Do marine benthos breathe what they eat?

Abstract. Intertidal benthos link tertiary predators and primary producers in marine food webs as well as directly contribute to sediment CO₂ emission. However, current methods for studying food sources of marine benthos are time-consuming and does not allow direct estimates on feeding regime-related CO₂ production. We examined the foods of mangrove crabs and gastropods as well as their corresponding CO₂ production by using cavity-ring down spectroscopy to measure the δ¹³C of consumer-respired CO₂, considering the effects of feeding regime, benthos taxa, and dominant feeding habit. Benthos taxa and feeding habit have significant impact on δ¹³C of respired CO₂. Particularly, the δ¹³C of crab (−23.9±0.4 ‰) respired CO₂ was significantly lower than that from gastropod (−17.5±1.3 ‰) respiration. The δ¹³C of deposit-feeder respired CO₂ was significantly higher than that from detritivores. There are significant differences in the amount of CO₂ emitted and δ¹³C of crab respired CO₂ under different feeding regimes. The differences reflect diet-switching and fuel-switching in the crabs, i.e. you breathe what you eat. Significant differences in CO₂ production of crabs also exist between those feeding on microphytobenthos (0.13±0.02 mmol g⁻¹ day⁻¹) and on field collection (0.31±0.03 mmol g⁻¹ day⁻¹). CO₂ production of crabs is strongly related to carapace width and length. The δ¹³C of respired CO₂ from mangrove crabs reflects their diet while crab-respired CO₂ 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 CO₂ fluxes in mangroves.