Abstract
Bioerosion is a process with a high socio-economic impact that contributes to coastal retreat, and likely to increase with climate change. Whereas limestone bioerosion is well explained by a combination of mechanical and chemical pathways, the bioerosion mechanisms of silicates, which are harder and chemically more resistant, remain elusive. Here we investigated the interface between siltstone and freshwater rock-boring bivalves Lignopholas fluminalis (Bivalvia: Pholadidae). Remains of a microbial biofilm were observed only in the poorly consolidated part of the rock within the macroborings created by bivalves. Secondary Mn-bearing minerals identified in the biofilm suggest that microbes promoted silicate rock weathering by dissolving Mn-rich chlorites. Moreover, hard mineral debris found in a biofilm attached to the shells likely contributed to the abrasion of the rock substrate. Thus, beyond the classical view of chemical and/or mechanical action(s) of macroborers, silicate bioerosion may also be facilitated by an unexpected synergistic association between macro- and microorganisms.
Highlights
Bioerosion is a process with a high socio-economic impact that contributes to coastal retreat, and likely to increase with climate change
These results are in reasonable agreement with the analyses reported by Bolotov et al.[8]
Imaging the rock substrate in crosssection further indicates that the grains display a packed and cohesive arrangement, as further suggested by the fact that individual grains did not tend to pop out during the focused ion beam (FIB) milling procedure (Fig. 2d)
Summary
Bioerosion is a process with a high socio-economic impact that contributes to coastal retreat, and likely to increase with climate change. The mechanisms of rock bioerosion associated to macroborers and especially bivalves have been a source of lively debate for decades, and can be schematically divided into two main pathways. It is generally admitted that chemical etching is only possible when boring occurs in (at least partly) calcareous substrates[5], as most of the common biologically secreted agents by macroborers exhibit a modest impact on the dissolution rate of silicate m inerals[9]. It is generally admitted that both mechanical abrasion and chemical etching occur synergistically, especially for living organisms that bore in calcareous rocks, where the substrate is first weakened chemically, while individual grains are subsequently excavated mechanically from the boring[5,9]
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