Direct contribution of invertebrate holobionts to methane release from coastal sediments

Sediment macrofauna play a vital role in sustaining aquatic food webs and biogeochemical cycles. Previous research demonstrated that bioturbation indirectly affects methane (CH₄) dynamics through mobilization of porewater and alteration of microbial processes in the surrounding sediment. However, little is known on the direct contribution of macrofauna holobionts (the assemblage of invertebrate host and associated microbiome) to biogeochemical fluxes. Here, we investigated how 19 taxa of macrofauna holobionts, from different estuarine habitats spanning 40° to 63° latitude, directly contribute to CH₄ fluxes. Deep burrowing infauna and deposit feeders were responsible for the highest CH₄ production, whereas epifauna and filter feeders promoted oxidative CH₄ consumption. Among the different environmental parameters, salinity was inversely correlated with CH₄ production by macrofauna holobionts, with the process suppressed at high salinity (≥ 33). This study provides empirical evidence on how functional traits and environmental factors influence sediment invertebrates' contribution to CH₄ fluxes.