Shellfish Populations Research Articles

Fishery resources of Sabah Al-Ahmad Sea City waterways: A potential contributor for Kuwait's fisheries

Recent reports demonstrate that Arabian Gulf Shellfish and Finfish fisheries are in serious decline, in particular those of Kuwait. This decline is attributed to over fishing, pollution, loss of nursery ground, reduction in riverine input via the Shatt Al-Arab, and climate change. When completed in 2018, Sabah Al-Ahmad Sea City, Kuwait, will contain circa 200 km of waterways providing over 50% of extra coast line for Kuwait. Seine netting and gargoor traps have been deployed annually, since the first phase (A1) of this coastal township was opened to the sea in 2004, to monitor Shell and Fin fish populations within the waterways. Present work describes the diversity and abundance of commercial (edible and potential ornamental value) species now inhabiting the waterways, which comprise over 60% of the species marketed in Kuwait. Analysis of catch data reveals that the waterways act as spawning, nursery and feeding habitats for important species such as Epinephelus coioides (Orange-Spotted Grouper), Penaeus semisulcatus (Banana Shrimp) and Portunus segnis (Blue Swimming Crab). As no commercial fishing is allowed, the Sea City waterways act as a significant conservation area for Kuwait's fish stocks.

Salix transect of Europe: variation in ploidy and genome size in willow-associated common nettle, Urtica dioica L. sens. lat., from Greece to arctic Norway.

BackgroundThe common stinging nettle, Urtica dioica L. sensu lato, is an invertebrate "superhost", its clonal patches maintaining large populations of insects and molluscs. It is extremely widespread in Europe and highly variable, and two ploidy levels (diploid and tetraploid) are known. However, geographical patterns in cytotype variation require further study.New informationWe assembled a collection of nettles in conjunction with a transect of Europe from the Aegean to Arctic Norway (primarily conducted to examine the diversity of Salix and Salix-associated insects). Using flow cytometry to measure genome size, our sample of 29 plants reveals 5 diploids and 24 tetraploids. Two diploids were found in SE Europe (Bulgaria and Romania) and three diploids in S. Finland. More detailed cytotype surveys in these regions are suggested. The tetraploid genome size (2C value) varied between accessions from 2.36 to 2.59 pg. The diploids varied from 1.31 to 1.35 pg per 2C nucleus, equivalent to a haploid genome size of c. 650 Mbp. Within the tetraploids, we find that the most northerly samples (from N. Finland and arctic Norway) have a generally higher genome size. This is possibly indicative of a distinct population in this region.

Enhanced surveillance of shellfish mortality to improve early detection and investigation of outbreaks of exotic or emerging infectious diseases: An example of a mass mortality outbreak of mussels, France 2014

This paper explores the relevance and feasibility of enhanced surveillance of mussel-related mortality based on regular telephone interviews of a key informant in a farming community. Based on qualitative analyses of data collected through semi-structured interviews, this method of participatory disease surveillance enabled the retrieval of high quality data during an outbreak of mussel mortality which occurred in Pertuis Charentais, France, in 2014.The findings illustrated that such an enhanced surveillance approach compared with the institutional shellfish health surveillance system could improve the early detection of outbreaks of mussel mortality by one week. This approach enabled a detailed description of the outbreak, showing higher incidence proportion in the Northern water bodies. It also captured relevant data for hypothesis generation for further outbreak investigations, integrating a global view of the health and disturbance of the coastal marine ecosystem. However, to be effective and sustainable, this flexible approach requires a pre-existing knowledge of the structure of the information network of the farmers’ community. Such a community-based enhanced surveillance could increase the reactivity of the entire system to enable the earliest possible and most appropriate interventions to protect shellfish populations against exotic or emerging infectious diseases. This would also help to improve the vigilance of mussel farmers and foster their commitment, which is an essential element for sustainable shellfish health surveillance.

