Figure 7 . Relative contributions of different forms of carbon to the released body carbon over the 8-d depuration period with different daily food rations (a ) and the allocation of the released body carbon of marine medaka (b ). Data are the mean ± SD (n =3–5). The error bars represent the standard deviations. DOC, dissolved organic carbon; CO2, carbon dioxide; PC, particulate carbon. The food rations are expressed as a percentage of the fish dry weight (DW). The values in brackets in subfigure (b) indicate the means of the above-noted ranges.
3.4 Carbon release from mesopelagic fish estimated using the carbon release model
The results showed that DVM mesopelagic fish ate 1.51–25.2 Pg zooplankton carbon and released 0.59–9.84 Pg C DOC, 0.42–6.95 Pg C CO2, and 0.15–2.56 Pg C PC annually in the global open ocean (Figure 8a). NM mesopelagic fish ingested and released similar amounts of carbon annually (Figure 8b, and see details in Text S5).
In total, of the 3.41–38.8 Pg zooplankton carbon ingested by all mesopelagic fishes per year in the global open ocean, 1.33–15.1 Pg of the ingested carbon was assimilated in the fish body, whereas the remaining unassimilated carbon was released as DOC (1.12–12.7 Pg C/y), CO2 (0.71–8.10 Pg C/y), and PC (0.26–2.91 Pg C/y) in seawater. Meanwhile, 0.57–6.30 Pg body carbon of the mesopelagic fish was lost annually as DOC (0.23–2.55 Pg C/y), CO2 (0.24–2.69 Pg C/y), and PC (0.10–1.07 Pg C/y). That is, mesopelagic fish in the global open ocean annually released 1.34–15.2, 0.95–10.8, and 0.35–3.97 Pg C in the forms of DOC, CO2, and PC, respectively.