Shell Thickening Research Articles

SEM observation of structural (non-mineralogical) alteration inside the previously crystallized nacreous layer of Crenomytilus grayanus (Bivalvia: Mytilidae)

A microstructural and mineralogical study shows the transition of aragonitic nacreous tablets to aragonitic prisms inside previously secreted nacre, i.e. without contact with the mantle or extrapallial fluid, in a field-collected mytilid bivalve Crenomytilus grayanus (D.). The intermediate zone between nacre and new prisms is represented by nacre tablets “stuck together” or by disordered calcium carbonate material. The modified nacre forms aragonitic lenses of prisms (ALPs). These lenses may reach 500μm in thickness below the tunnels excavated by the shell borers. ALPs are similar to myostracal prisms in mineralogy, morphology, and orientation, but differ from those in the outer shell layer. The process of ALPs formation is different to that of normal shell formation (e.g. nacre–prisms transition between prismatic and nacreous layers), remote biomineralization, extra shell thickening, as well as, shell repair, erosion, deformation or disease. Response to shell excavation by boring organisms is discussed as the reason for the appearance of ALPs.

Differences in shell strength of native and non-native oysters do not extend to size classes that are susceptible to a generalist predator

Whether non-native species proliferate to pest status can depend on top-down control from native predators. Among epifaunal molluscs, the shell serves as a main line of anti-predator defence and shell strength may determine the ease with which generalist predators can penetrate prey. We assessed whether, in eastern Australia, the faster growth of the non-native Pacific oyster, Crassostrea gigas, than that of the native Saccostrea glomerata comes at the cost of reduced investment in shell thickening, rendering the non-native oyster more susceptible to a generalist predator, the muricid gastropod Morula marginalba. Laboratory tests confirmed that among larger (>50-mm shell height) oysters, the shells of C. gigas were weaker than those of similar-sized S. glomerata. There were, however, no differences in shell strength or thickness between smaller S. glomerata and C. gigas of the size consumed by M. marginalba. In the absence of shell-strength differences among smaller oysters, M. marginalba preferentially consumed native over non-native oysters. When, however, M. marginalba had no choice of prey item, C. gigas was consumed at the same rate as the native oyster. Our results add to growing evidence that the invasion of C. gigas in eastern Australian estuaries is, at present, causing minimal disruption to trophic relationships.

Shell thickening and chambering in the oyster Crassostrea gigas: natural and anthropogenic influence of tributyltin contamination

Abnormal thickening and chambering in Crassostrea gigas oysters have been adopted for many years as bioindicators of available tributyltin (TBT) in coastal waters. Nevertheless, since natural causes can also induce the formation of multiple chambers, a field study and laboratory experimentation has been conducted with 72 examples of C. gigas in successive culture media. This work has enabled differences to be established between natural fine sediment‐induced characteristics and the influence of TBT on the shells. External shell deformities have been assessed using three biometric indices, shell thickness index, weight index and volume index. Internal differences have been observed in longitudinal sections of the shell: retraction of growth, stagnation of the adductor muscle scar and thinning of the chambers in the TBT‐polluted shell secretion. A new index, the opening chambers index, has been proposed, with a value of less than 1 in the TBT‐polluted environment and greater than 1 in shells secreted in an unpolluted production site. These conclusions should be borne in mind when C. gigas is used in biomonitoring programmes.

Shell Thickness Control of Nanoparticle/Polymer Assembled Microcapsules

Organic/inorganic composite microcapsules can be produced in water through a two-step charge-driven assembly of polyallylamine, citrate anions, and 13 nm silica nanoparticles. The shell is composed of nanoparticles intermixed with polymer, and is thick enough (100s of nm) to provide structural stability before or after drying. Controlling shell thickness, however, is currently difficult to perform. Presented here is a new method in which the shell wall can be thickened by contacting the as-synthesized capsules with silicic acid. This shell thickening was observed and quantified for a moderately broad, unimodal size distribution of capsular particles, through a combination of transmission electron and confocal fluorescence microscopies. Thermogravimetric analysis confirmed the deposition of additional silica, and Coulter counter measurements showed the mean capsule diameter of ∼4.5 ± 2.2 μm changed negligibly with silicic acid treatment. The shell-thickening process occurred in an inward direction, in which the nanosized silicic acid oligomers most likely diffused through the permeable capsule wall and deposited within the wall and on the inner shell wall surface. Adjustable shell wall thicknesses in hybrid microcapsules provide enhanced capability for chemical encapsulation, storage, and release applications.

