The current situation and potential effects of climate change on the microbial load of marine bivalves of the Greek coastlines: an integrative review

Global warming affects the aquatic ecosystems, accelerating pathogenic microorganisms' and toxic microalgae's growth and spread in marine habitats, and in bivalve molluscs. New parasite invasions are directly linked to oceanic warming. Consumption of pathogen-infected molluscs impacts human health at different rates, depending, inter alia, on the bacteria taxa. It is therefore necessary to monitor microbiological and chemical contamination of food. Many global cases of poisoning from bivalve consumption can be traced back to Mediterranean regions. This article aims to examine the marine bivalve's infestation rate within the scope of climate change, as well as to evaluate the risk posed by climate change to bivalve welfare and public health. Biological and climatic data literature review was performed from international scientific sources, Greek authorities and State organizations. Focusing on Greek aquaculture and bivalve fisheries, high-risk index pathogenic parasites and microalgae were observed during summer months, particularly in Thermaikos Gulf. Considering the climate models that predict further temperature increases, it seems that marine organisms will be subjected in the long term to higher temperatures. Due to the positive linkage between temperature and microbial load, the marine areas most affected by this phenomenon are characterized as ‘high risk’ for consumer health.     

Studies of the life-history and energetics of marine and brackish-water nematodes

Summary Aspects of the demography of Monhystera disjuncta were investigated at different temperatures (in agnotobiotic cultures) and in different feeding conditions (monoxenic cultures with different bacterial strains, and different densities in the feeding suspension with one strain). Embryonic development time, minimum generation time, egg deposition rate and adult longevity depend on temperature, quality and quantity of food offered. Body mass at maturity is an allometric function of food density. It is shown that a previously inferred selectivity in food uptake is an artifact of culture conditions. pH buffering and addition of sterols permit culture of the species on a wide variety of bacterial strains. M. disjuncta is less well adapted to take advantage of high food density than are nematodes from polysaprobic environments. The animals channel surplus energy intake into a larger body mass, without being able to increase their rate of population growth accordingly.     

Applications à la conchyliculture des récentes acquisitions sur la biologie des mollusques bivalves

Today, mollusc farming represents the fourth part of the mundial aquaculture production. These results have been permitted by the improvement of farming techniques commercially important but also by advances in the biology of a species. Valuable reproductive studies have been carried out in s.a. hatcheries on triploids and tetraploids animals. Since the last decade, advances in the knowledge of metabolism and growth mechanisms has helped the improvement of the brood stock. Nevertheless, the mundial expansion of bivalve farming increases the outbreak of strong epizooties. Investigations allow a valuable knowledge on the scope of molluscan defence mechanisms against pathogen agents. The results are discussed in relation to a possible selection for bivalve farming.     

Bivalve aquaculture‐environment interactions in the context of climate change

Coastal embayments are at risk of impacts by climate change drivers such as ocean warming, sea level rise and alteration in precipitation regimes. The response of the ecosystem to these drivers is highly dependent on their magnitude of change, but also on physical characteristics such as bay morphology and river discharge, which play key roles in water residence time and hence estuarine functioning. These considerations are especially relevant for bivalve aquaculture sites, where the cultured biomass can alter ecosystem dynamics. The combination of climate change, physical and aquaculture drivers can result in synergistic/antagonistic and nonlinear processes. A spatially explicit model was constructed to explore effects of the physical environment (bay geomorphic type, freshwater inputs), climate change drivers (sea level, temperature, precipitation) and aquaculture (bivalve species, stock) on ecosystem functioning. A factorial design led to 336 scenarios (48 hydrodynamic × 7 management). Model outcomes suggest that the physical environment controls estuarine functioning given its influence on primary productivity (bottom‐up control dominated by riverine nutrients) and horizontal advection with the open ocean (dominated by bay geomorphic type). The intensity of bivalve aquaculture ultimately determines the bivalve–phytoplankton trophic interaction, which can range from a bottom‐up control triggered by ammonia excretion to a top‐down control via feeding. Results also suggest that temperature is the strongest climate change driver due to its influence on the metabolism of poikilothermic organisms (e.g. zooplankton and bivalves), which ultimately causes a concomitant increase of top‐down pressure on phytoplankton. Given the different thermal tolerance of cultured species, temperature is also critical to sort winners from losers, benefiting Crassostrea virginica over Mytilus edulis under the specific conditions tested in this numerical exercise. In general, it is predicted that bays with large rivers and high exchange with the open ocean will be more resilient under climate change when bivalve aquaculture is present.     

