Empty Shells Research Articles

Experimental analysis of the effect of discrete aggregate on the bending stability of thin-walled cylindrical shells

The effect of a discrete aggregate on the bending stability of thin-walled cylindrical shells was studied. The samples for the study were made of aluminum alloy 3004 (temper H19). The samples were cantilevered; a vertical concentrated cross force was applied to its free end. Ten empty samples and ten samples 90% filled with iron powder were tested. The samples were loaded in stages by 10N, and when approaching the moment of buckling the samples were loaded by 1N or less. The force, deflection of the free end of the sample, and axial strain were recorded at each stage of loading. Displacement of the free end of the sample versus cross force diagrams is plotted. The buckling force was determined by the inflection point of the diagrams. The samples lost the stability in elasticity. The diagrams for the empty and filled samples for each series almost coincide until the loss of stability of the empty sample. This means that when the empty sample loses its stability, the buckle directed towards the center line is formed; and for the filled samples, the formation of buckles is prevented by the discrete material, therefore the critical force increased by 18.8%. The influence of discrete aggregate is considered on the basis of approximation [24] for tank trucks manufactured at the enterprise. The critical stress is calculated using the superposition principle, since the stability is lost in the elasticity. The critical stress for the filled tank is determined by the sum of the critical stress for an empty shell with the stresses created by the weight load and the hydrostatic pressure of the discrete filler. The calculation of critical stresses showed that for the pattern samples the influence of discrete filler is 8.3%, and for the full-sized tanks the influence of discrete filler on the value of the critical voltage is significant and amounts to 62%. We studied the effect of various discrete fillers on stability, such as river sand, iron and copper powders at different filling ratios of the samples. Due to an increase in powder density and filling volume, the value of the critical force increased. For the samples filled to 90% with the river sand had the critical force increase by 13.3%, while those filled with the iron powder had their critical force increase by 40.5%, the copper powder samples had an increase of the critical force by 43.1%.

Shell-Exchange Behavior in a Hermit-Crab-Like Tanaidacean (Crustacea: Malacostraca).

This study describes shell-exchange behavior in the hermit-crab-like tanaidacean Macrolabrum sp. (Pagurapseudidae: Pagurapseudinae) under captive conditions. I observed one shell exchange by Macrolabrum sp., the behavioral sequence of which was as follows: a shell-carrying tanaidacean 1) grasped the edge of the aperture of an empty gastropod shell with its right cheliped; 2) inspected the condition inside the shell four times by inserting the anterior portion of its body into the shell; and 3) moved into the shell, posterior end (pleotelson) first. The elapsed time from the initial grasping of the empty shell to completing the move into it was 2 min 20 sec. In contrast to a Pagurapseudes tanaidacean and hermit crabs, the individual of Macrolabrum sp. did not examine the external surface of the shell during the single shell exchange observed.

PH-depended protein shell dis- and reassembly of ferritin nanoparticles revealed by atomic force microscopy

Ferritin, a protein that is present in the human body for a controlled iron storage and release, consists of a ferrihydrite core and a protein shell. Apoferritin, the empty shell of ferritin, can be modified to carry tailored properties exploitable for targeted and direct drug delivery. This protein shell has the ability to dis- and reassemble depending on the pH value of the liquid environment and can thus be filled with the desired substance. Here we observed the dis- and reassembly process of the protein shell of ferritin and apoferritin in situ and in real space using atomic force microscopy. Ferritin and apoferritin nanoparticles adsorbed on a mica substrate exhibited a change in their size by varying the pH value of the surrounding medium. Lowering the pH value of the solution led to a decrease in size of the nanoparticles whereas a successive increase of the pH value increased the particle size again. The pH dependent change in size could be related to the dis- and reassembling of the protein shell of ferritin and apoferritin. Supplementary imaging by bimodal magnetic force microscopy of ferritin molecules accomplished in air revealed a polygonal shape of the core and a three-fold symmetry of the protein shell providing valuable information about the substructure of the nanoparticles.

