DOES MELONIS BARLEEANUM HAVE CELLULAR ADAPTATIONS TO PERMIT INHABITATION OF SEDIMENTS SUBJECT TO GAS HYDRATE DISSOCIATION?

Greenhouse gas venting into the oceans and atmosphere is important to understand and predict in the context of climate change. A puzzle exists regarding the carbonate of foraminiferal tests (shells) from methane seeps: Are the tests obtained from seep sediments actually grown during methane emissions? If so, this is a physiological conundrum because many of the foraminiferal species found in these sediments are not expected to have cellular adaptations required to allow their inhabitation of these “extreme” environmental conditions. In an effort to further establish if paleoceanographically-relevant foraminiferal species inhabit sediments impacted by gas hydrate dissociation, we examined the cellular ultrastructure of Melonis barleeanum collected from the Vestnesa gas hydrate province off Western Svalbard, Norway. Melonis barleeanum is sometimes considered a “high productivity” intermediate infaunal species from silty mud. M. barleeanum from the gas hydrate site had thickened, fibrous pore plugs, mitochondria concentrated at the cell periphery and under pore plugs, and relatively abundant peroxisomes that were not complexed with endoplasmic reticulum, as known for many chemocline benthic foraminifers. Initial evidence suggests one specimen had methanotrophic bacteria concentrated at its aperture, suggesting these bacteria may have served as a food source. We saw no evidence of endo- or ectosymbioses with prokaryotes. In sum, it appears that M. barleeanum can inhabit gas hydrate sites. Our next task is to determine if methanotrophs impact the stable isotope composition of M. barleeanum carbonate. Supported by a WHOI Independent Study Award and CAGE project #223259.