Pigment destruction by Calanus pacificus: impact on the estimation of water column fluxes

A microencapsulation technique for introducing pure compounds in zooplankton diets

“…The results of these experiments resolve at least two facets of the considerable debate in the literature as to whether Chl a and its pheopigment degradation products act as conservative tracers (e.g. Shuman and Lorenzen 1975;Conover et al 1986;Lopez et al 1988;Penry and Frost 1990). The consensus now seems to be that Chl a is indeed lost during copepod grazing experiments, but there has been a difference of opinion as to whether Chl a is degraded to nonfluorescent compounds or whether it is simply lost to the investigator.…”

“…2a) revealed them to be easily ingested and to pass through the digestive tract at about the same rate as an algal diet, producing a fecal pellet -40-60 min after ingestion (cf. Lopez et al 1988). The rather diffuse fluorescence of the microspheres in the microcapsules before ingestion intensified as the microcapsules were digested and the fecal pellet was produced (Fig.…”

“…However, recent studies show that pigment is indeed lost during digestion, to the extent that in several studies pigment recovery was significantly reduced to as low as 66% on a molar basis (Helling and Baars 1985;Conover et al 1986). Whether the loss of fluorescence is constant (Helling and Baars 1985;Dagg and Walser 1987) or varies (Head 1988;Lopez et al 1988) is still a matter of controversy.…”

“…The procedure generally followed that of Lopez et al ( 1988). Copepods were allowed to feed for only 45 min to avoid production of fecal pellets during the feeding period.…”

“…Reports of highly variable degradation rates, ranging from 0 to 100% (see table 7 of Lopez et al 1988), have made the mechanism very difficult to understand. All experiments performed to date have been carried out with whole cell material, which has left open the possibility that degradation could be due to enzymatic alteration by intracellular chlorophyllase or perhaps to the physical chemistry of reactions caused by other cellular constituents.…”