Quantifying bioturbation across coastal seascapes: Habitat characteristics modify effects of macrofaunal communities

Abstract

Bioturbation by benthic macrofauna communities plays a significant role in the setting and maintenance of important ecosystem functions and the delivery of associated ecosystem services. We investigated the context-dependence of bioturbation performed by natural benthic communities in the coastal northern Baltic Sea by quantifying three bioturbation metrics (particle mixing intensity, surface sediment reworking and bioturbation depth) across 18 sites ranging from cohesive muddy sediments to non-cohesive coarse sands, while accounting for the complexity of natural communities and habitat characteristics. We identified two distinct patterns of bioturbation; in fine sediments bioturbation rates were highly variable and in coarse sediments bioturbation rates were less variable and characterized by lower maximal values. Using distance-based linear multiple regressions, we found that 75.5% of the variance in bioturbation rates in fine sediment could be explained by key functional groups/species abundance and/or biomass (i.e. biomass of the gallery-diffusors and abundances of biodiffusors, surface modifiers, conveyors and gallery diffusors, respectively).In coarse sediment, 47.8% of the variance in bioturbation rates could be explained by a combination of environmental factors (grain size, organic matter content, buried plant material) and faunal functional groups, although fauna alone explained only 13% of this variance. Bioturbation in fine sediments was therefore more predictable based on the composition of benthic fauna. In coarse sediment, the bioturbation activities of benthic fauna were strongly modified by habitat characteristics (including the presence of buried plant material, sediment organic content and grain size) whereas in fine sediments this was not the case. Our results therefore highlight that variability in spatial patterns of bioturbation is a result of complex relationships between macrofauna community structure, sediment type and other habitat characteristics, likely modifying bioturbation performance of individual fauna.

The meagre future of benthic fauna in a coastal sea—Benthic responses to recovery from eutrophication in a changing climate

“…Unravelling the combined effects of nutrient loads and climate change on benthic macrofauna is important for understanding the future functioning of coastal ecosystems, as it is an important component linking the benthic and pelagic realms (Graf, ; Grall & Chauvaud, ; Griffiths et al, ). Benthic fauna contribute to organic matter processing and benthic–pelagic fluxes of nutrients, carbon and oxygen both directly through feeding and metabolism (Herman, Middelburg, van de Koppel, & Heip, ; Josefson & Rasmussen, ; Middelburg, ) and indirectly by bioturbation of the sediments (Bernard, Gammal, Järnström, Norkko, & Norkko, ; Meysman, Middelburg, & Heip, ; Stief, ).…”

Biological and physical drivers of bio-mediated sediment resuspension: A flume study on Cerastoderma edule

“…The resuspension of sediments with different levels of cohesiveness may be differently influenced by the effect of bioturbation activity. For instance, recent field observations Joensuu, et al, 2018;Bernard, et al, 2019;Hillman, et al, 2019), flume studies (Li, et al, 2017;Soissons, et al, 2019) and sediment transport models (Nasermoaddeli, et al, 2018) showed that bioturbators enhance the resuspension of fine sediment but have limited influence on coarse sediment.…”

Understanding Environmental Changes in Temperate Coastal Seas: Linking Models of Benthic Fauna to Carbon and Nutrient Fluxes

“…The impact of benthic fauna on nutrient and carbon cycling depends on e.g., density, biomass and the functional traits of individual species in the benthic community (Mermillod-Blondin et al, 2005;Norkko et al, 2013;Gammal et al, 2019), as well as on sediment structure (Braeckman et al, 2014;Bernard et al, 2019). Benthic animals process organic matter by consuming particulate organic matter (POM) and transforming a fraction of the ingested food into inorganic components that are respired and excreted (Figure 2).…”

“…Despite decades of bioturbation research, there still seems to be a lack of mechanistic understanding of the complex processes that determine bioturbation rates in natural settings, as well as the diverse effects of bioturbation on physical, chemical and biological processes in the sediment, especially in heterogeneous coastal areas. On top of the effects of individual traits, the environmental surroundings of those individuals also modify their behavior and metabolism, leading to different effects on biogeochemical fluxes, as shown for example in a series of recent studies of a coastal gradient in the Baltic Sea (Joensuu et al, 2018;Bernard et al, 2019;Gammal et al, 2019).…”