Linking environmental warming to the fitness of the invasive clam Corbicula fluminea

Climate warming is discussed as a factor that can favour the success of invasive species. In the present study, we analysed potential fitness gains of moderate warming (3 °C above field temperature) on the invasive clam Corbicula fluminea during summer and winter. The experiments were conducted under seminatural conditions in a bypass-system of a large river (Rhine, Germany). We showed that warming in late summer results in a significant decrease in the clams' growth rates (body mass and shell length increase) and an increase in mortality rate. The addition of planktonic food dampens the negative effect of warming on the growth rates. This suggests that the reason for the negative growth effect of temperature increase in late summer is a negative energetic balance caused by an enhanced metabolic rate at limited food levels. Warming during early summer revealed contrasting effects with respect of body mass (no warming effect) and shell length (increased shell growth with warming). This differential control of both parameters further enhances the loss of the relative (size-specific) body mass with warming. In contrast, warming in winter had a consistently positive effect on the clams' growth rate as demonstrated in two independent experiments. Furthermore, the reproduction success (as measured by the average number of larvae per clam) during the main breeding period (April) was strongly enhanced by experimental warming during winter, i.e. by eight times during the relatively cold winter 2005/2006 and by 2.6 times during the relatively warm winter 2007/2008. This strong, positive effect of moderate winter warming on the clams' fitness is probably one reason for the recent invasion success of C. fluminea in the northern hemisphere. However, warm summer events might counteract the positive winter warming effect, which could balance out the fitness gains.     

The impact of an introduced bivalve (Corbicula fluminea) on the benthos of a sandy stream

1. The effect of an exotic, burrowing bivalve ( Corbicula fluminea ) on the benthic fauna of a sandy-bottomed stream was assessed by field and laboratory experiments. Corbicula differs from other freshwater, non-native bivalves in that it both filter- and pedal-feeds and thus has the potential to influence the streambed community in different ways.
2. In the field, cages were used to vary the abundance of Corbicula in the streambed. Increasing abundance of Corbicula was negatively associated with the abundance of benthic bacteria and flagellates but had no apparent effect on other protists or meiofauna.
3. In the laboratory, we compared the effect of Corbicula on the benthic community when the bivalves were able both to filter- and pedal-feed with that when they were able only to filter-feed. Bivalves restricted to filter-feeding were placed in sediment lacking benthic fauna and organic matter, then the benthos in nearby natural sediment was compared with the community present when Corbicula was able to move freely through the sediment and both to filter- and pedal-feed. Corbicula able to pedal-feed were again associated with a decreased abundance of benthic flagellates and bacteria, as well as diatoms.     

区域气候变化对纳帕海湖滨植物生理生化特性的影响

高原湿地是我国重要的生态屏障,关乎流域生态安全。随着气候变暖和极端气候事件频发,探讨高原湿地植物对气候变化的生理生化响应及温度胁迫带来的伤害,对维系高原湿地生态系统的稳定,应对全球气候变化具有重要意义。以高原地区典型湿地纳帕海为研究对象,将适应了纳帕海湿地气候条件的4种优势植物连同生长基质组成的植物-土壤单元,移至不同区域气候条件的拉市海湿地和昆明滇池流域,分析气候变化影响下,4种湿地植物原位异地后的丙二醛(MDA)、游离脯氨酸(Pro)、可溶性糖(SS)、过氧化物酶(POD)含量等反映植物受到逆境胁迫的生理生化指标变化。研究结果表明,湿地植物虽是隐域植物,但气候变化对其生长产生显著影响,不同湿地植物对气候变化的适应性不同,水葱(Scirpus tabernaemontani)和茭草(Zizania caduciflora)等广布种能够很好地适应气候变暖,两者生物量均随温度上升而增加,在拉市海的增长率分别高达196%和190%,在昆明分别增至487%和408%,MDA、Pro、POD含量则随温度上升而下降,在拉市海的最高降幅分别为16%和24%、27%和12%、14%和58%,在昆明的最高降幅分别为31%和24%、52%和25%、48%和73%,气候的暖化更有利于其生长。刘氏荸荠(Heleocharis liouana)虽为广布种,尽管气候变化对其产生了胁迫,但能通过调节自身的代谢物质来抵御这种变化,反映了广布种对气候变化较强的适应性。小黑三棱(Sparganium simplex),对气候变化较为敏感,随温度的升高其生物量在拉市海的增长率达17%,而在温度更高的昆明则减少了20%,呈现先升高后下降的趋势,同时体内各相关抗逆指标也呈现先下降后上升的趋势,MDA降至0.001387μmol/g,后迅速增至0.002739μmol/g、Pro降至13.386891μg/g,后增至18.172878μg/g,温度升高到一定程度对其产生了不利影响。对于这样一种生态幅较窄的物种,随着气候条件的改变,其生存将面临极大的挑战,显示了高原湿地在全球变暖大背景下的脆弱性,以及高原湿地生态系统维系存在的潜在危机。     