Reflex of urban space changes and climate conditions in Biomphalaria glabrata population dynamics on potential schistosomiasis foci in northeastern Brazil

To understand better the space-disease process of urban schistosomiasis mansoni in northeastern Brazil, this study assessed four sites considered to be potential foci. Molluscs were collected monthly between January to December 2010, were assessed for species and infection, quantified, and measured; rainfall data were obtained; and water samples were analysed for faecal coliform. The specimens collected were identified as Biomphalaria glabrata . At all sites, we observed high levels of faecal coliforms. The sanitation projects within the Coqueiral and Japaozinho neighbourhoods positively influenced population of B. glabrata . A similar phenomenon occurred in the Soledade neighbourhood, where a portion of the study site was excavated for building construction. The population of molluscs and positivity increased during the rainy season whereas mmolluscs size was differently influenced by rainfall. Rainfall combined with anthropogenic activity influenced foci dynamics during the study period, indicating that schistosomiasis is well-established in the Aracaju urban environment, primarily due to the ability of Biomphalaria to adapt to manmade changes associated with precarious sanitation.

A comparison of mollusc diversity between the relatively pristine Marico River and the impacted Crocodile River, two major tributaries of the Limpopo River, South Africa

A study of the freshwater mollusc diversity was conducted at selected sites in the relatively pristine Marico River and the impacted Crocodile River, the major tributaries of the Limpopo River. Four surveys were conducted, two in an early (May 2013 and 2014) and two in a late (November 2013 and 2014) low-flow period. Semi-quantitative surveys were done by sampling the vegetation, as well as the substratum, with a standard SASS net for approximately 15 min each. Environmental parameters including water temperature, electrical conductivity (EC) and pH were measured at each site. Molluscs were identified up to species level, sorted, counted, and the presence of juvenile specimens recorded. Historical data for the 1/16 th degree square grids (loci), in which each of the sampling sites of the current study was located, were extracted from the National Freshwater Snail Collection at the Unit for Environmental Sciences and Management, Potchefstroom Campus of the North-West University. During this study, 20 and 9 species were recovered from the Marico and Crocodile Rivers, respectively, as compared to 13 and 12 species on record for these loci, respectively. Juvenile specimens were present during the four surveys at most of the sites. Canonical correspondence analyses were applied which revealed that biotopes, water temperature and EC played the most significant role in the distribution and abundance of species. The relatively high mollusc diversity and the fact that juveniles were present throughout the study, demonstrated that current habitat and environmental conditions were suitable to promote recruitment and the sustainability of diverse mollusc populations in the Marico River and its tributaries. However, in contrast to this, the exploitation of and habitat transformation in the Crocodile River has resulted in the decrease of biotopes which eventually could have led to the decrease in diversity and the establishment of P. acuta , an exotic invader species. Keywords : freshwater molluscs, biodiversity, Marico River, Crocodile River, environmental variables

Toxicity Of Sodium Dodecyl Sulfate tO Federally Threatened and Petitioned Freshwater Mollusk Species

Anthropogenically caused physical and chemical habitat degradation, including water pollution, have caused dramatic declines in freshwater mollusk populations. Sodium dodecyl sulfate (SDS), a surfactant with no USEPA Water Quality Criteria (WQC), is commonly used in industrial applications, household cleaners, personal hygiene products, and herbicides. In aquatic habitats, previous SDS studies have associated deformities and death to mollusks found in these systems. The objective of this study was to determine EC50 values for two freshwater juvenile unionids (Villosa nebulosa and Hamiota perovalis) and two freshwater caenogastropods (Leptoxis ampla and Somatogyrus sp.) endemic to the Mobile River Basin, USA, to SDS. Using the Trimmed Spearman-Karber method, EC50 values were calculated. Results found that EC50 values were: V nebulosa = 14,469 µg/L (95% CI: 13,436 – 15,581 µg/L), H. perovalis = 6,102 µg/L (95% CI: 4,727 – 7,876 µg/L), Somatogyrus sp. = 1,986 µg/L (95% CI: 1,453 – 2,715 µg/L), and L. ampla = 26 µg/L (95% CI: 6 – 112 µg/L). Freshwater gastropods were more sensitive to SDS than freshwater unionids. Leptoxis ampla was the most sensitive species tested and had such a low EC50 value that more protective regional criteria may be required. Therefore, future research should include additional testing on mollusk species, particularly regionally isolated species that may display increased sensitivity.

