Pigment ingestion and egg production rates of the calanoid copepod Temora longicornisr. implications for gut pigment loss and omnivorous feeding

We examined the relationship between egg production rate (E) and pigment ingestion rate (I, from gut content corrected for 33% loss) for adult female Temora longicornis in Long Island Sound on 47 occasions. Linear regression of E on I [both variables expressed in mass of nitrogen (N) female−1 day−1] was: EN = 0.0016 + 0.770 × IN. The slope, 0.77, is the apparent gross efficiency of egg production, equivalent to the gross growth efficiency (GGE) assuming that females partition all nitrogen for growth into egg production. Published work suggests that a GGE of 0.37 would be expected for herbivorous copepods. The discrepancy between the expected value of 0.37 and observed value of 0.77 could result from unquantified losses of gut pigment or because T.longicomis ingested a significant amount of nitrogen by feeding as a carnivore. We suggest that if T.longicomis females derive all of their nitrogen for growth by feeding on phytoplankton, and if no correction for pigment loss is employed, then the gut pigment method underestimates pigment ingestion by no more than a factor of two.