Impact of Dreissena fouling on the physiological condition of native and invasive bivalves: interspecific and temporal variations

The impact of Dreissena fouling on unionids has hardly been studied in Europe, despite the fact that in some ecosystems (e.g. Lake Balaton, Hungary) infestations of several hundreds to a thousand individuals per unionid have been observed. At present, the zebra mussel Dreissena polymorpha is a dominant species in Lake Balaton and in the last decade three other invasive bivalves were introduced, potentially increasing the pressure on native unionid survival. We examined whether the fouling of dreissenids (zebra and quagga (D. rostriformis bugensis) mussels) has a negative impact on native (Anodonta anatina, Unio pictorum and U. tumidus) and invasive (Corbicula fluminea and Sinanodonta woodiana) bivalves and whether there are any interspecific and temporal variations in fouling intensity and physiological condition measured by standard condition index and glycogen content. A significant negative impact was detected on native unionids only in July and September (no impact was detected in May), when the fouling rate was high. For invasive species, a significant negative impact was detected on S. woodiana with a high level of dressenid infestation; whereas no significant impact was detected on C. fluminea. Overall, this study confirms that Dreissena may threaten unionid species including the invasive S. woodiana, although high interspecific and temporal variations were observed. This situation should be taken into account in future ecological and conservational assessments because species respond differently to Dreissena fouling and effects seem to be more pronounced in late summer/early autumn. In addition, this study provides the first evidence that the invasive C. fluminea appear to be less vulnerable to dressenid fouling.     

Effects of invasive clam (Corbicula fluminea) die‐offs on the structure and functioning of freshwater ecosystems

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Nanostructure and crystallography of aberrant columnar vaterite in Corbicula fluminea (Mollusca)

Both the crystallographic and nanostructural organisation of aberrant columnar vaterite occurring in Corbicula fluminea were characterised in detail for the first time using electron microscopic and X-ray powder diffraction techniques. At the millimetre scale, only a confinement of the otherwise randomly oriented c-axis to the growth surface is observed. Domains of 100 or more individual vaterite columns with common c-axis orientation exist within this disordered material. Each column behaves as a single crystal on the scale of EBSD measurements, but is internally composed of smaller irregularly shaped and slightly misaligned crystalline units (0.3-1.3μm in dimension). These are in turn partitioned by porous boundaries into rounded nanodomains, up to 600nm in size. The geometry of the nanodomains and their respective boundaries might suggest formation by the accretion of vesicles. In addition to crystallographic textures, this observation indicates formation under significant biological control with wider implications for possible causes of the condition.     

