Life-stage-specific differences in exploitation of food mixtures: diet mixing enhances copepod egg production but not juvenile development

Development, egg production and hatching success of the calanoidcopepods Temora longicornis and Pseudocalanus elongatus weremeasured in food mixtures to test their ability to obtain acomplete nutrition by combining different nutritionally poorfood species. In all the food mixtures used, the copepods failedto moult past the first copepodite stage, and the mortalitywas high. In sharp contrast, mixing two nutritionally poor foodspecies often resulted in egg production which was not significantlydifferent from nutritionally high quality food, although hatchingsuccess in many mixtures was low. Whereas egg production wassignificantly correlated with particulate organic nitrogen inthe diet, and independent of the highly unsaturated fatty acids(HUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid(DHA), hatching increased with increasing DHA and EPA concentration.Growth and juvenile mortality were, however, independent ofeither nitrogen or HUFAs in the diet. Our results show thatadult copepods are effective in combining their nutrition fromseveral food sources, whereas juveniles are not. We suggestthat there are species- and life-stage-specific differencesin nutritional requirements and/or in the ability to digestand/or assimilate essential nutrients from food mixtures, whichmay significantly contribute to the success of copepod populationsin nature.