Shellfish Populations Research Articles

Socio-ecological impacts of industrial aquaculture and ways forward to sustainability

In recent decades, we have witnessed a rapid increase in world aquaculture production, the so-called ‘blue revolution’. So as to provide a holistic overview of the socio-ecological threats coupled with this increase, a literature review has been conducted. The following seven major socio-ecological impacts were identified: (i) the damage and destruction of natural environments, (ii) discharges; (iii) a risk to wild fish and shellfish populations, (iv) spatial conflicts, (v) threats to food security, (vi) unfairness in the access to commons; and (vii) the unequal distribution of benefits. So as to move forward from ‘blue revolution’ to a ‘blue evolution’ and attain sustainable aquaculture, the following tools have been identified as instrumental for the transition process: technical, management, governance and legal aspects.

Influence of abiotic factors on biodiversity of the populations of bivalve molluscs of the Lower Zarafshan reservoirs

The length of the reservoir area on the banks of the Zarafshan River and the presence of all biotopes inhabited by molluscs of the Unionidae and Corbisulidae families have made the basin a comfortable aquatic ecosystem for molluscs. The influence of rivers and fisheries on the formation of the fauna of bivalve molluscs in reservoirs is significant. We found that 10 species and 2 subspecies of bivalve molluscs were distributed in the Kuymazor reservoir and 8 species and 2 subspecies of bivalve molluscs in Shurkul. Reservoirs of Sinanodonta species are shown for the first time by us. These molluscs belong to the ecological groups like peloreophilic, rheophilic and pelolimnophilic. In the water reservoirs of Uzbekistan, the spread of bivalve molluscs by groups has common features. In all water reservoirs, an ecological group called peloreophil prevails, but the species belonging to the ecological group atre different in different water bodies. Such species of pedloelphils as Sinanodonta gibba, S. orbicularis, Corbiculina tibetensis and C. ferghanensis are predominantly found in rivers, fish farms, and water reservoirs. The most common species in the canals are Corbiculina tibetensis and C. ferghanensis. The next frequent occurrence in water reservoirs is the ecological group of rheophiles.

Population structure and symbiotic relationships of the invasive speciesSinanodonta woodiana(Lea, 1834) in water bodies of Ukraine

Understanding the process of penetration and distribution of the invasive speciesSinanodonta woodianais important for predicting associated changes in biodiversity and the structure of freshwater communities. The biomass, density, age and sex structure of mollusk populations were analyzed. An increase in the size of Chinese pond mussels was noted after the introduction: the shell length of individuals from a pond (Romanivka village, 2017) was 24,2% more than of mollusks from the Velyka Repida river (Matroska village, 2004), and in 2019 it increased by another 14,7% (by 42,5% compared to the shell length of the mollusks from the Velyka Repida river). The body weight ofS. woodianafrom the river was 125,3 g, while in the pond there was a 2,13-fold increase in body weight in 2017, with a further increase in this indicator by another 23,6% in 2019 and another 37,7% in 2020. The relative number ofS. woodianaand native speciesUnio pictorumandAnodonta anatinain 2017 was 26,3%, 47,4% and 26,3%, in 2020 – 64,0%, 16,0% and 20,0% respectively. Ciliates of the genusConchophthirusandTrichodina,Aspidogaster conchicola,Helobdella stagnalis, larvae ofChironomussp. are in a symbiotic relationship withS. woodiana. The most commonConchophthirussp. – in 21,6% of individuals. Further spread ofS. woodianato the cold regions of Ukraine and the formation of new populations in the already developed regions should be expected.

Limpet (Cellana spp.) shape is correlated with basalt or eolianite coastlines: Insights into prehistoric marine shellfish foraging and mobility in the Hawaiian Islands

Marine molluscs are highly diverse in size, anatomical structure, behaviour, and habitat and can provide information on human foraging, mobility, diet, and palaeoenvironments. Molluscs occupy a variety of substrates including rocky shores, coral reefs, mud flats, and sandy beaches and shell morphology reflects their habitat and mode of life (e.g., mobility, method of feeding, defence against predators). The north windward coast of west Moloka‘i, Hawaiian Islands, consists mostly of smooth basalt boulders, with sections of eolianite (limestone) shoreline. These contrasting littoral shores influence the composition of the rocky shore intertidal mollusc populations, but both support large numbers of the ubiquitous Hawaiian limpet (Cellana exarata, C. sandwicensis, C. talcosa). We investigated if limpet shell shape (i.e., form and dimensions) varied between shoreline types by multi-year sampling of modern mollusc populations on basalt and eolianite coastlines. Using multiple discriminant analysis, modern shell shape was compared to archaeological limpet assemblages from three late prehistoric habitation sites adjacent to basalt and eolianite shorelines. Our results demonstrate that archaeological shell shape correlates to modern limpet shell shape from nearby basalt or eolianite coastlines suggesting low forager mobility during late prehistory.