Use of side-scan sonar for estimations of Crassostrea brasiliana (Lamarck, 1819) stocks in subtidal banks on the south coast of Brazil

Abstract Uncontrolled extractivism has led to a worldwide reduction in oyster stocks. The use of new and more efficient management tools for impacted environments must increase. The application of such tools requires previous biological and environmental knowledge of the resident populations of these bivalve mollusks. Technical difficulties are usually associated with studies of submerged oyster banks, and these difficulties result in a considerable lack of biological data on the oysters that inhabit subtidal zones. This study aimed to survey Crassostrea brasiliana (also known as C. gasar) stocks in submerged banks and to evaluate a method with which to measure the extent of the banks and identify and quantify the oysters in the banks with the use of side-scan sonar. This study was conducted on 10 oysters banks located in the subtidal zone of Guaratuba Bay, on the south coast of Brazil. The prospection of all these banks was later validated by diving, and oyster samples (n = 20/bank) were collected for species identification with a molecular method. Only one bank contained oysters that were generically classified as Crassostrea sp.; those in the remaining banks being identified as C. brasiliana. The prospected banks contained oysters of various sizes (average 1.5 m, n = 1,107) that were heterogeneously scattered in the riverbeds. The total number of oysters in the 10 sampled banks was estimated to be 21,159.13 oysters or 1 oyster/4.5 m², which represents a low oyster density in the study site. The results validate the use of side-scan sonar as an efficient means with which to prospect for oysters in banks located within subtidal zones.

Characterization of novel expressed sequence tag-simple sequence repeat markers and analysis of genetic diversity in four geographic populations of Thais luteostoma.

In this study, the genetic diversity in four geographic populations (Yushan Island, Zhoushan, Wenzhou, and Xiamen) of Thais luteostoma was analyzed using 21 microsatellite loci. The results of this study showed that the alleles obtained from different populations ranged from 2 to 8. The average number of alleles and effective alleles were 4.59 and 3.16, respectively. The observed heterozygosity and expected heterozygosity values were in the range 0.338-0.372 and 0.452-0.495, respectively. The polymorphism information content ranged from 0.273 to 0.785. We observed a high level of genetic diversity at 9 of the 21 microsatellite markers in these populations. The genetic differentiation indices of the four geographic populations ranged from 0.0312 to 0.0565, showing a medium level of genetic differentiation. The genetic distances among populations ranged from 0.158 to 0.465. The UPGMA tree indicated that the Yushan Island and Zhoushan populations clustered first, and these subsequently clustered with the Wenzhou and Xiamen populations, indicating that the Xiamen shellfish population was least related to the other populations. The information regarding the shellfish population structure obtained in this study would facilitate the genetic breeding and conservation of T. luteostoma.

Application of zonality conceptual model of chronic effects of ionizing radiation for studying the behavior of Sr-90 in terrestrial ecosystems

Behavior of Sr-90 radionuclide in the system of «soil-plants-mollusc shells» was investigated on the example of biotope of regional radioactive waste storage facility. The purpose of the study was to examine the possibility of applying the conceptual model of zonality of chronic effects of ionizing radiation in natural populations in the investigation of behavior of radioactive strontium in terrestrial ecosystems and to identify radioecological zones of biological effects of chronic exposure to ionizing radiation of the mollusc population based on of the bio-geochemical regularities of technogenic migration of Sr-90 within the «soil-plants-mollusc shells» system. The study was conducted on the experimental site which represented the biotope of the regional radioactive waste storage facility. Analysis of samples of soil, plant (Urtica dioica) and terrestrial molluscs was implemented by the method of radiochemical separation followed with measuring the activity of the radionuclide using scintillation spectrometer «BETA-01C». Annual exposures to external beta-radiation received by tissues of molluscs irradiated by Sr-90 and its daughter radionuclide Y-90 contained in the shells were calculated using Levinger and Marinelli formula.It was discovered that dose rates of irradiation of molluscs Bradybaena Fruticicola fruticum are within 0.03–1.60 Gy/year. Structuring of experimental data was implemented based on the obtained data on the specific activity of Sr-90 in the system under study in accordance with model by G.G.Polikarpov. Three ecological zones were identified on the experimental site with regular variation of specific activity of Sr-90 in mollusс shells. In the zone of physiological masking concentration of radionuclide in mollusc shells can be by one order of magnitude and even more higher than in the plant. In the zone of ecological masking and the zone of pronounced environmental effects specific activities of the radionuclide are reduced as compared to its concentration in plants by 8 and 40 times, respectively (no decrease of specific activities of the radionuclide in the plant is regisrered). The implemented studies allow formulating the conclusion on the possibility of adaptation of indicators of Sr-90 migration in terrestrial ecosystems.

