For a decade field investigators have used the concentration of chlorophyll-derived pigments in the digestive system of copepods as a way of estimating natural feeding rates because the measurement can be done immediately on field caught animals, thereby allowing estimates of natural variance in the feeding process and bypassing incubation procedures which result in uncertainty and artifacts. Recently, the method has been criticized because pigment budgets on some occasions do not arrive at a full accounting for chlorophyll. However, the method has been so insightful in oceanic ecology that it continues to be used in spite of the contention that budgets indicate assimilation of pigment or other unknown source of loss is of major importance. This investigation will try to establish sources of error and suggest new methodology for field measurements of chlorophyll-derived pigments in animal guts. %%% Feeding by grazers in the sea is a fundamental process which underlies not only population dynamics and individual growth, but also transformation of particulate material and release of dissolved components utilized by microbial food webs. Much debate over the years has turned on our inability to know how fast animals feed in nature in the sea and how much variation is involved in the process. Most experimental approaches involve confining animals in containers of various sizes with known or natural food supplies. The errors introduced by catching and confining the animals are almost always invoked as reasons why the results are not very clear cut. A method that does not subject the animals to containers was considered a important step ahead almost a decade ago. Not surprisingly, the method has been shown to be very useful in describing feeding patterns and rates of natural populations of grazers in the sea. It has also been shown to have some deficiencies which this investigation will explore in an attempt to refine our understanding of the method and suggest changes that will make results more quantitative.