Draft genomes of Perkinsus olseni and Perkinsus chesapeaki reveal polyploidy and regional differences in heterozygosity

Perkinsus spp. parasites have significant impact on aquaculture and wild mollusc populations. We sequenced the genomes of five monoclonal isolates of Perkinsus olseni and one Perkinsus chesapeaki from international sources. Sequence analysis revealed similar levels of repetitive sequence within species, a polyploid genome structure, and substantially higher heterozygosity in Oceanian-sourced isolates. We also identified tandem replication of the rRNA transcriptional unit, with high strain variation. Characterized gene content was broadly similar amongst all Perkinsus spp. but P. olseni Oceanian isolates contained an elevated number of genes compared to other P. olseni isolates and cox3 could not be identified in any Perkinsus spp. sequence. Phylogenetics and average nucleotide identity scans were consistent with all P. olseni isolates being within one species. These are the first genome sequences generated for both P. olseni and P. chesapeaki and will allow future advances in diagnostic design and population genomics of these important aquatic parasites.

Mud Clam’s (Anodentia edentula) Density and Distribution Pattern in Kalangan Mangrove Forest Ecosystem

The excessive use of Mud Shells (Anodentia edentula) as a staple food by the people of Kalangan Village, Central Tapanuli Regency caused the decline of the shellfish population. This is marked by the scattering of mud shells at research sites and often people conduct shell-searching activities at low tide. Therefore, a scientific study is needed to know the density and distribution patterns as the basis for the possibility of cultivation activities, management of mud shell germplasm (Anodentia edentula), and mangrove ecosystems in kalangan area in the future optimally, sustainably, and sustainably. The study was conducted in September 2020, using the 1x1m2 transect method purposive sampling at low tide. The results showed that the density of Mud Shells (Anodentia edentula) amounted to 150 ind/m2 in Station I, 0 ind/m2 in Station II with distribution pattern clustering, and 43 ind/m2 in Station III with distribution pattern random. With the evidence that there is a research station that contain zero mud clam and with unsimilarity in distribution pattern that should be clustering in every research station, therefore it can be concluded that the abudance of mud clam in the ecosystem already decline both quantifically and qualitativelyand requires conservation and cultivation action to ensure its existence in the future.

New data on morphology of <i>Unio abyssinicus</i>(Bivalvia: Unionidae) from Ethiopia

A relict and endemic species of the Blue Nile drainage basin, the mussel Unio abyssinicus, is under the threat of extinction, with the continuing decline in area, while data on the localities and biology of the mollusk are scarce. A new find of the mollusk population in the Duko river, located in the Oromiya Region of south-western Ethiopia, gives additional information about distribution of this species. The morphology of siphons of U. abyssinicus has been studied for the first time, the features of siphonal papillas are compared with those of the other mussel species. The data on the beak sculpture as well as the morphology of the hinge teeth have been clarified. Some new data on biology of the mussel are provided.