Functional morphological analysis of evolution of ribbing in pliocene viviparid shells from Croatia

Posilovic, H., & Bajraktarevic, Z. 2010: Functional morphological analysis of evolution of ribbing in pliocene viviparid shells from Croatia. Lethaia, 10.1111/j.1502-3931.2009.00209.x. This paper provides a functional analysis of Pliocene freshwater gastropods from the phylogenetic lineage of Viviparus neumayri to Viviparus ornatus. On this section of the phylogenetic line, it is possible to follow the continuous evolution of the shell ornamentation (shouldering and rib formation) from ancestral V. neumayri with smooth shell to V. ornatus with spiral ribs. The shell morphology and possible structural function of rib development is discussed from the analytical point of view, but also by Finite Element Modelling. Spiral rib development in the viviparids is not correlated with shell thickening, but rather with strengthening of the shell is achieved through development of spiral ribs, with direct biomechanical and evoloutionary significance. □Croatia, functional morphology, gastropod shell evolution, Pliocene, viviparid evolution.

Is water temperature responsible for geographic variation in shell mass of Littorina obtusata (L.) snails in the Gulf of Maine?

A latitudinal cline in length-standardized shell thickness and mass of Littorina obtusata in the Gulf of Maine (GoM) has been attributed to predation by the European green crab Carcinus maenas. However, latitudinal variation in water temperature may also contribute to this cline. To investigate this hypothesis, we grew snails from 2 thin-shelled and 2 thick-shelled populations in warm (16 °C) and cold (10 °C) water treatments, representing summer temperatures of southern and northern parts of the GoM, respectively. Snails grown in warmer water showed a markedly greater increase in shell length (50%) and shell mass (60%) compared to conspecifics grown in colder water, but shell mass standardized for length was only weakly (relative to clinal variation) and not consistently (among populations) affected by temperature. Our experimental snails made shells that were lighter, when standardized for length, than conspecifics grown in nature. This “shell thinning” was particularly apparent in warmer water, because experimental snails diverted the increased calcification afforded by warmer water parallel (shell elongation) rather than perpendicular (shell thickening) to the axis of shell coiling. Interestingly, we estimate that if 16 °C snails had only grown to the length of 10 °C snails and used the additional shell material they produced to make their shell thicker rather than longer, they would have produced a shell comparable in mass to that of snails from the same population and shell length grown in nature. We conclude that water temperature is not directly responsible for natural variation in size-standardized shell thickness of L. obtusata in the GoM, but that it may contribute to this pattern indirectly, for example by facilitating the snail's plastic phenotypic response (shell thickening) to predation risk.

Use of Caged Nucella Lapillus and Crassostrea Gigas to Monitor Tributyltin‐Induced Bioeffects in Irish Coastal Waters

Caging studies have been previously reported to be useful for providing valuable information on biological effects of mollusks over short periods of time where resident species are absent. The degree of imposex in caged dog whelk (Nucella lapillus), was measured using the vas deferens sequence index (VSDI) and the Relative Penis Size Index (RPSI) and the extent of shell thickening in caged Pacific oyster (Crassostrea gigas) was investigated at t = 0 and t = 18 weeks. Nucella lapillus, when provided with mussels as a food source at the control site at Omey Island on the west Irish coast, did not demonstrate imposex features, whereas those transplanted to port areas did. Dunmore East exhibited the highest level of imposex (3.25 VDSI and 2.37 RPSI). Shell thickening was evident in C. gigas transplanted to Dunmore East, with low effects evident at the control location, Omey Island, and Dublin Bay at t = 18 weeks. Dry weight whole-body concentrations of organotins were most elevated in all species held at Dunmore East compared with other locations. Greatest delta15N and delta13C enrichment was observed within the tissues of the predatory N. lapillus in all three test sites. Increased assimilation in the Dublin Bay oysters might have been influenced by the presence of more nutrients at this location. Surficial sediment organotin levels were most elevated in the Dunmore East <2-mm fraction (22,707 microg tributyltin/kg dry weight), whereas low organotin levels were determined from Dublin and Omey Island sediments. The valuable application of cost-effective caging techniques to deliver integrated biological effects and chemical measurements in the absence of resident gastropod populations in potential organotin/tributyltin hotspot locations is discussed.

