Shellfish Populations Research Articles

Using a weight-structured oyster population dynamic model to explore top-down control of coastal water quality in a subtropical embayment

Abstract The natural filtering capacity of oysters and other suspension filter-feeders has seen them put forward as a potential water quality management option. However, the specifics of how many oysters would be required to clean a system are not necessarily straightforward to evaluate because of the size-dependence of oyster physiological rates along with the dynamic coupling that exists between the oysters and the environment. We use a weight-structured shellfish population model and a nutrient–phytoplankton–detritus model to answer the question of how many oysters it would take to clean a large estuary located in Queensland, Australia. Modelling results indicate that improvements in the water quality are not seen until the stocking density of oysters exceeds 0.09 ind. m−3 and that local water quality guidelines are not fully met until the density exceeds 1.80 ind. m−3. At these densities, the corresponding times to filter the entire volume of the study area are 52–38 d (0.09 ind. m−3) and 1.80–1.35 d (1.80 ind. m−3), respectively. This research highlights that regulatory feedback pathways exist between a shellfish population and the water quality constituents that they control through filtration. While the use of oysters and other filter-feeders may be an appealing approach to nutrient management and top-down control of phytoplankton, the practicalities of deploying oysters at a system-scale may be the greatest barrier to this option.

Analysis of cytogenetic stability in natural populations of terrestrial mollusks (based on DNA comet assay)

Abstract-Alkaline gel electrophoresis of isolated cells (comet assay) was used to assess degree of nuclear DNA damage in populations of terrestrial mollusks Bradybaenafruticum Müll., Chondrula tridens Müll., Cepaea vindobonensis Fer., and Stenomphalia ravergieri Fer. living in the forest-steppe landscape of the southern part of the Mid-Russian Upland. Evidence of differences in the parameters studied was found. The age dynamics of the degree of damage of the genetic apparatus was observed. Possible causes of the identified differences are discussed.

Late miocene-pliocene paleoclimatic evolution documented by terrestrial mollusk populations in the western Chinese Loess Plateau.

The Neogene eolian deposits in the Chinese Loess Plateau (CLP) are one of the most useful continental deposits for understanding climatic changes. To decipher Late Neogene paleoclimatic changes in the CLP, we present a terrestrial mollusk record spanning the time interval between 7.1 and 3.5 Ma from the western CLP. The results indicate four stages of paleoclimatic evolution: From 7.1 to 6.2 Ma, cold and dry climatic conditions prevailed as evidenced by high values of the total number of cold-aridiphilous (CA) mollusk species and by low values of all of the thermo-humidiphilous (TH) mollusk indices. From 6.2 to 5.4 Ma, the climate remained cold and dry but was not quite as dry as during the preceding phase, as indicated by the dominance of CA mollusks and more TH species and individuals. From 5.4 to 4.4 Ma, a warm and moist climate prevailed, as indicated by high values of the TH species and individuals and by the sparsity of CA species and individuals. From 4.4 to 3.5 Ma, all of the CA indices increased significantly and maintained high values; all of the TH indices exhibit high values from 4.4 to 4.0 Ma, an abrupt decrease from 4.0 Ma and a further increase from 3.7 Ma. The CA species of Cathaica pulveraticula, Cathaica schensiensis, and Pupopsis retrodens are only identified in this stage, indicating that the CA species were diversified and that the climate was becoming drier. Moreover, the CA mollusk group exhibits considerable diversity from 7.1 to 5.4 Ma when a cold, dry climate prevailed; whereas the diversity of the TH group was high during the relatively warm, wet interval from 5.4 to 4.4 Ma. This indicates that variations in the diversity of the CA and TH mollusk groups were closely related to climatic changes during the Late Miocene to Pliocene.