Breeding, planktonic and settlement factors shape recruitment patterns of one of the last remaining major population of Pinna nobilis within Spanish waters

The pen shell, Pinna nobilis L., is a critically endangered bivalve threatened by mass mortality events throughout the Mediterranean, but the Alfacs Bay (Ebro Delta) still hosts many healthy individuals. Herein, we study the main factors controlling recruitment patterns in this locality, including gonadal development and abundance of critical life-stages, as well as the effect of environmental factors. Growth records from empty shells suggested a single major peak of recruitment during a period of 11 years, although many juveniles were found in two very shallow sand bars possibly acting as a barrier for water circulation and as a trap for larvae. Collectors deployed outside these sand bar areas showed zero settlers, and the availability of planktonic larvae was very low. Gonadal examination evidenced breeding throughout the summer period with successive hermaphroditism, but 20% of individuals were simultaneous hermaphrodites, a condition that has been associated with environmental stress and that could lead to in-breeding depression and potentially reduced fertility. Yet, given the large size of the population and the wide breeding period observed, planktonic processes causing larval mortality such as freshwater discharges from rice locally important rice agriculture are also proposed as possible impacts accounting for patterns of low larval availability.

Declining freshwater mussel diversity in the middle and lower reaches of the Xin River Basin: Threat and conservation.

Freshwater mussels provide important functions and services for aquatic ecosystems, but populations of many species have been extirpated. Information on biodiversity plays an important role in the conservation and management of freshwater mussels. The Xin River Basin is a biodiversity hotspot for freshwater mussels in China, with more than 43 species known, but populations of which are decreasing. Here, we quantify the diversity of freshwater mussels in the middle and lower reaches of the Xin River Basin and study the correlation of habitat characteristics and freshwater mussel diversity. Compared to the historical period, the number of species, density, and biomass of freshwater mussels decreased 33%, 83%, and 82% in the current period, respectively. Fifty two percent of recorded species were empty shells, and 14 native freshwater mussels were not found in the study area. Four species are currently listed as vulnerable species using IUCN criteria and their global status. The assemblage structure of freshwater mussels exhibits significant spatial differences, and there was a correlation with substrate and physicochemical parameters. The main tributary of the Xin River with higher freshwater mussel diversity should be established as one large protected area because the nestedness component was the main pattern of beta diversity. These results indicated freshwater mussel diversity was declining rapidly, which can help focus conservation effort for freshwater mussel biodiversity.

The exploitation strategy determines the resource partitioning in hermit crabs

Hermit crabs approach sites of predated gastropods and gastropods in decomposition to obtain a new shell. Crabs reaching a site of a recent predatory event may not only find the shell empty but also encounter a predator. The attendance at sites where gastropods are decomposing may be less risky, but the use of these shells will depend on the crab's ability to extract the flesh. We tested the responses of two coexisting species of hermit crabs to chemical cues of potential empty shells at different levels of predatory risk and constraints to occupy it. The crabs were exposed in a Y-maze to chemical odors simulating gastropods in decomposition vs. a control, freshly predated gastropods vs. control, and gastropods in decomposition vs. predated gastropods. We also tested the ability of each species to extract the flesh of a dead snail. Contrary to expectation, individuals of both species avoided the two odors of shells. When the crabs were presented with the two chemical cues, Calcinus californiensis approached more to odors from gastropods in decomposition, whereas Clibanarius albidigitus approached more to odors from predated snails. The behavioral response of C. californiensis agrees with its greater ability to extract the flesh, which may allow it to obtain a new shell at relatively low risk. The lower ability of C. albidigitus to remove the flesh matches its preference for cues of predated gastropods rather than decomposed gastropods. Our results show that the flesh of gastropods needs not to be an obstacle to the use of their shells. The exploitation strategy sets the resource partitioning in these hermit crabs. The ability to remove the flesh, feed on dead gastropods, and occupy the shell makes hermit crabs exceptional as they exploit a limited resource as refuge and food.

