Shellfish Culture Research Articles

An ecosystem model for estimating potential shellfish culture production in sheltered coastal waters

A generic ecosystem model has been developed for estimating the potential production of shellfish culture and the effect of that cultivation on the pelagic ecosystem in sheltered coastal waters. The model describes the dynamics of a simple food web, nutrient cycling and growth of shellfish. The design of the model is closely tied to the temporal and spatial scales that are important in determining the sustainable production level for a particular embayment. The pelagic ecosystem, mussel energetics, population dynamics and hydrodynamics are coupled to allow fully dynamic predictions of the effect of the shellfish density. When applied to Beatrix Bay, an intensive culture embayment in the Pelorus Sound of New Zealand, the model successfully captured main features of the observed system behaviour. The hydrodynamic regime of the bay controls mussel growth and production. Although high fluxes of water into the bay suppress nutrient and carbon cycling signals in the system, the model simulations demonstrated that the mussel cultivation can have considerable effects on the ecosystem of the bay including food depletion and nutrient cycling. One of the most obvious effects is nutrient enhancement through mussel excretion at low cultivation densities, which promotes primary production particularly during the N-limitation period in summer. The sensitivity analysis identified uncertainty in some parameters and indicated areas for which experimental studies could lead to model improvement. The modelling exercise has established a primary predictive tool for managing mussel aquaculture of a coastal embayment to estimate relationships between the stock level and the growth rate of mussels, and the potentially achievable harvest and stocking density.

Linking ocean conditions to year class strength of the invasive European green crab, Carcinus maenas

Once a non-native species arrives and survives in an area, its long-term persistence depends on its recruitment success. If conditions are not favorable for recruitment it will ultimately disappear. The European green crab (Carcinus maenas) has a 6 year life span and has persisted at low densities in Oregon and Washington coastal estuaries for the past 12 years. We show here that after the arrival of the strong founding year class of 1998, significant self- recruitment to the Oregon and Washington popula- tions occurred only in 2003, 2005 and 2006. Warm winter water temperatures, high Pacific Decadal Oscillation and Multivariate ENSO (El Nino South- ern Oscillation) Indices in March, late spring transi- tions and weak southward shelf currents in March and April are all correlated with the these strong year classes. Cold winter water temperatures, low Pacific Decadal Oscillation Indices, early spring transitions and strong southward (and offshore) currents in March and April are linked to year class failure. Right now, green crabs are still too rare to exert a measurable effect on the native benthic community and on shellfish culture in Oregon and Washington. How- ever, if their numbers were to increase, we would be able to predict the arrival of strong year classes from ocean conditions and alert managers and shellfish growers of possible increases in predation pressure from this invader.

An experimental test of colonization ability in the potentially invasive Didemnum perlucidum (Tunicata, Ascidiacea)

Exotic species invasions are one of the greatest threats to marine systems and ascidians have many characteristics that favor transport, colonization and establishment into new regions. Didemnum perlucidum is a widespread species that has been introduced into tropical ports around the world. Here we examine the colonizing ability of D. perlucidum by experimental use of artificial plates in a shellfish culture. The experiment comprised paired plates for colonization (bare and occupied) in 16 monthly replicates. Recruitment and space occupation were compared between bare and occupied plates and an estimation of reproductive effort was based on the number of larvae produced in each of ten colonies collected on the culture structures. D. perlucidum reproduced continuously but greatest reproduction occurred between December 2006 and May 2007. While recruitment was somewhat greater (number of new colonies) on bare plates, this species can colonize already occupied substrates and, surprisingly, colony area was always similar between treatments. Thus, while fewer colonies formed on occupied plates, once formed, colonies grew at rates similar to those on clean plates. Thus, D. perlucidum colonizes substrates very efficiently, especially when unoccupied space is available.