Presence and development of populations of the introduced brown alga Sargassum muticum in the southwest Netherlands

Of the three Brachionus species used in aquaculture, Brachionus rubens, B. calycilorus and B. plicatilis, the latter is most widely used in raising marine fish and shrimp larvae due to its tolerance to the marine environment. In freshwater aquaculture the use of B. rubens and B. calycilorus is limited, probably because inert food products are readily available as feed for freshwater larvae.The rotifer Brachionus plicatilis is used in large numbers as the first food organism in intensive cultures of marine fish and shrimp larvae. An adequate supply of these rotifers relies on mass cultures. The reproductive rate of rotifers in these cultures depends on food quality and quantity, salinity, temperature and pH of the medium. Removal of waste products from culture tanks leads to higher and more efficient production of rotifers over extended periods of time. Rotifers have to be enriched with polyunsaturated fatty acids, which are essential for proper development and survival of marine fish and shrimp larvae.The future use of preserved rotifers and their resting eggs may help to overcome unforeseen failures of live cultures and may lead to more efficient use of these organisms in raising freshwater and marine fish and shrimp larvae.     

Influence of seston quantity and quality on growth of tropical cladocerans.

The seston of the small, shallow, and tropical lake Monte Alegre was tested for quantity and quality for cladocerans by growth bioassays, which were carried out in spring (Daphnia gessneri and Moina micrura), summer (D. gessneri, M. micrura, Ceriodaphnia cornuta, and Simocephalus mixtus), and winter (D. gessneri and D. ambigua). Cohorts of newborns originating from ovigerous females collected in the lake or from laboratory cultures were submitted, at a room temperature of 23 degrees C to the following treatments: (1) the chlorophytes Ankistrodesmus falcatus and/or Scenedesmus spinosus; (2) lake seston; and (3) lake seston + chlorophytes. Growth rate, clutch size, and fecundity were evaluated. Seston alone was not the best food for promoting cladoceran growth. There were seasonal differences in food quantity and quality with spring and summer seston being better for growth than that of the winter. Adding chlorophytes to the seston increased clutch size and fecundity for most species in summer and winter, but not in spring. Energy limitation seems to be the most important factor influencing cladoceran growth in summer and especially in winter.     

Bivalve condition index as an indicator of aquaculture intensity: A meta-analysis

Shellfish aquaculture implies the placement of artificial structures in the coastal environment and the alteration of natural bivalve populations, which calls for the establishment of legislative regulatory frameworks based on an ecosystem approach. One of the challenges for policy makers is the need to monitor the effectiveness of management actions. In this study, a meta-analysis across different bays, covering a large spatial scale in Atlantic Canada, was performed to test the response of two potential indicators of aquaculture intensity: (1) the bivalve growth using both Dynamic Energy Budget (DEB) and Scope For Growth (SFG) approaches, and (2) the bivalve condition index (CI = (meat weight/shell weight) × 100). Our underlying premise was that overstocking of bivalves leads to increased competition for food resources, which might ultimately have a significant effect on bivalve growth performance and the CI. Bivalve growth performance for cohorts of Mytilus edulis and Crassostrea virginica were simulated by combining satellite remote sensing (temperature and chlorophyll) with individual based models using both DEB and SFG approaches. These models were calibrated for each cohort, by adjusting the half-saturation coefficient of the food ingestion function term (X_K), which is a common parameter related to feeding behavior in both approaches. A significant correlation between X_K and lease coverage (lease area/bay area, dimensionless) was found for M. edulis. However, because of unrealistic X_K values in some M. edulis cohorts and the lack of consistent simulations for C. virginica precluded using X_K as a reliable indicator of aquaculture intensity. By contrast, according to the observed results CI emerged as a good indicator of aquaculture intensity for both species. A General Additive Model (GAM) for C. virginica provided a regression that included the initial dry meat weight as a linear term and the lease area as a non-linear term, explaining a total deviance of 59.9% in describing final CI values. The GAM for M. edulis included only non-linear terms, lease coverage, and lease area, explaining a total deviance of 61.0%. Since the CI theoretically integrates the effects of changing trophic conditions over time, the good relationship between the CI and lease/bay characteristics provides a scientific framework for its use as a reliable ecological indicator of aquaculture intensity. From an applied perspective, this finding is of relevance because the CI is easy to measure and is widely available in government and industry datasets.     