A new model for the drying of droplets containing suspended solids after shell formation

The novel droplet drying model introduced by the authors in a previous paper [Handscomb, C.S., Kraft, M., Bayly, A.E., 2008. A new model for the drying of droplets containing suspended solids. Chemical Engineering Science, in press, doi:10.1016/j.ces.2008.04.051] is extended to droplets drying in the presence of a surface shell. The model now incorporates shell thickening, along with a description of wet and dry shell drying. Structural properties of the shell are included in the model and influence the predicted dried particle morphology. Comparisons between model predictions and experimental data from the literature are presented for two systems of interest: detergent crutcher mix and colloidal silica. These simulations demonstrate the model is capable of predicting dried particle morphology together with other properties of interest such as moisture profiles and moments of the solids particle-size distribution.

Luminescence enhancement of Mn doped ZnS nanocrystals passivated with zinc hydroxide

Mn-doped ZnS nanocrystals prepared by solvothermal method have been successfully coated with different thicknesses of Zn(OH) 2 shells through precipitation reaction. The impact of Zn(OH) 2 shells on luminescent properties of the ZnS:Mn nanocrystals was investigated. X-ray diffraction (XRD) measurements showed that the ZnS:Mn nanocrystals have cubic zinc blende structure. The morphology of nanocrystals is spherical shape measured by transmission electron microscopy (TEM). ZnS:Mn/Zn(OH) 2 core/shell nanocrystals exhibited much improved luminescent properties than those of unpassivated ZnS:Mn nanocrystals. The luminescence enhancement was observed with the Zn(OH) 2 shell thickening by photoluminescence (PL) spectra at room temperature and the luminescence lifetime of transition from 4T 1 to 6A 1 of Mn 2+ ions was also prolonged. This result was led by the effective, robust passivation of ZnS surface states by the Zn(OH) 2 shells, which consequently suppressed nonradiative recombination transitions.

Response to Comment on "Divergent Induced Responses to an Invasive Predator in Marine Mussel Populations"

Preliminary DNA analysis indicates that only a few Mytilus trossulus mussels were present in our study of M. edulis . Excluding these M. trossulus did not influence the outcome of our analyses. Our study provides essential evidence that populations of M. edulis respond differently to the two crab predators, and the adaptive significance of shell thickening in mollusks is well established.

Specificity of induced defenses in Mytilus edulis and asymmetrical predator deterrence

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 334:145-153 (2007) - doi:10.3354/meps334145 Specificity of induced defenses in Mytilus edulis and asymmetrical predator deterrence Aaren S. Freeman* Zoology Department, University of New Hampshire, 46 College Road, Durham, New Hampshire 03824, USA *Email: afreeman@unh.edu ABSTRACT: Induced defenses of prey have become widely recognized in several marine taxa, yet their specificity to particular predators and impacts on subsequent predation are seldom investigated. In this study, Mytilus edulis showed highly specific induced defenses in response to predators with different attack strategies. The mussels developed significantly heavier shells only in the presence of waterborne cues from Carcinus maenas, a crushing crab predator, and significantly heavier adductor muscles only in the presence of waterborne cues from Asterias vulgaris (= Asterias rubens), a predatory sea star that pries bivalves open. However, mussels effectively thickened their shells in response to cues from predators by either increasing allocation to shell (in response to C. maenas), or reducing linear shell growth (in response to A. vulgaris and, to a lesser extent, the predatory whelk Nucella lapillus). These different mechanisms of shell thickening in response to all 3 predators defended the mussels from subsequent crab predation, increasing handling times of mussels by predatory C. maenas by more than 48%. In contrast, only mussels with increased adductor muscle weight (an induced response to A. vulgaris) were subsequently protected from the sea star. These results suggest that although induced defenses in M. edulis are specific to predators with different attack strategies, diffuse selection by C. maenas may allow predator specific responses to be adaptive even when predator composition changes. KEY WORDS: Blue mussel · Asterias vulgaris · Carcinus maenas · Nucella lapillus · Asterias rubens · Inducible defense · Phenotypic plasticity Full text in pdf format PreviousNextExport citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 334. Online publication date: March 26, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Determinate growth and variable size at maturity in the marine gastropod Amphissa columbiana

