Several assumptions of models predicting a metabolic advantage for vertically migrating zooplankton (especially the model of Enright, 1977) were tested experimentally with Daphnia. The experiments focused on the nutritional aspects of the problem. In one set of experiments, starvation
was found to enhance the feeding rate of Daphnia above the incipient limiting food concentration, but not below where required by the model. The duration of this effect of starvation depended on the food concentration, but was short; thus this enhancement of feeding rate cannot compensate
for several hours of reduced food intake. In another set of experiments, the growth of Daphnia was not affected by the differing chemical composition of algae found in the beginning and the end of the light phase. Although algae contained more carbohydrates in the evening, daphnids
grew at the same rate when they received either “morning” or “evening” algae at the same carbon concentration. In addition, when natural food was used, although the higher particulate concentration in lake water collected in the evening (compared to morning samples)
permitted better growth of Daphnia, daphnids under simulated “non-migration” food conditions grew better than those under “migration” conditions. Finally, in a third set of experiments, algal growth was not enhanced when exclusively nocturnal grazing was simulated
in a laboratory system, contradicting model predictions. This was probably due to the coupling of nutrient regeneration with grazing. In total the experiments did not provide evidence that a metabolic advantage is the selective force behind vertical migration in Daphnia.
The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.