What is bioturbation? The need for a precise definition for fauna in aquatic sciences

Abstract

The term 'bioturbation' is frequently used to describe how living organisms affect the substratum in which they live. A closer look at the aquatic science literature reveals, however, an inconsistent usage of the term with increasing perplexity in recent years. Faunal disturbance has often been referred to as particle reworking, while water movement (if considered) is re ferred to as bioirrigation in many cases. For consistency, we therefore propose that, for contemporary aquatic scientific disciplines, faunal bioturbation in aquatic environments includes all transport processes carried out by animals that directly or indirectly affect sediment matrices. These processes include both particle reworking and burrow ventilation. With this definition, bioturbation acts as an 'umbrella' term that covers all transport processes and their physical effects on the substratum. Particle reworking occurs through burrow construction and maintenance, as well as ingestion and defecation, and causes biomixing of the substratum. Organic matter and microorganisms are thus displaced vertically and laterally within the sediment matrix. Particle reworking animals can be categorized as biodiffusors, upward conveyors, downward conveyors and regenerators depending on their behaviour, life style and feeding type. Burrow ventilation occurs when animals flush their open-or blind-ended burrows with overlying water for respiratory and feeding purposes, and it causes advective or diffusive bioirrigation ex change of solutes between the sediment pore water and the overlying water body. Many bioturbating species perform reworking and ventilation simultaneously. We also propose that the effects of bioturbation on other organisms and associated processes (e.g. microbial driven biogeochemical transformations) are considered within the conceptual framework of ecosystem engineering.

Oxygen dynamics in shelf seas sediments incorporating seasonal variability

“…Overall, this study suggests that diffusive processes do not generally dominate the benthic oxygen demand in cohesive sediments, supporting previous findings where macrobenthic activity can dominate oxygen uptake in shelf sediments that receive a regular (in this case annual) supply of carbon (Jahnke et al 2005). The presence of fauna, measured here by biomass, is known to influence the difference between TOU and DOU rates in coastal sediments , with speciesspecific effects (Kristensen et al 2012). …”

“…In contrast, Diffusive Oxygen Uptake (DOU) rates are representative of the diffusive oxygen exchange across the sediment-water interface (Fischer et al 2009;Jorgensen and Revsbech 1985;Rabouille et al 2003;Rasmussen and Jorgensen 1992), related to microbial respiration and chemical oxidation (Glud et al 2016;Revsbech 1989a). The difference between TOU and DOU can be used to ascertain the relative contribution of the fauna mediated oxygen uptake (FOU), which both refers to the respiration and activity of the macrofauna itself, as well as the stimulation of microbial respiration within the sediments due to the introduction of oxygen-rich water into deeper sediment layers through bioirrigation and bioturbation (Glud 2008;Glud et al 2016;Kristensen et al 2012). The contribution of FOU to TOU is typically higher in coastal, slope and shelf sediments, compared to deep-sea sediments where the abundance of macrofauna is lower Wenzhofer and Glud 2002).…”

Response of seafloor ecosystems to abrupt global climate change

“…Estimates for bioturbation depth disturbance in deep-sea sediments are commonly assumed to be ∼10 cm, although shallower (2-5 cm) (30,31) and deeper (20 cm) depths are reported (32). Very high sediment volumes are displaced as a result of spatangoid movement (33), and these physical changes produce complex biogeochemical interactions in sediments associated with changes in primary productivity and nutrient flux (34).…”

Mediation of nitrogen by post-disturbance shelf communities experiencing organic matter enrichment

“…Conveyors include burrow-building species that are vertically oriented in the sediment typically feeding head-down (upward conveyors) or head-up (downward conveyors) at depth in the sediment. Regenerators are excavators that dig and continuously maintain burrows in the sediment and by doing so they mechanically transfer sediment from depth to the surface (Solan et al 2004;Kristensen et al 2012). Density and biomass was summed to obtain the total of each reworking mode.…”