Growth and morphometric relationships of the bean clam Donax punctatostriatus Hanley, 1843 in a sandy beach of southern Sinaloa, Mexico

There have been no published studies of the genus Donax in the eastern tropical Pacific. This work describes the morphometric relationships, growth and mortality of the bean clam Donax punctatostriatus Hanley, 1843 in the sandy beach of Isla de la Piedra, south of Mazatlan Bay, Mexico. Direct collections by hand were performed during 20 monthly sample periods (November 2008 to June 2010) in the intertidal zone of the beach. A total of 2,324 clams of different sizes were removed from the sand, then measured and weighed in the laboratory. The length range of the shells was 2.78-25.64 mm (mean = 12.61 ± 4.04 mm). The length-weight relationship of the total sample indicated isometric growth ( a = 0.0002 g; b = 3.0 g mm -1 , R 2 = 0.97); there was positive allometric growth in the recruits (<6.99 mm) ( b = 3.4) and in juveniles ( b = 3.2); in adults there was negative allometric growth ( b = 2.6). Negative allometry of the length/width (log Wd = -0.239 + 0.922 log L) and height/width (log Wd = -0.054 + 0.900 log H) ratio of adults is consistent with a more compressed form of their shell, which assists rapid burying behavior in the sand. The maximum-recorded size of an empty shell (39 mm) was used to set the value of L ∞ and to estimate K with the Shepherd (SLCA) method. The average growth rate during the life cycle was 0.43 mm yr -1 . Values of L ∞ between 29.16 and 34.22 mm were estimated with the Powell-Wetherall method using different class intervals. The mortality coefficient estimated with various methods was variable (0.84-1.15 yr -1 ). The growth of the clam is rapid and the mortality high, probably because of the characteristics of the habitat, in a subtropical region with high hydrodynamics and sediment transport.

Experimental confirmation of empty snail shells as limiting resources for specialized bees and wasps

Observational studies have suggested that the presence of snail shells correlates with the presence of specialized adopters, particularly bees and wasps (Hymenoptera: Aculeata). However, should the empty shells be considered limiting resources once they are present in the respective habitat even if observational studies suggested low ratio of occupied relative to total shells? We performed a manipulative experiment, which consisted of the addition of marked snail shells of six terrestrial species that dominate the open and semi-open central European habitats to 21 sites with naturally present shells. We deployed empty shells for the spring and summer 2017, allowed their inhabitants to undergo a diapause during the follow-up winter period and complete metamorphosis. The specialized bee and wasp species abundantly occupied the provided shells and the occupancy rates were several times higher in experimentally provided shells compared to the naturally present shells. These differences in occupancy rates were higher at anthropogenic compared to natural sites and at sites with more limited availability of naturally present shells. In contrast, the few sites at which the examined resource was superabundant, both the naturally present and the experimentally provided shells were occupied only to a limited extent. The species composition of assemblages that occupied the experimentally provided and naturally present shells were similar, and the differences in species composition between the natural and anthropogenic sites resembled those exhibited in the naturally present shells. In conclusion, we experimentally confirmed that empty snail shells serve as limiting resources for specialized bees and wasps even at sites where the naturally present shells are perceived as abundant.

