Shell properties of commercial clam Chamelea gallina are influenced by temperature and solar radiation along a wide latitudinal gradient

Using Museum collections to assess the impact of industrialization on mussel (Mytilus edulis) calcification

Mytilus edulis is a commercially and ecologically important species found along the east coast of the United States. Ecologically, M. edulis improves water quality through filtration feeding and provides habitat formation and coastal protection through reef formation. Like many marine calcifiers, ocean warming, and acidification are a growing threat to these organisms-impacting their morphology and function. Museum collections are useful in assessing long-term environmental impacts on organisms in a natural multi-stressor environment, where acclimation and adaptation can be considered. Using the American Museum of Natural History collections ranging from the early 1900s until now, we show that shell porosity changes through time. Shells collected today are significantly more porous than shells collected in the 1960s and, at some sites, than shells collected from the early 1900s. The disparity between porosity changes matches well with the warming that occurred over the last 130 years in the north Atlantic suggesting that warming is causing porosity changes. However, more work is required to discern local environmental impacts and to fully identify porosity drivers. Since, porosity is known to affect structural integrity, porosity increasing through time could have negative consequences for mussel reef structural integrity and hence habitat formation and storm defenses.

Experimental Study on the Tridacna squamosa Shell: Distinctive Structure and Mechanical Behavior

Tridacna squamosa, Lamarck, 1819 (Bivalvia Cardiida Cardiidae, known as the fluted giant clam) is one of the largest-sized bivalve shells, which is equipped with a strong and tough bioceramic shell to effectively protect itself from the attack of predators. To better understand the mechanical defense mechanism, the relationship between the microstructure, composition, and mechanical properties of the Tridacna squamosa shell was investigated. We find that the Tridacna squamosa shell is composed of aragonite CaCO₃ and a small portion of organic matter, which are well-arranged, assembling a multiscale, inhomogeneous, and anisotropic structure. Three levels of microstructure units are identified, including the smallest aragonite rods, medium sheets, and block-like lamellae. Such multiscale structures are the main contributor to creating abundant fracture surfaces much larger than the case for single mineral components, leading to multiple toughening mechanisms observed in Vickers indentation experiments, such as pulled-out of mineral platelet and crack deflection. The material inhomogeneity in the cross-sectional direction indicates that the material is stronger at the inner layer than that at the outer layer, which also facilitates an effective defense against the predator attack. This study may provide insights into the design of biomaterials with the desired mechanical properties.

Oxygen and carbon isotope variations in Chamelea gallina shells: Environmental influences and vital effects

Stable isotopes in mollusc shells, together with variable growth rates and other geochemical properties, can register different environmental clues, including seawater temperature, salinity and primary productivity. However, the strict biological control over the construction of biominerals exerted by many calcifying organisms can constrain the use of these organisms for paleoenvironmental reconstructions. Biologically controlled calcification is responsible for the so called vital effects that cause a departure from isotopic equilibrium during shell formation, resulting in lower shell oxygen and carbon compared to the equilibrium value. We investigated shell oxygen and carbon isotopic composition of the bivalve Chamelea gallina in six sites along with a latitudinal gradient on the Adriatic Sea (NE Mediterranean Sea). Seawater δ¹⁸ O and δ¹³ C_DIC varied from North to South, reflecting variations in seawater temperature, salinity, and chlorophyll concentration among sites. Shell δ¹⁸ O and δ¹³ C differed among sites and exhibited a wide range of values along with the ~400 km latitudinal gradient, away from isotopic equilibrium for both isotopes. These results hampered the utilization of this bivalve as a proxy for environmental reconstructions, in spite of C. gallina showing promise as a warm temperature proxy. Rigorous calibration studies with a precise insight of environment and shell growth are crucial prior to considering this bivalve as a reliable paleoclimatic archive.

