Combined effect of burrowing mangrove crabs and tides on carbon fluxes

Abstract

Sesarmid crabs act as mangrove ecosystem engineers due to their burrowing behavior in the sediment. The burial of leaves inside the sediment suggests a positive relationship between crab activity and carbon storage in mangrove forests. However, crab burrows increase the sediment-air interface and, thus, might amplify CO2 fluxes from the sediment. Additionally, the tidal export of carbon from burrows acting as preferential flow paths may offset the enhancing effect of crab burrows on carbon storage. In this study, we investigated the interactive effect of burrowing crabs and tidal flows on mangrove carbon storage in a laboratory experiment. Significantly higher dissolved organic carbon (DOC) concentrations in the porewater were found in microtidal compared to mesotidal treatments, while the total amount of outflowing DOC was similar across tidal treatments. No significant effect of burrowing crabs on the DOC content of the porewater was found. Significantly lower CO2 fluxes into the atmosphere were found in treatments with crabs present which is contrary to previous studies. We suggest that lower CO2 flux values were a result of collapsed burrows that preserved the particulate organic carbon (POC) in deeper sediment layers. Previous studies, showing enhanced CO2 fluxes from crab burrows, have been carried out in the field and did not take the potential of burrow collapse into account. We stress the importance of considering temporal variability in crab burrow stability and spatial variability in tidal dynamics when evaluating their interactive effect on carbon fluxes in mangrove forests.