Agent-based modelling, molluscan population dynamics, and archaeomalacology

Abstract Agent-based modelling (ABM) is an emerging archaeological tool that offers insights into processes which are archaeologically invisible or difficult to detect. Here we illustrate the potential of ABM for archaeomalacology, posing two research questions and comparing ABM results with Pacific archaeological sequences. The first analysis considers how molluscan energetic return rates (ERR) and age of reproductive maturity (ARM), singularly or in combination, influence prey population resilience. The second analysis assesses how prey spatial structure affects foraging efficiency and prey susceptibility to resource depression. Consistent with expectations from evolutionary ecology and life history theory, the ABM results demonstrate that both ERR and ARM influence prey population resilience (or vulnerability). However, the analysis also demonstrates that ARM is the more important variable and taxa with high ERR (i.e., large-bodied) are disproportionately affected by human harvesting. Not only are efficient foragers more likely to target high ERR taxa, but these prey often have delayed ARM and un-foraged individuals are more likely to be smaller and immature, with disadvantages for population stability and recovery. In short, early-maturing taxa are highly resilient, while late-maturing organisms are more vulnerable; these outcomes also are observed archaeologically. The ABM analyses also demonstrate the effects of prey spatial structure on molluscan susceptibility to resource depression. High prey aggregation initially allows for high foraging efficiency, but prey abundance and encounter rates often rapidly decline. In contrast, when prey are dispersed, search time is greater, leading to lower encounter rates and reduced foraging efficiency, but greater prey population stability. Our ABM and archaeological examples further illustrate that while general principles can be derived, the resilience and spatial structure of specific prey populations, as well as foraging outcomes, are context dependent and continuously evolving. Finally, we note that model departures from theoretical expectations serve to stimulate further research, including use of additional parameters, consideration of novel contextual evidence, and/or investigation of social, technological or environmental hypotheses.

The effects of sampling on the analysis of archeological molluscan remains: A quantitative approach

Sampling is a practice that affects all stages of archeological research, and is a method frequently employed to manage the potentially vast quantities of material recovered from excavations. Current sampling methods used in the analyses of shell middens are largely based on those developed by the California School, and can be characterized by the implementation of small sample sizes during the excavation and analysis of shell deposits. The wider archeological sampling literature, however, has repeatedly demonstrated that the use of small sample sizes has the potential to result in the loss of substantial quantities of material, often grossly underestimating an assemblage's richness, and skewing abundance distributions. There is therefore a need to re-evaluate the current sampling methods used in the analysis of shell deposits. We use five ecological diversity indices to examine and quantify the effects of sampling on the recovery and interpretation of molluscan remains, using material from the Peel Island Lazaret Midden, southeast Queensland, as a case study. This research demonstrates that the use of small sample sizes does indeed affect measures of richness and evenness for molluscan populations, with marked differences being recorded for the two sample sizes used in this study. Results show that while subsamples are able to detect some trends in taxonomic richness and evenness, the degree of difference present between the results from the two sample size indicates that subsamples reduce interpretive accuracy. We conclude that, in addition to determining the appropriate sampling strategy during excavation or recovery of midden deposits as highlighted by previous research, there is also a need for researchers to assess sampling practices during the analyses of molluscan assemblages. The methods employed in this study can be easily applied and offer a robust means of determining the effects and adequacy of sampling.

Cryptic infection of a broad taxonomic and geographic diversity of tadpoles by Perkinsea protists

The decline of amphibian populations, particularly frogs, is often cited as an example in support of the claim that Earth is undergoing its sixth mass extinction event. Amphibians seem to be particularly sensitive to emerging diseases (e.g., fungal and viral pathogens), yet the diversity and geographic distribution of infectious agents are only starting to be investigated. Recent work has linked a previously undescribed protist with mass-mortality events in the United States, in which infected frog tadpoles have an abnormally enlarged yellowish liver filled with protist cells of a presumed parasite. Phylogenetic analyses revealed that this infectious agent was affiliated with the Perkinsea: a parasitic group within the alveolates exemplified by Perkinsus sp., a "marine" protist responsible for mass-mortality events in commercial shellfish populations. Using small subunit (SSU) ribosomal DNA (rDNA) sequencing, we developed a targeted PCR protocol for preferentially sampling a clade of the Perkinsea. We tested this protocol on freshwater environmental DNA, revealing a wide diversity of Perkinsea lineages in these environments. Then, we used the same protocol to test for Perkinsea-like lineages in livers of 182 tadpoles from multiple families of frogs. We identified a distinct Perkinsea clade, encompassing a low level of SSU rDNA variation different from the lineage previously associated with tadpole mass-mortality events. Members of this clade were present in 38 tadpoles sampled from 14 distinct genera/phylogroups, from five countries across three continents. These data provide, to our knowledge, the first evidence that Perkinsea-like protists infect tadpoles across a wide taxonomic range of frogs in tropical and temperate environments, including oceanic islands.

