Mollusk shell alterations resulting from coastal contamination and other environmental factors

Insights into pollution characteristics and human health risks of plasticizer phthalate esters in shellfish species

The ubiquitous application of phthalate esters (PAEs) as plasticizers contributes to high levels of marine pollution, yet the contamination patterns of PAEs in various shellfish species remain unknown. The objective of this research is to provide the first information on the pollution characteristics of 16 PAEs in different shellfish species from the Pearl River Delta (PRD), South China, and associated health risks. Among the 16 analyzed PAEs, 13 were identified in the shellfish, with total PAE concentrations ranging from 23.07 to 3794.08 ng/g dw (mean = 514.35 ng/g dw). The PAE pollution levels in the five shellfish species were as follows: Ostreidae (mean = 1064.12 ng/g dw) > Mytilus edulis (mean = 509.88 ng/g dw) > Babylonia areolate (mean = 458.14 ng/g dw) > Mactra chinensis (mean = 378.90 ng/g dw) > Haliotis diversicolor (mean = 335.28 ng/g dw). Dimethyl phthalate (DMP, mean = 69.85 ng/g dw), diisobutyl phthalate (DIBP, mean = 41.39 ng/g dw), dibutyl phthalate (DBP, mean = 130.91 ng/g dw), and di(2-ethylhexyl) phthalate (DEHP, mean = 226.23 ng/g dw) were the most abundant congeners. Notably, DEHP constituted the most predominant fraction (43.98 %) of the 13 PAEs detected in all shellfish from the PRD. Principal component analysis indicated that industrial and domestic emissions served as main sources for the PAE pollution in shellfish from the PRD. It was estimated that the daily intake of PAEs via shellfish consumption among adults and children ranged from 0.004 to 1.27 μg/kgbw/day, without obvious non-cancer risks (< 0.034), but the cancer risks raised some alarm (2.0 × 10-9-1.4 × 10-5). These findings highlight the necessity of focusing on marine environmental pollutants and emphasize the importance of ongoing monitoring of PAE contamination in seafood.

Multi- and transgenerational effects of environmental chemicals on mollusks: An underexplored experimental design in aquatic (eco)toxicological studies

(Eco)toxicological studies frequently evaluate the effects of chemicals in one life stage of organisms, but the use of these outcomes can only partially estimate populational effects. In this regard, multi- and/or transgenerational studies should be performed in order to provide information on contaminant effects in a populational functioning context. The present review aimed to summarize and critically evaluate the current knowledge regarding multi- and/or transgenerational effects of traditional and emerging environmental chemicals on mollusks. Results showed that these kinds of studies were performed in aquatic mollusks (bivalve and gastropod), being Gastropoda the mollusk Class most frequently studied. Additionally, freshwater species and multigenerational studies were more common for this class. For the Bivalvia class, only marine species were evaluated, and transgenerational exposure was more commonly assessed. The effects were reported for 15 species, highlighting the marine bivalves Crassostrea gigas and Saccostrea glomerata, and the freshwater gastropod Lymnaea stagnalis. Multi- and transgenerational effects were described for 8 environmental chemical groups, mainly metals, pesticides, and pharmaceuticals. In general, multi- and transgenerational exposure induced biometric, developmental, and reproductive impairments in mollusks, indicating that environmental chemicals might lead to generational impairments, reduced population growth and reproductive capacity, and decreased fitness. The current study indicated that bivalves and gastropods are suitable organism models to assess the multi- and transgenerational adverse effects induced by traditional and emerging environmental chemicals.

