Bioerosion of siliceous rocks driven by rock-boring freshwater insects

Macrobioerosion of mineral substrates in fresh water is a little-known geological process. Two examples of rock-boring bivalve molluscs were recently described from freshwater environments. To the best of our knowledge, rock-boring freshwater insects were previously unknown. Here, we report on the discovery of insect larvae boring into submerged siltstone (aleurolite) rocks in tropical Asia. These larvae belong to a new mayfly species and perform their borings using enlarged mandibles. Their traces represent a horizontally oriented, tunnel-like macroboring with two apertures. To date, only three rock-boring animals are known to occur in fresh water globally: a mayfly, a piddock, and a shipworm. All the three species originated within primarily wood-boring clades, indicating a simplified evolutionary shift from wood to hardground substrate based on a set of morphological and anatomical preadaptations evolved in wood borers (e.g., massive larval mandibular tusks in mayflies and specific body, shell, and muscle structure in bivalves)

Symbiotic cooperation between freshwater rock-boring bivalves and microorganisms promotes silicate bioerosion

International audienceBioerosion is a process with a high socioeconomic 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. Bioerosion is a commonplace strategy developed by living organisms, which consists in boring hard substrates of various origins, including biological materials (e.g., wood, shells, and bones) 1 , mud 2 , rocks 3 and even synthetic materials. Depending on the nature of the substrate and the borer, bioerosion ensures a wide range of metabolic activities and ecosystem services, ranging from nutrition 4 to the creation of microhabitats protected from predators for themselves as well as for secondary dwellers 5. Gaining knowledge into the occurrence, rates and mechanisms of boring is of fundamental importance for a series of reasons. First and historically, mankind has been confronted with macroborers through the damages caused by shipworms on vessels, wooden wharfs and docks 5,6. More broadly, bioerosion has socioeconomic impacts whenever manufactured materials are damaged, including plastic, metals and concrete materials such as levees or coastal defences 3,6. Second, bioerosion contributes to element recycling, shaping landscapes through the weakening of rocky shorelines and participating to coastal retreat 5 , for which the current rates are likely to be modified drastically as a result of climate change 6. Third, the creation of microhabitats by macroborers such as bivalves is correlated with a significant increase of the abundance of species assemblages, thus partly contributing to local faunal biodiversity 7. Finally, fossil records of macro-bioerosion may be used as a biological proxy to estimate the paleo-location of intertidal and shallow subtidal marine environments, marking ancient shorelines 8. 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. First, rock boring can ope

Nuclear Melt Glass from Experimental Field, Semipalatinsk Test Site

Investigation of shocked materials provides unique information about behavior of substances in extreme thermodynamic conditions. Near surface nuclear tests have induced multiple transformations of affected soils. Examination of nuclear glasses and relics of entrapped minerals provides a unique database on their behavior under an intense temperature flash. In this work, several types of nuclear fallout particles from historic tests at the Semipalatinsk test site are investigated using complementary analytical methods. Distribution of radionuclides in all types of samples is highly heterogeneous; domains with high content of radionuclides are often intermixed with non-active materials. There is no general correlation between chemical composition of the glassy matrix and content of radionuclides. In aerodynamic fallout, the main fraction of radionuclides is trapped in the outer glassy shell. Relics of quartz grains are always devoid of radionuclides, while glass regions of high activity have different composition. In contrast to underground tests, iron-rich minerals are not necessarily radioactive. In most cases, the glassy matrix in anhydrous and is strongly polymerized, and the Q3 silicate groups dominate. Temperature-induced transformations of entrapped minerals are discussed. Investigation of zircon grains shows absence of a direct correlation between degree of decomposition into constituting oxides, morphology of resulting baddeleyite, and maximum experienced temperature. For the first time, temperature history of a nuclear ground glass is estimated from Zr diffusion profiles from decomposing zircon grain