Resilient biotic response to long-term climate change in the Adriatic Sea

Preserving adaptive capacities of coastal ecosystems, which are currently facing the ongoing climate warming and a multitude of other anthropogenic impacts, requires an understanding of long-term biotic dynamics in the context of major environmental shifts prior to human disturbances. We quantified responses of nearshore mollusk assemblages to long-term climate and sea-level changes using 223 samples (~71,300 specimens) retrieved from latest Quaternary sediment cores of the Adriatic coastal systems. These cores provide a rare chance to study coastal systems that existed during glacial lowstands. The fossil mollusk record indicates that nearshore assemblages of the penultimate interglacial (Late Pleistocene) shifted in their faunal composition during the subsequent ice age, and then reassembled again with the return of interglacial climate in the Holocene. These shifts point to a climate-driven habitat filtering modulated by dispersal processes. The resilient, rather than persistent or stochastic, response of the mollusk assemblages to long-term environmental changes over at least 125 thousand years highlights the historically unprecedented nature of the ongoing anthropogenic stressors (e.g., pollution, eutrophication, bottom trawling, and invasive species) that are currently shifting coastal regions into novel system states far outside the range of natural variability archived in the fossil record.

The Mantle Transcriptome of Chamelea gallina (Mollusca: Bivalvia) and Shell Biomineralization

Simple Summary

Chamelea gallina is a bivalve mollusc that represents one of the most important fishery resources in the Mediterranean basin. In this species, the thickness and sturdiness of the shell valves are two important characteristics as they are decisive for protection against predators and survival of specimens rejected in the sea because caught under commercial size. The aim of this work is to investigate the ability of this species to modulate the expression of genes encoding proteins involved in shell biomineralization process in response to abiotic and biotic factors. Our findings, obtained through a multidisciplinary approach, highlighted a different shell mineralization behaviour in C. gallina clams collected in sampling sites characterized by different salinity and food availability. Moreover, this study provided the first comprehensive transcriptome from mantle, the tissue responsible for shell formation. Therefore, these results contribute to increase knowledge on this process and might help in adopting ad hoc management plans for this fishery resource.

Abstract

The striped venus Chamelea gallina is a bivalve mollusc that represents one of the most important fishery resources of the Adriatic Sea. In this work, we investigated for the first time the ability of this species to modulate the expression of genes encoding proteins involved in biomineralization process in response to biotic and abiotic factors. We provided the first comprehensive transcriptome from the mantle tissue of clams collected in two sampling sites located along the Italian Adriatic coast and characterized by different environmental features. Moreover, the assessment of environmental parameters, scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements on valves were conducted to better contextualize RNA sequencing (RNA-Seq) data. Functional annotation of differentially expressed genes (DEGs) and SEM observations highlighted a different shell mineralization behaviour in C. gallina clams collected from two selected sites characterized by diverse environmental parameters.

Innovative Vibrating Hydraulic Dredge for Striped Venus (Chamelea gallina) Fishing

This work proposes the experimentation of an innovative hydraulic dredge for clam fishing (Chamelea gallina) in the Adriatic Sea (Italy). This innovative gear aimed at increasing the selectivity of the typical hydraulic dredge used currently, while at the same reducing the impact on benthos through the conception, installation, and experimentation of innovative technological solutions, consisting mainly of a vibrating bottom panel on the dredge and a “warning device” on the dredge mouth. Comparative experiments of the traditional vs. the modified gear, employing two boats fishing in parallel on the northern coast of Abruzzi (Adriatic Sea) and contrasting the catch with both paired comparisons and through modelling, showed that the innovative hydraulic dredge retains fewer undersize clams while yielding similar amounts of commercial product, moreover of higher quality; at the same time, it takes on board less discard, and catches significantly less vagile fauna. In short, the innovative gear is gaining five times over a list of six parameters considered as positive and/or advantageous for the clam fishery. The results allow proposals of potential improvements to clam-fishing instruments to make the selection processes more effective while promoting a lower impacting fishery, which is essential for clam management.

Micro-CT for Biological and Biomedical Studies: A Comparison of Imaging Techniques

Several imaging techniques are used in biological and biomedical studies. Micro-computed tomography (micro-CT) is a non-destructive imaging technique that allows the rapid digitisation of internal and external structures of a sample in three dimensions and with great resolution. In this review, the strengths and weaknesses of some common imaging techniques applied in biological and biomedical fields, such as optical microscopy, confocal laser scanning microscopy, and scanning electron microscopy, are presented and compared with the micro-CT technique through five use cases. Finally, the ability of micro-CT to create non-destructively 3D anatomical and morphological data in sub-micron resolution and the necessity to develop complementary methods with other imaging techniques, in order to overcome limitations caused by each technique, is emphasised.