Microplastics in rocky shore mollusks of different feeding habits: An assessment of sentinel performance

Microplastics (MPs) accumulation in rocky shore organisms has limited knowledge. This study investigated MPs accumulation in filter-feeding oysters, herbivorous limpets and carnivorous snails to assess their performance as sentinel species in the MPs trophic transfer. The samples were obtained along a contamination gradient in the Santos Estuarine System, Brazil. All three studied species showed MPs concentrations related to the contamination gradient, being the oysters the species that showed the highest levels, followed by limpets and snails (average of less and most contaminated sites of 1.06-8.90, 2.28-5.69 and 0.44-2.10 MP g-1, respectively), suggesting that MPs ingestion rates are linked to feeding habits. MPs were mainly polystyrene and polyacetal. The polymer types did not vary among sites nor species. Despite minor differences in percentages and diversity of size, shape, and color classes, the analyzed species were equally able to demonstrate dominance of small, fiber, transparent, black and blue MPs. Thus, oysters, limpets, and snails are proposed as sentinels of MPs in monitoring assessments.

A multiscale computational framework for the development of spines in molluscan shells

From mathematical models of growth to computer simulations of pigmentation, the study of shell formation has given rise to an abundant number of models, working at various scales. Yet, attempts to combine those models have remained sparse, due to the challenge of combining categorically different approaches. In this paper, we propose a framework to streamline the process of combining the molecular and tissue scales of shell formation. We choose these levels as a proxy to link the genotype level, which is better described by molecular models, and the phenotype level, which is better described by tissue-level mechanics. We also show how to connect observations on shell populations to the approach, resulting in collections of molecular parameters that may be associated with different populations of real shell specimens. The approach is as follows: we use a Quality-Diversity algorithm, a type of black-box optimization algorithm, to explore the range of concentration profiles emerging as solutions of a molecular model, and that define growth patterns for the mechanical model. At the same time, the mechanical model is simulated over a wide range of growth patterns, resulting in a variety of spine shapes. While time-consuming, these steps only need to be performed once and then function as look-up tables. Actual pictures of shell spines can then be matched against the list of existing spine shapes, yielding a potential growth pattern which, in turn, gives us matching molecular parameters. The framework is modular, such that models can be easily swapped without changing the overall working of the method. As a demonstration of the approach, we solve specific molecular and mechanical models, adapted from available theoretical studies on molluscan shells, and apply the multiscale framework to evaluate the characteristics of spines from three distinct populations of Turbo sazae.

Upwelling as a stressor event during embryonic development: Consequences for encapsulated and early juvenile stages of the marine gastropod Acanthina monodon

Upwelling phenomena alter the physical and chemical parameters of the sea's subsurface waters, producing low levels of temperature, pH and dissolved oxygen, which can seriously impact the early developmental stages of marine organisms. To understand how upwelling can affect the encapsulated development of the gastropod Acanthina monodon, capsules containing embryos at different stages of development (initial, intermediate and advanced) were exposed to upwelling conditions (pH = 7.6; O2 = 3 mg L-1; T° = 9 °C) for a period of 7 days. Effects of treatment were determined by estimating parameters such as time to hatching, number of hatchlings per capsule, percentage of individuals with incomplete development, and shell parameters such as shell shape and size, shell strength, and the percentage of the organic/inorganic content. We found no significant impacts on hatching time, number of hatchlings per capsule, or percentage of incomplete development in either the presence or absence of upwelling, regardless of developmental stage. On the other hand, latent effects on encapsulated stages of A. monodon were detected in embryos that had been exposed to upwelling stress in the initial embryonic stage. The juveniles from this treatment hatched at smaller sizes and with higher organic content in their shells, resulting in a higher resistance to cracking 30 days after hatching, due to greater elasticity. Geometric morphometric analysis showed that exposure to upwelling condition induced a change in the morphology of shell growth in all post-hatching juveniles (0-30 days), regardless of embryonic developmental stage at the time of exposure. Thus, more elongated shells (siphonal canal and posterior region) and more globular shells were observed in newly hatched juveniles that had been exposed to the upwelling condition. The neutral or even positive upwelling exposure results suggests that exposure to upwelling events during the encapsulated embryonic phase of A. monodon development might not have major impacts on the future juvenile stages. However, this should be taken with caution in consideration of the increased frequency and intensity of upwelling events predicted for the coming decades.

