Subsurface activity of benthic foraminifera in relation to porewater oxygen content: laboratory experiments

In a series of laboratory experiments, we examined the migratory activity of some common benthic foraminifera in relation to subsurface oxygen concentrations in porewaters. Our results clearly demonstrate that foraminifera are capable of migrating through anoxic sediments, reinforcing the idea that some common benthic foraminifera are facultative anaerobes. We observed that migration was not completely random; there seemed to be a bias towards upward migration when buried without a subsurface oxic zone. Although this migration can be taken as a response to the absence of oxygen, it was not directly linked to gradients of oxygen as these were not present at that depth and a large portion of the assemblages continued to inhabit deeper sediment layers. The relatively higher percentage of soft-shelled foraminifera in the oxic zone suggests that they may be less tolerant to anoxic conditions than hard-shelled foraminifera. This possible differential tolerance may be one factor that will determine the survival or success of different species buried in deeper sediment layers.