Linking behaviours, sediment reworking, bioirrigation and oxygen dynamics in a soft-bottom ecosystem engineer: The mud shrimp Upogebia pusilla (Petagna 1792)

Abstract

Despite the role of bioturbation in controlling biogeochemical processes taking place at the sediment-water interface, little is still known about how animal behaviours influence sedimentary biogeochemical processes. In the present work, we used the mud shrimp Upogebia pusilla as model organism to assess the effect of behaviour types/intensities on sediment reworking, bioirrigation and sediment oxygen dynamics based on three sets of seasonal experiments. We identified four main behaviours: “Resting”, “Walking”, “Ventilating” and “Burrowing”. Mud shrimp were much more active (i.e., not “Resting”) during summer than during winter and to a lesser extent spring due to elevated temperature. There were three distinct components of sediment reworking. The first one consisted in the expulsion of sediment particles from the burrow to the sediment-water interface, the second one to the transfer of sediment downward within the burrow and the third one to the transport and compaction of sediment across burrow walls. Temporal changes in the intensities of all components correlated tightly since they all resulted from “Burrowing”. The temporal dynamics of porewater exchange and oxygen dynamics were clearly discontinuous and in direct relation with “Ventilating”. However, other behaviours, and especially “Burrowing” were also involved in the control of this dynamics through the modulation of oxygen availability within the burrow, which is cuing the onset of ventilation at a 12–25% saturation threshold. These results underline the importance of taking into account changes in animal behaviour types/intensities at the appropriate temporal scales when assessing the impact of bioturbation on biogeochemical processes taking place at the sediment-water interface.