Growth of Corbicula fluminea (bivalvia) fed artificial and algal diets

Laboratory experiments were conducted to assess the growth of Corbicula fluminea Müller (1774) fed mixed diets of the green alga Ankistrodesmus and five artificial foods (nine-grain cereal, rice flour, rye bran, denatured brewer's yeast and Ralston Purina trout chow). Clams lost weight after 30 days on each artificial diet; however, weight losses were significantly less than those of control clams which were not fed (p < 0.05). In contrast, clam growth was positive in each treatment which included Ankistrodesmus. There was no significant difference in the tissue growth of clams fed on an Ankistrodesmus monoculture and Ankistrodesmus supplemented with each artificial diet (p > 0.2). Therefore, we conclude that all of the artificial diets evaluated were of nutritional value. However, the alga Ankistrodesmus appears to be a superior food item. In subsequent experiments, clams were fed on diets consisting of various combinations of six genera of green algae (Pedinomonas, Ankistrodesmus, Chlamydomonas, Chlorella, Scenedesmus, and Selenastrum). All trialgal combinations of Chlamydomonas, Chlorella, Scenedesmus, and Ankistrodesmus and a dialgal culture of Chlamydomonas and Chlorella resulted in strong positive tissue growth. No other dialgal or monoalgal culture resulted in similar growth. Cultures of Selenastrum were found to be toxic, and their filtrate was determined to inhibit Corbicula filtration.     

Valve closure responses of the Asiatic clam Corbicula fluminea exposed to cadmium and zinc

The valve movement patterns of immobilized Asiatic clams (Corbicula fluminea) were monitored during exposure to constant concentrations of cadmium (0.0, 0.1, 0.2, 0.3, and 0.4 mg 1^–1) or zinc (0.0, 0.1, 0.3, 0.5, and 0.9 mg 1^–1) for 24 h following a 24-h acclimation period. Data indicate that the duration of response was concentration dependent and toxicity related. Durations of periods with valves parted declined as the concentration of heavy metal increased. Behavior was consistent for both mean time to first closure following the initial exposure and mean time per valve parting episode over a 24-h exposure period. Mean time per valve parting episode during the 24-h exposure period ranged from 600 minutes for control trials to 36 and 69 minutes for the highest concentrations of cadmium and zinc tested, respectively. There was no association between durations of periods with valves sealed and solutions of cadmium; however, lengthening durations of periods with valves sealed coincided with exposure of clams to progressively more concentrated zinc solutions. In addition, Asiatic clams demonstrated a greater rate of response (decline in the duration of periods with valves parted) to progressively more concentrated solutions of cadmium than to comparable increases in the concentrations of zinc solutions.     

Low dissolved oxygen levels reduce anti-predation behaviours of the freshwater clam Corbicula fluminea

1. When dissolved oxygen levels decline in aquatic systems, prey may be unable to maintain behaviours protecting them from predators. We examined how oxygen availability affected anti‐predator responses in the freshwater clam, Corbicula fluminea. 2. When attacked, bivalves protect their soft tissues by closing their protective valves. This reduces vulnerability to small predators, but ventilation and oxygen uptake are suspended. We found that after a simulated attack, clams under low oxygen conditions reopened their valves sooner than clams under high oxygen conditions, suggesting that hypoxia increases vulnerability to predation. 3. Bivalves may also evade predators through burial into the substratum. Deeper burial confers greater refuge from predators, but increases the costs of ventilation. In a second experiment, we studied how burial depth of C. fluminea is affected by oxygen availability. Additionally, we examined whether clams changed burial depth following a simulated attack by a small predator, and whether this response was affected by oxygen availability. Our results offered partial support for the hypothesis that burial depth is reduced under hypoxic conditions, but the simulated attack did not affect burial depth in any oxygen treatments.     

非生物因子对河蚬重金属富集量的影响

对影响长江口滨岸带河蚬体内重金属富集量的4个主要非生物因子依次进行分析。结果表明,较高温度有助于河蚬对Cu、Zn、Cr、Ni的吸收;盐度对河蚬的重金属累积量影响比较复杂,仅在秋季表现出一定相关性,春季盐度影响不大;河蚬体内Cu含量与沉积物粒径存在显著正相关,Zn与沉积物中有机质含量存在一定正相关,Pb与沉积物中有机质含量存在着负相关;河蚬体内重金属元素两两间的相关性明显,多种元素间的相互作用机理值得进一步探讨。     

Heat shock protein response to thermal stress in the Asiatic clam,Corbicula fluminea