Evaluation of marine subareas of Europe using life history parameters and trophic levels of selected fish populations

European marine waters include four regional seas that provide valuable ecosystem services to humans, including fish and other seafood. However, these marine environments are threatened by pressures from multiple anthropogenic activities and climate change. The European Marine Strategy Framework Directive (MSFD) was adopted in 2008 to achieve good environmental status (GEnS) in European Seas by year 2020, using an Ecosystem Approach. GEnS is to be assessed using 11 descriptors and up to 56 indicators. In the present analysis two descriptors namely “commercially exploited fish and shellfish populations” and “food webs” were used to evaluate the status of subareas of FAO 27 area. Data on life history parameters, trophic levels and fisheries related data of cod, haddock, saithe, herring, plaice, whiting, hake and sprat were obtained from the FishBase online database and advisory reports of International Council for the Exploration of the Sea (ICES). Subareas inhabited by r and K strategists were identified using interrelationships of life history parameters of commercially important fish stocks. Mean trophic level (MTL) of fish community each subarea was calculated and subareas with species of high and low trophic level were identified. The Fish in Balance (FiB) index was computed for each subarea and recent trends of FiB indices were analysed. The overall environmental status of each subarea was evaluated considering life history trends, MTL and FiB Index. The analysis showed that subareas I, II, V, VIII and IX were assessed as “good” whereas subareas III, IV, VI and VII were assessed as “poor”. The subareas assessed as “good” were subject to lower environmental pressures, (less fishing pressure, less eutrophication and more water circulation), while the areas with “poor” environment experienced excessive fishing pressure, eutrophication and disturbed seabed. The evaluation was based on two qualitative descriptors (“commercially exploited fish and shellfish populations” and “food webs”) is therefore more robust.

Malacological and parasitological surveys along the Xe Bangfai and its tributaries in Khammouane Province, Lao PDR

Malacological and parasitological observations were conducted along the Xe Bangfai River between 2010 and 2012 after a dermatitis outbreak. Mollusc populations were surveyed at 28 stations. Mollusc family and species lists were compiled. A sub-sample of 4033 snails from 10 gastropod families was screened for the presence of trematode cercariae. The findings demonstrated that mollusc populations declined after the initial operation of the Nam Theun 2 hydropower project. The species composition of the snail populations also underlined ecological changes. No definitive cause of cercarial dermatitis was found. However, cercariae resembling echinostome and xiphidiocercariae were respectively observed in one population of Bithyniidae and one population of Neotricula aperta . Further hydrobiological studies are thought to be necessary to study the succession of the molluscan community in the Xe Bangfai River until populations become stable.

Introduction to the Special Section on Marine Cultivation among Indigenous Peoples of the Northwest Coast