四十里湾栉孔扇贝清滤率、摄食率和吸收效率的现场研究

运用生物沉积法在四十里湾不同海区对栉孔扇贝的生理生态学特征进行了研究。 1龄栉孔扇贝 (4 1 .1± 4.1 mm,软体干重 0 .48± 0 .1 0 g/ ind)清滤率变化范围为 0 .72～ 2 .5 4(平均 1 .2 7) L/ (ind· h)或 1 .65～ 5 .97(平均 2 .61 ) L/ (g· h)。清滤率受 TPM的变化影响不大 ,而摄食率却随 TPM的升高而升高。 2龄扇贝 (软体干重 1 .91± 0 .3 2 g/ ind)清滤率为2 .0 9～ 3 .99(平均 3 .1 0 ) L/ (ind· h)。栉孔扇贝吸收速率与 POM呈正相关关系 ,而与饵料质量 (POM/ TPM)无明显的相关性。1龄扇贝和 2龄扇贝吸收效率没有显著差别 ;扇贝对 POM的吸收效率与 TPM (或 POM)关系不大 ,却与饵料质量呈明显的正相关关系 ;扇贝对 POC、PON和 PP的吸收效率平均分别为 68.9%、64.0 %和 63 .6%。在沿岸养殖海域 ,栉孔扇贝通过大量的滤水摄食以及较高的吸收效率对生态系统的能量流动和物质循环产生影响。     

A review of the feedbacks between bivalve grazing and ecosystem processes

This paper gives an overview of interactions betweenbivalve grazing and ecosystem processes, that mayaffect the carrying capacity of ecosystems for bivalvesuspension feeders. These interactions consist of anumber of positive and negative feedbacks.Bivalve grazing can result in local food depletion,which may negatively influence bivalve growth. On alarger scale, it may induce a top-down control ofphytoplankton biomasss, and structural shifts inphytoplankton composition. In the case of harmfulalgal blooms, phytoplankton may negatively affectbivalve grazing rates.The processing of large amounts of particulate mattermay change nutrient cycling on the scale of estuaries,and can result in changes in the inorganic nutrientpool available for phytoplankton, through regenerationand reduced storage of nutrients in algal biomass.This can reduce nutrient limitation of thephytoplankton and stimulate algal growth rates.Observations from mesocosm studies suggest that apositive feedback from bivalve grazing onphytoplankton growth may also change the physiologicalstate of the algae and improve food quality. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sustainability performance indicators for suspended bivalve aquaculture activities

Investigations into interactions between suspended bivalve farms and the marine environment generally focus on effects to the seafloor beneath farms. This is appropriate in situations where the level of development will be determined by the ability of the growing environment to absorb waste products, such as in the case for finfish culture operations. By contrast, sea-based suspended bivalve culture development is more often controlled by the ability of the water-column environment to supply particulate food material. Therefore, there is a need to develop methodologies and frameworks for assessing the ‘scope for growth’ of bivalve culture, and the level of environmental interactions associated with particular development levels. The work presented here details a set of functional performance indicators that can be used to assess the level of interactions between the culture and the water-column growing environment, and also the farmed biomass with respect to carrying capacity milestones.     