A recent approach to evaluate environmenta induced damages has been damages has been suggested, based on the stress response. The approach involves the detection of stress protein induction in organisms to infer about environmental conditions in their surroundings. However, to be an indicator of adverse biological effects in the environment, the elevation of stress proteins should be compared to a response pattern for the experimental species. JuvenileCorbicula fluminea, collection from a control site, were submited to heat-shock stress in the laboratory to obtain the stress response pattern under normal and extreme conditions. Acclimated to 26°C, the specimens were submited to 29, 32, 35 and 38°C, for 96 h. After 1, 2, 4, 8, 24, 48, 72 and 96 h of exposure, clams were removed from each vial and prepared for stress protein analysis. Animals from the control site were frozen in liquid nitrogen at the time of collection, and prepared for stress protein analysis. Hsp60 and 70 were detected by immunoreactivity after separation on 12.5% polyacrylamide gels and transference to nitrocellulose by western blotting, to determine the stress protein concentrations. The result showed that hsp70 increased at 4h from the beginning of the experiment and progressed over the 96 h experimental period in animals exposed to 35°C. However hsp70 levels decreased between 4 h and 24 h for the clams stressed at their lethal temperature of 38°C. Immunoblotting with hsp60 showed similar reactivity. At 38°C there was an increase in the amount of hsp60 at 4h, reaching a maximum eight-fold level at 8h. By 96h, the amount decreased to levels lower than those observed at 4h. At 38°C the level of hsp60 began to decrease at 8 h and continue to decline to 24 h when the clams died. The data support the hypothesis of increasing concentrations of stress protein until the heat shock approaches the thermal limits for the species. The results of this research suggest the usefulness of using the stress response as a diagnostic in environmental toxicology. They confirm that the sps response may serve as a valid biomonitoring tool under chronic, sublethal exposures when it is still possible to prevent effects at organismal or higher organizational levels.     

Detection and phylogenetic analysis of norovirus in Corbicula fluminea in a freshwater river in Japan

To study the molecular epidemiology of noroviruses (NoVs) in bivalves residing in freshwater rivers, we detected, quantified and phylogenetically analyzed the NoV genome in purified concentrates obtained from the gills and digestive diverticula of Corbicula fluminea in a freshwater river in Gunma Prefecture, Japan. We detected the NoV genome in 35 of the 58 C. fluminea samples. Based on our phylogenetic analysis, the NoV genome detected in the samples was classified into 4 genotypes (GI/1, GI/2, GI/3 and GI/4) in genogroup I and 5 genotypes (GII/3, GII/4, GII/5, GII/8 and GII/12) in genogroup II. The phylogenetic tree showed wide genetic diversity among the genogroups. In addition, more than 10(4) copies of the NoV genome were detected in 2 of 35 samples. These results suggest that the freshwater bivalve C. fluminea is a reservoir for NoVs, similar to seawater bivalves such as oysters.     

Identifying potential drivers of distribution patterns of invasive Corbicula fluminea relative to native freshwater mussels (Unionidae) across spatial scales

This study aimed to identify the importance of ecological factors to distribution patterns of the invasive Clam (Corbicula fluminea) relative to native mussels (family: Unionidae) across seven rivers within the Mobile and Tennessee basins, Southeast United States. We quantitatively surveyed dense, diverse native mussel aggregations across 20 river reaches and estimated mussel density, biomass, and species richness along with density of invasive C. fluminea (hereafter Corbicula). We measured substrate particle size, velocity, and depth in quadrats where animals were collected. Additionally, we characterized reach scale environmental parameters including seston quantity and quality (% Carbon, % Nitrogen, % Phosphorous), water chemistry (ammonium [NH4+], soluble reactive phosphorous [SRP]), and watershed area and land cover. Using model selection, logistic regression, and multivariate analysis, we characterized habitat features and their association to invasive Corbicula within mussel beds. We found that Corbicula were more likely to occur and more abundant in quadrats with greater mussel biomass, larger substrate size, faster water velocity, and shallower water depth. At the reach scale, Corbicula densities increased where particle sizes were larger. Mussel richness, density, and biomass increased with watershed area. Water column NH4+ increased at reaches with more urban land cover. No land cover variables influenced Corbicula populations or mussel communities. The strong overlapping distribution of Corbicula and mussels support the hypothesis that Corbicula are not necessarily limited by habitat factors and may be passengers of change in rivers where mussels have declined due to habitat degradation. Whether Corbicula is facilitated by mussels or negatively interacts with mussels in these systems remains to be seen. Focused experiments that manipulate patch scale variables would improve our understanding of the role of species interactions (e.g., competition, predation, facilitation) or physical habitat factors in influencing spatial overlap between Corbicula and native mussels.     

