EXPERIMENTAL STUDIES ON FOOD DEPENDENCY OF DEVELOPMENT TIMES AND REPRODUCTIVE EFFORT (FECUNDITY AND EGG SIZE) OF TROPODIAPTOMUS-CUNNINGTONIIN RELATION TO ITS NATURAL DISTRIBUTION IN LAKE MALAWI

The influence of food supply on postembryonic durations, egg productio n, and functional feeding responses (FFRs) of Tropodiaptomus cunningto ni was measured in relation to food supply under laboratory conditions at around 26.5 degrees C. Growth and fecundity was determined in 20 m u m-filtered lake water with seven levels of Cryptomonas sp. enrichmen t (0 to 2.5 mg C . l(-1)). FFRs were measured in GF/C-filtered lake wa ter at six food enrichment levels (0 to 1 mg C . l(-1)). Naupliar dura tions (N-1-C-1) showed little response to increasing food supply, wher eas total (N-1-C-6), and thus cope podite (C-1-C-5) durations showed a continuous monotonic decline over the food range tested. Egg producti on continued to increase with rising food supply, although clutch size was only weakly related to food level. Individual egg volume declined markedly with clutch size, which ranged from one to eight eggs, under both laboratory and field conditions. Filtration rates of up to 8 and 28 ml . individual(-1) . day(-1) were measured in stage 3/4 nauplii a nd adult females. Maximal ingestion rates amounted to 37 % and 27 % bo dy C . d(-1), and estimated metabolic maintenance demands of these sta ges were only met at food levels of 0.65 and 0.85 mg C . l(-1), far ab ove those prevailing in the surface waters of L. Malawi. These experim ental findings are discussed in relation to field data presented on as pects of the distribution of T. cunningtoni in L. Malawi, on which bas is we suggest that naupliar development relies largely on lipid reserv es, while copepodite growth and egg production by adults in situ may d epend on deep chlorophyll maxima.