Chemical contamination in coastal areas alters shape, resistance and composition of carnivorous gastropod shells

Morphological, structural and compositional alterations in shells of molluscs have been proposed as putative biomarkers of chemical contamination in coastal zones. Despite this, few studies were carried out using top predator gastropods which tend to be more susceptible to contamination exposure. Thus, the present study assessed disturbances on shells of Stramonita brasiliensis considering compression resistance and organic and mineralogical matrix composition, related to morphometric alterations. Results showed reductions in compression resistance and organic matrix content associated with higher contaminated sites. In addition, a predominance of calcite polymorphs was seen in shells obtained in polluted areas. Such outputs were consistent with local contamination levels which may have induced the observed alterations. Thus, changes in mollusc shells showed good performance as potential biomarkers of coastal contamination, being probably observed in other species of carnivorous gastropods around the world.

Live and Live-Dead Intraspecific Morphometric Comparisons as Proxies for Seagrass Stability in Conservation Paleobiology

Comparisons of life and death assemblages are commonly conducted to detect environmental change, including when historical records of live occurrences are unavailable. Most live-dead comparisons focus on assemblage composition, but morphology can also vary in species with environmental variables. Although live-dead morphologic comparisons are less explored, their data could be useful as a proxy in conservation paleobiology. We tested the potential for geometric morphometric data from live-and dead-articulated Stewartia floridana (Bivalvia: Lucinidae) to serve as proxies for seagrass occurrence and stability. The study area is at the northern end of Pine Island in Charlotte Harbor, FL, United States, an estuarine system with substantial seagrass loss in the 20th century and subsequent partial recovery. The area sampled has had relatively stable seagrass occurrences since at least the early 2000s. Live and dead-articulated S. floridana samples were collected from two transects through a patchy seagrass meadow, with sampled sites ranging from bare sand to 100% seagrass cover. Dead-articulated specimens were also collected from three adjacent transects. Live S. floridana shape covaried significantly with seagrass taxonomic composition and percent cover at the time of collection based on two-block partial least squares analysis, although shape differences between seagrass end members (100% Halodule wrightii and 100% Syringodium filiforme) were not significant by multivariate analysis of variance (MANOVA). Instead, specimens from 100% H. wrightii had significantly greater Procrustes variance. Live S. floridana shape data placed in categories describing seagrass stability over 6 years prior to sampling (and reflecting sclerochronologic estimates of maximum longevity) differed significantly based on MANOVA. For live and dead S. floridana from the same transects, shape differed significantly, but allometric trends did not. In addition, patterns of morphologic variation tied to seagrass stability were detected in dead-articulated valve shape. Dead shells from adjacent transects differed significantly in shape and allometric trend from both live and dead specimens collected together. We infer that morphometric differences recorded fine-scale spatial and temporal patterns possibly tied to environmental change. Therefore, geometric morphometrics may be a powerful tool that allows for death assemblages to track seagrass distributions through time prior to systematic monitoring, including in areas under high anthropogenic stress.

Mollusc shell shape as pollution biomarkers: Which is the best biological model?

Alterations in mollusc shells have been proposed contamination biomarkers. We used geometric morphometrics analyses associated with analytical determinations of contaminants to select suitable biological models among species widely distributed on coastal zones. The study was carried out using Lottia subrugosa (herbivore limpet), Crassostrea brasiliana (filter-feeder bivalve), and Stramonita brasiliensis (carnivore gastropod) obtained along a marked contamination gradient at Santos Estuarine System (Brazil). L. subrugosa and S. brasiliensis presented distinct shapes along the gradient, while no significant differences in shell form were seen for C. brasiliana. Indeed, limpets and snails presented morphometric parameters consistent with measured contamination levels hazardous substances. Based on cross-validation models, the reliability of morphometric responses was over 75% for the herbivore and carnivore species. In addition, for S. brasiliensis, a 95.2% confidence was detected in most contaminated sites. Therefore, shell alterations on carnivorous gastropods should be further investigated, seeking to be effectively employed as pollution biomarkers.