Metallothionein responses in the Asiatic clam (Corbicula fluminea) after exposure to trivalent arsenic

The main objective of this work was to evaluate arsenic effects on metallothionein (MT) induction by exposing a freshwater Asiatic clam (Corbicula fluminea) to different concentrations of this metalloid. The presence of MT-like proteins was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis and compared with a standard rabbit MT. In addition, the polarographic response showed good correspondence between standard MT and MT-like curves from C. fluminea, allowing MT quantification. The results show that clams exposed to different concentrations of arsenic are able to induce significant levels of MTs. Although variability was found in MT induction, significant differences in MT levels were found after 28 days of exposure in all treatments in comparison with the controls, suggesting that exposure to arsenic induced MT-like proteins in C. fluminea.     

Effects of photoperiod on sodium flux in Corbicula fluminea (Mollusca:Bivalvia)

• 1.1. A significant diurnal rhythm of net sodium flux was demonstrated in the freshwater clam Corbicula fluminea entrained to either a 12L:12D or 24L photoperiod.
• 2.2. Highest net flux occurred during the dark hours on 12L: 12D. The overall mean net flux over 24 hr was not significantly different from a steady state condition.
• 3.3. Net flux values of clams on a 24L photoperiod were negative and significantly lower than the net flux on a 12L:12D photoperiod.
• 4.4. The 12L: 12D net sodium flux rhythm pattern is similar to rhythmic patterns of other physiological processes in another freshwater clam.

     

The effect of phytoplankton and suspended sediment on the growth of Corbicula fluminea (Bivalvia)

Juvenile Corbicula fluminea Müller (1774) were cultured at 15.3 °C in the laboratory on eight combinations of suspended sediment and phytoplankton. Sediment concentrations were 2.6, 25, 50, and 150 mg l^–1. Chlorophyll a levels were 15.6 and 62.5 µg l^–1. Clam tissue growth was found to be independent of silt concentration but increased at the higher chlorophyll level (p < 0.05). The growth experiment was repeated at 24 °C with chlorophyll a concentrations of 18.9 and 112.6 µg l^–1. Growth was again greater at the higher phytoplankton level (p < 0.05). These results demonstrate that Asiatic clam populations are food-limited most of the growing season in the Northern and Western portions of California's eutrophic Sacramento-San Joaquin Delta where chlorophyll a levels average less than the lower of these values. Comparisons of clam growth in the laboratory and estuary support the food limitation hypothesis as at the higher food concentration laboratory tissue growth was 2.3 and 3.8 times greater during the high and low temperature evaluations than in the estuary.     

Metallothionein responses in the Asiatic clam (Corbicula fluminea) after exposure to trivalent arsenic

The main objective of this work was to evaluate arsenic effects on metallothionein (MT) induction by exposing a freshwater Asiatic clam (Corbicula fluminea) to different concentrations of this metalloid. The presence of MT-like proteins was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis and compared with a standard rabbit MT. In addition, the polarographic response showed good correspondence between standard MT and MT-like curves from C. fluminea, allowing MT quantification. The results show that clams exposed to different concentrations of arsenic are able to induce significant levels of MTs. Although variability was found in MT induction, significant differences in MT levels were found after 28 days of exposure in all treatments in comparison with the controls, suggesting that exposure to arsenic induced MT-like proteins in C. fluminea.     

Activities of the three ammonia-forming enzymes in the tissues of the brackish-water bivalve Corbicula japonica

• 1.1. Activities of the three ammonia-forming enzymes, glutamate dehydrogenase, AMP deaminase and serine dehydrase (SerDH), were measured in tissues of gill, digestive diverticula, mantle and foot muscle of the brackish-water bivalve Corbicula japonica.
• 2.2. High levels of SerDH activity were detected in gill and digestive diverticula, while the activity levels of the other two enzymes were low.
• 3.3. The result suggests the significance of SerDH in amino acid degradation of this species.