Do marine benthos breathe what they eat?

Abstract

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.