Population growth capacities and regulatory factors in monospecific cultures of the cladocerans Moina micrura and Diaphanosoma excisum and the copepod Thermocyclops decipiens from Cote d'Ivoire (West Africa)

The cladocerans Moina micrura and Diaphanosoma excisum and the copepod Ther mocyclops decipiens were studied in microcosms (0.8 m(3)) under semi-contro lled experimental conditions at 25-29 degrees C for 32 days, by daily sampl ing after an initial monospecific inoculation. For each species, the time s eries began with an exponential population growth phase. M. micrura showed a higher: daily population growth rate (mean = 1.19) than D. excisum (0.78) and T. decipiens (0.45). The growth phase of M. micrura coincided with bac terial and phytoplanktonic peaks while the growth phase of the two other sp ecies followed these peaks. After this phase, M. micrura quickly disappeare d (day 10), while D. excisum biomass decreased but showed a second increase , followed by a stabilization sequence. T. decipiens biomass had a slower i ncrease and stabilized after day 17. The passage to sexual reproduction in relation to crowding was the main regulating factor for M. micrura, whereas food limitation was important for D. excisum. For T. decipiens, population growth was limited by decreased recruitment to copepodite stages which cou ld have resulted from cannibalism exerted by older stages. (C) 2000 Ifremer /Cnrs/lnra/Ird/Cemagref/Editions scientifiques et medicales Elsevier SAS.