A Global Overview of Restorative Shellfish Mariculture

Farming of marine organisms (mariculture) represented 36% of global aquaculture, with molluscs representing 58.8% in live weight. Mollusc populations in some locations are, however, threatened by degradation of the ecosystems and/or over-fishing. This threat is increasingly being addressed through Restorative Shellfish Mariculture (RSM), as opposed to mariculture alone. There is no general consensus in the literature on what can and cannot be considered RSM. While maximization of benefits other than provisioning services is often considered a prerequisite, in other cases the maximization of fisheries yields is prioritised. Here we define RSM as the farming of marine shellfish, implying some form of intervention during the species life cycle, in order to address negative socio-ecological issues arising from the unsustainable use of marine ecosystems, independent of the final ownership regime of the resource. Strategies for developing RSM were reviewed and classified along a gradient from the most conservation-oriented (e.g. habitat restoration, reintroduction of locally extinct endangered species), to the most fisheries-oriented (including some forms of fisheries enhancement), and classified as Non-hatchery Dependent or Hatchery Dependent strategies. We reviewed the targeted species and strategies implemented across 584 individual projects developed in the last decades in North America, Europe, Asia, Oceania and South America. We found that some 48 species, including 34 bivalves and 15 gastropods were targets of RSM in 34 countries. US projects accounted for ca. three quarters of the total (N=438), with Philippines, Japan and Australia also being home to a large number. More than 90% of the projects involved five species, namely the eastern oyster (Crassostrea virginica, N=379), the giant clam (Tridacna gigas, N=65), the Olympia oyster (Ostrea lurida, N=25), the bay scallop (Argopecten irradians, N=25) and the hard clam (Mercenaria mercenaria,N=15). Of the RSM projects, 51% used Non-hatchery dependent methods, mostly habitat restoration providing substrata for settlement, whilesome 49% involved hatcheries. Some three percent of the projects combined both methods. This review provides an overview of the breadth and depth and aims of RSM globally, develops a broad definition of the activity, and proposes a structure for classifying RSM.

Why are they here? Local variables explain the distribution of invasive mollusk species in neotropical hydropower reservoirs

Reservoirs are a common sight in most rivers systems in the world and a frequent problem related to them is the introduction of non-native invasive mollusk species. We aimed to determine which local variables (near-site land use, physical habitat structure, water quality) were most strongly associated with the local distribution of invasive non-native mollusks in neotropical hydropower reservoirs. We used data from three neotropical reservoirs to calculate which local variables most influenced the presence or absence of the three non-native invasive mollusk species (i.e., Corbicula fluminea, Limnoperna fortunei and Melanoides tuberculata) found in them. We found that the presence of both C. fluminea and L. fortunei were positively correlated with local anthropogenic disturbances, likely because it was associated with more frequent human access to the water body and increased introductions of larval mollusks. Conversely, M. tuberculata was negatively correlated with total phosphorus concentration, which is linked to agriculture and urbanization in the reservoir catchments. Additionally, we found that C. fluminea and M. tuberculata presence was positively related to each other, implying a biological facilitation process between these two species. Our findings suggest that anthropogenic disturbances are important for the local distribution of invasive non-native mollusks in neotropical reservoirs and can be used by environmental managers and decision-makers to help manage invasive mollusk populations in neotropical hydropower reservoirs.

Comparative analysis of population characteristics of two viviparid species (Mollusca: Viviparidae) in water bodies of Ukraine

The study presents new information on the population characteristics of two river snail species, Viviparus viviparus (Linnaeus, 1758) and V. contectus (Millet, 1813), in the water bodies of Ukraine in 2007–2018. The analyzed features include data of the species distribution, numbers and biomass, age and sex ratio population structure, fertility, growth and production. Ecological factors (flow rate, temperature, the concentration of oxygen, pH, organic matter) that limit the distribution of two Viviparidae species in varying biotopes were identified. Recently, the frequency of occurrence, and the number and biomass of populations V. viviparus and V. contectus have been observed to decrease. The probable reason is the declining environmental conditions induced by the climatic changes and anthropogenic pressure. In waters of Ukraine, maximum age is five years for V. viviparus mollusks and six years for V. contectus. High anthropogenic pressure disturbs age structure of viviparid species in water bodies, causing higher ratios of middle-age (two to four year old) snails and decreased or absent young (up to one year old) and oldest (five−six year old) mollusks. The major factor here is high level of saprobity of water bodies, which is accompanied by formation of hypoxic zones and causes significant death rates in the youngest and oldest mollusks. Those are the most vulnerable age classes in mollusk populations.

Vodní měkkýši Zoologické zahrady hl. m. Prahy [Aquatic molluscs of Prague Zoo

The Prague zoological garden is one of the most famous zoos in Europe. It covers an area of 58 ha on the right bank of the Vltava River (a tributary of the Elbe River). Aquatic molluscs of this zoo were studied mostly in 2019. Altogether 17 species were found at various outdoor habitats such as an old oxbow of the Vltava River, artificial pools, wetlands and small watercourses. Poor communities consisting of 1–4 species were found in most sites while 5–6 species were recorded at only four sites. Bithynia tentaculata, Gyraulus albus, and the non-native Physa acuta and Gyraulus parvus belonged among the most often recorded species. More diverse communities and numerous populations of aquatic molluscs were found mainly at sites overgrown with vegetation. On the contrary, it was difficult to find molluscs in habitats poor in vegetation with predatory pressure (e. g. water birds) and eutrophication.