Identification of an estrogen receptor gene in the natural freshwater snail Bithynia tentaculata

Mollusks have received increasing interest in ecotoxicological studies but so far the available scientific analyses of how their genes are affected by anthropogenic pollutants are scarce. The focus of this study is to identify an estrogen receptor (er) gene in the common prosobranch snail Bithynia tentaculata and to test a hypothesis that 17α-Ethinylestradiol (EE2) will modulate er gene expression after short-term exposure. We set up exposure experiments with a total of 144 snails, which were collected from a natural population in southern Sweden. Snails were exposed to either 10ng/L or 100ng/L EE2 during 24h and/or 72h. From the isolated B. tentaculata RNA we successfully identified and characterized a novel er gene and phylogenetic analyses strongly indicate that the Bithynia er gene is an ortholog to the human ERα (ESR1, NR3A1). We found a significant interaction between EE2-dose and exposure duration on the er's gene expression (Two-way ANOVA; p=0.04). We also found a significant difference in the gene expression of the er when comparing the control and 100ng/L treatment groups after 72h in female snails (One-way ANOVA; p=0.047). The results from this study should be useful for future field-related studies of estrogen receptors in natural populations of mollusks.

Sponge bioerosion accelerated by ocean acidification across species and latitudes?

In many marine biogeographic realms, bioeroding sponges dominate the internal bioerosion of calcareous substrates such as mollusc beds and coral reef framework. They biochemically dissolve part of the carbonate and liberate so-called sponge chips, a process that is expected to be facilitated and accelerated in a more acidic environment inherent to the present global change. The bioerosion capacity of the demosponge Cliona celata Grant, 1826 in subfossil oyster shells was assessed via alkalinity anomaly technique based on 4 days of experimental exposure to three different levels of carbon dioxide partial pressure (pCO2) at ambient temperature in the cold-temperate waters of Helgoland Island, North Sea. The rate of chemical bioerosion at present-day pCO2 was quantified with 0.08–0.1 kg m−2 year−1. Chemical bioerosion was positively correlated with increasing pCO2, with rates more than doubling at carbon dioxide levels predicted for the end of the twenty-first century, clearly confirming that C. celata bioerosion can be expected to be enhanced with progressing ocean acidification (OA). Together with previously published experimental evidence, the present results suggest that OA accelerates sponge bioerosion (1) across latitudes and biogeographic areas, (2) independent of sponge growth form, and (3) for species with or without photosymbionts alike. A general increase in sponge bioerosion with advancing OA can be expected to have a significant impact on global carbonate (re)cycling and may result in widespread negative effects, e.g. on the stability of wild and farmed shellfish populations, as well as calcareous framework builders in tropical and cold-water coral reef ecosystems.

The potential impact of climate change on the infectious diseases of commercially important shellfish populations in the Irish Sea—a review

AbstractThe Irish Sea and surrounding regions are a rich source of shellfish production as a result of captive fishing and aquaculture. Key species produced include lobsters (Homarus gammarus), edible crabs (Cancer pagurus), langoustines (Nephrops norvegicus), flat oysters (Ostrea edulis), cockles (Cerestoderma edule) and blue mussels (Mytilus edulis). The role played by infectious disease in limiting the sustainability of the production of these species is largely neglected. This review summarizes our knowledge of the key diseases of commercially important crustaceans and bivalve molluscs and attempts to determine their role in limiting the population of animals available for food production both at present and in the future. It shows that the key diseases threatening the sustainability of shellfish production are bitter crab disease in langoustines and edible crabs, and a wide range of diseases caused by micro- and macro-parasites in some bivalve molluscs including oysters and cockles. Oceanographic models are also employed to predict how changes in climate over the next half century may affect these key diseases and their hosts as found in the Irish Sea. It is concluded that the paucity of information on the potential transfer of some disease agents in pelagic larval stages of hosts and vectors is a major hurdle in predicting how some changes in environmental conditions may influence the prevalence and severity of shellfish diseases in coming years.

Twenty years of seagrass networking and advancing seagrass science: The International Seagrass Biology Workshop Series.

