Assessing behavioural traits of benthic foraminifera: implications for sediment mixing

Abstract

The assessment of behavioural traits of marine organisms is increasingly recognized as a key issue to understanding their role in ecosystem processes such as bioturbation and nutrient cycling. The movement ability of intertidal foraminifera suggest that they may have a role, yet to be quantified, in benthic-pelagic coupling through their movement on the sediment surface, at the sediment-water interface and within the sediment. In this context, we investigated the behavioural traits of 5 benthic foraminiferal species typical of European temperate mudflats under standardized trophic light and temperature conditions. Behavioural traits related to motion of Ammonia tepida, Haynesina germanica, Cribroelphidium williamsoni, Miliammina fusca and Quinqueloculina seminula were assessed through their travelled distance, velocity, tortuosity of the path, position in the sediment and activity index. By analogy with macrofauna bioturbation functional groups, we describe the studied foraminifera as biodiffusor species with 3 sub-groups defined according to their vertical position in the sediment. C. williamsoni belongs to the epifaunal-biodiffusors, A. tepida and H. germanica belong to the surficial-biodiffusors, and Q. seminula and M. fusca are considered gallery-biodiffusors. Our results further suggest that features such as velocity, activity and tortuosity may mediate sediment-mixing intensity. Therefore, Q. seminula, H. germanica and C. williamsoni, which are the most active species, would have a larger effect on particle reworking rates than the less active A. tepida and M. fusca. Our results suggest that benthic foraminifera may play an underestimated role in bioturbation processes.