A four decades multiparametric investigation in a Mediterranean dynamic ecosystem: Mollusc assemblages answer to the environmental changes

The ecosystem changes of “Marinello coastal lakes” - a brackish dynamic area located on the Tyrrhenian coast of Sicily (Italy) - have been examined through the analysis of the adaptive response of mollusc assemblages to the geomorphological and environmental changes. In particular, we have contextually analysed the changes in salinity, mud and organic carbon together with mollusc abundance and distribution, comparing the data sets from several multidisciplinary investigations that we performed in about forty years.Our studies have evidenced that the space-time dynamics of the geomorphological, environmental and trophic parameters have led the progression of Marinello ecosystem, favoring the onset of transient windows of connectivity (TWCs) between different habitats. TWCs, by supporting continuous re-arrangements of mollusc populations, have contributed to increase the functional and ecological complexity of the system. Salinity in particular has proven to be the most affecting factor on the diversification of mollusc assemblages, explaining 63% and 44% of variation for brackish and marine species respectively. In addition, the distribution of both detritus and suspension feeders has been mostly affected by salinity.The interannual analysis of the mollusc assemblages has shown in the whole system a generalised increase in the number of species, likewise, also the species richness recorded in each basin generally increased with the time. Metapopulations in the Marinello ecosystem have shown to be related to significant modifications in the habitat patches, in turn connected to the anthropogenic interventions or to the geomorphological progression of the entire physiographic system.Significant relationships among biotic and abiotic parameters have highlighted important implications on the ecosystem functioning, suggesting their possible application in the improvement of investigation tools for the transitional environments.

Integrated Modeling to Evaluate Climate Change Impacts on Coupled Social-Ecological Systems in Alaska

The Alaska CLimate Integrated Modeling (ACLIM) project represents a comprehensive, multi-year, interdisciplinary effort to characterize and project climate-driven changes to the Eastern Bering Sea ecosystem, from physics to fishing communities. Results from the ACLIM project are being used to understand how different regional fisheries management approaches can help promote adaptation to climate-driven changes to sustain fish and shellfish populations and to inform managers and fishery dependent communities of the risks associated with different future climate scenarios. The project relies on iterative communications and outreach with managers and fishery dependent communities that has informed the selection of fishing scenarios. This iterative approach ensures that the research team focuses on policy relevant scenarios that explore realistic adaptation options for managers and communities. Within each iterative cycle, the interdisciplinary research team continues to improve: methods for downscaling climate models, climate-enhanced biological models, socio-economic modeling, and management strategy evaluation within a common analytical framework. The evolving nature of the ACLIM framework ensures improved understanding of system responses and feedbacks are considered within the projections and that the fishing scenarios continue to reflect the management objectives of the regional fisheries management bodies. The multi-model approach used for projection of biological responses facilitates the quantification the relative contributions of climate forcing scenario, fishing scenario, parameter, and structural uncertainty with and between models. Ensemble means and variance within and between models informs risk assessments under different future scenarios. The first phase of projections of climate conditions to the end of 21st century are complete, and projections of catch for core species under baseline (status quo) fishing conditions and two alternative fishing scenarios. The ACLIM modeling framework serves as a guide for multidisciplinary integrated climate impact and adaptation decision making in other large marine ecosystems.

Carbon Mineralization Associated with Aquaculture of the Northern Quahog Mercenaria mercenaria

Molluscs mineralize carbon as calcium carbonate in shells within a protein matrix that is a small portion of the total shell mass. In parts of Florida, the northern quahog Mercenaria mercenaria is cultured in mesh bags in shallow coastal marine habitats. These habitats were selected by the State of Florida for their pre-existing lack of large molluscan populations, so most of the shell material harvested by aquaculture operations would not otherwise exist. The carbonate content of shell material was quantified by coulometry, and shell production was estimated per harvested clam, and per unit area per year. The majority of the shell material harvested (about 91%) was M. mercenaria, and the remainder came from other species of molluscs that grew in or on the mesh bags. Of the non-Mercenaria shell material, most (8.5% of total percentage) came from oysters (Crassostrea virginica and Ostrea stentina), and the rest from at least 37 other species of molluscs and other shelled taxa. Each harvested market-size clam represented approximately 2.93 g of mineralized carbon, including shell material that was not part of the marketed clams. Clam leases in full production produced about 1.0 × 103 g of mineralized carbon per square meter per year, including nonclam shell material, and the Florida northern quahog industry produced about 534 metric tons of mineralized carbon in 2008. This mineralization resulted in an estimated atmospheric efflux of 374 tons of metabolic-independent carbon in the form of carbon dioxide, from the Florida northern quahog industry in 2008.