SEAGRASSES are a group of some 72 species of marine flowering plants found in the world’s shallow coastal oceans (Green and Short 2003, Short et al. 2011). There is now scientific consensus that they create an important marine habitat not only by themselves, but also as a component of more complex ecosystems within marine coastal zones. Seagrasses contribute to the health of coral reefs and mangroves, salt marshes and oyster reefs (Dorenbosch et al. 2004; Duke et al. 2007; Heck et al. 2008; Unsworth et al. 2008). Seagrasses have high primary productivity and are a basis of many marine food webs through direct herbivory and the through a detrital cycle (Hemminga and Duarte, 2000). They have enormous value in providing nutrients (N and P) and organic carbon to other parts of the oceans, including the deep sea, and they contribute significantly to carbon sequestration (Suchanek et al. 1985; Duarte et al. 2005). Armed with this knowledge today it is interesting to remember that it is only just over a hundred years since scientists first began speculating on the roles and values of seagrass in the marine environment, with the first focus occurring in Europe on eelgrass (Zostera marina). Many at the time discounted seagrass as an important primary producer (den Hartog 1980). It was not until after the 1930s, when vast areas of Zostera marina were lost in the northern hemisphere from a wasting disease that scientists and governments started to understand and investigate the value of seagrass to coastal ecosystems (Milne and Milne 1951). The loss of Zostera marina led to obvious declines in migratory waterfowl, crustaceans, finfish and shellfish populations (Thayer et al. 1984) In response to those concerns about ongoing losses of Zostera marina and other seagrass species, a meeting of scientists in Fairbanks, Alaska in early 1973 decided to coordinate seagrass research globally. This led to the first International Seagrass Workshop being organized and held in Leiden, The Netherlands, later that year. The report of that conference (McRoy and Helfferich 1977) makes interesting reading, looking back from the perspective of the 21st century. There is only one contribution from the southern hemisphere (Larkum 1977) with Australia referred to as a “little known region”. What we now know as the centre of seagrass biodiversity, Insular Southeast Asia and the broader Indo Pacific region, receives no mention at all. A significant and long-lasting outcome of the Leiden meeting was the birth of the journal “Aquatic Botany”.

Natural capital and ecosystem services for sustainable livelihoods in Costa Vicentina, Portugal

Event Abstract Back to Event Natural capital and ecosystem services for sustainable livelihoods in Costa Vicentina, Portugal Rui Santos1*, Paula Antunes1*, Pedro Clemente1 and Marta Calvache1 1 CENSE – Centre for Environmental and Sustainability Research Faculdade de Ciências e Tecnologia Universidade Nova de Lisboa, Portugal The OpenNESS project, funded by EC FP7, aims to translate the concepts of Natural Capital (NC) and Ecosystem Services (ES) into operational frameworks that provide tested, practical and tailored solutions for integrating ES into land, water and urban management and decision-making, while promoting local stakeholders well-being. Central to the project is a multi-scale case study approach, designed to ground concepts and theories on real world observations and analysis. This paper presents one of the project case studies, located in the Portuguese southwest coast – Costa Vicentina. This case study is focused on the use of NC and ES concepts to design instruments for sustainable management of living resources (algae, shellfish and fish) and to promote a sustainable nature-based tourism. The research aims to (1) identify the linkages between marine natural capital stocks (e.g. bottom algae, shellfish populations,...) with ES provision; (2) explore the perceptions and importance of ES to local stakeholders’ wellbeing and their economic value; and (3) evaluate the use of ES in land-use planning and conservation, and the potential of different policy instruments and governance arrangements to ensure the delivery of ES and to promote local stakeholders well-being. The combination of methods such as ES mapping, monetary and non-monetary valuation of ES, and system dynamics modelling, will ultimately be used to inform and support decision makers and policy instruments design. The research is rooted on a participatory process involving the main stakeholder groups, thus fostering dialogue and social learning. Keywords: natural capital, ecosystem services, governance, system dynamics modelling, Conservation of Natural Resources Conference: IMMR | International Meeting on Marine Research 2014, Peniche, Portugal, 10 Jul - 11 Jul, 2014. Presentation Type: Poster Presentation Topic: BIODIVERSITY, CONSERVATION AND COASTAL MANAGEMENT Citation: Santos R, Antunes P, Clemente P and Calvache M (2014). Natural capital and ecosystem services for sustainable livelihoods in Costa Vicentina, Portugal. Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2014. doi: 10.3389/conf.fmars.2014.02.00097 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 21 May 2014; Published Online: 18 Jul 2014. * Correspondence: Dr. Rui Santos, CENSE – Centre for Environmental and Sustainability Research Faculdade de Ciências e Tecnologia Universidade Nova de Lisboa, Lisboa, Portugal, rfs@fct.unl.pt Dr. Paula Antunes, CENSE – Centre for Environmental and Sustainability Research Faculdade de Ciências e Tecnologia Universidade Nova de Lisboa, Lisboa, Portugal, mpa@fct.unl.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Rui Santos Paula Antunes Pedro Clemente Marta Calvache Google Rui Santos Paula Antunes Pedro Clemente Marta Calvache Google Scholar Rui Santos Paula Antunes Pedro Clemente Marta Calvache PubMed Rui Santos Paula Antunes Pedro Clemente Marta Calvache Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Large-Scale Development of Gene-Associated Single-Nucleotide Polymorphism Markers for Molluscan Population Genomic, Comparative Genomic, and Genome-Wide Association Studies

