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 cyclopoid copepods, Cyclops vicinus and Mesocyclops leuckarti, exploit the same food resources. The food requirements of juveniles of the two cyclopoid copepods were investigated. Moreover, the importance of algae for the predaceous adults was studied. Nauplii of both M.leuckarti and C.vicinus successfully developed into copepodites when fed the motile algae Chlamydomonas reinhardtii, Chlamydomonas sphaeroides and Cryptomonas sp. Threshold food concentrations for naupliar development varied between offered algae and between the two cyclopoid species. The food threshold for successful naupliar development, when reared on C.reinhardtii, 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 Cryptomonas 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 required for copepodite development differed for the two cyclopoid species. Cyclops vicinus was able to develop to the adult stage on a pure diet 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 the presence of B.rubens. Under similar food conditions, mortality was higher for M.leuckarti than for C.vicinus. Mesocyclops leuckarti females were very dependent on animal food. The predation rate of M.leuckarti was not lower in the presence of algae. Egg production of M.leuckarti 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.