy Bay is the place of post nuptial molting of the golden-eye males arriving from all places neighboring the White Sea. During summer, there might be up to 15,000-20,000 birds of this species. Goosander males also come there for molting. The number of the latter species is estimated by Bianki et al. (1995) at 1,000-2,000 birds.

As pointed out above, the molting places of common eider males are located mainly in two areas within the White Sea - in shallow waters in the vicinity of the Solovetskiy Archipelago and along the Terskiy coast. In the latter area other sea duck species (presumably west Siberian populations) molt, in particular the king eider (Somateria spectabilis) and Steller s eider (Polysticta stelleri ). The total duck molting numbers in these areas during recent years have not been estimated because from the 1970s no ornithological observations have been undertaken.

It is well known that the east Atlantic migration route of aquatic and near-water bird species runs over the White Sea. Millions of birds migrate along this route twice a year, when autumnal migration is more prolonged in comparison with the vernal. The major stream of migrating birds moves in the eastern part of the sea through Onezhskiy Bay and along the Terskiy coast. A less busy migration route runs through the western part of the Bassein including the outer part of Kandalakshskiy Bay. Large species of gulls migrate using other routes and in this period have less close connections with the marine ecosystems.

According to some estimates, the total number of aquatic birds migrating over the White Sea exceeds 10 million. Of them, approximately 5 million belong to a single species of sea duck, namely, the long-tailed duck (Scott and Rose, 1996). In addition, this route is used by a significant number of other migrating sea duck species and, first of all, by the scoter (Melanitta nigra) and common scoter. The total number of migrating specimens of the former species reaches 1.6 million, while that of the latter is somewhat less - 1 million (Scott and Rose, 1996). According to the observations conducted in Onezhskiy Bay in the autumn of 1999 a significant number of these birds are capable of crossing the White Sea without stopovers. The visible number (visually registered by the observer on the land) might vary for different birds within the range of 0.4-37.5% of the total population of migrating birds (Levio et al., 2001). According to the observations of these authors in the autumn of that year, the most numerous migrating flock of birds was the long- tailed duck, but the number of the registered specimens was only 6.2% of the total population. Additionally, the number of counted red-throated divers constituted 27.1% of the total population.

The most common places used by migrating aquatic birds species as stopovers are located on the Terskiy coast and within the vast Soroksiy shallow-water areas, located between Bolshoy and Maly Zhuzhmy islands and the Sumskiy fjords in Onezhskiy Bay. According to the assessments made by Bianki et al. (1995) during the peak of autumnal migration approximately 26,000 long-tailed ducks reside there simultaneously. Bianki et al. (1995) assume that the majority of flocks do not stay in the area for more than one day. Thus, during the period of autumnal migration approximately 600,000 birds of this species stopover in these areas. Other common sea duck species, namely the common scoter and scoter, are less numerous. The intensity of the observable migration of the former species varies from year to year within significant ranges. On average, during the first-half of October in 1983 and 1984 the common scoter distribution density was 31 birds km-2in the fjords and 10-12 birds km-2in off-sea parts and continental bays (Bianki et al., 1995).

In addition, common charadriiforms migrate across the White Sea and have their stopovers. In spring, the knots (Calidris canutus) fly in large numbers across Kandalakshskiy Bay, while the dunlins (Calidris alpina) and bar-tailed godwits (Aimosa lapponica) come there in lesser numbers. The autumnal migration of char- adriiforms is especially intense over Onezhskiy Bay. There are not only dunlins and bar-tailed godwits, but also gray plovers (Pluvialis squatarola), golden plovers (Pluvialis apricaria), whimbrels (Numenins phaeopus), and other species regularly observed.

5.3.2 Trophic chains

All birds nesting in the coastal area and on islands of the White Sea are connected to some extent to the marine ecosystem. Even river ducks, such as the mallard, pintail, and widgeon, feed frequently on mollusks found in the littoral zone. Particularly multifaceted are the connections with the sea of typical colonial sea birds, sea ducks, and some near-water bird species. Based on their dietary characteristics, they can be divided into three groups: fish phagous, benthos phagous, and euryphagous birds. This division is fairly provisional because the trophic behavior of birds is rather flexible and allows them to actively use other types of available food.

Of the White Sea birds, cormorants, divers, and sea ducks/mergansers are referred to as typical fish phagous species. Cormorants as in other areas of the Barents Sea region, catch mainly bottom and demersal fish species. According to the observations by Bianki et al. (1995), the basis of their diet in this region is cod with an insignificant admixture of navaga, Arctic sculpin, and some other fish species.

In Onezhskiy Bay during the autumnal migration period, fish constitute up to 70% of the total amount of food for red-throated and black-throated divers (Bianki et al., 1995). The navaga and smelt also feed in this area during this period. Obviously, during other seasons and in other areas the divers must prey on other fish species, probably due to their higher abundance. Like other species of fish phagous bird species, fish divers can feed on other types of food like polychaetes and crustaceans, though these constitute only a supplementary source of food.

The goosander and red-breasted merganser feed mainly on gobies, gunnels, and stickleback (Bianki et al., 1995). It should be remembered that all these data are probably exclusively appropriate to Kandalakshskiy Bay. Our data indicate that in other regions of the White Sea the goosander also hunts very actively for the sand eel. Specialized ichthyophagous alciforms are the main catchers during the reproduc- tion phase. Nevertheless, the short-billed guillemot feeds mostly on bottom fish species (e.g., gobies and gunnels), while the razorbill feeds on pelagic fish species, viz. the sand eel (Bianki et al., 1995). It should be mentioned that such specializa- tion probably reflects close trophic connections existing in alciform birds in the White Sea as in other areas. For instance, along the Murmanskiy coast in the Barents Sea, the black guillemot only catches gobies in the period when the number of sand eels and capelin are low (Krasnov et al., 1995). Analogous cases, when nestling birds refused to eat gobies brought by their parents, were reported several times.