Taphonomic field experiment in a freshwater shallow lake: alteration of gastropod shells below the sediment–water interface

Abstract We conducted a taphonomic field experiment to evaluate the effects of (1) depth below the sediment–water interface (SWI) and (2) time of exposure on the accrual of damage (particularly through dissolution) to empty mollusc shells in freshwater environments. The experiment, which lasted 30 months, was carried out in the littoral area of Lake Nahuel Rucá, a shallow freshwater lake in the Pampa plain of Argentina. Bags (0.5-cm mesh) containing empty, cleaned shells of the freshwater gastropods Heleobia parchappii, Biomphalaria peregrina and Pomacea canaliculata were buried at three different depths (5, 20 and 35 cm) below the SWI. Damage was assessed every 3 months. All experimental shells exhibited fine-scale surface alteration, but the extent of this damage was relatively low, even in shells recovered after 30 months of exposure. Most of the damage consisted of minor pitting. For H. parchappii and B. peregrina, shell surface alteration varied significantly with depth, but not with time; in both species, alteration occurred mainly at the beginning of the experiment. For P. canaliculata, shell surface alteration varied significantly only with respect to time and this was the case for all three burial depths. All shells of this species exhibited a lower level of damage than what was observed for H. parchappii and B. peregrina. These differences may be related to the fact that P. canaliculata is characterized by a larger and thicker shell than the other two species. The shell attributes of larger size and greater thickness are known to confer a greater resistance to shell dissolution. In addition, the reactive surface area available for dissolution varies with shell size. Larger-sized shells have a lower potential for dissolution than smaller shells due to their lower surface-area-to-volume ratio. In contrast, species such as H. parchappii and B. peregrina, which have smaller and thinner shells, are likely to be more rapidly destroyed because they are more vulnerable to dissolution and have less preservation potential. Our results demonstrate that dissolution is a significant taphonomic process affecting shells even during burial and that the influence of dissolution on shell alteration might be significant in cases of long persistence within the taphonomically active zone. Consequently, we suggest that when working on taphofacies in the context of aquatic environments, assessments of taphonomic alteration should include changes at and below the SWI.

Nassarius foveolatus (Gastropoda, Nassariidae), a new record of an exotic species in Brazil

Exotic species are those that occur in an area beyond their natural limit and they are considered invasive when they cause harm to the economy, environment, or human health. In coastal environments, ballast water and inlays on the hull and other parts of vessels are the main ways of introducing invasive aquatic alien species. Nassarius foveolatus (Dunker, 1847) is native from the Central and East Indian Ocean to the East China Sea. The first specimens (empty shells) of N. foveolatus were collected manually on November 11, 2017 on the Rocio footbridge, located in the Paranaguá Estuarine Complex, on the coast of the State of Paraná, southern Brazil. Posteriorly, live specimens were collected in other localities of this bay. It is already possible to infer that the specimens of N. foveolatus occur together with the native specimens of N. vibex (Say, 1822), having the same niche. As previously only N. vibex existed in that place, at least a displacement of this native species has been occurred. However, certainly future ecological studies may confirm this displacement and additional consequences to the local ecosystem, as nassariids can be predators and scavengers. Control procedures should be also greatly implemented.

Spatial distribution and substrate preferences of the non-indigenous amphipod Gammarus roeselii Gervais, 1835

Gammarus roeselii is one of the successful non-indigenous species recently established in the Ticino River basin (Northern Italy). G. roeselii is not usually considered to be a real threat to native gammarids because no evidence has been reported so far on its effects on biodiversity and habitats. In this study, we assessed the spatial distribution of G. roeselii in the secondary hydrographic system of the southern part of the sub-lacustrine Ticino River basin and examined substrate preferences on the basis of laboratory experiments. We found that G. roeselii is well established in this area, occurring in almost all the seminatural streams, reaching high densities. Furthermore, we found that this species has a preference for two distinct types of substrate: empty shells of the bivalve Corbicula fluminea, which provide a suitable shelter for the introduced amphipod, and aquatic plants, which provide food resources. Conversely, preference for inorganic substrates, such as stones, was lower. In addition, the results indicate that G. roeselii easily inhabits the water column. The high adaptability of G. roeselii, combined with its capacity to exploit different niches and its swimming ability, are ecological characteristics that can favour its colonisation of new areas.

