Enhanced erodibility of fine-grained marine sediments by Hydrobia ulvae

Abstract

The common mud snail Hydrobia ulvae is a widespread and dominant deposit feeder on fine-grained substrata along the European Atlantic coastline. Previous studies have shown that mud snail activities such as grazing, faecal pellet production and mucous production may influence physical properties of the surface sediment layer and thus depositional and erosional processes. To quantify the influence of Hydrobia density on key parameters such as erosion threshold and erosion rate, a shortterm laboratory experiment was conducted. Snails were placed on fine-grained sediment at densities of 10 000 and 50 000 ind m À 2 and erosion experiments were carried out one, three and five days after establishment of the sediment beds. Controls without H. ulvae were treated the same way. The presence of H. ulvae significantly increased the erosion rate and decreased the erosion threshold compared to snail-free control plots. The erosion rate was increased by a factor of 2 to 4 when H. ulvae were present and showed stronger influence by the snail than the erosion threshold. Snail density did not affect the erosion threshold, but the erosion rate doubled with an increase in density from 10 000 to 50 000 ind m À 2 . The erosion rate was only marginally different after one day but the difference increased over time and the erosion rate was significantly different for all treatments after five days. No significant time dependence was observed for the erosion threshold. The results generally confirm results obtained in situ and differences can be related to different hydrodynamic conditions under field and laboratory conditions. D

Benthic community-mediated sediment dynamics

“…bivalves, crustaceans, gastropods, polychaetes) are generally considered to have a destabilising effect on the sediment surface, either directly or through grazing on MPB aggregates. (Blanchard et al 2000, de Deckere et al 2001, Andersen et al 2002, Orvain et al 2004.…”

A model of sediment transport under the influence of surface bioturbation: generalisation to the facultative suspension-feeder Scrobicularia plana

“…For example, the common mud snail Hydrobia ulvae disrupts the upper layers of sediment while crawling, and this effect induces a decrease in bed resistance. As a result, this leads to an enhancement of the rates of fluff layer erosion in the presence of actively crawling snails (Blanchard et al 1997, Andersen et al 2002, Orvain et al 2003. Particle binding is also a result of the large quantities of mucus that are secreted by this motile gastropod within the fluff layer, and mucus must contribute to the gradual disruption by tracks during fluff layer erosion, some of the tracks being able to resist strong currents, while others are rapidly eroded (Orvain et al 2003).…”

Technical Note: The effects of five different defaunation methods on biogeochemical properties of intertidal sediment

“…burrowing and feeding, can significantly alter properties of sediments, such as erodibility, porosity, permeability and grain size (Meadows and Tait, 1989;Meadows et al, 1990). Erosion on mudflats is mediated by the interplay between biological and physical processes (de Brouwer et al, 2000;Defew et al, 2002;Tolhurst et al, 2006b) and can be significantly altered by fauna (Austen et al, 1999;Widdows et al, 2000;Andersen et al, 2002) and flora (Friend et al, 2003;Tolhurst et al, 2006a). Often, an organism can have multiple synergistic or antagonistic influences on properties and processes that may vary temporally and/or spatially (e.g.…”