The Arctic tern is also referred to as a typical ichthyophagous bird. Throughout the entire distribution area, gobies are the major component of Arctic tern rations during the reproduction phase (Bianki et al., 1995; Krasnov et al., 1995). During nesting this bird species feeds exclusively on fish. It is the opinion of some authors, Bianki (1993) in particular, that the abundance of Arctic tern nesting sites, at least in the western White Sea, depends directly on the abundance of the three-spined stickleback. This dependence seems to us rather exaggerated and not confirmed by reliable field data. In recent years in the White Sea, including

Kandalakshskiy Bay, a growth in the three-spined stickleback abundance has been observed, without observing a respective increase in the numbers of nesting Arctic terns.

In the White Sea, avifauna benthosphagous birds are the most numerous group, consisting firstly of sea ducks including the common eider and common species of charadriiforms. The major types of diet for sea ducks and large charadriiforms are bivalves, among which the blue mussel is common. Small charadriiforms feed mainly on gastropods, littorinas, and on hydrobials in particular. Despite this, the dietary composition of all these species differs noticeably. The common eider, with its strong beak, feeds effectively on bivalves and gastropods, crustaceans (including crabs), and even fish. Seasonal variations in the diet are characteristic of this species (Bianki, 1993). Thus, during winter in numerous polynyas located near the Terskiy coast, this species of sea duck actively catches fish, in particular polar cod (Shklyarevich, 1979). According to the available observations (Bianki, 1993), the common scoter shows the greatest stenophague character. Bivalves play a decisive role in its diet. At the same time, the richest diet is characteristic of long-tailed ducks. They mostly feed on bivalve crustaceans, which account for up to one-third of the pellet

amount.

To the third group, namely euryphagous birds, all species of large gulls are mainly ascribed. For the White Sea, these are the herring gull, common gull, and great black-backed gull and, to a lesser extent, the black-backed gull nesting nowadays exclusively in Onezhskiy Bay. Fish and mollusks constitute the basis of the diet of these species through the entire White Sea. Fish is most important when nestlings are being brought up. As gulls are known for a remarkable flexibility in their dietary preferences, large gulls might rather effectively exploit any sources of food available to them. In particular in the White Sea large gulls willingly eat polychaetes (nereises) during their migration . Thus, from the observations made by Bianki et al. (1995), the occurrence of nereises can reach 10%. In periods of insufficient traditional natural food, especially in the post-nesting period, the above-mentioned bird species search for food on territories of coastal towns and settlements, landfills, and harbor constructions. In such cases, the so-called cultural environment is the only place where birds can survive during unfavorable times.

5.3.3 Factors limiting the development of bird populations in the White Sea

Availability of food resources determines the gravitation of sea and aquatic birds to nest in the shallow waters of the White Sea. Any changes in the trophic situation in these areas lead to respective changes in both the location of colonies and abundance of birds. According to Bianki (1993), an eight-fold decrease (in comparison with the 1960s) of the three-spined stickleback population caused a decline in the number of Arctic terns nesting in Kandalakshskiy Bay. Destructive changes of zostera settlings in some shallow-water parts of the White Sea led to a near-complete disappearance of migration rest sites for the whooper swan.

For the endemic population of common eider in the White Sea, the most important factors determining the population dynamics are wintering conditions. Specific features of the hydrological and ice regimes, and food base status in polynyas (es- pecially in polynyas in Onezhskiy Bay) determine the physiological state of the mature element of the bird populations at the beginning of the reproduction season, and finally the abundance of nestlings.

During the reproduction season, anthropogenic-based anxiety can seriously affect the location of nesting sites, aquatic birds broods, and accumulations of molting males belonging to some sea duck species. Even a short-term impact at the start of the nesting period causes a mortality increase in the aquatic birds progeny. A prolonged impact, in particular a lack of control over small-size ship movements across the sea, and visiting of the seas islands by the local population during summer, forces aquatic bird broods and molting accumulations to move away to less favorable sites. A long-term impact of these anxiety factors leads to a distinct change in nesting tendencies of some sea duck species, in particular the common eider. In such conditions, the bird species starts nesting on large islands covered with forests where the impact of anxiety is less pronounced; however, this safe distance from the nesting site to the costal water, and food availability for the juveniles, is less favourable.

An excessive density of common eider broods on limited areas of quiet nesting sites might lead to the outburst of heminthosis accompanied by an increased mortality of nestlings. In the absence of anthropogenic stress, broods are sparsely distributed along the continental coasts. Naturally, this lowers the risk of helmintho- sis source formation (Koryakin, 1997).

Unfortunately, the anthropogenic anxiety level at nesting sites in the White Sea, notably in Onezhskiy and Kandalakshskiy Bays, is fairly high.

The majority of small islands in Onezhskiy Bay and unprotected islands (not included in the State Reserve Area) in Kandalakshskiy Bay are very frequently visited by the local population. Inevitably, this results in a significant decline in bird reproduction success in these areas.

During recent decades, the threat of oil contamination of the most important areas for ornithological fauna of the White Sea has became real. In particular, oil tankers cruise in Kandalakshskiy Bay, including the fjord area in the vicinity of the Kandalaksha State Natural Reserve boundaries, where a significant part of both sea and aquatic b

Date: 2016-03-03; view: 728