Deposit-feeding of Nonionellina labradorica (foraminifera) from an Arctic methane seep site and possible association with a methanotroph

[摘要] Several foraminifera are deposit feeders that consume organicdetritus (dead particulate organic material with entrained bacteria).However, the role of such foraminifera in the benthic food web remainsunderstudied. Foraminifera feeding on methanotrophic bacteria, which are 13 C-depleted, may cause negative cytoplasmic and/or calcitic δ 13 C values. To test whether the foraminiferal diet includesmethanotrophs, we performed a short-term (20 h) feeding experiment with Nonionellina labradorica from an active Arctic methane-emission site (Storfjordrenna, Barents Sea)using the marine methanotroph Methyloprofundus sedimenti and analysed N. labradorica cytology via transmissionelectron microscopy (TEM). We hypothesised that M. sedimenti would be visible post-experiment in degradation vacuoles, as evidenced by their ultrastructure.Sediment grains (mostly clay) occurred inside one or several degradationvacuoles in all foraminifers. In 24 % of the specimens from the feedingexperiment degradation vacuoles also contained bacteria, although none couldbe confirmed to be the offered M. sedimenti . Observations of the apertural area after20 h incubation revealed three putative methanotrophs, close to clayparticles, based on bacterial ultrastructural characteristics. Furthermore,we noted the absence of bacterial endobionts in all examined N. labradorica but confirmedthe presence of kleptoplasts, which were often partially degraded. In sum,we suggest that M. sedimenti can be consumed via untargeted grazing in seeps and that N. labradorica can be generally classified as a deposit feeder at this Arctic site.

[学科分类] 大气科学