Mollusca is the second most diverse group of animals in the world. Despite their perceived importance, omics-level studies have seldom been applied to this group of animals largely due to a paucity of genomic resources. Here, we report the first large-scale gene-associated marker development and evaluation for a bivalve mollusc, Chlamys farreri. More than 21,000 putative single-nucleotide polymorphisms (SNPs) were identified from the C. farreri transcriptome. Primers and probes were designed and synthesized for 4500 SNPs, and 1492 polymorphic markers were successfully developed using a high-resolution melting genotyping platform. These markers are particularly suitable for population genomic analysis due to high polymorphism within and across populations, a low frequency of null alleles, and conformation to neutral expectations. Unexpectedly, high cross-species transferability was observed, suggesting that the transferable SNPs may largely represent ancestral genetic variations that have been preserved differentially among subfamilies of Pectinidae. Gene annotations were available for 73% of the markers, and 65% could be anchored to the recently released Pacific oyster genome. Large-scale association analysis revealed key candidate genes responsible for scallop growth regulation, and provided markers for further genetic improvement of C. farreri in breeding programmes.

Reaction of mollusk population to emissions from the Middle Ural Copper Smelter

A quantitative study of the mollusk population of the herbaceous layer has been carried out in the secondary upland meadows in a gradient of pollution with emissions from the Middle Ural Copper Smelter (MUCS) (city of Revda, Sverdlovsk oblast). The total abundance of mollusks is 1.3 times lower in a moderately polluted area than in reference areas. The mollusks disappear entirely from the grass cover in close proximity to the smelter. The reasons for the change in the mollusk population structure may be as follows: a heavy-metal toxic effect under conditions of environmental acidification, a lack of available Ca due to its depletion from the upper soil horizons, a reduction in species diversity, and a simplification of meadow grasscover architecture (which modifies the hydrothermal regime in the herbaceous layer). Apparently, a combination of these effects eliminates mollusks from the herbaceous layer, a trend which is not observed in the case of environmental pollution with only heavy metals.

TOXICIDAD DE LOS BIOPLAGUICIDAS AGAVE AMERICANA, FURCRAEA ANDINA (ASPARAGACEAE) Y SAPINDUS SAPONARIA (SAPINDACEAE) SOBRE EL CARACOL INVASOR MELANOIDES TUBERCULATA (THIARIDAE)