Individuals of Amphissa columbiana from the intertidal zone of San Juan Island, Washington, U.S.A., typically have either shells with very thin, delicate apertural lips, or shells with thick, robust lips. In laboratory observations, thin-lipped snails grew rapidly but were not sexually mature, while thick-lipped snails grew very slowly or not at all and were sexually mature. These observations are consistent with the hypothesis that A. columbiana displays determinate growth, as has been inferred for many columbellids on the basis of intraspecific variation in shell form. Sizes of mature snails were very variable, with the largest individuals weighing 4.5 times more than the smallest (wet weight, excluding shell). I tested the hypothesis that maturation and associated shell thickening are phenotypically plastic responses to the presence of predators. Exposure to effluent from the predatory crab Cancer productus in the laboratory had no effect on shell form or relative shell weight (an index of shell thickn...

Distribution of butyltin and derivatives in oyster shells and trapped sediments of two estuaries in Cantabria (Northern Spain)

Distribution of butyltin compounds (BTs) and derivatives (monobutyltin, MBT; dibutyltin, DBT and tributyltin, TBT) was analysed in Crassostrea gigas oyster shells and the sediments trapped in the shell chambers, from two different estuaries in Cantabria (Northern Spain), with very different environmental conditions, where previous data have not been reported. Inorganic tin analysis in oyster shells was performed in order to study the degradation of BTs. Shell thickening and losses in biological growth are related with the presence of TBT, and were determined using three morphological indexes. Total BTs concentrations, expressed as Sn, ranged from 18.0 ng g −1 to 176.7 ng g −1 in sediments, and from 2.4 ng g −1 to 11.1 ng g −1 in oyster shells. Total inorganic tin concentrations ranged from 1775.0 ng g −1 to 4781.3 ng g −1 in oyster shells. The amount of BTs in oyster shells has been associated with the concentrations in the sediments trapped in the shell chambers. Partition coefficients between oyster sediments and oyster shells show the affinity of BTs by the sediments and the higher inorganic tin in oyster shells does not seem to be related to the BTs pollution.

Early Paleogene climate and productivity of the Eastern Equatorial Atlantic, off the western coast of Ghana

Early Paleogene warmth is consistent with global observation, although temperature reconstructions were characterized by some degree of uncertainty. In spite of applied corrections, the suggested epifaunal benthic foraminifera maximum temperature range (23.65–30.36 °C) was still above the proposed maximum tropical sea surface temperature of ∼27 °C, confirming that foraminiferally derived temperatures are strongly dependent on assumptions. Paleoclimate and paleoproductivity of the Eastern Equatorial Atlantic were poorly correlated ( R 2 < 0 ) due to major anomalies. δ 1 3 C isotopic signatures have been largely and independently used to resolve discrepancies in eight anomalous depths identified in this study, in view of overlapping δ 1 8 O isotopic signatures. The last three anomalies are consistent with the dramatic onset of global cooling which occurred during this interval. The first five still remain anomalous, challenging the conventional view that glacial oceans are more productive than interglacial oceans. Discrepancies in these anomalous depths could have been due to artifacts, preservation biases related to dissolution, and/or shell thickening or encrustation. However, this study suggests extratropical variability and climate dynamics, reflecting regional anomalies due to upwelling or feedback mechanisms of poleward heat transport, which are prevalent in the Eastern Equatorial Atlantic.

