The uniqueness and diversity of the Baikal organic world give evidence of the abundance of different ecological niches in it and complexity of biocenotic relations. In the primary output sources, the structure of biotopes and differences of the abiotic environment parametres the Baikal is subdivided into two zones – the coastal zone and the deep water one. The coastal zone includes the shelf, the upper part of the deep water slope as deep as 250-300 m and takes 1/5 of the lake area. The deep water zone takes 4/5 of the lake area and is subdivided into epipelagic which corresponds to the layer of active waters circulation and bathypelagic which lies below that layer.
The trophic (food) chain of the open pelagic (250-300 m down) is formed by several species of phytoplankton, epishura, a vegetarian kind of crustacea, omnivorous bathypelagic amphipoda macrohectopus, two species of golomyankas, two species of pelagic bull-heads, the omul and the fresh water seal, nerpa.
The primary chain, the Baikal products, are represented by 10-12 species of algae. Among them diatoms, peridineas and partly gold ones dominate. Lake Baikal is characterized by long vegetation (about 11 months) and intensive algae development under the ice. According to long-term average data up to 82% of the yearly biomass is synthesized in spring. The average quantity and biomass of the spring algae in the Southern Baikal is 3 times bigger than in the Northern Baikal (1,025 and 344 mg/m respectively!). The summer phytoplankton is poor. Its yearly primary output is about 21,100 kg/hectare.
The main consumer of the primary output is the epishura. As a rule, it makes up 80-90% of the mesozooplankton biomass and is food for the next trophic levels. It is also food of the omul from the fry to young fish and is a permanent component of the grown-up omul’s food ration.
The next component of the Baikal pelagic trophosphere is the macrohectopus inhabiting the thick of epi- and bathypelagic. It is not spread evenly, forming schools or thickening fields. It mostly feeds on epishura or algae. Macrohectopus, in its turn, is the main food of golomyankas, omul and other kinds of fish. In all the seasons of the year the central basin of the Baikal is distinguished by the abundance of macrohectopus, where its biomass is 3-4 times greater than in the neighbouring ones. The yearly output of macrohectopus in the lake is 8 thousand tons.
The main marketable object in the lake pelagic is the omul taking one of the highest levels of the ecosystem’s productive chain. The omul biomass in the 80ies is within 20-30 thousand tons.
The important consumer of the golomyanka and bull-head fishes is the nerpa (Baikal seal). An individual nerpa eats about 3 kg of fish a day. A flock of nerpas of 68 thousand head eat 77.5 thousand tons of fish a year, 68 thousand tons of golomyanka out of them. The nerpa crowns the food pyramid of the lake.
In the 70-80ies great attention was paid to the research of the structure of the Baikal pelagic ecosystem by the way of synchronic registration of abiotic factors: temperature, physical transparency, currents, the water colour, sun radiation and emulsions. At the same time biotic characteristics of the bacterio- and phytoplankton, photosynthesis intensity, meso- and macroplankton were researched in the testing areas of different characteristic parts of the Southern, Middle and Northern Baikal.
The characteristic of the Baikal pelagic ecosystem would not be full without considering some changes in its structure and functions within 10-15 years which cannot be explained by the climate cyclic recurrence. Thus, according to the data submitted by G.I. Popovskaya, nowadays eutrophication is recorded on a big territory adjacent to the big rivers’ mouths, especially the Selenga river. In the thick of the water of the southern Baikal open pelagic massive appearance of the wide-spread algae genus called Nitzchia acicularis is registered. In some years it was dominating whereas in the previous 50ies-60ies that genus was not registered in Lake Baikal or was found individually.
We should not underestimate the fact of changing the development cycle rate and the quantity of endemic and formerly dominating diatomic species, Melosira bacalensis. The question of that genus cycle character was formerly well known and was widely discussed in the special literature. Periods productive in melosira were repeated at Lake Baikal every 3-4 years. Now the rhythm of the species development has been destroyed: from 1974 to 1990 outbreaks of its reproduction were registered only twice, and the latest rise of the algae quantity in the under-ice period (1982) did not cause the transformation of the zooplankton community (mass cyclopes development), which used to be a natural phenomenon before.
The second group of facts is more known to ichthyologists and is the foundation of an incessant discussion. The question is that the quantity of zheltokrylka (yellow-fin) has become lower and in depression for many years, and that phenomenon is significant for explaining of the present-day biological values of the omul. The zheltokrylka was introduced into the category of commercially important fish in 1942 and was like that until 1971. In 1956 the catch of it was 18 thousand metric centners, by 1971 it had been reduced to 1 thousand metric centners, and the commercial fishing was ceased. From 1971 to 1982 the species was in depressive state, in 1983 increase of the spawning school was registered in the strait of the Maloye sea.
In the specialists’ opinion, decrease of the zheltokrylka quantity is conditioned by many factors. It is important to mention the complex of anthropogenic influence aggravated by the species’ vulnerability in the spawning and embryo period (coastal flow, people’s getting out the spawn, overcatch of the brood fishes during spawning and probably raise of the water level in the past). The recorded decrease of the zheltokrylka abundance within many years could not but affect the quantity of the omul which feeds on that high-calorie fish.
The above mentioned facts allow us to make the following conclusion. The Baikal is unique as well as its fauna, flora and its ecosystem on the whole, all the links of which are closely interrelated. Violation or relaxation of any link causes irreversible changes in the whole ecosystem. Therefore, the strategy of using biological and other resources of the lake should be strictly regulated not to violate the centuries-old balance of the Baikal ecosystem. The strategy should be based on the state law on the Baikal as the lake of a special usage and preservation conditions.