PRELIMINARY STUDIES ON THE SEASONAL VARIATIONS OF CLADOCERA IN LAKE TAI-HU

This paper contains the results of qualitative and quantitative studies on the seasonal variations of cladocera in Lake Tai-Hu. The observations were carried out between August 1959 and July 1960. The results obtained are summarized as follows:1. The cladocera are rather rich in species. There are 44 species among which Leptodora kindtii (Focke), Sida crystallina (O. F. Mueller), Diaphanosoma brachyurum (Lieven), Diaphanosoma sarsi Richard, Daphnia pulex (de Geer), Daphnia longispina (O. F. Mueller), Scapholeberis mucronata (O. F. Mueller), Ceriodaphnia rigaudi Richard, Moind macrocopa Straus, Bosmina longirostris (O. F. Mueller), Bosmina coregoni Baird, Bosmina fatalis Burckhard, Bosminopsis deitersi Richard, lliocryptus agilis Kurz, Camp-tocercus rectirostris Schoedler, Alona intermedia Sars, Alona rectangula Sars, Rhyncho-talona falcata (Sars), Graptoleberis testudinaris (Fischer) and Chydorus sphaericus (O. F. Mueller) are very commonly found in the Lake.2. Each cladoceran species has its own seasonal history, and usually a few common species in one month are apparently absent in the following month. As a result of this peculiarity of seasonal variations, the species number of cladocera changes in every month. The maximum occurs in September while the minimum occurs in January and February.3. The individual number of the total cladocera varies from month to month. It reaches a maximum in September and drops down to a minimum in February.4. Among the cladocera of the Lake Ceriodaphnia rigaudi Richard, Bosmina coregoni Baird and Diaphanosoma sarsi Richard are the dominant species in individual number. The seasonal fluctuations of the individual number of the total cladocera are mainly affected by the fluctuations of the individual number of these predominant species.5. Both qualitative and quantitative seasonal variations of cladocera are correlated with seasonal changes of the environmental factors, particularly water temperature.