Exploitation and restoration of bivalve shellfish resources: case studies presented at the Tenth International Conference on Shellfish Restoration

In this issue of Aquaculture International a selection of papers that were presented at the Tenth International Conference on Shellfish Restoration (ICSR) is published. The conference was held in November 2007 in Vlissingen, The Netherlands, with over 200 participants from 30 countries. The theme of the conference was broader than shellfish restoration alone: the focus was ‘‘innovation in the exploitation and management of shellfish resources.’’ During the conference, six invited speakers gave an overview on various topics within the field of shellfish research. In 80 oral and over 30 poster presentations, organized in 14 sessions, many aspects of shellfish exploitation and management were addressed for 4 days. The contributions in this issue cover topics related to the culture and exploitation of bivalve shellfish in various parts of the world as well as results of shellfish restoration projects both in the USA and in New Zealand. The possible threat by proliferation of the Pacific oysters is addressed for the Wadden Sea. The outcomes of the conference are summarized in a synthesis paper. The special issue addresses both aquaculture and ecological topics by case studies from a variety of sites, showing the close link between shellfish aquaculture and ecology. It shows that shellfish culture, shellfish restoration and nature conservation are related issues that need to be addressed in concert in order to achieve a sustainable exploitation. The cooperation with the ICSR organization in the USA and with Rick DeVoe and Dorothy Leonard in organizing the conference is gratefully acknowledged.

Synthesis of the 10th ICSR conference: innovation in the exploitation and management of shellfish resources

Sustainable exploitation and management of shellfish populations is an important issue for stakeholder groups such as shellfish industry, nature conservation NGO’s and governments. Shellfish culture depends in many cases on natural processes and it often occurs in protected coastal areas, that are also under high pressure by other human activities. Uncertainty in resource availability (recruitment, algal production and quality, space) puts pressure on the industry and asks for sustainable innovations in resource exploitation. For environmental protection, knowledge is required of impacts of shellfish exploitation and of successful methods for restoration and improvement of exploitation. Regulation and management of exploited shellfish resources, particularly in nature conservation areas, is a priority issue for governmental institutions as conflicts of interest are manifest. Knowledge is required of technological and management innovations to contribute to solutions and create new opportunities. These issues have been addressed during the conference in a series of parallel sessions. Session chairs (names in brackets) compiled a comprehensive review of actual research issues that were presented during the sessions. The presentations are summarized in this conference synthesis. For the topic on recruitment (Luca van Duren and Karsten Reise) the primary statement is that the combination of invasive species and climate change launched a revolutionary turnover in coastal shellfish communities. New species profit from changes in climate conditions while existing species suffer from it. Major research topics should focus on the various types of feedback under field conditions: positive when adults provide habitat or substrate for (gregarious) settlement, negative in terms of adult filtration of larvae. More knowledge is needed on secondary migration and settlement, dispersal potential of larvae and loss through flushing. There is a need for practical knowledge to improve spat collection and survival, in order to achieve sustainable exploitation and reduce benthic seed fishery.

Fast detection of Vibrio species potentially pathogenic for mollusc

Vibrio tasmaniensis, Vibrio splendidus and Vibrio neptunius species were distributed worldwide and associated with aquaculture and have been reported as the cause of diseases in aquatic organisms. Polyphasic analyses for bacterial identification are not feasible for routine diagnostic because of the time involved. The aim of this study is to design three PCR primer sets that can assist with fast detection of these species. They were designed from the 16S ribosomal RNA gene, and PCR conditions were found. Each PCR test successfully identified all the tested strains of each target species. The combined specificity of V. tasmaniensis and V. splendidus primer sets offered the best coverage (86%) in terms of separating target organisms from other related species. The primer set of V. tasmaniensis showed a lower sensitivity limit (500fg of DNA) than the V. splendidus set (1pg) and both sets gave positive amplification using homogenized tissues from inoculated clams, with 102 and 104cfu/g of clam, respectively. The primer set of V. neptunius was highly specific, showing only cross-reaction with V. parahaemolyticus species from 44 tested species. Its sensitivity limit was 100pg of DNA. A small number of biochemical tests were proposed concurrently with the PCR to differentiate the cross-reacting bacteria. The time of detection of the three tested species was reduced and the further affected animals can be diagnosed in a rapid fraction of time. The detection of virulent strains of V. tasmaniensis pointed to the risk of mollusc culture outbreaks.