Contamination gradient affects differently carbonic anhydrase activity of mollusks depending on their feeding habits

Aquatic organisms that inhabit coastal areas are often exposed to several contaminants. It is known that the bioaccumulation of contaminants can be amplified according to the species feeding habits and contaminant properties. As a consequence, species can experience different effects to contaminant exposure even if they inhabit the same area. The present study aimed to investigate the activities of carbonic anhydrase (CA), Ca²⁺-ATPase, and Mg²⁺-ATPase in different tissues (soft tissue, mantle, and gill) of three mollusk species (Lottia subrugosa, Stramonita brasiliensis, and Crassostrea brasiliana) with different feeding habits (herbivore, carnivore, and filter-feeder, respectively) which were sampled within a known contamination gradient at Santos Estuarine System (Southeastern Brazil). From the three enzymes tested, only CA was affected by the presence of contaminants within the contamination gradient evaluated. In general, the CA activity from the three species were lower in contaminated sites when compared to the reference site. The contrasting CA activity response observed in S. brasiliensis compared to L. subrugosa and C. brasiliana could be related to the tissue-specificity of this enzyme activity and species feeding habits (filter-feeders can accumulate more contaminants than herbivores and even carnivores). Results indicated that C. brasiliana mantle is the most suitable tissue for the use of CA analysis as a biomarker.

Monitoring of coastal pollution using shell alterations in the false limpet Siphonaria pectinata

Lipid peroxidation level (LPO), shell biometry, shape, elemental content, and microstructure were studied in three populations of Siphonaria pectinata in the complex lagoon-channel of Bizerte across a coastal pollution gradient (northern Tunisia). LPO was found in higher concentrations in harbour populations, and shells had centred apex and were flattened. Shells were also thicker, particularly in the inner layer, with many fibrous inter-beds formed. Difference in crystallization pattern was observed in numerous shells from all three populations, being more common in harbours. From the control station to the contaminated stations, shell elemental changes were observed, with a decrease in Ca, P, Sr, and S and an increase in Cl, Cd, Cu, Fe, and K. All of these findings suggested that shell alterations could be used as a good biomarker for coastal contamination.

The utility of jellyfish as marine biomonitors

Jellyfish are abundant in coastal waters across broad latitudinal ranges and are often considered pests and a group that can cause phase shifts in marine ecosystems. Recent studies have highlighted their potential as biomonitors of contaminants including metals, herbicides and nutrients. Traditionally, sedentary organisms like molluscs and annelid worms have been used, but some jellyfish have similar characteristics of localised distributions and in some cases sedentary behaviour. Broad gradients in contaminant accumulation have been shown for a number of planktonic jellyfish species. An alternative biomonitoring candidate is the tropical/sub-tropical upside-down jellyfish (Cassiopea spp.). In laboratory and field deployments, Cassiopea accumulate measurable contaminants over days to weeks, making them ideal for detecting short-term pulses. Furthermore, the decay curve of contaminants varies temporally post-exposure and contaminant type. This can provide an estimate of the timing of exposure. Cassiopea, along with other jellyfish, have the potential to be an interesting and valuable group of organisms for monitoring coastal impacts.