The thermal regime of an intertidal mytilus californianus Conrad population on the Central Oregon Coast

Data describing the thermal environment of an intertidal population of Mytilus californianus Conrad were collected over a four-year period. A formula estimating tissue temperature during exposure to air was established and used to calculate the internal temperature of mussels each hour of the day in a mussel bed located at +3 ft above mean low low water level. The resulting thermal regime was then discussed in terms of average temperature, daily extremes, and periods of heating and cooling. From experiments using radioactive labelled Isochrysis it was found that periods of exposure lead to increased assimilation efficiency. The thermal regime was used to calculate scope for growth by incorporating both its acute and acclimatizing effects on oxygen consumption, filtration rate, and assimilation. Particulate food levels had a greater effect upon seasonal values for scope for growth than temperatures within the normal environmental range. An energy budget was established for animals at various heights in the intertidal to produce a quantitative picture of the decrease in scope for growth with height. An exposure period may lead to slight increases in energy available for growth during winter. Maximum temperature changes may induce spawning at advantageous times. The implications for reconstructing and predicting thermal regimes of intertidal animals are discussed.     

Are zooplankton food resources poor in the vegetated littoral zone of shallow lakes?

1. The distribution of zooplankton in shallow lakes is negatively related to macrophyte density. However, the abundance of their food along density gradients of macrophytes is unknown. A common but untested assumption is that food quantity and quality for pelagic zooplankton is poor in the littoral zone owing to the deleterious influence of macrophytes on phytoplankton. 2. We tested this assumption with a combination of a field survey and laboratory experiments. We collected seston samples from the littoral and pelagic zones of four shallow temperate lakes and related food quantity (phytoplankton biovolume) and quality to macrophyte abundance (per cent volume infested). Seston food quality was assessed in three ways: N/C and P/C ratios, polyunsaturated fatty acid content and phytoplankton community composition. In the laboratory, we measured the growth and reproduction of Daphnia pulicaria on diets consisting of seston from the littoral and pelagic zones in one lake. 3. In our four study lakes, food quantity was not significantly influenced by macrophyte abundance, and food quality was generally high. Laboratory experiments showed increased juvenile growth, but no significant change in D. pulicaria reproduction, when feeding on littoral resources compared to pelagic resources. 4. Our results suggest that there is no nutritional cost to pelagic zooplankton inhabiting the littoral zone. Therefore, it is likely that other factors (e.g. predation, abiotic factors) are involved in determining zooplankton habitat use.     

Abiotic factors controlling the establishment and abundance of the invasive golden mussel Limnoperna fortunei

Limnoperna fortunei (Bivalvia, Mytilidae), a freshwater bivalve native to Southern Asia, has been an invasive species in South America since 1991. It spread upstream in the La Plata basin reaching the Paraguay River in the vicinity of the Pantanal wetland, Brazil, around 1998. The role of abiotic factors in controlling establishment and abundance of this species is not well known, making projections of its risk of further spread difficult. This study evaluates the importance of abiotic factors to L. fortunei populations established in rivers of the Pantanal, focusing on larval and juvenile densities and taking advantage of a wide range of seasonal variability in water temperature, flow, dissolved oxygen, and suspended material. Temperature, river stage (influencing several water characteristics) and water velocity are the main variables related to the larval and juvenile densities. In the Pantanal, environmental variables vary over a broader range compared with other South American locations, subjecting L. fortunei to oxygen depletion, low calcium, low pH, and high water velocity and suspended solids, associated with low chlorophyll a concentrations. The combined effect of several of these conditions may explain the relatively low densities in some Pantanal sites. However, they probably will not prevent the persistence of populations in the Pantanal and the eventual establishment of viable populations in upriver systems connected to the Pantanal. These results are pertinent not only to this species but also to other aquatic invasive invertebrates whose expansion may be limited by thermal extremes, episodic oxygen depletion, and waters that are too dilute or acidic for optimal biocalcification.     