Survey of mussel (Mytilus)species at Scottish shellfish farms

Mytilus trossulus and its hybrids with the native species Mytilus edulis and also Mytilus galloprovincialis have been recently detected in both farmed and natural populations of mussels in Scotland, adding complexity to the known M. edulis×M. galloprovincialis hybrid zone in Europe. Mytilus trossulus was first found in Scotland at aquaculture sites, where it was associated with significant losses in production and reductions in profitability. Mytilus trossulus and its hybrids have been identified at higher frequencies in farm stock than in natural intertidal populations, raising concerns about the potential wider impact of M. trossulus genotypes at mussel aquaculture sites in Scotland. The present study clarifies the composition of Mytilus species in cultivation at Scottish mussel aquaculture farms, by screening samples from 41 mussel aquaculture sites using a high-throughput real-time PCR methodology. Mytilus edulis alleles were detected at all sites. Mytilus galloprovincialis alleles were detected from samples collected at 39 sites, and M. trossulus alleles were found at five sites. Overall, M. trossulus genotypes were restricted in their geographical distribution. It is suggested that, in order to support the sustainability of the Scottish shellfish cultivation industry, the economic impact arising from the presence of M. trossulus could be limited through good management practice.

OYSTER FARMING AND EXTERNALITIES: THE EXPERIENCE OF THE BAY OF BOURGNEUF

The history of the French shellfish industry is marked by a series of overfishing crises occurring in most of the open-access shellfish beds. When the concession system was introduced (1852), it was designed to cope with congestion and overfishing issues more than with the development of shellfish culture. After closing the production cycle in the late 19th century, the oyster industry kept suffering major crises such as massive disease outbreaks. Their occurrence can be analyzed in terms of overexploitation resulting from environmental externalities. We will show that this can create a backward-bending supply curve for oysters, using the Bay of Bourgneuf as a case study. In this bay, 400 firms, mostly family-sized, are being conceded 1,000 ha and sell 10,000 tons of Crassostrea gigas oysters a year. The paper presents a typology of farmers based on a survey that shows that farmer behavior can be aggregated into three main groups.

Evaluating the economic potential of horizontally integrated land-based marine aquaculture

Coastal aquaculture development is frequently associated with negative environmental impacts, competition for resources and conflict. Consequently, a new paradigm of ecologically-sound, socially responsible and economically viable aquaculture development based on systems-thinking, resource use efficiency and joint analysis with stakeholders is needed. Horizontal integration, combining aquaculture production systems to optimise resource use efficiency constitutes a promising approach in this regard. Research shows that an array of horizontally integrated systems are technically viable, however, few studies have combined this with consideration of the managerial, financial and economic demands. A bioeconomic modelling approach was employed here to assess the broader implications of adopting horizontally integrated land-based marine aquaculture in temperate and warm water settings. The temperate system, integrating fish, microalgae and shellfish culture and a polishing lagoon was developed on the Atlantic coast of France. Modelling outcomes predicted that when all costs were considered this approach failed to generate a positive Internal Rate of Return (IRR) over ten years. Subsequent scenarios showed a worthwhile return (ten-year IRR 19.4%) was generated when land and labour opportunity costs were omitted and a 20% premium on products included. The warm water system developed near Eilat, Israel combined sea urchins, shrimp and seaweed culture with a constructed wetland. Assuming baseline production of one million sea urchins annually from year three onwards, modelling outcomes showed a reasonable ten-year IRR of 18%. Reducing sea urchin mortality from 15% to 9% annually resulted in an IRR of 29.4%, while assuming that Salicornia spp. production would reach 33 kg m−2 y−1 in the wetland resulted in an IRR of 133.4%. Findings suggest that bioeconomic modelling can contribute to the optimisation of horizontally integrated aquaculture systems, helping elucidate promising scenarios and identify key constraints and priorities for targeted research and development. Bioeconomic modelling of other horizontal integration strategies, such as shrimp culture with shellfish, macroalgae and mangrove wetlands could elucidate economically viable approaches to much needed ecologically-sound and socially responsible practices. However, modelling should be supplemented by market analysis, including assessment of consumer attitudes, comprehensive risk assessment, ethical review, environmental impact assessment and joint assessment with stakeholders. Moreover, an enabling institutional framework is a prerequisite to more widespread adoption of horizontal integration; policy initiatives and regulatory tools focused on internalising environmental costs of aquaculture development will be critical.

