Responses of growth to elevation fail to explain vertical zonation of suspension-feeding bivalves on a tidal flat

Summary Five species of suspension-feeding bivalves were transplanted to each of two elevations on a tidal flat at Shark Bay, Western Australia, at six replicate locations spaced at 1-km intervals along the shore. Four species exhibited greatly reduced growth at the higher elevation, while the fifth species did not respond to elevation. The magnitude of the % reductions in growth with increased elevation was 2–3 times the % reduction in average daily submergence, confirming a previous suggestion that differences in feeding time alone are insufficient to explain completely the reduced growth of suspension-feeding bivalves at higher tidal elevatios. All four species that responded showed the same pattern of higher growth lower on the shore, even though transect sampling showed that two were normally abundant only high on the shore while the other tow were naturally restricted to elevations low on the shore. Consequently, knowledge of how individual growth within species varies with tidal elevation fails to explain observed zonation patterns with elevation in this guild of suspension-feeding bivalves. The paradoxical distribution pattern of those two species that were rare at the lower tidal elevations, where they actually grew more rapidly, implies that some biological agent(s) of mortality not physiological stress set(s) their lower distributional limit on the shore. Biological rather than physical factors commonly, although not universally, set lower distributional limits of invertebrates in rocky intertidal zones, but this study provides the first experimental data to explore this concept in marine soft sediments.     

Review of methods to probe single cell metabolism and bioenergetics

Single cell investigations have enabled unexpected discoveries, such as the existence of biological noise and phenotypic switching in infection, metabolism and treatment. Herein, we review methods that enable such single cell investigations specific to metabolism and bioenergetics. Firstly, we discuss how to isolate and immobilize individuals from a cell suspension, including both permanent and reversible approaches. We also highlight specific advances in microbiology for its implications in metabolic engineering. Methods for probing single cell physiology and metabolism are subsequently reviewed. The primary focus therein is on dynamic and high-content profiling strategies based on label-free and fluorescence microspectroscopy and microscopy. Non-dynamic approaches, such as mass spectrometry and nuclear magnetic resonance, are also briefly discussed.     

Age-related difference in bioenergetics of lung and heart mitochondria from rats exposed to ozone

Bioenergetics of isolated lung and heart mitochondria from adult and aged rats were examined in the presence of glutamate (NAD-linked substrate) or succinate + rotenone (FAD-linked substrate) following ozone exposure (3.0 ppm, 8 hr). In controls, several differences were observed between adults and aged in both organ preparations. Following exposure, all bioenergetic parameters were decreased significantly in lung preparations from both adult and aged rats. In heart mitochondria, the respiration rates in state 3 and in uncoupled state, and the ADP/O ratio were decreased significantly in both exposed age groups. The respiratory control ratio (RCR) was decreased significantly only in the aged exposed rats. These results suggest that acute exposure to high levels of ozone alters energy production in both lung and heart mitochondria of adult and aged rats.     

A field study of the relationship between pre-planting density of Globodera pallida and the growth and yield of two potato cultivars of differing tolerance

Non-resistant but tolerant cv. Cara and non-resistant but relatively intolerant cv. Pentland Dell were grown in split plots encompassing a range of population densities of potato cyst nematode, Globodera pallida. Light interception and its efficiency of conversion were estimated by regular ground cover measurements and plant harvests. It was concluded that increasing levels of infestation with G. pallida only slightly decreased the efficiency of utilisation of intercepted radiation. Heavy infestation of G. pallida initially decreased the top growth and light interception of both cultivars by similar proportions, but in later harvests, this adverse effect markedly decreased for Cara whereas it slightly increased for Pentland Dell. This difference was due to the heavily infested Cara eventually achieving and maintaining 100% ground cover whereas the equivalent Pentland Dell never exceeded 75% ground cover. Consequently, final tuber yields were decreased much more for Pentland Dell than for Cara though the decreases in tuber yield were less than those for top growth. The importance of nematode effects on top growth, and hence on light interception, with regard to both yield losses and tolerance differences, were clearly demonstrated. Both linear and logarithmic models were used to describe the relationship between the initial population density of G. pallida and yield, and the implications of differences in tolerance on the parameters in the logarithmic model are discussed.     

