Organic matter (OM) remineralization plays a key role in controlling the biogeochemistry of marine sediments.
Through their burrowing activities, bioturbating macrofauna not only induces physical, chemical and biological
modifications, which can affect microbial communities responsible for organic matter remineralization, but it
could also directly affect the distribution and bioavailability of sedimentary organic matter. Through in situ experiments
manipulating crab and burrow density in intertidal soft-bottoms, we assessed if crab-bioturbation affects
benthic metabolism, and the amount, distribution, and bioavailability of sedimentaryOM. Crab-bioturbation
enhanced overall benthic metabolismand benthic flux of dissolved OMtoward thewater column at bothmudflat
and saltmarsh zones. Moreover, our results revealed that bioturbation also changes the quality, bioavailability
and distribution of sedimentary OM in mudflats and saltmarshes. Overall, bioturbation enhanced the proportion
of labile organic carbon of bioturbated sediments and homogenized the sediment column in terms of their proportion
of labile organic carbon. However, crabs also generated biogenic structures (e.g.,mounds) that could promote
spatial heterogeneity of high nutritional-value OM. Bioturbation-induced changes on benthic metabolism
and on OMavailabilitywould result in a reduction of the storage capacity of carbon in our intertidal systems. Previous
works indicated that crab-burrows trap detritus and OM-rich sediments. Our results suggest that detritus
are efficiently remineralized at bioturbated sediment, and finally they are quickly exported to the water column
as CO2 and DOC. Thus, crabs are modifying the OM processing at intertidal soft bottoms, and the ways in which
carbon is exported to coastal waters.