Fiddler crab bioturbation stimulates methane emissions in mangroves: Insights into microbial mechanisms

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Mangrove ecosystems are pivotal in blue carbon capture, yet they can also release varying levels of methane (CH4). Fiddler crabs are known players in carbon (C) cycling within mangrove ecosystems, but their precise contributions to CH4 emissions and microbially-driven processes are not yet well understood. We compared CH4 emissions, soil physicochemical properties, and methanogenic and methanotrophic communities in non-bioturbated and bioturbated soils within two mangrove communities: Sonneratia apetala (SA) and Pongamia pinnata (PP). The presence of fiddler crabs led to an increase in CH4 emission rates in the bioturbated soil, ranging from 86% to 430% compared to un-bioturbated soil. The bioturbated soil also exhibited higher levels of ammonium, pH, and dissolved organic carbon (DOC) but with lower concentrations of nitrate, sulfate, salinity, and total nitrogen. Moreover, an increase was observed in the abundance methanogenic communities, but the abundance and diversity of methanotrophic communities was reduced in the bioturbated soil. The increased abundance of Methanosarcina and reduced abundance of type II methanotrophs in the bioturbated soil could result in an overall increase in CH4 emissions. This study result highlights that bioturbation can greatly influence CH4 emissions in mangroves and emphasizes the importance of considering the ecological role of fiddler crabs in the evaluation of coastal blue carbon sequestration.