Seasonal dynamics of trophic relationships among co-occurring suspension-feeders in two shellfish culture dominated ecosystems

The temporal dynamics of carbon and nitrogen isotope values of co-occurring suspension-feeders in two shellfish culture areas (Normandy, France) were investigated over two years to evaluate the inter-specific trophic partitioning and relative contributions of organic matter sources to benthic suspension-feeders' diet. Oysters ( Crassostrea gigas), mussels ( Mytilus edulis), cockles ( Cerastoderma edule), slipper limpets ( Crepidula fornicata), and sand-mason worms ( Lanice conchilega) were sampled in an estuarine environment (Baie des Veys, east Cotentin, Normandy), while oysters, mussels, slipper limpets, and honeycomb worms ( Sabellaria alveolata) were sampled in an open-marine environment (Lingreville-sur-mer, west Cotentin, Normandy). Whatever the sampling period, the bivalves, C. gigas and M. edulis, exhibited the lowest values of δ 13C and δ 15N compared with the other species. Feeding relationships among suspension-feeders in both C. gigas culture areas exhibited temporal variations due to the marine/estuarine influence and seasonal changes in food supply. In the open-marine ecosystem, the contribution of phytoplankton remained the most important for all species except S. alveolata, while in the estuarine ecosystem, microphytobenthos and/or macroalgae detritus contributed a larger extent to the organisms' diets. During phytoplankton bloom periods (e.g. May and July) suspension-feeders, except for S. alveolata, relied strongly on phytoplankton; however, the majority of suspension-feeders exhibited different opportunistic behaviour in winter when phytoplankton biomass might be a limiting factor. We hypothesized that differences in particle capture and selection by the suspension-feeders influenced their isotopic values. Feeding ecology of suspension-feeders partly explained why competition was limited and why ecosystems can often support unexpectedly large numbers of suspension-feeders. We also showed that understanding ecosystem characteristics of the organic matter sources is of primary importance to determine the extent to which members of the suspension-feeding guild potentially compete for food.

Impact of an open-sea suspended mussel culture on macrobenthic community (Western Adriatic Sea)

The potential impact of a suspended mussel farm on the coastal macrobenthic communities of the Western Adriatic Sea was seasonally evaluated through a multi-control sampling strategy over 1 year. Both univariate biological indices and multivariate analysis indicated that the variations of benthic macrofauna were mainly due to seasonality rather than location of the sampling sites in respect to the farm, and that the main species contributors were common to most sites and seasons. Most of these species are known as indicators of organic enrichment and/or pioneer species in recolonization of defaunated bottoms and commonly occur in the macrobenthic populations inhabiting the seabed of the North-Central Adriatic Sea between 12 and 15 m depth. Only the different abundances of filter- and deposit-feeders gave some evidence of a limited, spatial influence on the culture in the surroundings. The external sites showed a significant difference compared to the reference sites (ANOSIM: R = 0.395, P = 0.5). The overall results suggest that open-sea mussel culture has minimal detrimental effects on the zoobenthic communities of the Western Adriatic Sea that are usually in an immature stage due to subsequent environmental and anthropogenic disturbances. Although one-year study might not be sufficient to evaluate the effects of mussel culture, the results of this work represent a useful tool for the monitoring of the potential environmental impact of mussel farms to ensure the sustainable development of shellfish culture in the Italian shallow coastal waters.

American (Urosalpinx cinerea) and Japanese oyster drill (Ocinebrellus inornatus) (Gastropoda: Muricidae) flourish near shellfish culture plots in The Netherlands

Two non-native muricid gastropods are known from The Netherlands since 2007, i.e. the American oyster drill Urosalpinx cinerea and the Japanese oyster drill Ocinebrellus inornatus. Both species reproduce and slowly increase their area of distribution. Eight vacant shells of another non-native muricid, Hexaplex trunculus, have been collected in 2007, 2008 and March 2009. The latter species from southern Europe has recently been observed along the western coast of Europe in areas of shellfish culture. Vacant shells of Haustellum brandaris and Ocenebra erinacea, two more non-native muricids, have been collected as well.

