Functional trait responses to sediment deposition reduce macrofauna-mediated ecosystem functioning in an estuarine mudflat

Abstract

Abstract. Human activities, among which dredging and land use change in river basins, are altering estuarine ecosystems. These activities may result in changes in sedimentary processes, affecting biodiversity of sediment macrofauna. As macrofauna controls sediment chemistry and fluxes of energy and matter between water column and sediment, changes in the structure of macrobenthic communities could affect the functioning of an entire ecosystem. We assessed the impact of sediment deposition on intertidal macrobenthic communities and on rates of an important ecosystem function, i.e. sediment community oxygen consumption (SCOC). An experiment was performed with undisturbed sediment samples from the Scheldt river estuary (SW Netherlands). The samples were subjected to four sedimentation regimes: one control and three with a deposited sediment layer of 1, 2 or 5 cm. Oxygen consumption was measured during incubation at ambient temperature. Luminophores applied at the surface, and a seawater-bromide mixture, served as tracers for bioturbation and bio-irrigation, respectively. After incubation, the macrofauna was extracted, identified, and counted and then classified into functional groups based on motility and sediment reworking capacity. Total macrofaunal densities dropped already under the thinnest deposits. The most affected fauna were surficial and low-motility animals, occurring at high densities in the control. Their mortality resulted in a drop in SCOC, which decreased steadily with increasing deposit thickness, while bio-irrigation and bioturbation activity showed increases in the lower sediment deposition regimes but decreases in the more extreme treatments. The initial increased activity likely counteracted the effects of the drop in low-motility, surficial fauna densities, resulting in a steady rather than sudden fall in oxygen consumption. We conclude that the functional identity in terms of motility and sediment reworking can be crucial in our understanding of the regulation of ecosystem functioning and the impact of habitat alterations such as sediment deposition.

The scale‐dependent effect of environmental filters on species turnover and nestedness in an estuarine benthic community

“…Under this circumstance, oxygen penetration depth never exceeds a few centimeters and becomes a major limiting factor for sediment‐dwelling organisms (Mestdagh et al. ). In addition, sessile or less motile benthic fauna that lives on the substratum or in tubes often have a limited capacity to escape the constant deposition of sediments, and suspension feeders risk damaging their respiratory apparatus (Stevens , Mestdagh et al.…”

“…Contrary to the salinity gradient, which represents a transition along distinct but suitable conditions for life in aquatic systems, several factors make one end of the sedimentary gradient highly inhospitable for many species. In mud bottoms, superficial fine sediment acts as physical barrier that increases the contribution of anaerobic pathways to the overall decomposition and relocates the reoxidation of reduced solutes upwards (Hohaia et al 2014, Mestdagh et al 2018. Under this circumstance, oxygen penetration depth never exceeds a few centimeters and becomes a major limiting factor for sediment-dwelling organisms (Mestdagh et al 2018).…”

“…In mud bottoms, superficial fine sediment acts as physical barrier that increases the contribution of anaerobic pathways to the overall decomposition and relocates the reoxidation of reduced solutes upwards (Hohaia et al 2014, Mestdagh et al 2018. Under this circumstance, oxygen penetration depth never exceeds a few centimeters and becomes a major limiting factor for sediment-dwelling organisms (Mestdagh et al 2018). In addition, sessile or less motile benthic fauna that lives on the substratum or in tubes often have a limited capacity to escape the constant deposition of sediments, and suspension feeders risk damaging their respiratory apparatus (Stevens 1987, Mestdagh et al 2018.…”

“…Under this circumstance, oxygen penetration depth never exceeds a few centimeters and becomes a major limiting factor for sediment-dwelling organisms (Mestdagh et al 2018). In addition, sessile or less motile benthic fauna that lives on the substratum or in tubes often have a limited capacity to escape the constant deposition of sediments, and suspension feeders risk damaging their respiratory apparatus (Stevens 1987, Mestdagh et al 2018. Experiments have shown that even thin layers of deposition may reduce species diversity by nearly 50%, with the strongest effect on those taxa living on the sediment-water interface (Lohrer et al 2004).…”

“…Experiments have shown that even thin layers of deposition may reduce species diversity by nearly 50%, with the strongest effect on those taxa living on the sediment-water interface (Lohrer et al 2004). Consequently, the macrofauna in these locations is typically depauperated or characterized by dense benthic assemblages consisting of only a few generalist species (Magni et al 2005, Mestdagh et al 2018; Appendix S2: Fig. S5).…”