Una de las familias de plantas más estudiadas para la búsqueda de nuevos agentes terapéuticos es la Asparagaceae, la cual comprende 2480 especies, Agave americana L., conocida como cabuya azul y Furcraea andina Trel. conocida como cabuya pertenecen a esta familia. Sapindus saponaria L. (Sapindaceae) conocida como boliche o choloque, es una planta arbórea de amplia distribución, en cuyos frutos se ha observado efectos larvicidas sobre garrapatas, actividad antimicrobiana, espermicida, fungicida y molusquicida. Melanoides tuberculata (Muller 1774) (Gastropoda: Thiaridae) es un caracol actualmente de distribución cosmopolita, con énfasis en el ámbito tropical y que presenta una alta importancia ecológica como invasora por su impacto sobre la diversidad de caracoles nativos, ya que desplaza y amenaza con desaparecer o por lo menos decrecer las poblaciones de moluscos nativos, debido a su alto potencial biótico, ser prolífica y a su tasa reproductiva alta. De esta forma, el objetivo de este trabajo fue evaluar la toxicidad aguda de las hojas de A. americana, F. andina y frutos de S. saponaria sobre M. tuberculata. El punto final de lectura fue la mortalidad del caracol M. tuberculataa 24 h de exposición, con recuperación en agua limpia a 24 h. Los valores de CL (Concentración letal media), NOEC (concentración de 50 efectos no observables) y LOEC (concentración más baja de efectos observables) presentaron la siguiente secuencia en orden de toxicidad decreciente: A. americana > F. andina > S. saponaria. El extracto acuoso de A. americana presentó los mejores efectos molusquicidas sobre M. tuberculata en comparación a las otras dos plantas empleadas.

Intensifying collection and size increase of the tessellated nerite snail (Nerita tessellata) at the Coconut Walk site, Nevis, northern Lesser Antilles, AD 890–1440

Recent archaeological investigation at the Coconut Walk site on the Caribbean island of Nevis revealed dense 40 cm deep midden deposits that accumulated between cal AD 890–1440. Analysis of invertebrate faunal remains reveals an assemblage dominated by nerite snails. We measured the length and width of more than 2700 tessellated nerite (Nerita tessellata) shells to investigate evidence for changing mean size that might be indicative of intensifying human predation pressure or other cultural and natural processes. Contrary to similar archaeomalacological studies in which size decline is detected, we observed a statistically significant size increase for N. tessellata over time. This size increase is coupled with increasing levels of tessellated nerite exploitation at the Coconut Walk site. Results suggest that tessellated nerite use was sustainable over several centuries of site occupation. Our findings have important implications for investigations of anthropogenic impacts on prehistoric mollusc populations. In addition, the findings reported here provide important insight into human subsistence patterns during the Late Ceramic Age in the Caribbean and a framework for comparison with observations from other Pre-Columbian sites in the Caribbean.

The study of ontogenetic trajectory reveals the timing of reproductive events in Ancylus fluviatilis (Gastropoda: Planorbidae)

We analysed ontogenetic shape change in the planorbid limpet Ancylus fluviatilis (Müller, 1774) in two rivers in Southern Italy. We developed a new method to discriminate among different cohorts in Ancylus, based on principal component analysis. The method is useful when shape change during growth is allometric, as in our study model. We discovered that bivoltinism occurs in Ancylus in Southern Italy, contrary to previous accounts, which invariably describe A. fluviatilis as a semelparous and univoltine species, although acknowledging difficulty in discriminating among cohorts. The methods presented here may potentially help research in reproductive traits in many other mollusc populations where shape change during ontogeny is demonstrated to be allometric.

Diversity and distribution of Mollusca in relation to the physico-chemical profile of Gho-Manhasan stream, Jammu (J K)

The present communication is aimed at assessing the molluscan diversity and distribution under the impact of some physico-chemical variables on them in Gho-Manhasan stream (a distributory of Chenab), Jammu (J & K). The study involved bottom sampling for 12 months (June, 2010 to July, 2011) from the banks of the stream and registered a total of 11 taxa of freshwater molluscs from class Gastropoda and Bivalvia representing 54.453 and 45.546% of the total population of molluscs. Numerically, Pissidium mitchelli (Bivalvia) was the most abundant taxa followed by Melanoides tuberculata (Gastropoda). Lymnea luteola, Bellamya bengalensis, Physella acuta, Gyraulus ladacensisshowed less frequent appearance whereas Lamellidens corrianus and Corbicula cashmeriensis were recorded as rare taxa. Analysis of the data revealed that the physico-chemistry of the stream exercised profound effect on the diversity and distribution of the malacofauna. Significant changes in molluscan assemblages were primarily due to changes in the stream water quality. Coefficient of correlation (r) between molluscs and physico-chemical parameters revealed significant relationship with bivalves. Key words: Physico-chemical profile, distributory, gastropoda, bivalvia, malacofauna and correlation.