A non-lethal method to assess element content in the endangered Pinna nobilis

The fan shell Pinna nobilis is the largest bivalve endemic to the Mediterranean and is actually a strongly endangered species. Due to the biological, ecological, and historical relevance of this species, the research of a non-lethal method to relate the element content in organism's tissues and environment can provide information potentially useful to evaluate environmental pollution and organism physiological status. In this study, a screening on element concentration in the animal growing environment (seawater and sediments) and in four soft tissues (hepatopancreas, gills, mantle, and muscle), and two acellular tissues (calcite shell layer, and byssus) was performed. The comparison among these results was used to assess whether the no-lethal acellular tissue element concentration can be used to reveal the element presence in the environment and soft tissues. Elements, such as B, Ag, As, Mn, Mo, Pb, or Se, showed a possible relationship between their presence in the byssus and soft tissues. In the byssus Cr, Sb, Sn, and V have shown to be mostly related to the environment, more than the soft tissues, and might be used to draw a historical record of the exposure of the organism. The element concentration in the calcite shell layer did not relate with environmental element concentrations. Essential elements, like Cu, Fe, Ni, and Zn, were present in calcite shell layer and byssus and are likely related to their biological activity in the organism. The research also gave an overview on the presence of pollution and on the preferential intake route of the element. In summary, this study, performed on a limited number of specimens of this protected species, indicated that element concentration in the byssus can be applied as non-lethal method to monitor this endangered species and its interaction with the elements in the growing environment.

Embryonic shell shape as an early indicator of pollution in marine gastropods

Gastropods shell shape has been proposed as a good indicator of environmental changes while geometric morphometric (GM) is a powerful tool to detect such changes. Shell shape pattern in adults of the marine gastropod Buccinanops deformis was proved to be correlated with imposex incidence and maritime traffic in populations of Patagonia. We explore through GM the shell shape variation of B. deformis intracapsular embryos in pre-hatching stages of development, in two populations with contrasting maritime traffic and imposex incidence. Embryonic shell shape from polluted and unpolluted areas was significantly different in apex, lateral, aperture and siphonal channel. The same shell shape pattern was observed previously in B. deformis adult specimens. Our results demonstrate that the embryonic shell shape is an early biomarker that could be used as a tool to detect the response to environmental pollution studying abundant egg capsules laid in the field but protecting reproductive adults.

Shell form and enzymatic alterations in Lottia subrugosa (Gastropoda, Lotiidae) transplanted to a contaminated site

Studies have shown that shell morphology and enzymatic activities in mollusks are affected by contaminants exposure. However, the correlation between enzymatic activities and the biomineralization process are not fully understood. The present study used a transplant bioassay and field sampling to evaluate shell measurements and the activities of carbonic anhydrase, Ca²⁺-ATPase, and Mg²⁺-ATPase in Lottia subrugosa sampled in Brazilian sites under different contamination levels. Results showed that, in general, shells from the reference site (Palmas) were more rounded than the ones from the contaminated site (Balsa). Effects in enzymatic activities in specimens from transplant bioassay were attributed to the known high contaminant levels present at Balsa. While the lack of enzymatic activity alterations during field sampling was attributed to physiological adaptation to contaminants exposure. Enzymatic activities were not correlated to shell biometric parameters in field sampling, indicating that these enzymes were not related to shell alterations detected in the present study.

Biomineral proteomics: A tool for multiple disciplinary studies

The hard tissues of animals, such as skeletons and teeth, are constructed by a biologically controlled process called biomineralization. In invertebrate animals, biominerals are considered important for their evolutionary success. These biominerals are hieratical biocomposites with excellent mechanical properties, and their formation has intrigued researchers for decades. Although proteins account for ~5 wt% of biominerals, they are critical players in biomineralization. With the development of high-throughput analysis methods, such as proteomics, biomineral protein data are rapidly accumulating, thus necessitating a refined model for biomineralization. This review focuses on biomineral proteomics in invertebrate animals to highlight the diversity of biomineral proteins (generally 40-80 proteins), and the results indicate that biomineralization includes thermodynamic crystal growth as well as intense extracellular matrix activity and/or vesicle transport. Biominerals have multiple functions linked to biological immunity and antipathogen activity. A comparison of proteomes across species and biomineral types showed that von Willebrand factor type A and epidermal growth factor, which frequently couple with other extracellular domains, are the most common domains. Combined with species-specific repetitive low complexity domains, shell matrix proteins can be employed to predict biomineral types. Furthermore, this review discusses the applications of biomineral proteomics in diverse fields, such as tissue regeneration, developmental biology, archeology, environmental science, and material science.