Bivalves rapidly repair shells damaged by fatigue and bolster strength

ABSTRACT Hard external armors have to defend against a lifetime of threats yet are traditionally understood by their ability to withstand a single attack. Survival of bivalve mollusks thus can depend on the ability to repair shell damage between encounters. We studied the capacity for repair in the intertidal mussel Mytilus californianus by compressing live mussels for 15 cycles at ∼79% of their predicted strength (critically fracturing 46% of shells), then allowing the survivors 0, 1, 2 or 4 weeks to repair. Immediately after fatigue loading, mussel shells were 20% weaker than control shells that had not experienced repetitive loading. However, mussels restored full shell strength within 1 week, and after 4 weeks shells that had experienced greater fatiguing forces were stronger than those repetitively loaded at lower forces. Microscopy supported the hypothesis that crack propagation is a mechanism of fatigue-caused weakening. However, the mechanism of repair was only partially explained, as epifluorescence microscopy of calcein staining for shell deposition showed that only half of the mussels that experienced repetitive loading had initiated direct repair via shell growth around fractures. Our findings document repair weeks to months faster than demonstrated in other mollusks. This rapid repair may be important for the mussels’ success contending with predatory and environmental threats in the harsh environment of wave-swept rocky coasts, allowing them to address non-critical but weakening damage and to initiate plastic changes to shell strength. We highlight the significant insight gained by studying biological armors not as static structures but, instead, as dynamic systems that accumulate, repair and respond to damage.

Palladium Cube with Pt Shell Deposition for Localized Surface Plasmon Resonance Enhanced Photodynamic and Photothermal Therapy of Hypoxic Tumor

Multifunctional phototherapy nanoagents for imaging-guided synergistic photothermal therapy (PTT) and photodynamic therapy (PDT) are highly desirable in the field of solid tumor therapy. Nevertheless, the tumor microenvironment (TME) inherently charactered...

4-Mercaptobenzoic Acid Labeled Gold-Silver-Alloy-Embedded Silica Nanoparticles as an Internal Standard Containing Nanostructures for Sensitive Quantitative Thiram Detection

In this study, SiO2@Au@4-MBA@Ag (4-mercaptobenzoic acid labeled gold-silver-alloy-embedded silica nanoparticles) nanomaterials were investigated for the detection of thiram, a pesticide. First, the presence of Au@4-MBA@Ag alloys on the surface of SiO2 was confirmed by the broad bands of ultraviolet-visible spectra in the range of 320–800 nm. The effect of the 4-MBA (4-mercaptobenzoic acid) concentration on the Ag shell deposition and its intrinsic SERS (surface-enhanced Raman scattering) signal was also studied. Ag shells were well coated on SiO2@Au@4-MBA in the range of 1–1000 µM. The SERS intensity of thiram-incubated SiO2@Au@4-MBA@Ag achieved the highest value by incubation with 500 µL thiram for 30 min, and SERS was measured at 200 µg/mL SiO2@Au@4-MBA@Ag. Finally, the SERS intensity of thiram at 560 cm−1 increased proportionally with the increase in thiram concentration in the range of 240–2400 ppb, with a limit of detection (LOD) of 72 ppb.

In vivo characterization of bivalve larval shells: a confocal Raman microscopy study

In vivo confocal Raman microscopy (CRM), polarized light microscopy and Fourier transform infrared spectroscopy (FTIR) were used to determine if a significant amount of amorphous calcium carbonate (ACC) exists within larval shells of Baltic mytilid mussels ( Mytilus edulis -like) and whether the amount of ACC varies during larval development. No evidence for ACC was found from the onset of shell deposition at 21 h post-fertilization (hpf) until 48 hpf. Larval Mytilus shells were crystalline from 21 hpf onwards and exhibited CRM and FTIR peaks characteristic of aragonite. Prior to shell deposition at 21 hpf, no evidence for carbonates was observed through in vivo CRM. We further analysed the composition of larval shells in three other bivalve species, Mercenaria mercenaria , Crassostrea gigas and Crassostrea virginica and observed no evidence for ACC, which is in contrast to previous work on the same species. Our findings indicate that larval bivalve shells are composed of crystalline aragonite and we demonstrate that conflicting results are related to sub-optimal measurements and misinterpretation of CRM spectra. Our results demonstrate that the common perception that ACC generally occurs as a stable and abundant precursor during larval bivalve calcification needs to be critically reviewed.

The Moyjil site, south-west Victoria, Australia: chronology

An unusual shell deposit at Moyjil (Point Ritchie), Warrnambool, in western Victoria, has previously been dated at 67±10 ka and has features suggesting a human origin. If human, the site would be one of Australia’s oldest, justifying a redetermination of age using amino acid racemisation (AAR) dating of Lunella undulata (syn. Turbo undulatus) opercula (the dominant shellfish present) and optically stimulated luminescence (OSL) of the host calcarenite. AAR dating of the shell bed and four Last Interglacial (LIG) beach deposits at Moyjil and Goose Lagoon, 30 km to the west, confirmed a LIG age. OSL analysis of the host sand revealed a complex mixing history, with a significant fraction (47%) of grains giving an early LIG age (120–125 ka) using a three-component mixing model. Shell deposition following the LIG sea-level maximum at 120–125 ka is consistent with stratigraphic evidence. A sand layer immediately below the shell deposit gave an age of ~240 ka (i.e. MIS 7) and appears to have been a source of older sand incorporated into the shell deposit. Younger ages (~60–80 ka) are due to bioturbation before calcrete finally sealed the deposit. Uranium/thorium methods were not applicable to L. undulata opercula or an otolith of the fish Argyrosomus hololepidotus because they failed to act as closed systems. A U–Th age of 103 ka for a calcrete sheet within the 240 ka sand indicates a later period of carbonate deposition. Calcium carbonate dripstone from a LIG wave-cut notch gave a U–Th age of 11–14 ka suggesting sediment cover created a cave-like environment at the notch at this time. The three dating techniques have collectively built a chronology spanning the periods before and after deposition of the shell bed, which occurred just after the LIG sea-level maximum (120–125 ka).

TIDAL PERIODICITY IN MICROGROWTH BANDS OF BLOOD CLAM Anadara indica (Bivalvia: Arcidae): A POSSIBLE ENVIRONMENTAL SCLEROCHRONOMETER IN THE TROPICS

This study examining the microgrowth periodicity of wild type Anadara indica (Gmelin, 1791) being submerged for 29 d in the cage and field plot. Individual clams showed daily increment growth that conforms to semilunar tidal cycle of 14.8 d. The shell therefore provided record about the absolute growth history of the organism, presumably including the environmental conditions under which shell deposition took place. Shell accretion decreased in rhythm to the gonad development and spawning measured as Condition Index. The significantly departed sex ration to 0.25:1 in favour of > 35 mm shell length females indicating the occurrence of male to female sex reversal, likewise its con-specific A. granosa (Linne, 1758) and A. antiquata (Linnaeus, 1758). It is thought that habitat overlap between A. granosa and A. indica, combined with irresponsible fisheries of the local people which commercially caught small size male clams caused the shift in population dominance among these two species, i.e., from A. granosa to A. indica. However, this study showed that A. indica might as well thrive in areas close to intertidal region likewise A. granosa, where tidal periodicity role as a forcing function to the environment.