Developmental aspects of biomineralisation in the Polynesian pearl oyster Pinctada margaritifera var. cumingii

The shell biomineralisation with special reference to the nacreous region is observed during the development of the Polynesian pearl oyster. Ultrastructural changes were studied and timed for the first time from planktonic larval shells to two-year-old adult shells. During the first two weeks following fertilization, the prodissoconch-I shell structure is undifferentiated and uniformly granular. The prodissoconch-II stage which develops during the next two weeks acquires a columnar organization. Metamorphosis is characterized by the formation of the dissoconch shell with all the elements of an adult shell and marks the onset of the development of the nacre. Nucleation starts within an organic matrix from point sources forming ‘crystal germs’ which expand circularly until they fuse. The orientation of the contour lines of scalariform growth margins indicates the direction of shell growth. Five zones of growth (Z) were characterized. One-month-old shells show a homogenous zone, without particular figures (Z0). The contour lines are initially parallel to the growing shell edge (Z1), later becoming labyrinthic (finger prints, Z2) or perpendicular to the edge (Z3). A fourth zone (Z4) characterized by spiral growth and associated with the shell thickening is observed later in the umbo region. This development results from a gradual lowering of the rate of mineralisation over time and from changes in growth pattern from a predominant increase in size, shifting toward an increase in the thickness of the shell. The mineralisation patterns of the shells from larvae reared in hatchery conditions and larvae from the field appear similar. The use of quantified information on shape, density, and distribution of nucleation sites as an indicator of growth conditions is discussed.

Unusual belemnite — incoceramid bivalve association from the Albian (late Early Cretaceous) of Queensland, Australia

An unusual occurrence in the upper Albian Toolebuc Formation of Queensland, Australia, of penetration of a guard of the belemnite Dimitobelus (Dimitobelus) stimulus into the disc of an indeterminate inoceramid bivalve, is the first report of this type of shell damage in the fossil record. The belemnite punctured completely both valves of the bivalve to the maximum diameter of the belemnite guard, by inferred compaction from sediment overburden during post-mortem biostratinomic processes. Shell thickening of the inoceramid bivalve by shearing of prismatic layers at the site of puncture indicates that the bivalve shell behaved plastically during the puncture and that the great flexibility of the prismatic layers was facilitated by the relatively thin shell and presence of organic sheaths around individual prisms. This flexibility may have been advantageous during a predatory attack, by allowing the maintenance of a seal during breakage of the shell margin.

Lethal and sub-lethal effects of phototrophic endoliths attacking the shell of the intertidal mussel Perna perna

Animals that bore into calcareous material can cause considerable damage to molluscan shells. In contrast, smaller microbial phototrophic endoliths have until recently been thought of as relatively benign. Phototrophic endoliths (primarily cyanobacteria) infest the shells of 50 to 80% of midshore populations of the mussel Perna perna (L.) in South Africa. This infestation causes clearly visible shell degradation, and we record here ecologically important lethal and sub-lethal effects (e.g. changes in growth and reproductive output) of the endoliths on their mussel hosts. Endolith infestation reduced the strength of shells significantly and also affected shell growth. In situ marking of shells, using the fluorochrome calcein, showed that infested and non-infested mussels increased in shell length at the same rate. However, the rate of increase in shell thickness (associated with shell repair) was significantly faster in infested than in uninfested individuals. This increase in the rate of shell thickening was not sufficient to compensate for rapid endolith-induced shell degradation and, around the site of adductor muscle attachment, infested shells were thinner than their uninfested counterparts. The shells of 18% of recently dead mussels had holes induced by endolith erosion. This effect was highly size dependent, and the proportion of mortality due to endoliths rose to almost 50% for the largest mussels. The re-routing of energy due to shell repair had important sub-lethal effects on the reproductive rates of mussels. During the reproductive period, mean dried flesh mass for large (>70 mm), non-infested P. perna was substantially higher than for infested individuals. This difference was almost entirely due to differences in gonad mass, which was approximately 100% higher for non-infested mussels. We conclude that, by attacking the shell, phototrophic endoliths reduce both the longevity and reproductive output of large mussels on the midshore.