High-frequency backscattering enhancements from elastic cylindrical shells in water: Observations and ray theory

Sometimes elastic features for acoustically illuminated targets in water are relegated primarily to low frequency bands. For empty spherical shells however, a pronounced high-frequency backscattering elastic-enhancement was observed and modeled using ray-theory [G. Kaduchak, D. H. Hughes, and P. L. Marston, J. Acoust. Soc. Am. 96, 3704–3714 (1994)]. That phenomenon was termed a backwards wave enhancement because the wave phase and group velocities guided on the shell move in opposite directions and required a modified ray diagram. In the present research, this type of backscattering enhancement is demonstrated and modeled for empty cylindrical elastic shells in water. While the full ray-theory requires solving for complex roots descriptive of elastic waves on fluid-loaded shells, it was found helpful to first consider the properties of ordinary Lamb waves on plates whose thickness was selected to be that of the shell of interest. A search for different roots of Lamb’s Equation confirms that a root exists that exhibits opposing phase and group velocities in the frequency region of interest. As expected from the model, the associated backscattering enhancements are localized in frequency though they can be easily identified using tone bursts. [Work supported by Office of Naval Research.]Sometimes elastic features for acoustically illuminated targets in water are relegated primarily to low frequency bands. For empty spherical shells however, a pronounced high-frequency backscattering elastic-enhancement was observed and modeled using ray-theory [G. Kaduchak, D. H. Hughes, and P. L. Marston, J. Acoust. Soc. Am. 96, 3704–3714 (1994)]. That phenomenon was termed a backwards wave enhancement because the wave phase and group velocities guided on the shell move in opposite directions and required a modified ray diagram. In the present research, this type of backscattering enhancement is demonstrated and modeled for empty cylindrical elastic shells in water. While the full ray-theory requires solving for complex roots descriptive of elastic waves on fluid-loaded shells, it was found helpful to first consider the properties of ordinary Lamb waves on plates whose thickness was selected to be that of the shell of interest. A search for different roots of Lamb’s Equation confirms that a root exists ...

A preliminary study on the traits of Chamelea gallina (Linnaeus, 1758) in the Gulf of Antalya, Mediterranean Coast of Turkey (Levantine Sea)

This study aimed to examine on some properties and to draw attention to why it cannot create an intensive stock amount of Chamelea gallina (Linnaeus, 1758) in the Gulf of Antalya in the Mediterranean coast of Turkey, Levantine Sea. Specimens of C. gallina displayed total shell legths of 6 to 32 mm, mean 14.5 mm and total weights of 0.1 to 11.44 g, mean 1.82 g. The total shell length and total weight relationship of C. gallina was calculated as TW =0.3333 * TSL 2.9894 (R² =0.9850). The mean meat yield was found as 12.10±0.9264%. A small number of C. gallina samples were collected. The majority of the collected striped venus were determined as empty shell. It was observed that the razorfish (Xyrichtys novacula) were fed with C. gallina during research. Finally, these results may draw attention the reasons why this species cannot form an intensive stock amount. It is thought that the empty shells of the striped venus can be caused from feeding of the razorfish (X. novacula) with C. gallina and environmental factor changes.Keywords: Chamelea gallina; length; weight; meat yield; mediterranean

Age and size characteristics of alien mollusks Viviparus viviparus L. in the coastal thanatocoenosis of Novosibirsk reservoir