Losers can win: Thermoregulatory advantages of regenerated claws of fiddler crab males for establishment in warmer microhabitats

Fiddler crab males present a hypertrophied claw, which is used for sexual and aggressive displays, fights with competitors, and has been proposed as an important thermoregulatory organ for heat control. Two claw morphologies can be observed within fiddler crab populations: brachychelous claws (unregenerated) and leptochelous claws (regenerated). The leptochelous morphotype presents less muscle mass and longer fingers, resulting in a less advantageous weapon in fights. Considering their slender shape, we hypothesized that the leptochelous morphotype would present lower thermal inertia and be more efficient at body heat dissipation. We evaluated the role of the fiddler crabs' claw shape as a heat sink and how this influences their distribution between unshaded and shaded microhabitats. We tested in the field whether the proportion of adult male Leptuca uruguayensis with leptochelous claws was higher in unshaded microhabitats than shaded ones. In the laboratory, we tested if heat transfer between the body and claw is higher in leptochelous males than in brachychelous males. Spontaneous waving behaviour and active time above the surface were compared between both morphotypes in the field during the hottest period of the day. Leptuca uruguayensis with regenerated claws comprised more than 60% of the sampled male population of unshaded microhabitats compared to 18% in shaded microhabitats. Leptochelous males showed a mean heat transfer between body to claw 35% higher than that observed for brachychelous males. During the hottest period of the day, brachychelous males waved approximately 28% more than leptochelous males. Moreover, brachychelous males spent less time under the sediment surface since the surface temperature increased, while activity of leptochelous males was not associated with a temperature increase. Therefore, regenerated claws may be advantageous for the establishment of L. uruguayensis males in warmer and unshaded microhabitats because they are more efficient for heat loss and allow crabs to cool down, spending less time waving. Our study shows the relevant context of winners and losers in the face of climate change and highlights the importance of morphological variations in thermoregulatory structures for the occupation of thermal niches.

Climate variation during the Holocene influenced the skeletal properties of Chamelea gallina shells in the North Adriatic Sea (Italy)

Understanding how marine taxa will respond to near-future climate changes is one of the main challenges for management of coastal ecosystem services. Ecological studies that investigate relationships between the environment and shell properties of commercially important marine species are commonly restricted to latitudinal gradients or small-scale laboratory experiments. This paper aimed to explore the variations in shell features and growth of the edible bivalve Chamelea gallina from the Holocene sedimentary succession to present-day thanatocoenosis of the Po Plain-Adriatic Sea system (Italy). Comparing the Holocene sub-fossil record to modern thanatocoenoses allowed obtaining an insight of shell variations dynamics on a millennial temporal scale. Five shoreface-related assemblages rich in C. gallina were considered: two from the Middle Holocene, when regional sea surface temperatures were higher than today, representing a possible analogue for the near-future global warming, one from the Late Holocene and two from the present-day. We investigated shell biometry and skeletal properties in relation to the valve length of C. gallina. Juveniles were found to be more porous than adults in all horizons. This suggested that C. gallina promoted an accelerated shell accretion with a higher porosity and lower density at the expense of mechanically fragile shells. A positive correlation between sea surface temperature and both micro-density and bulk density were found, with modern specimens being less dense, likely due to lower aragonite saturation state at lower temperature, which could ultimately increase the energetic costs of shell formation. Since no variation was observed in shell CaCO₃ polymorphism (100% aragonite) or in compositional parameters among the analyzed horizons, the observed dynamics in skeletal parameters are likely not driven by a diagenetic recrystallization of the shell mineral phase. This study contributes to understand the response of C. gallina to climate-driven environmental shifts and offers insights for assessing anthropogenic impacts on this economic relevant species.

