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Abstract

Length growth, instar durations, fecundity and mortality rates of five species of microcrustacean zooplankton from a tropical reservoir were measured in relation to food quantity and temperature in laboratory cultures. Three cladocerans (Ceriodaphnia cornuta, Moina micrura, Diaphanosoma excisum), one calanoid copepod (Heliodiaptomus viduus), and one cyclopoid copepod (Mesocyclops thermocyclopoides) were studied. Filtered seston (45 mu m mesh) from a local pond was used for food. Two food concentrations were employed: (1) 10 mu g chlorophyll l(-1) (ca 0.25 mg Cl-1), and (2) 50 mu g chlorophyll l(-1) (ca 1.25 mg Cl-1). Food levels and water temperature (22.5, 27.5, and 32.5 degrees C) used, roughly covered the ranges found in the reservoir. Although all the three growth parameters were often affected to some degree by temperature and food, the quantitative response of the species differed. Also, the species reacted differently to the three possible interactions (i.e. food x temperature, food x instar, and temperature x instar). This contributed to the overall differences in the species responses. For the cladocerans, instar durations were always affected by temperature. The food did not affect the duration time of the adults and that of the combined juvenile instars, the latter except in one case significantly. For the two copepods food level affected the duration times of naupliar and copepodite instars, but the effect of temperature was only significant for H. viduus. The development times observed for H. viduus were extraordinary long compared with values reported in the literature for other tropical calanoids. This suggests that food conditions in our culture were adversely affecting its growth rates.