An example of multi-habitat restoration: Conceptual assessment of benefits from merging shellfish-reef and boulder-reef restorations

Multi-habitat restoration should be considered for conservation of habitat-types that are ecologically-related and regularly co-occur. Multi-habitat restoration has been used to a limited extent for marine habitats including oysters, mangroves and seagrass. Recent increases in research and understanding of shellfish-reefs and boulder/cobble-reefs means they should likewise be considered for integrated restoration. Importantly, boulders have recently been used as the foundation for several large-scale oyster-reef restorations. These would benefit from improved recognition that multiple distinct habitat-types are involved each associated with distinct knowledge pools. These habitat-types mostly have similar restoration objectives, they often co-occur pre-disturbance, and they share varied taxa. These linkages mean that opportunities may be missed if restorations are only considered separately in contexts where an integrated approach is feasible; restoration of one habitat may benefit from concurrent restoration of the other and the sum of benefits from integration may outweigh the sum from restorations done separately. Here, I discuss concepts concerning five potential synergies: 1) boulders provide natural hard-substrata that initiates shellfish recruitment, 2) boulders produce beneficial hydrological heterogeneity, increasing recruitment of some shellfish species, 3) shellfish generate self-sustaining supplies of novel hard-substrata habitat used by boulder/cobble species thus expanding the original restoration site footprint, 4) large shellfish populations strengthen valuable ecological functions in boulder habitats, and 5) boulders and shells together increase overall diversity of available hard-substrata types, and thus of associated specialist species. Not only restoration outcomes, but also objectives and planning can be improved by integrating knowledge from both habitat-types to encompass these five synergies.

AGE PECULIARITIES AND SEASONAL DYNAMICS OF HAMETOGENESIS IN POPULATIONS OF ESPERIANA ESPERI (GASTROPODA, PECTINIBRANCHIA, MELANOPSIDAE) OF UKRAINE

Article are presents the results of features of gametogenesis and its seasonal dynamics in Esperiana esperi (Ferussac, 1823). In Ukraine, these rheophilic mollusks are common in the coastal stretches of large rivers that form part of the hydroelectric network of its Right Bank. The populations of these animals belong to the category of polycyclic, that is, consisting of individuals of several generations, with a maximum life expectancy of about two years. The study found that gametogenesis in E. esperi is a synchronous process that occurs under the same environmental conditions during spermatogenesis and ovogenesis. Examination of the histological sections of the sex glands of these mollusks revealed that it is a stage process that involves five stages of maturity of the gonads: the beginning of gametogenesis, active gametogenesis, pre-spawning, spawning and post-spawning stages, which are characteristic for certain seasons of the year. According to the analysis, there is a direct correlation between the stages of gametogenesis and the temperature conditions of the environment. Accordingly, gametogenesis in southern mollusk populations has been found to occur earlier than northern populations. The number of mature oocytes determines the time of occurrence of fertility peaks, which occur mainly in July for northern populations and for June for the same southern populations of molluscs, indicating a different temperature optimum. According to the latter, the highest levels of stability are characterized by southern populations of the species studied. Generalized information on the number of oocytes also characterizes the duration of periods of E. esperi life cycles from the northern and southern territories of the habitat in Ukraine under current climatic conditions. These molluscs are found to have the longest reproduction period, which lasts about a year. Reproduction takes only 3.5 months, and post-reproduction takes 1-3 (as an extreme rarity - up to 7 months in northern populations).

Commentary on: Abundance and distribution of microplastics within surface sediments of a key shellfish growing region of Canada.

