Effects of food and feeding regime on CO fluxes from mangrove consumers - Do marine benthos breathe what they eat?

Intertidal benthos link tertiary predators and primary producers in marine food webs as well as directly contribute to sediment CO emission. However, current methods for studying food sources of marine benthos are time-consuming and does not allow direct estimates on feeding regime-related (including different diets, active versus dormant) CO production. We examined the food sources of mangrove crabs and gastropods as well as their corresponding CO production using cavity-ring down spectroscopy to measure the δC-CO respiration for consumers, considering the effects of feeding regime, benthos taxa, and dominant feeding habit. Benthos taxa and feeding habit have significant impact on δC-CO respiration. Particularly, the δC-CO respiration for crabs (-23.9 ± 0.4‰) was significantly lower than that for gastropods (-17.5 ± 1.3‰). The δC-CO respiration for deposit-feeders was significantly higher than that for detritivores. There are significant differences in the amount of CO emitted and δC-CO respiration for crabs under different feeding regimes. The differences reflect diet-switching and fuel-switching by the crabs, i.e. 'you breathe what you eat'. Significant differences in CO production of crabs also exist between those feeding on microphytobenthos in the laboratory (0.13 ± 0.02 mmol g day) and on field collection (i.e. just collected from the field) (0.31 ± 0.03 mmol g day). CO production of crabs is strongly related to carapace width and length. The δC-CO respiration for mangrove crabs reflects their diet while crab-respired CO flux is related to crab size. These relationships enable partitioning the feeding habit and food sources of key benthos, and help incorporate their contribution into the overall sediment-atmosphere CO fluxes in mangrove forests.