Abstract
Methane and nitrous oxide are potent greenhouse gases (GHGs) that contribute to climate change. Coastal sediments are important GHG producers, but the contribution of macrofauna (benthic invertebrates larger than 1 mm) inhabiting them is currently unknown. Through a combination of trace gas, isotope, and molecular analyses, we studied the direct and indirect contribution of two macrofaunal groups, polychaetes and bivalves, to methane and nitrous oxide fluxes from coastal sediments. Our results indicate that macrofauna increases benthic methane efflux by a factor of up to eight, potentially accounting for an estimated 9.5% of total emissions from the Baltic Sea. Polychaetes indirectly enhance methane efflux through bioturbation, while bivalves have a direct effect on methane release. Bivalves host archaeal methanogenic symbionts carrying out preferentially hydrogenotrophic methanogenesis, as suggested by analysis of methane isotopes. Low temperatures (8 °C) also stimulate production of nitrous oxide, which is consumed by benthic denitrifying bacteria before it reaches the water column. We show that macrofauna contributes to GHG production and that the extent is dependent on lineage. Thus, macrofauna may play an important, but overlooked role in regulating GHG production and exchange in coastal sediment ecosystems.
Highlights
Methane (CH4) and nitrous oxide (N2O) in the atmosphere constitute a severe threat to Earth’s climate, with up to 28 and 265 times greater warming potential than carbon dioxide (CO2), respectively[1]
The specific aims of the study were to: (1) test if and by how much macrofauna alters sediment-water fluxes of CH4 and N2O; (2) quantify direct macrofaunal release of these greenhouse gases (GHGs); (3) estimate the carbon source of methanogenesis associated with the bivalve microbiome; (4) quantify methanogenic symbionts associated with macrofauna
Polychaetes of the genus Marenzelleria can colonize the deep sediment layers down to 7–15 cm depth[15,25], which coincides with the zone of sedimentary methane production in these low saline coastal sediments[26,27]
Summary
Methane (CH4) and nitrous oxide (N2O) in the atmosphere constitute a severe threat to Earth’s climate, with up to 28 and 265 times greater warming potential than carbon dioxide (CO2), respectively[1] Human activities such as industrial production, intensive agriculture, and livestock farming have substantially increased the levels of greenhouse gas (GHG) emissions. A debate has arisen whether benthic invertebrates would be effective in counteracting human pressures on aquatic environments[10,11] Supporters of this paradigm have proposed that bivalve activity may alleviate nutrient loading because of high turnover rates of nutrients by incorporation into shellfish, which are subsequently removed from ecosystem for human consumption[12,13]. To our knowledge, the first information to date on direct CH4 and N2O release by macrofaunal organisms characterized by different functional traits, and their regulation of methanogenic activity in coastal marine sediments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