Analysis of coastal and offshore aquaculture: Application of the FARM model to multiple systems and shellfish species

The Farm Aquaculture Resource Management (FARM) model has been applied to several shellfish species and aquaculture types. The performance of the FARM model, developed to simulate potential harvest, key financial data, and water quality impacts at the farm-scale, was tested in five systems in the European Union: Loch Creran, Scotland (Pacific oyster), Pertuis Breton, France (blue mussel), Bay of Piran, Slovenia (Mediterranean mussel), Chioggia, Italy (Mediterranean mussel) and Ria Formosa, Portugal (Manila clam). These systems range from open coasts to estuaries, and are used for shellfish aquaculture by means of different cultivation techniques (e.g. oyster bottom culture in Loch Creran and mussel longlines and poles in Pertuis Breton). The drivers for the FARM model were supplied by measured data, outputs of system-scale models or a combination of both. The results (given in total fresh weight) generally show good agreement with reported annual production (shown in brackets) at each farm: simulated production of 134 tons of Pacific oyster in Loch Creran (150 tons, − 10%), 2691 tons of blue mussel in Pertuis Breton (2304 tons, + 17%), 314 tons of Mediterranean mussel in the Bay of Piran (200 tons, + 57%), 545 tons of Mediterranean mussel in Chioggia (660 tons, − 17%) and 119 tons of Manila clam in Ria Formosa (104 tons, + 15%). The nitrogen mass balance for each farm was also determined with the FARM model. The net removal of nitrogen (N) by the farms was estimated to correspond to 1206 population equivalents per year (PEQ y − 1 ) in Loch Creran, 93503 PEQ y − 1 in Pertuis Breton, 9196 PEQ y − 1 in the Bay of Piran, 97916 PEQ y − 1 in Chioggia and 8613 PEQ y − 1 in Ria Formosa. The aggregate income due to both the shellfish sale and substitution value of land-based fertilizer reduction or nutrient treatment was estimated to be about 700 k€ y − 1 in Loch Creran, 30,706 k€ y − 1 in Pertuis Breton, 3000 k€ y − 1 in the Bay of Piran, 30,000 k€ y − 1 in Chioggia, and 5000 k€ y − 1 in Ria Formosa. Outputs of FARM may be used to analyse the farm production potential and profit maximization according to seeding densities and/or spatial distribution. Results of a marginal analysis for all the study sites were determined. As an example, profit maximization in Loch Creran was obtained with 97 tons of seed, resulting in a total production of 440 tons (profit of 2100 k€ for a culture period of about 2 years). FARM additionally integrates the well-known ASSETS model, for assessment of farm-related eutrophication impacts. The assessment results for the five study sites show that water quality is either maintained or improved in all farms under standard conditions of culture practice. FARM results may be used by farmers to analyse farm production potential and by managers for environmental assessment of farm-related water quality impacts, whether positive or negative. It is a useful tool for all stakeholders for the valuation of nitrogen credits, which may be traded as part of an integrated catchment management plan. The FARM results were scaled up to determine a net value of 11–17 billion € y − 1 of ecosystem goods and services, provided by shellfish culture towards reducing eutrophication in the coastal waters of the European Union. These numbers highlight the role that extractive organic aquaculture plays in integrated coastal zone and nutrient emissions management.

First record of the purple dye murex Bolinus brandaris (Gastropoda: Muricidae) and a revised list of non native molluscs from Galician waters (Spain, NE Atlantic)

The purple dye murex Bolinus brandaris (Linnaeus, 1758) has been reported for the first time from O Grove inlet (Galicia, NW Spain) in 2007. The presence of the shell mounds shows that this Mediterranean gastropod is commonly recorded in O Grove inlet together with another exotic muricid: Hexaplex trunculus. To the extent of our knowledge, this is the northernmost record of this species on the NE Atlantic coast. This species is the newest entry into a list of 23 aquatic and benthic exotic molluscs species from Galician waters. Most of them are introduced marine species, which arrived accidentally, or not, in the Galician region as a consequence of ship transport, shellfish culture and trade.

