Natalia G. Melnik

The under-ice and bottom periods in the life cycle of Aulacoseira baicalensis (K. Meyer) Simonsen, a principal Lake Baikal alga

The under-ice development of the meroplanktonic diatom Aulacoseira baicalensis was studied, using underwater video recording. This is an ice alga, which not only succeeds in vegetating under the ice, but also reproduces intensively in interstitial water-filled spaces inside the ice. This report yields first results of the underwater filming done during the under-ice period of 2000. Our studies have shown that the A. baicalensis aggregations on the ice bottom can be easily destroyed by water currents and drift away as large flakes up to tens of centimetres in size. These macro-aggregations are capable of free-floating in the water-column for some time, gradually sinking to the bottom. Cells in the aggregations continue to divide, and they cover objects on the bottom with peculiar mucous coats. These coats act as a major food resource for bottom invertebrates.

Seasonal dynamics of primary production in the pelagic zone of southern Lake Baikal

Abstract We measured primary production by phytoplankton in the south basin of Lake Baikal, Russia, by in situ 13C-bicarbonate incubations within the period March–October in two consecutive years (1999 and 2000). Primary production was highest in the subsurface layer, possibly due to near-surface photoinhibition of photosynthesis, even under 0.8 m of ice cover in March. Areal primary production varied from 79 mg C m−2 day−1 (March) to 424 mg C m−2 day−1 (August), and annual primary production was roughly estimated as 75 g C m−2 year−1, both of which are within the lower range of previous estimates. Size fractionation measurements revealed that phytoplankton in the <20 μm fraction accounted for 72%, 96%, and 85% of total primary production in March, August, and October, respectively. The contribution of picophytoplankton (<2 μm) to total primary production ranged from 41% to 62%. A large fraction (82%–98%) of particulate organic carbon was associated with particles in the <20 μm fraction. These results suggest that nano- and picophytoplankton play an important role as primary producers in the pelagic ecosystem of Lake Baikal.

Nutritional diagnosis of phytoplankton in Lake Baikal

To diagnose the nutritional status of phytoplankton in Lake Baikal, surveys for the determination of concentrations of particulate carbon (PC), nitrogen (PN) and phosphorus (PP) and their ratios were conducted at six stations in March, June, August and October 1999. The concentrations of PC and PN were lower than, and those of PP were similar to, those in another mesotrophic lake except at the station near the mouth of the largest input river, Selenga River, of Lake Baikal. The PC : PN : PP ratio was 102 : 13 : 1, considerably close to the Redfield ratio. The ratio was constant against spatiotemporal changes. These indicate that phytoplankton in Lake Baikal were exposed to no deficiency in nitrogen nor phosphorus. From a viewpoint of the nutritional status of phytoplankton, Lake Baikal might be viewed as an ocean rather than as a lake.

Role of phytoplankton size distribution in lake ecosystems revealed by a comparison of whole plankton community structure between Lake Baikal and Lake Biwa

The influence of the size distribution of phytoplankton on changes in the planktonic food web structures with eutrophication was examined using natural planktonic communities in two world-famous lakes: Lake Baikal and Lake Biwa. The size distribution of phytoplankton and the ratio of heterotrophic to autotrophic biomass (H/A ratio), indicating the balance between primary production and its consumption, were investigated in the lakes of different trophic status. The results revealed that microphytoplankton (>20μm) in mesotrophic Lake Biwa, and picophytoplankton (<2μm) or nanophytoplankton (2–20μm) in oligotrophic Lake Baikal, comprised the highest proportion of the total phytoplankton biomass. The H/A ratio was lower in Lake Biwa (<1) than in Lake Baikal (>1). The low H/A ratio in Lake Biwa appeared to be the consequence of the lack of consumption of the more abundant microphytoplankton, which were inferior competitors in nutrient uptake under oligotrophic conditions but less vulnerable to grazing. As a result, unconsumed microphytoplankton accumulated in the water column, decreasing the H/A ratio in Lake Biwa. Our results showed that food web structure and energy flow in planktonic communities were greatly influenced by the size distribution of phytoplankton, in conjunction with bottom-up (nutrient uptake) and top-down (grazing) effects at the trophic level of primary producers.

