MEPS 191:195-205 (1999)  -  doi:10.3354/meps191195

ABSTRACT: Oikopleura dioica is an excellent model for studying food flow through the digestive system because of its transparency, non-motility and because fecal pellets move along the digestive system in an orderly sequence which can be easily timed. By observing fecal pellet circulation within the gut of healthy individuals, we have concluded that the average number of fecal pellets inside the gut of O. dioica is 2.878 ± 0.015 (mean ± SE, n = 43). Thus, gut passage time (GPT, min) can be estimated from the time interval between successive fecal pellets (DI, min fecal pellet^-1) as GPT = 2.878 DI. This establishes the basis for estimating GPT from simple fecal pellet production rate incubations, and is one way of determinating GPT without manipulating food concentration or quality, a major shortcoming of current techniques. In laboratory experiments, GPT of O. dioica was independent of body size. At 15ºC, GPT (min) decreased with increasing food concentration (FC, µg C l^-1) when the prymnesophyte Isochrysis galbana (4.5 µm in size), the prasinophyte Tetraselmis suecica (10 µm) or the chlorophyte Chlorella sp. (3 µm) were used as food, according to the power function GPT = 29.4 FC^-0.245. There were no significant differences in GPT between algal types. The GPT of O. dioica exhibited a Q₁₀ of 0.687 over a temperature range of 10 to 20ºC, independent of food concentration. Since the interaction between food concentration and temperature was not significant, GPT can be estimated as GPT = 51.67e^-0.0376t FC^-0.245.

KEY WORDS: Appendicularian · Feeding · Gelatinous zooplankton · Oikopleura · Tunicate · Gut passage time · Gut pigment