Shrimp and Mollusc Culture at the Bandon Bay in Thailand: A Situation Analysis

Shrimp and Mollusc Culture at the Bandon Bay in Thailand: A Situation Analysis

Shellfish culture in Chile

The present situation and future projections regarding shellfish culture in Chile are analysed. Production has increased exponentially, mainly of the 'Chilean mussel' Mytilus chilensis (Hupe) and the 'northern scallop' Argopecten purpuratus (Lamarck). At present, seven species are cultured, two of which were introduced. The total invertebrate production corresponding to cultures has increased from 1.6% to 38% over the last 15 years. The effects of the following factors on present and future levels of shellfish culture in Chile are discussed: disease, fouling, borers, red tide and environmental variations caused by the cultures themselves. Potential culture of approximately 70 commercially endemic species not only constitutes an economic option, but also favours their conservation.

Cellular Defense Mechanisms in Bivalve Molluscs

Many bivalve species are cultured widely around the world due to their commercial importance. As a result of the increases in areas and production associated with intensive culture, mass mortalities of bivalves caused by a wide variety of agents have become a serious problem. Various infectious diseases represented by protozoan and bacterial diseases have been threatening shellfish culture industries, and hence, many investigations have been made on the defense mechanisms, as well as diseases, in bivalves. The molluscan defense mechanism is comprised of the only innate immunity, which is also dependent on cellular components such as hemocytes possessing phagocytic and bactericidal activities and on humoral defense molecules such as lectin and lysozyme. In this review, we summarize cellular defense mechanisms in bivalve molluscs focusing on hemocytes: 1) morphology and classification, 2) functional profiles (phagocytosis, encapsulation, wound repair), 3) reactive oxygen species, 4) effects of natural and anthropogenic environmental factors, and 5) stress and signaling pathways.

Primary production enhancement by artificial upwelling in a western Norwegian fjord

To enhance primary production rate for shellfish cultivation in fjords, a large-scale artificial upwelling experiment was carried out in a western Norwegian fjord during the summers of 2004 and 2005. Pumping 2 m3 s–1 brackish surface water to a depth of 30 m created an artificial upwelling of nutrient-rich deeper water. The entrainment of deeper water into the buoyant brackish plume resulted in a transport of about 450 kg d–1 nitrate, 760 kg d–1 silicate and 75 kg d–1 phosphate to an intrusion depth of 8 to 10 m. The artificial upwelling approximately tripled mean chlorophyll a (chl a) concentration and related primary production rate during the summer within an influence area of 10 km2 near the head of the fjord. The size of the area of influence and the relative increase of the algae biomass within it depend on both the water exchange and the photosynthetic effectiveness. The relatively high silicate content of the deeper water stimulated diatom growth inside the area influenced by the artificial upwelling. A higher stable level of phytoplankton biomass, dominated by nontoxic species, would probably increase the carrying capacity of seston-feeding shellfish and could form the basis of more predictable mussel cultivation in fjords.

The Metal Content of Bivalve Molluscs of a Coastal Lagoon of NW Mexico

The lagoonal system Altata-Ensenada del Pabellón supports important traditional fisheries and mollusc cultures and receives urban and agricultural effluents. The annual mean Cd contents of the oyster and mussel Crassostrea gigas and Mytella strigata of the inner mangrove swamps were higher than that of the clam Megapitaria squalida, which lives in areas under marine influence. Crassostrea corteziensis had the highest Cu and Zn contents, showing that it is a strong accumulator of both metals and especially of Zn, and there were no significant differences in the Pb content of the three species.

The American oyster drill, Urosalpinx cinerea (Say, 1822), introduced to The Netherlands – increased risks after ban on TBT?

A few specimens and egg capsules of the American oyster drill, Urosalpinx cinerea, have been found in the Oosterschelde, an area of shellfish culture in The Netherlands. Probably U. cinerea was introduced with imported shellfish from south-east England. It is expected that the oyster drill will establish itself firmly in The Netherlands. The ban on anti-fouling paints containing tributyltin has increased the risk of