Threshold elemental ratios for carbon versus phosphorus limitation in Daphnia

1. The transition from carbon (C) to phosphorus (P) limited growth in Daphnia depends not only on the C : P ratio in seston, i.e. food quality, but also on food quantity. Carbon is commonly believed to be limiting at low food because of the energetic demands of basal metabolism. The critical C : P ratio in seston (otherwise known as the threshold elemental ratio, TER) above which P is limiting would then be high when food is scarce. 2. A new model that differentiates between the C : P requirements for growth and maintenance is presented that includes terms for both C and P in basal metabolism. At low food the calculated TERs for Daphnia of around 230 are only slightly higher than values of 200 or so at high intake. Seston C : P often exceeds 230, particularly in oligotrophic lakes where phytoplankton concentration is low and detritus dominates the diet, indicating the potential for limitation by P. 3. The analysis highlights the importance of P, as well as C, in maintenance metabolism and the overall metabolic budget, such that food quality is of importance even when intake is low. Further measurements of C and P metabolism at low food, in particular basal respiration and excretion rates, are needed in order to improve our understanding of the interacting roles of food quantity and quality in zooplankton nutrition.     

我国沿海四爿藻的室内培养

在水产养殖中,四爿藻是一种重要的饵料资源,从我国沿海(包括广东、浙江、山东等省)采集到的海洋单细胞绿藻四爿藻,用毛细管法挑取进行单种培养,然后在固体培养基中稀释划线分离得到无菌纯培养物,利用改良的Guillard &; Ryther(Guillard F)培养基、海洋Ⅲ号培养基和改良的海洋Ⅲ号培养基对四爿藻进行了实验室培养。结果发现,改良的海洋Ⅲ号培养基中四爿藻的生长速率最快,最适pH范围为7．0～8．0,加入维生素B12(10μg·L^-1),也可以适当增加四爿藻的生长速率。这种改良的海洋Ⅲ号培养基配制简单,适合于水产养殖中四爿藻的规模生产。     

Integrating the Concept of Resilience into an Ecosystem Approach to Bivalve Aquaculture Management

Bivalve aquaculture has become increasingly important for marine protein production and is an alternative to exploiting natural resources. Its further and sustainable development should follow an ecosystem approach, to maintain both biodiversity and ecosystem functioning. The identification of critical thresholds to development remains difficult. The present work aims at combining the calculation of the system’s ecological carrying capacity (ECC) with the ecosystem view of resilience for a bay system exposed to bivalve (scallop) aquaculture. Using a trophic food-web model, a stepwise further expansion of culture activities was simulated, and the impact on the system was evaluated twofold: First, a recently developed approach to estimating ECC was used, and second, a resilience indicator was calculated, which is based on the distribution of consumption flows within the trophic network (sensu Arreguín-Sanchez in Ecol Model 272: 27–276, 2014). Results suggest that a culture expansion beyond present-day scale would (a) cause a shift in community composition towards a system dominated by secondary consumers, (b) lead to the loss of system compartments, affecting ecosystem functioning, and (c) result in a decrease in resilience, emphasizing the need to regulate aquaculture activities. The applicability and potential of this presented method in the context of an ecosystem-based approach to aquaculture is discussed. This work aims at adding to the ongoing discussion on sustainable bivalve aquaculture and is expected to help guide aquaculture management.     

Biofouling in marine aquaculture: a review of recent research and developments

Biofouling in marine aquaculture is one of the main barriers to efficient and sustainable production. Owing to the growth of aquaculture globally, it is pertinent to update previous reviews to inform management and guide future research. Here, the authors highlight recent research and developments on the impacts, prevention and control of biofouling in shellfish, finfish and seaweed aquaculture, and the significant gaps that still exist in aquaculturalists’ capacity to manage it. Antifouling methods are being explored and developed; these are centred on harnessing naturally occurring antifouling properties, culturing fouling-resistant genotypes, and improving farming strategies by adopting more sensitive and informative monitoring and modelling capabilities together with novel cleaning equipment. While no simple, quick-fix solutions to biofouling management in existing aquaculture industry situations have been developed, the expectation is that effective methods are likely to evolve as aquaculture develops into emerging culture scenarios, which will undoubtedly influence the path for future solutions.     

