MEIOFAUNA OF THE PROFUNDAL ZONE OF THE NORTHERN PART OF LAKE-LADOGA AS AN INDICATOR OF POLLUTION

Benthic meiofauna was sampled at 19 stations, mainly in the northern p art of Lake Ladoga, from depths between 13 and 199 m and from types of environment ranging from sheltered areas near pollution sources to le ss polluted open areas. About 80 taxa were identified, of these 70 to the species level. The greatest numbers of species were oligochaetes ( 24 species) and harpacticoids (8 species). Certain quantitative ratios of meiofauna were shown to be correlated with environmental data. The species of the oligochaete families Lumbriculidae and Aeolosomatidae and the harpacticoids as a collective group, excluding Canthocamptus s taphylinus, were most clearly confined to the less eutrophied environm ents. The oligochaete species Amphichaeta leydigii, Dero digitata and Tubifex tubifex, the resting stages of Cyclopinae, and Eucyclops serru latus among the Eucyclopinae were most clearly concentrated in the eut rophicated or polluted environments. The groups of Naididae, Cladocera and Eucyclopinae did not have much value as indicators. Shannon diver sity index correlated positively with the total phosphorus content of the water, and number of species decreased with increasing depth. In g eneral, it seems that the pollution tolerance of the meiofauna in a ve ry large lake such as Lake Ladoga is high, presumably due to the effec tive mixing of water masses.