This formal comment is in response to “Abundance and distribution of microplastics within surface sediments of a key shellfish growing region of Canada” written by Kazmiruk and colleagues in 2018. This article presents microplastics concentrations in sediment, primarily microbeads, within Baynes Sound, British Columbia, which are some of the highest that have been reported anywhere in the world. The authors cite the local shellfish industry as the likely source of this high degree of contamination and present the industry as a substantial risk to the environment. However, the authors do not sufficiently justify the efficacy of their methodology, and there are several flaws which call into question the legitimacy of their findings. In this commentary, we address the microplastic abundances reported by the authors, and methodological concerns. Furthermore, we provide additional data to elucidate some of this study’s more contentious findings. Specifically, we seek to clarify the visual identification of microbeads and microfibres, and the microplastic concentration within shellfish populations, water, and sediment, within the Baynes Sound shellfish growing region.

Fitting Competing Models of the Population Abundance Distribution: Land Snails from Nikopol Manganese Ore Basin Technosols

Abstract This paper examines the temporal dynamics of terrestrial mollusks of the Nikopol manganese ore basin technosols. The research was carried out at the Research Centre of the Dnipro Agrarian and Economic University in Pokrov (Ukraine). Sampling was carried out in 2012–2014 on four variants of artificial soil: formed on red-brown clays, on loess-like loams, on gray-green clays, and on humus-rich layer. The distribution of the number of individuals in a mollusk population was described by broken stick, Motomura, log-normal, Zipf, and Zipf-Mandelbrot models. It was shown that the series of models that best describe mollusk abundance distribution is specific for a particular species and technosols type and generally is invariant over time.

Sustainable harvesting of Conomurex luhuanus and Rochia nilotica by Indigenous Australians on the Great Barrier Reef over the past 2000 years

Offshore island colonisation and use around the northern Australian coastline in the mid-to-late Holocene is associated with expanding Aboriginal and Torres Strait Islander populations and intensifying land-use activities. However, few explicit tests of the long-term effects of shellfish forager decision-making and associated impacts on intertidal ecosystems in these newly colonised island environments have been undertaken. We report morphometric analyses on two key reef flat Great Barrier Reef shellfish species, strawberry conch Conomurex luhuanus (n = 360) and top shell Rochia nilotica (n = 45), from two late Holocene archaeological shell midden assemblages on Lizard Island, northeast Queensland. Human foraging pressure was assessed through reconstructions of population age structure across time, highlighting the importance of determining size-at-age habitat preferences and species behaviour patterns when assessing long-term anthropogenic impacts on shellfish populations. Results show no evidence for resource depression across the late Holocene which is broadly in keeping with previous findings at other locales on the Great Barrier Reef, but contrary to expectations of resource intensification models. We conclude that the rich and abundant resources of reef flat environments were resilient to relatively low intensity and likely episodic Indigenous foraging. This sustainability contrasts with the scale and impacts of intensive industrialised harvesting in the historic period.

Tributyltin: A Bottom–Up Regulator of the Crangon crangon Population?

The restrictions and the concerted action of the global ban on the use and presence of tributyltin (TBT) in marine applications to protect ecosystems in the marine environment in 2008 was mainly based on the economic impact on shellfish industries and the dramatic extinction of local mollusc populations in the past. In contrast to the vast datasets on effects on molluscs, the knowledge on impacts on species from other taxa remained in the uncertain until almost two decades ago. The assumption on a long-term TBT-mediated pernicious metabolic bottom-up regulation of the crustacean Crangon crangon population was provoked by the outcome of an EU-project ‘Sources, Consumer Exposure and Risks of Organotin Contamination in Seafood’. This study reported high TBT body burdens in C. crangon in 2003, at the start of the transition period to the global ban. Experimental research on the TBT impact in C. crangon focused on agonistic interference with natural ecdysteroid hormones at the metabolic pathways regulating growth and reproduction and the biogeochemical distribution of the chemical. In this paper, metabolic, topical and population-relevant biological endpoints in C. crangon and other crustaceans are evaluated in relation to the temporal and spatial trends on TBT’s occurrence and distribution in the field during and after the introduction of the tributyltin restrictions and endocrine-related incidents. Arguments are forwarded to relate the German Bight incident on growth and reproduction failure in the C. crangon population, despite the lack of direct evidence, to the pernicious impact of tributyltin in 1990/91 and previous years. The extreme occurrence of TBT in C. crangon from other parts of the southern North Sea and evidence on the high body burdens as dose metrics of exposure also feeds the suspicion on detrimental impacts in those areas. This paper further demonstrates the complexity of distinguishing and assessing the individual roles of unrelated stressors on a population in an integrated evaluation at the ecosystem level.