Physical and biological controls on larval dispersal and connectivity in a highly energetic shelf sea

Connectivity within marine species plays a fundamental role in population dynamics, genetic diversity, spread of disease, and resilience to human exploitation. However, for shellfish species that are sessile as adults, the larval‐dispersal stage remains largely unresolved. Appreciation of larval connectivity is therefore crucial to population genetics and marine management. We describe a coupled three‐dimensional hydrodynamic and Lagrangian particle tracking model used to simulate larval transport and show how temporal and spatial hydrodynamic changes, together with larval behavior, are likely to affect dispersal. A case study of Irish Sea (United Kingdom) shellfish populations incorporates a wide range of hydrodynamic environments that are prevalent in other marine systems around the world. Our simulations tested two main processes that control larval dispersal: hydrodynamics and vertical migration. Simulated larval cohorts were released from estuaries and soft sediment locations in regions that were oceanographically distinct. Larvae originating from exposed areas could migrate offshore (low retention and high connectivity) and disperse farther than larvae that remained in flood‐dominant estuaries, which promote retention. Simulated self‐recruitment and connectivity with neighboring populations (∼ 50 km apart) were generally high, although well‐developed mesoscale residual currents were important, controlling dispersal pathways offshore. Vertical migration strategies, synchronized either with the tide (tidal stream transport) or with the Earth's rotation (diel transport), enabled more larvae to remain close to the coast, and simulations indicated higher retention than for passive larvae. However, the probability of connectivity with other populations and potential survivorship was greater for tidal strategies than for passive (although passive transport populated more distinct areas albeit in smaller proportions, as more larvae remained stranded offshore), or diel, where larvae remained close to their release location.

Identifying optimal sites for natural recovery and restoration of impacted biogenic habitats in a special area of conservation using hydrodynamic and habitat suitability modelling

Selection of sites for successful restoration of impacted shellfish populations depends on understanding the dispersion capability and habitat requirements of the species involved. In Strangford Lough, Northern Ireland, the horse mussel (Modiolus modiolus) biogenic reefs cover only a fraction of their historical range with the remaining reefs badly damaged and requiring restoration. Previous experimental trials suggest that translocation of horse mussels accelerates reef recovery and has therefore been proposed as a suitable restoration technique. We used a series of coupled hydrodynamic and particle dispersal models to assess larval dispersion from remnant and translocated populations to identify suitable areas for adult live M. modiolus translocation in Strangford Lough, Northern Ireland. A maximum entropy model (MAXENT) was used to identify if dispersing larvae could reach habitat suitable for adult M. modiolus. From these we predicted if translocated mussels will reseed themselves or be able to act as larval sources for nearby reefs. The dispersal models showed that the remnant M. modiolus populations are largely self-recruiting with little connectivity between them. The majority of larvae settled near the sources and movement was largely dependent on the tides and not influenced by wind or waves. Higher reef elevation resulted in larvae being able to disperse further away from the release point. However, larval numbers away from the source population are likely to be too low for successful recruitment. There was also little connectivity between the Irish Sea and Strangford Lough as any larvae entering the Lough remained predominantly in the Strangford Narrows. The areas covered by these self-seeding populations are suitable for M. modiolus translocation according to the MAXENT model. As a result of this work and in conjunction with other field work we propose a combination of total protection of all remaining larval sources and small scale translocations onto suitable substrata in each of the identified self-recruiting areas.

