The influence of food and temperature on the life cycle characteristics of tropical cladoceran species from Kalaweewa Reservoir, Sri Lanka

Abstract

This study analyses the effect of food concentration and temperature on growth, body size, development and reproduction on tropical cladoceran species: Diaphanosoma excisum, Moinamicrura, Daphnia lumholzi and Ceriodaphnia cornuta from Kalawewa Reservoir in Sri Lanka. A review of relevant literature is given which deals with tropical plankton ecology, with ecological factors affecting growth, body size, development and reproduction and with the structure and functioning of cladoceran filtering limbs. The contents of this thesis falls into three parts of which the first contributes the major portion: experimental, field and the application of experimental findings to field data. Long term growth experiments were carried out at three temperatures and six food concentrations. Animals were examined daily from neonate to fifth adult instar. Organic carbon content of different-sized animals which had been reared on different food concentrations were analysed. Computed length/carbon weight relationships were applied to measured lengths in order to obtain body size in terms of weight. Different growth curves were fitted to obtain the best fit at different food-temperature combinations. The growth rates for the juvenile, the primiparous female and fifth instar adult were computed for defined food-temperature combinations and compared. Significant relationships are given on embryonic and post-embryonic development with food quantity and temperature, both separately and in combination. The effect of food level and temperature on reproduction were evaluated in relation to age and stage at maturity, fecundity and on the size of the young produced. The filtering structure was examined for a possible explanation of the observed differences in life-cycle characteristics of the four species. The nutritional level of the reservoir was estimated four times in terms of total particulate carbon and chlorophyll "a" content. The field population was examined to determine the length/carbon weight relationships, the size of the primipara and the size of the neonates. The field data was related with the experimental findings to see the possibility of applying an indirect method of predicting the field nutritional conditions. The interpretations of the findings were discussed finally, particularly in relation to the comparisons between temperate and tropical species.