Figure 1 .
Schematic
diagram of the carbon release model. Ingested food carbon is absorbed
after digestion. Unabsorbed food carbon is released as feces through
defecation. The absorbed carbon is first allocated to the metabolic
carbon pool (e.g., blood and liver). Part of the absorbed carbon in the
metabolic carbon pool is released from the fish through respiration and
excretion.
The remaining absorbed carbon is further assimilated into the structural
carbon pool (e.g., white muscle). Meanwhile, part of the structural
carbon is replaced, transformed through catabolism and reproduction, and
released from the fish. The solid and dotted lines show the carbon flows
starting from the ingested food and from the structural carbon in the
fish body, respectively. The released carbon originating from ingested
food and the fish body are called the food carbon release (red solid
arrow lines) and the body carbon release (red dotted arrow lines),
respectively. All the released carbon is in the form of dissolved
organic carbon (DOC), CO2, and particulate carbon (PC).
To
develop the conceptual model, we examined the food carbon release and
body carbon release parameters of a model marine zooplankivorous fish,
marine medaka (O. melastigma ), through short-term (36 h)
depuration (the process of releasing 14C from the
fish) experiments performed by labeling fish food with14C, and through long-term (8 days) depuration
experiments performed by labeling the bodies of the fish with14C. The lab experiments were also designed to be
extrapolated to mesopelagic fish. By using carbon release parameters
derived from the model fish and parameters from the literature, we
composed the model scenarios for estimating the carbon release of
mesopelagic fish in the global open ocean (Figure 2).
Figure
2 .
A
flow chart
showing
the relationships among the conceptual model, the experimental work
parameterizing model fish carbon release, and the model scenarios for
estimating the carbon release of mesopelagic fish. DOC,
CO2, and PC indicate dissolved organic carbon, carbon
dioxide, and particulate carbon, respectively.