Viviparus viviparus L. is the most numerous alien species of the Novosibirsk reservoir. In some parts of the reservoir V. viviparus creates settlements with a very high density. After the death of mollusks in the bottom sediments and on the banks of the reservoir, large areas of accumulation of empty shells are formed. Due to their strong structure, the shells are poorly decomposed and can serve as a generalized indicator of the state of the mollusk population over a long time. We analyzed the size and age characteristics of the V. viviparus shells in thanatocenoses of the Novosibirsk reservoir coast. Empty shells of river snails were collected on the shores of the middle (near the village of Chingis, Ordynskoye and in the Karakansky Bay) and the lower (near the village of Borovoye, Bystrovka, Leninsky and in the Berdsky Bay) parts of the Novosibirsk Reservoir in May, 24–26, 2018. Shells height and width were measured with an electronic caliper with an accuracy of 0.1 mm. Age of mollusks was determined by the marks of a winter growth stop on the shell. It is shown that in the thanatocenoses of the middle part and in the bays of the reservoir, shells of young mollusks (the second and third years of life) prevailed. In the lower part of the reservoir, the coastal thanatocoenosis contained larger shells of adult mollusks (fourth and fifth years of life). In general, the most of V. viviparus individuals in the Novosibirsk reservoir die before they reach the age limit. It is suggested that the premature death of most river snails can be caused by significant seasonal fluctuations in the water level of the reservoir, during which the littoral is drained.

Investigation of the pyrolysis characteristics and kinetics of oil-palm solid waste by using Coats–Redfern method

The pyrolysis kinetics of oil-palm solid waste was investigated by performing experiments on its individual components, including empty fruit bunch, fibre, shell, as well as the blends by using a simultaneous thermogravimetric analyser at a heating rate of 10°C/min under nitrogen atmosphere and setting up from initial temperature of 30°C to a final temperature of 550°C. The results revealed that the activation energy and frequency factor values of empty fruit bunch, fibre, and shell are 7.58–63.25 kJ/mol and 8.045E-02–4.054E + 04 s−1, 10.45–50.76 kJ/mol and 3.639E-01–5.129E + 03 s−1, 9.46–55.64 kJ/mol and 2.753E-01–9.268E + 03, respectively. Whereas, the corresponding values for empty fruit bunch–fibre, empty fruit bunch–shell, fibre–shell, empty fruit bunch–fibre–shell are 2.97–38.35 kJ/mol and 1.123E-02–1.326E + 02 s−1, 7.95–40.12 kJ/mol and 9.26E-02–2.101E + 02 s−1, 9.14–50.17 kJ/mol and 1.249E-01–2.25E + 03 s−1, 8.35–45.69 kJ/mol and 1.344E + 01–4.23E + 05 s−1, respectively. It was found that the activation energy and frequency factor values of the blends were dominantly due to the role of the components with a synergistic effect occurred during pyrolysis.

Sound Insulation and Reflection Properties of Sonic Crystal Barrier Based on Micro-Perforated Cylinders.

A sonic crystal barrier, consisting of empty micro-perforated cylindrical shells, was built on the campus at the Universitat Politècnica de València in 2011 and characterised by using a non-standardised measurement technique. In this paper, the sonic crystal barrier, upgraded with rubber crumb inside the micro-perforated cylindrical shells, was characterised by using standardised measurement techniques according to EN 1793-5 and EN 1793-6. As a result of the characterisation, sound insulation properties of the barrier were shown to be a combination of the absorptive properties of the individual building units and the reflective properties of their periodic distribution. In addition, its performance was compared with a similar barrier consisting of rigid polyvinyl chloride (PVC) cylinders, which was recently characterised using the same standardised techniques. In comparison with the barrier based on PVC cylinders, the barrier investigated here produced a broadband enhancement of the sound insulation and lower reflection indices in the targeted frequency range. It was also shown that the influence of leakage under the barrier and the width of the temporal window on sound insulation was negligible. While EN 1793-5 and 1793-6 allow a direct comparison of the performance of different noise barriers, the applicability to this new type of barriers requires further investigation.