Tributyltin Biomonitoring in Portuguese Estuaries with the Portuguese Oyster (Crassostrea Angulata)

In Portugal the measurement of shell thickening (Shell Thickness Index or STI) in the Portuguese oyster Crassostrea angulata was used to evaluate bioavailable tributyltin (TBT) in estuaries. Valves from living C. angulata populations and relict valves were collected in 1989–90 over the entire Sado estuary and they showed shell thickening (low STI) increasing with time. Portuguese oyster reproduction had recently ceased in the Sado estuary. Relict oyster valves from the Tagus estuary showed no shell thickening. Caged cultchless Portuguese oyster spat showed valve thickening after two and four months exposure to TBT-painted panels, and when transplanted to the Sado estuary. Spat exposed to an increasing series of TBT-painted panels had increased mortality, TBT tissue concentrations and shell thickening. Oyster spat transplanted to the Sado estuary and a canal in the Aveiro estuary had low STI at four months, but not when transplanted to another Aveiro estuary site or the Viana do Costelo and Figuera da Foz estuaries. Adult oysters with low STI, including those for market sale, had lower tissue TBT concentrations than spat and were not considered hazardous to human health. The STI bioassay using transplanted oyster spat was easily measured in four months, related to TBT exposure, independent of overall growth and a better indicator of bioeffective TBT than tissue TBT concentration.

Rayleigh–Taylor instability evolution in ablatively driven cylindrical implosions

The Rayleigh–Taylor instability is an important limitation in inertial confinement fusion capsule designs. Significant work both theoretically and experimentally has been done to demonstrate the stabilizing effects of material flow through the unstable region. The experimental verification has been done predominantly in planar geometry. Convergent geometry introduces effects not present in planar geometry such as shell thickening and accelerationless growth of modal amplitudes (e.g., Bell–Plesset growth). Amplitude thresholds for the nonlinear regime are reduced, since the wavelength λ of a mode m decreases with convergence λ∼R/m, where R is the radius. Convergent effects have been investigated using an imploding cylinder driven by x-ray ablation on the NOVA laser [J. L. Emmet, W. F. Krupke, and J. B. Trenholme, Sov. J. Quantum Electron. 13, 1 (1983)]. By doping sections of the cylinder with opaque materials, in conjunction with x-ray backlighting, the growth and feedthrough of the perturbations from the ablation front to the inner surface of the cylinder for various initial modes and amplitudes from early time through stagnation was measured. Mode coupling of illumination asymmetries with material perturbations is observed, as well as phase reversal of the perturbations from near the ablation front to the inner surface of the cylinder. Perturbation growth is observed due to convergence and compressibility alone, without the effects of acceleration, and scales as ∼1/ρR, where ρ is the mass density. Imaging is performed with an x-ray pinhole camera coupled to a gated microchannel plate detector.

Incidence of abnormal shell thickening in the Pacific oyster Crassostrea gigas in Poole Harbour (UK), subsequent to the 1987 TBT restrictions

Juvenile Crassostrea gigas stock were experimentally deployed in 1989 at three locations within Poole Harbour (Dorset, UK); a mariculture and boating centre characterized until 1987 by high TBT levels, and abnormal shell thickening in C. gigas, preventing culture. After six months, the stock grown at sites adjacent to shellfish beds and featuring low boat densities, showed normal growth, whereas that grown within an embayment featuring high boat densities, showed the onset of abnormal thickening. Grossly thickened senescent C. gigas recovered from a commercial shellfish bed showed recent reversion to normal growth. These results suggest that since the 1987 UK restrictions on TBT use, levels within much of the Harbour have declined sufficiently to allow a return to C. gigas mariculture, but that levels remain too high within areas of high boat density. The study also compares the effectiveness of three established methods for assessing the degree of shell thickening.