This special section features recent ethnoecological studies of key fish and shellfish species used by tribes and First Nations of the Northwest Coast of North America. The papers present ethnographic studies of the region’s largely overlooked indigenous mariculture practices, and seek to reframe them as a form of cultivation rather than simple Bconservation^ or Bresource management.^ The introductory essay by Thornton, Deur, and Kitka outlinesmajor debates concerning indigenous conservation. Using salmon as a prototypical case, the authors review a wide range of material, social, and spiritual techniques involved in their cultivation, including forms of habitat enhancement and transplantation not previously documented. With this example, this essay outlines why a cultivation perspective is both more appropriate in the case of salmon and other marine species, and is less prone to narrow ethnocentric interpretations in the case of Northwest Coast peoples. The authors define cultivation as any conscious effort to create specific conditions for advantageous engagement or relations with another being; as such, cultivation includes a range of processes that often enhance resource output, even if their proximate goals may accentuate comparatively immaterial objectives such as demonstrating interspecific respect between human communities and communities of prey species. On the Northwest Coast, marine Bbeings^ cultivated in this manner are typically high value fish and invertebrates, such as salmon, halibut, herring, eulachon, and various clams and other shellfish. The mechanisms and motivations for cultivation are similar to those traditionally applied to other types of resources, such as staple plant foods—a theme documented along this coast in recent related literatures. This essay is followed by two case studies on indigenous cultivation of less emphasized species: herring (Thornton) among the Tlingit and Haida and shellfish (Deur et al.) among the Kwakwaka’wakw. As with salmon, indigenous cultivation of herring and shellfish involved a wide range of practical knowledge and techniques that helped not only to increase their productivity and abundance but also to make these species more accessible, resilient, and predictable. In both cases, the ethnographic investigations, combined with information from the archaeological record, suggest that these techniques are of significant antiquity, extending back well before the historical era. They also suggest strong parallels to salmon and other keystone resources in their emphasis not merely on Bconservative^ motives relating to enhancing and sustaining resource output, but on a broader range of cultivation principles and modalities. Collectively the papers argue that humans, as cultivators of keystone species, may have become keystone species themselves in terms of their contribution to ecosystem functioning and stability. The success of indigenous cultivation complexes in maintaining and enhancing salmon, herring, and shellfish populations over the longue duree further point to their relevance and potential applications to contemporary management questions. These cases provide insights for fisheries and ecosystem services management and restoration efforts that typically lack a strong historical ecological and ethno-stewardship perspective. They also provide insights for contemporary indigenous communities seeking to maintain not only the integrity of dietary staples and cultural keystone species, but also the vitality of foundational cultural practices associated with their sustainment. * Thomas F Thornton thomas.thornton@ouce.ox.ac.uk

Interactive effects of climate change with nutrients, mercury, and freshwater acidification on key taxa in the North Atlantic Landscape Conservation Cooperative region.

The North Atlantic Landscape Conservation Cooperative LCC (NA LCC) is a public-private partnership that provides information to support conservation decisions that may be affected by global climate change (GCC) and other threats. The NA LCC region extends from southeast Virginia to the Canadian Maritime Provinces. Within this region, the US National Climate Assessment documented increases in air temperature, total precipitation, frequency of heavy precipitation events, and rising sea level, and predicted more drastic changes. Here, we synthesize literature on the effects of GCC interacting with selected contaminant, nutrient, and environmental processes to adversely affect natural resources within this region. Using a case study approach, we focused on 3 stressors with sufficient NA LCC region-specific information for an informed discussion. We describe GCC interactions with a contaminant (Hg) and 2 complex environmental phenomena-freshwater acidification and eutrophication. We also prepared taxa case studies on GCC- and GCC-contaminant/nutrient/process effects on amphibians and freshwater mussels. Several avian species of high conservation concern have blood Hg concentrations that have been associated with reduced nesting success. Freshwater acidification has adversely affected terrestrial and aquatic ecosystems in the Adirondacks and other areas of the region that are slowly recovering due to decreased emissions of N and sulfur oxides. Eutrophication in many estuaries within the region is projected to increase from greater storm runoff and less denitrification in riparian wetlands. Estuarine hypoxia may be exacerbated by increased stratification. Elevated water temperature favors algal species that produce harmful algal blooms (HABs). In several of the region's estuaries, HABs have been associated with bird die-offs. In the NA LCC region, amphibian populations appear to be declining. Some species may be adversely affected by GCC through higher temperatures and more frequent droughts. GCC may affect freshwater mussel populations via altered stream temperatures and increased sediment loading during heavy storms. Freshwater mussels are sensitive to un-ionized ammonia that more toxic at higher temperatures. We recommend studying the interactive effects of GCC on generation and bioavailability of methylmercury and how GCC-driven shifts in bird species distributions will affect avian exposure to methylmercury. Research is needed on how decreases in acid deposition concurrent with GCC will alter the structure and function of sensitive watersheds and surface waters. Studies are needed to determine how GCC will affect HABs and avian disease, and how more severe and extensive hypoxia will affect fish and shellfish populations. Regarding amphibians, we suggest research on 1) thermal tolerance and moisture requirements of species of concern, 2) effects of multiple stressors (temperature, desiccation, contaminants, nutrients), and 3) approaches to mitigate impacts of increased temperature and seasonal drought. We recommend studies to assess which mussel species and populations are vulnerable and which are resilient to rising stream temperatures, hydrological shifts, and ionic pollutants, all of which are influenced by GCC.