Life in the fast lane: Temperature,density and host species impact survival and growth of the fish ectoparasite Argulus foliaceus

With expanding human populations, the food sector has faced constant pressure to sustainably expand and meet global production demands. In aquaculture this frequently manifests in an animal welfare crisis, with fish increasingly farmed under high production, high stress conditions. These intense environments can result in fish stocks having a high susceptibility to infection, with parasites and associated disease one of the main factors limiting industry growth. Prediction of infection dynamics is key to preventative treatment and mitigation. Considering the climatic and technology driven changes facing aquaculture, an understanding of how parasites react across a spectrum of conditions is required. Here we assessed the impact of temperature, infection density and host species on the life history traits of Argulus foliaceus, a common palearctic fish louse, representative of a parasite group problematic in freshwater aquaculture and fisheries worldwide. Temperature significantly affected development, growth and survival; parasites hatched and developed faster at higher temperatures, but also experienced shorter lifespans when maintained off the host. At high temperatures, these parasites will likely experience a short generation time as their life history traits are completed more rapidly. A. foliaceus additionally grew faster on natural hosts and at lower infection densities. Ultimately such results contribute to prediction of population dynamics, aiding development of effective control to improve animal welfare and reduce industry loss.     

Temperature and the effects of elemental food quality on Daphnia

1. We examined the responses of two species of Daphnia to changes in food phosphorus (P) content, with animals reared at three different water temperatures. Specifically, we measured mass‐specific growth rate (MSGR), body P content and respiration rate of Daphnia magna and Daphnia pulex acclimatised to 10, 17.5 and 25 °C and fed food carbon : phosphorus (C : P) ratios of either 150 or 500. 2. The responses of these three physiological variables to temperature–food quality interactions were species‐specific. There was a significant interactive effect of temperature and food quality on D. magna, as the greatest proportional effect of food quality on growth was observed at 10 °C and reductions in body P because of low food P content were relatively greater at 25 °C. These effects may reflect the temperature dependence of mechanisms that reduce elemental constraints associated with food quality in D. magna. By contrast, there were no interactive effects between food quality and temperature on MSGR, body P or mass‐specific respiration of D. pulex. 3. It thus appears that temperature can alter food quality effects on Daphnia but the nature of these alterations depends upon the daphniid species and its thermal adaptability. Significant temperature–food quality interactions will complicate efforts to understand zooplankton nutrition in nature and warrant future consideration.     

The Good,the Bad and the Plenty: Interactive Effects of Food Quality and Quantity on the Growth of Different Daphnia Species

Effects of food quality and quantity on consumers are neither independent nor interchangeable. Although consumer growth and reproduction show strong variation in relation to both food quality and quantity, the effects of food quality or food quantity have usually been studied in isolation. In two experiments, we studied the growth and reproduction in three filter-feeding freshwater zooplankton species, i.e. Daphnia galeata x hyalina, D. pulicaria and D. magna, on their algal food (Scenedesmus obliquus), varying in carbon to phosphorus (C∶P) ratios and quantities (concentrations). In the first experiment, we found a strong positive effect of the phosphorus content of food on growth of Daphnia, both in their early and late juvenile development. Variation in the relationship between the P-content of animals and their growth rate reflected interspecific differences in nutrient requirements. Although growth rates typically decreased as development neared maturation, this did not affect these species-specific couplings between growth rate and Daphnia P-content. In the second experiment, we examined the effects of food quality on Daphnia growth at different levels of food quantity. With the same decrease in P-content of food, species with higher estimated P-content at zero growth showed a larger increase in threshold food concentrations (i.e. food concentration sufficient to meet metabolic requirements but not growth). These results suggest that physiological processes such as maintenance and growth may in combination explain effects of food quality and quantity on consumers. Our study shows that differences in response to variation in food quality and quantity exist between species. As a consequence, species-specific effects of food quality on consumer growth will also determine how species deal with varying food levels, which has implications for resource-consumer interactions.