Age–size structure of common bivalve mollusc populations in the White Sea: the causes of instability

Inter-annual fluctuations in the recruitment rate and size–age structure are typical for marine bivalve beds. Until now there is no common opinion about the causes of this variability. One of them may be related to the adult–larval interactions in mollusk populations. To test this suggestion and to reveal the possible causes of inter-annual instability in bed recruitment level we analyzed the long-term (9–30 years) dynamics of the size–age structure of 22 populations of 9 bivalve species in the White Sea. Inter-annual variability in the successful recruitment was typical of most studied bivalve beds. This phenomenon was apparently caused, on the one hand, by the intensity of molluscs’ intraspecific interactions, and on the other (no less), by the juvenile survival in their first winter. The bivalve stationary beds in the White Sea are likely the exception from the general rule. They can be formed in case of a relatively stable level of annual recruitment with a decrease in intensity of intraspecific competition. However, in this case, the stability of the bed size–age structure can be easily disrupted under unfavourable conditions for spat survival in their first winter.

Mesolithic middens and molluscan ecology: a view from southern Britain

Large accumulations of marine shells are characteristic of mesolithic coastal sites in northwest Europe, but how intensively shellfish were exploited remains controversial. Excavation of a midden on the Isle of Portland and ecological study of presentday molluscs suggest that prehistoric human exploitation may have had a significant impact on local shellfish populations.

Growth of BivalveAtrina vexillumin the Gulf of Thailand

The flag pen shell Atrina vexillum is probably one of the most economically important pinnid species in the Indo-West Pacific. Its populations have suffered a threatening decline during past decades. Despite the need for conservation, knowledge of the ecology of this pinnid is practically absent. The condition of the mollusc population is generally inferred from age- and growth-related data of the investigated mollusc. A combination of Mg:Ca ratios, growth increments on the external shell surface, and annual muscle scar rings on the inner shell surface were used to estimate the age and growth rates of 4. vexillum from 3 subareas in the Gulf of Thailand along the southwestern coast of Vietnam. This study showed that the molluscs were ≤10.5 y old and had a shell length of ≤438 mm. Shell growth rates had a seasonal pattern, with an extended period of very slow growth during the cold season and a short period of slow growth during late spring and summer. The growth rates of A. vexillum varied greatly with subareas. In moving inward in the Gulf (toward its top), the A. vexillum growth rates were slower and its life span was shorter. There were statistically significant differences between subareas in environmental parameters, such as water salinity, temperature, concentrations of suspended particulate matter and suspended organic carbon, chlorophyll a, and oxygen concentration. In the inner subareas, A. vexillum is subject to quite a set of unfavorable environmental factors, such as lower and more changeable water salinity, warmer water temperature, greater concentration of suspended particulate matter, and lower oxygen concentration in the water compared with the outer subarea of the Gulf. The obtained data are a first contribution to the knowledge of the ecology of this little-studied mollusc.

Complete mitochondrial genome of Concholepas concholepas inferred by 454 pyrosequencing and mtDNA expression in two mollusc populations

Despite the great relevance of mitochondrial genome analysis in evolutionary studies, there is scarce information on how the transcripts associated with the mitogenome are expressed and their role in the genetic structuring of populations. This work reports the complete mitochondrial genome of the marine gastropod Concholepas concholepas, obtained by 454 pryosequencing, and an analysis of mitochondrial transcripts of two populations 1000km apart along the Chilean coast. The mitochondrion of C. concholepas is 15,495 base pairs (bp) in size and contains the 37 subunits characteristic of metazoans, as well as a non-coding region of 330bp. In silico analysis of mitochondrial gene variability showed significant differences among populations. In terms of levels of relative abundance of transcripts associated with mitochondrion in the two populations (assessed by qPCR), the genes associated with complexes III and IV of the mitochondrial genome had the highest levels of expression in the northern population while transcripts associated with the ATP synthase complex had the highest levels of expression in the southern population. Moreover, fifteen polymorphic SNPs were identified in silico between the mitogenomes of the two populations. Four of these markers implied different amino acid substitutions (non-synonymous SNPs). This work contributes novel information regarding the mitochondrial genome structure and mRNA expression levels of C. concholepas.