Mollusk shell alterations resulting from coastal contamination and other environmental factors

Effects of contamination on aquatic organisms have been investigated and employed as biomarkers in environmental quality assessment for years. A commonly referenced aquatic organism, mollusks represent a group of major interest in toxicological studies. Both gastropods and bivalves have external mineral shells that protects their soft tissue from predation and desiccation. These structures are composed of an organic matrix and an inorganic matrix, both of which are affected by environmental changes, including exposure to hazardous chemicals. This literature review evaluates studies that propose mollusk shell alterations as biomarkers of aquatic system quality. The studies included herein show that changes to natural variables such as salinity, temperature, food availability, hydrodynamics, desiccation, predatory pressure, and substrate type may influence the form, structure, and composition of mollusk shells. However, in the spatial and temporal studies performed in coastal waters around the world, shells of organisms sampled from multi-impacted areas were found to differ in the form and composition of both organic and inorganic matrices relative to shells from less contaminated areas. Though these findings are useful, the toxicological studies were often performed in the field and were not able to attribute shell alterations to a specific molecule. It is known that the organic matrix of shells regulates the biomineralization process; proteomic analyses of shells may therefore elucidate how different contaminants affect shell biomineralization. Further research using approaches that allow a clearer distinction between shell alterations caused by natural variations and those caused by anthropogenic influence, as well as studies to identify which molecule is responsible for such alterations or to determine the ecological implications of shell alterations, are needed before any responses can be applied universally.

Environmental influence on calcification of the bivalve Chamelea gallina along a latitudinal gradient in the Adriatic Sea

Environmental factors are encoded in shells of marine bivalves in the form of geochemical properties, shell microstructure and shell growth rate. Few studies have investigated how shell growth is affected by habitat conditions in natural populations of the commercial clam Chamelea gallina. Here, skeletal parameters (micro-density and apparent porosity) and growth parameters (bulk density, linear extension and net calcification rates) were investigated in relation to shell sizes and environmental parameters along a latitudinal gradient in the Adriatic Sea (400 km). Net calcification rates increased with increasing solar radiation, sea surface temperature and salinity and decreasing Chlorophyll concentration in immature and mature shells. In immature shells, which are generally more porous than mature shells, enhanced calcification was due to an increase in bulk density, while in mature shells was due to an increase in linear extension rates. The presence of the Po river in the Northern Adriatic Sea was likely the main driver of the fluctuations observed in environmental parameters, especially salinity and Chlorophyll concentration, and seemed to negatively affect the growth of C. gallina.

Mechanical properties of Chamelea gallina shells at different latitudes

In this work we evaluate the mechanical properties of Chamelea gallina shells, collected at various locations in the Adriatic Sea, through compression tests. We present an analytical model for the extraction of the material Young's modulus and ultimate strength, based on the approximation of the valves with a simpler geometry. The effect of porosity and the computation of the energy dissipated at fracture are also discussed. Results show a dependence of the mechanical performance on the location at which the samples were collected, i.e. latitude, and thus the environmental factors can affect the rigidity, strength and toughness of the shells. These findings integrate preliminary results published in a previous work.

Styrene impairs normal embryo development in the Mediterranean mussel (Mytilus galloprovincialis)

This study analysed the effects of styrene, a main monomer in plastic manufacturing and acknowledged to be amongst the most common plastic leachates, on early embryo development of the Mediterranean mussel. Embryotoxicity tests showed that styrene impaired normal embryo development at concentrations (0.01 μg/L-1 mg/L) encompassing the environmental range. Occurrence of normal D-veligers was significantly reduced up to 40% of the total, and larval size was reduced of about 20%. D-veligers grown in the presence of styrene (0.1 and 10 μg/L) showed significant reduction of total Multixenobiotic resistance (MXR) efflux activity that was not apparently related to transcriptional expression of genes encoding P-glycoprotein (ABCB) and Mrp (ABCC), the two main ABC transporters of embryonal MXR system. Indeed, ABCB transcription was not affected by styrene, while ABCC was up-regulated. At these same concentrations, transcriptional profiles of 15 genes underlying key biological functions in embryo development and potential targets of adverse effects of styrene were analysed. Main transcriptional effects were observed for genes involved in shell biogenesis and lysosomal responses (down-regulation), and in neuroendocrine signaling and immune responses (up-regulation). On the whole, results indicate that styrene may affect mussel early development through dysregulation of gene transcription and suggest the possible conservation of styrene mode of action across bivalve life cycle and between bivalves and humans, as well as through unpredicted impacts on protective systems and on shell biogenesis.