Molluscs emergent, Part II: themes and trends in the scientific investigation of molluscs and their shells as past human resources

Recent work in three major research themes involving molluscs is reviewed: 1. molluscs in past human diets and subsistence systems, sclerochemistry and seasonality studies on mollusc harvesting times using stable isotopes of oxygen; 2. the impact of foraging on mollusc populations, resource management strategies, and settlement patterns and mobility of coastal foragers; and 3. mollusc shells as artefacts and personal ornaments, including manufacture and use, provenance studies and exchange systems, and human cognition. Most of the discussion is about marine molluscs and their shells, although land snails and freshwater shells are also considered, where appropriate.

Effects of osmotic stress on predation behaviour of Asterias rubens L.

Environmental stress plays an important role in determining ecosystem functioning and structure. In estuarine areas both tidal and seasonal salinity changes may cause osmotic stress on predators, affecting their behaviour and survival. The interaction between these predators and their prey may affect performance, thus influencing predator impact on prey populations. The common starfish, Asterias rubens, inhabits estuarine areas, such as the Dutch Wadden Sea, that exhibit large seasonal variation in salinity (10–32PSU). In those areas A. rubens exerts top down control on its prey, thus representing an important shellfish predator. This predation may impact on cultured and natural shellfish populations. However, the effects of osmotic stress on A. rubens performance may influence its effect on prey. Although the effect of salinity in A. rubens survival has been extensively studied, the impact on its predation behaviour and acclimation capacity remains unclear. In this study, we analyse the performance of A. rubens preying on mussels (Mytilus edulis) after a salinity decrease and monitor its acclimation capacity over a period of 22days. Our experiments demonstrated that salinity affected performance by reducing feeding activity and altering size prey selection. Moreover, as acclimation occurred, A. rubens predation performance improved in all sub-lethal treatments. We conclude that osmotic stress caused by decreasing salinity potentially influences A. rubens distribution, abundance, and potential impact on prey populations. However the magnitude of the change in salinity (from 31 to a minimum of 10PSU) and its timescale (3weeks) mediate this effect.

Impact of deforestation on pearl mussel habitats in the Russian section of the Baltic Sea basin

Changes in the vegetation cover associated with intensive forest extermination may have a strong effect on the riverine environment, including the chances of survival for bivalve mollusc populations in small streams and rivers. In order to check this hypothesis, drainage area properties of the rivers with extinct and existing pearl mussel populations in the Russian section of the Baltic Sea basin were compared. Preservation of forest vegetation along the river banks of the studied rivers was correlated with the presence of pearl mussel populations. Traditional agriculture turned out to be, in some cases, more harmful for river ecosystems than urbanization and industrialization.

Another unique river: A consideration of some of the characteristics of the trunk tributaries of the Nile River in northwestern Ethiopia in relationship to their aquatic food resources

Aquatic food resources are important components of many modern human hunter-gatherer diets and yet evidence attesting to the widespread exploitation of this food type appears rather late in the archaeological record. While there are times when, for example, the capture of fish and shellfish requires sophisticated technology, there are other cases when the exact ecological attributes of an individual species and the particulars of its environment make it possible for these foods to be incorporated into the human diet with little or no tool use and only a minimal time investment. In order to better understand the full set of variables that are considered in these sorts of foraging decisions, it is necessary to detail the attributes of each particular aquatic environment. We discuss here some of the characteristics of the trunk tributaries of the Nile and Blue Rivers in the Horn of Africa. Unlike typical perennial rivers, these ‘temporary’ rivers flow only during a brief but intense wet season; during the much longer dry season, the rivers are reduced to a series of increasingly disconnected waterholes, and the abundant and diverse fish and mollusk populations are trapped in ever smaller evaporating pools. The local human population today utilizes a number of diverse capture methods that range from simple to complex, and vary according to the size and depth of the waterhole and the time of the year. When we view the particular characteristics of an individual river system, we find that each river is ‘unique’ in its individual attributes. The Horn of Africa is believed to be along the route that modern humans followed on their migration out of Africa, and it is likely that the riverine-based foraging behaviors of these populations accompanied our species on its movement into the rest of the Old World.