MEASURING FEEDING RATES OF PELAGIC HERBIVORES - ANALYSIS OF EXPERIMENTAL-DESIGN AND METHODS

We have re-evaluated the experimental methods and statistical procedures used to determine the relationship between feeding rates of pelagic herbivores and food concentration. Analysis of our own experiments, on Calanus pacificus feeding on Gyrodinium resplendens, and of other published research on this subject suggests the need for improvements in experimental design and methodology. We show that the use of "mean concentration" is statistically erroneus. First, it produces an artificial increase in the degrees of freedom that may result in the acceptance of nonsignificant regression lines. Second, it negates the value of replication, which is required to estimate sources of error. We present an example of how replication may be used to improve control over sources of error. Furthermore, we recommend the use of initial concentration rather than mean concentration. Finally, we introduce alternative methods to determine clearance and ingestion rates that enable the investigator to use replication and thus to estimate experimental errors.