Laboratory studies of the population dynamics of the rotifer Brachionus calyciflorus pallas

The rotifer Brachionus calyciflorus was grown in two-stage algal-rotifer chemostat culture under food limitation on the coccoid green alga Chlorella vulgaris. Steady-state cultures were perturbed in a variety of ways. When the perturbation consisted of a pulse addition of food, rotifer biovolume concentration went through a transient phase consisting of an increase followed by a decrease back to the original steady state. This was accompanied by size structure changes in the population including an increase followed by a decrease in egg production. When cultures were perturbed instantaneously by increasing or decreasing the dilution rate by changing pump speed, rotifer biovolume concentration made smooth transitions to new steady states. These transitions were accompanied by changes in the size structure of the population. When cultures were perturbed by changing the dilution rate through replacement of the culture vessel by a different sized vessel, rotifer biovolume concentrations oscillated before entering new steady states. Changes in the size structure of populations were associated with these transient phases. The data here widen the range of behaviors observed for animals grown in single species continuous cultures. Classical chemostat growth models, such as the Monod-Herbert model, cannot account for all of the responses to perturbations observed. In addition, the toxicity of the chrysophyte flagellate Poterioochromonas malhamensis to the rotifer Brachionus angularis was investigated. Fed rotifers exposed to the flagellate experienced a mortality rate indistinguishable from starvation. Unfed rotifers experienced a higher mortality rate. A dose response was observed to flagellate concentration.