Distribution of planktonic copepods of Lake Baikal

Abstract Net samples taken in the pelagic zone of Lake Baikal have revealed 6 Calanoida species, 14 Cyclopoida species and 1 Harpacticoida species. The paper reports the occurrence and abundance of these species in different pelagic biotopes of the lake in 1988–1995.

Carbon and nitrogen isotope studies of the pelagic ecosystem and environmental fluctuations of lake baikal

Publisher Summary This chapter presents a study, which determines the carbon and nitrogen isotope ratios of various pelagic organisms and fish scale specimens to elucidate the food web structure in Lake Baikal and to reconstruct fluctuations in global and lacustrine environments in the recent past. It seeks to emphasize that our fish scale specimens can serve as a valuable medium for recording changes in paleo-lacustrine environments. Carbon and nitrogen isotope ratios are measured in pelagic organisms collected in Lake Baikal and in scale specimens of omul fish collected. The nitrogen isotope ratio of the pelagic organisms showed a clear trend toward step-wise enrichment with trophic level. The carbon isotope data suggests that pelagic phytoplankton are the primary carbon source of the pelagic food web, because the carbon isotope values of the consumers are close to those of pelagic phytoplankton. The carbon isotope values recorded in omul scales showed a trend to gradually decrease. The trend reflected the decreasing carbon isotope values in atmospheric carbon dioxide, which is caused by the release of fossil–fuel carbon into the atmosphere. Periodic variations are observed in the carbon isotope value records of omul scales, which may be related to variations in ecological or physiological factors.

Feeding ecology of two planktonic sculpins, Comephorus baicalensis and Comephorus dybowskii (Comephoridae), in Lake Baikal

Planktonic sculpins (Comephorus baicalensis and Comephorus dybowskii) are endemic to Lake Baikal, and their migration behavior is characterized by their strange movements, which occur only vertically. We investigated their detailed food sources at each growth stage by stable isotope analyses in combination with stomach content analysis. At all growth stages, both fishes and amphipods were the main diet for C. baicalensis, whereas amphipods alone were the main diet for C. dybowskii. Our results indicate that the relationship between the two species shifts from a competitive interaction to a predator–prey interaction with the growth stages of C. baicalensis.

Biodiversity and food chains on the littoral bottoms of Lakes Baikal, Biwa, Malawi and Tanganyika: working hypotheses

Boreal Lake Baikal, temperate Lake Biwa, and tropical Lakes Malawi and Tanganyika each possess high biodiversities of benthic organisms in their littoral areas. Two general mechanisms influencing the evolutionary development of these high biodiversities can be hypothesized; i.e., a bottom-up constraint depending on the availability of food resources, and a top-down effect exerted by predators especially within the fish assemblage. The bottom-up constraint may be prominent where the abundance of benthic organisms in the grazing-food-chain is restricted by a seasonally lowest production, referring chiefly to attached algae, and large fluctuations in the abundance of primary producers provide a resource that is eventually utilized by benthic organisms of the detritus-food-chain. The top-down effect may be realized where the most of benthic organisms are supported by a constantly large primary production. These hypotheses help to explain, for the lakes we cite, the facts that diverse grazing-food-chain organisms live on the littoral bottom of tropical lakes where there is relatively constant large algal production due to suitable conditions of water temperature and light penetration through the year; while on the other hand, detritus-food-chain organisms are predominant on the littoral bottom of a boreal lake with seasonally fluctuating algal production and its pronounced lowest production in a year. In fish communities, segregations in habitat and food resource are important mechanisms allowing development of high species packing, while cohabitation within predatory fishes increases their feeding success due to the decrease of defensive efficiency by the threat of a variety of attacking methods. A further top-down effect may be exerted by scale-eating fishes, especially in Lake Tanganyika. The presence of such predatory and harmful members may promote more dense packing of prey members to increase their mutual defense efficiency.