THE INFLUENCE OF FOOD RESOURCES ON THE DEVELOPMENT, SURVIVAL AND REPRODUCTION OF THE 2 CYCLOPOID COPEPODS - CYCLOPS-VICINUS AND MESOCYCLOPS-LEUCKARTI

Laboratory experiments were conducted to determine whether the two cyc lopoid copepods, Cyclops vicinus and Mesocyclops leuckarti, exploit th e same food resources. The food requirements of juveniles of the two c yclopoid copepods were investigated. Moreover, the importance of algae for the predaceous adults was studied. Nauplii of both M.leuckarti an d C.vicinus successfully developed into copepodites when fed the motil e algae Chlamydomonas reinhardtii, Chlamydomonas sphaeroides and Crypt omonas sp. Threshold food concentrations for naupliar development vari ed between offered algae and between the two cyclopoid species. The fo od threshold for successful naupliar development, when reared on C.rei nhardtii, was lower for M.leuckarti (0.3 mg C l-1) than for C.vicinus (0.5 mg C l-1), whereas a similar food threshold was found using Crypt omonas sp. (0.3 mg C l-1) and C.sphaeroides (<0.2 mg C l-1). Naupliar development time was inversely related to food concentration. Food req uired for copepodite development differed for the two cyclopoid specie s. Cyclops vicinus was able to develop to the adult stage on a pure di et of any one of the three algal species, whereas M.leuckarti required a prey supply of the rotifer Brachionus rubens. Food composition, i.e . algal species, algal concentration and rotifer abundance, influenced copepodite survivorship of both cyclopoids and was always higher in t he presence of B.rubens. Under similar food conditions, mortality was higher for M.leuckarti than for C.vicinus. Mesocyclops leuckarti femal es were very dependent on animal food. The predation rate of M.leuckar ti was not lower in the presence of algae. Egg production of M.leuckar ti was low on a pure algal diet and significantly higher when B.rubens was present. The results were used to discuss the life cycle strategy and the possibility of exploitative competition of the two cyclopoid copepods.