Preparation and characterization of encapsulated phase change materials in presence of gamma alumina for thermal energy storage applications

Modified gamma alumina/fatty acids composite phase change materials (PCMs) were prepared via encapsulation with poly(St-co-DVB) shell by phase inversion emulsification method. The gamma alumina (γ-Al2O3) nanoparticles were modified by cetyl trimethylammonium bromide (CTAB). The modified gamma alumina (M-γ-Al2O3) was added into fatty acid mixture, which composed of oleic acid (OA) and capric acid (CA) besides to n-hexadecane. Thus, the effect of alumina addition on the morphological and thermal properties of composite PCMs was investigated. The attachment of CTAB onto gamma alumina nanoparticles was verified by thermogravimetric analysis (TGA) method. The morphological and chemical characterization of empty shell material (PS-DVB shell), microencapsulated PCM and composite PCMs was investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy, respectively. Furthermore, the thermal properties of the PCMs were examined by differential scanning calorimetry (DSC), thermogravimetric analyses and heat storage rate measurement.

COMMON-SENSE LEGITIMATION OF INFORMAL PRACTICES IN PRESENT-DAY SERBIA

As a part of a larger research within the Horizon 2020 project Closing the Gap Between Formal and Informal Institutions in the Balkans, 38 semi-structured interviews with citizens of Serbia have been conducted in the period July – October 2017. These comprise the database used for analysis of “narratives of informality” – stories of how the research participants legitimize (or rationalize) informal practices (using connections and acquaintances to “get things done”, giving/receiving bribe, exchange of favors, etc.), supplemented by the analysis of participants’ attitudes towards informal practices, particularly when using them themselves. An insight into the respondents’ ideas of informality was gained through describing and understanding doxa – beliefs of an individual as “a quasi-perfect correspondence between the objective order and the subjective principles of organization (with which) the natural and social world appear as self-evident” (Bourdieu) or senso comune (Gramsci) – “naturalized”, unreflected, practical knowledge taking the form of self-explanatory content of common sense, that which is taken for granted, what “everybody knows“, the knowledge of the world that is undisputed – “just the way it is”, the domain of indefinite beliefs and incoherent views of the world, the knowledge which “legitimizes with the absence of legitimizing”. The assumption is that the “quality” of doxa, in the sense of its positive or negative orientation, has a large impact on the possibility of changes in formal practices and procedures – in some cases serving as a stimulus for change, and as an obstacle to changes in others – situations in which the new/imported rules remain “empty shells” with little influence in social life.

Patterns of shell utilization by hermit crabs as a proxy of gastropod population dynamics

ABSTRACTHermit crabs are known to use empty gastropod shells, which allows them to grow and avoid predation and desiccation stress. However, shell benefits lessen with crab growth and natural damages so that hermit crabs are always in search for new and better-quality shells. This makes these organisms dependent on the input of newer shells, presenting adaptations to locate new released shells, as perception of chemical cues liberated by predated gastropods. The allocation from older to newer shells suggests that the patterns of shell utilization by hermit crabs may reflect populational changes of gastropod species. In this scenario, we aimed to investigate whether a recognized population decline of the intertidal gastropod Olivella minuta in summer can be explained by mortality or intertidal migration. To do so, we analysed patterns of shell availability and use (number and quality) by hermit crabs before and after the population decline. Contrary to our mortality hypothesis, there was no increase in availability and occupancy of newer shells in the area, as well as no increase in shell quality after the period of population decline of gastropods. There were also no general changes in the size distribution of available and occupied shells. Thus, it is likely that O. minuta migrates towards lower areas of the intertidal to avoid thermal stress and mortality due to summer higher temperatures.

Scattering and radiation force dependence on properties of empty elastic spherical shells: Low-frequency phase-shift derivation.

It is helpful to evaluate scattering and acoustic radiation forces on spheres for idealized cases in which the effects of energy dissipation are ignorable. Let x denote the product of the acoustic wave number and the sphere's radius. Previously expansions were obtained for fluid and solid spheres involving powers of x and algebraic expressions containing material properties. The present analysis concerns the case of empty elastic shells and reveals how expansion coefficients also depend on shell thickness. Incident waves considered are plane traveling and standing waves, though relevance to Bessel wave-fields is also noted. The expansions give leading-order corrections to the usual Rayleigh scattering approximation.