Indicators of short-term growth in bivalves: Detecting environmental change across ecological scales

Marine benthic communities function within the constraints of changing environmental conditions. To better understand the dynamics of this relationship, increased knowledge of physiological mechanisms that link environmental conditions to ecological responses is imperative. Here we develop a synthesis demonstrating the potential to link biochemical/physiological and population/community level responses based on the effects of increased sedimentation, hypoxia, food availability, and habitat characteristics on bivalve physiology using two soft-sediment, suspension-feeding species, Austrovenus stutchburyi and Paphies australis. Nucleic acid ratios (RNA:DNA, RNA:protein or total RNA content) have been successfully used as indirect measures of short-term growth in a range of marine organisms. Bivalve nucleic acid ratios were analysed over several temporal and spatial scales in a combination of laboratory experiments, field experiments, transplants and surveys, and only by synthesising results from several different studies were clear patterns in bivalve RNA dynamics revealed. The magnitude of response in RNA content (RNA) varied seasonally, along environmental gradients, and with bivalve species and size class. The major factor affecting RNA was enhanced food availability, which appeared to have the potential to mask any negative effects of stressors. Over the short-term (10-14 days), elevated suspended sediment concentrations or single deposition of terrigenous clay did not affect RNA, but over the longer term (months), transplantation of bivalves to turbid sites and repeated deposition of clay had a slight negative effect on RNA. In the laboratory, hypoxia did not affect the fast increase in RNA in response to added food or the slow decrease in RNA in response to starvation. In addition, a species-specific baseline RNA content was indicated, possibly representing the basal metabolism of a species. Thus, RNA was more sensitive to factors facilitating growth than to factors inhibiting growth, indicating that RNA could be a good indicator of factors related to energy acquisition, while not being as sensitive to stressors. By assessing the variability in response across time and space scales, and considering the context and time scale of both the stressor and the response, organism-level measures may be used as part of an integrated approach in impact assessment and ecological experiments.     

The multi-xenobiotic resistance phenotype as a tool to biomonitor the environment

Organisms use a variety of cellular mechanisms to avoid the effects of toxins. These strategies include de-toxification of putative toxins, sequestration of the toxins or the utilization of transport mechanisms to actually prevent the entry and accumulation of toxins in the cells. These toxin avoidance mechanisms, which presumably evolved in response to natural toxins, can also be used to counter the effects of anthropogenic compounds introduced into the environment by the activities of our modern society. In this article we discuss (1) the use of transport mechanism strategies to protect against toxins and (2) the possible use of these mechanisms as biomarkers indicative of exposure to man-made toxins. We will first review the characteristics of these transport mechanisms, including their biology, genetics and molecular properties and then discuss their use as biomarkers.     

The multi-xenobiotic resistance phenotype as a tool to biomonitor the environment

Organisms use a variety of cellular mechanisms to avoid the effects of toxins. These strategies include de-toxification of putative toxins, sequestration of the toxins or the utilization of transport mechanisms to actually prevent the entry and accumulation of toxins in the cells. These toxin avoidance mechanisms, which presumably evolved in response to natural toxins, can also be used to counter the effects of anthropogenic compounds introduced into the environment by the activities of our modern society. In this article we discuss (1) the use of transport mechanism strategies to protect against toxins and (2) the possible use of these mechanisms as biomarkers indicative of exposure to man-made toxins. We will first review the characteristics of these transport mechanisms, including their biology, genetics and molecular properties and then discuss their use as biomarkers.     

Larval growth and development of cultured Pacific bonito

A method is described for rearing the offspring of wild-captured Pacific bonito. Six basic stages of post-embryonic development were determined based on ontogenetic changes in morphology and behaviour. Each stage corresponded with a different food source preference, related to the development of new swimming and predatory behaviours. A controlled environment is required to study the processes underlying development of those behaviours adeptly performed by bonito and other scombrids, including high-efficiency swimming and visually guided predation on other advanced species.     

Investigation on the presence of domoic acid in Greek shellfish

In the framework of the national monitoring program for marine biotoxins in bivalve molluscs for 2002 and 2003, a total of 862 samples were examined to investigate the presence of domoic acid (DA). Samples mainly consisted of mussels (Mytilus galloprovincialis) and venus clams (Venus verucosa) from various Greek harvesting areas. In 2002, 83% of all samples examined contained less that 1 μg DA/g, while in 2003 this percentage was 95%. In both years, DA was only detected in springtime without any sample exceeding the regulatory level. In 2002, the highest value was 14.0 μg/g in mussels, while in 2003 these were 4.2 μg/g in mussels and 5.6 μg/g in venus clams. This is the first report regarding the presence of ASP toxins in Greek shellfish.     

Biofouling leads to reduced shell growth and flesh weight in the cultured mussel Mytilus galloprovincialis

Competitive interactions between cultured mussels and fouling organisms may result in growth and weight reductions in mussels, and compromised aquaculture productivity. Mussel ropes were inoculated with Ciona intestinalis, Ectopleura crocea or Styela clava, and growth parameters of fouled and unfouled Mytilus galloprovincialis were compared after two?months. Small mussels (≈50?mm) fouled by C. intestinalis and E. crocea were 4.0 and 3.2% shorter in shell length and had 21 and 13% reduced flesh weight, respectively, compared to the controls. Large mussels (≈68?mm) fouled by S. clava, C. intestinalis and E. crocea were 4.4, 3.9 and 2.1% shorter than control mussels, respectively, but flesh weights were not significantly reduced. A series of competitive feeding experiments indicated that S. clava and C. intestinalis did not reduce mussels’ food consumption, but that E. crocea, through interference competition, did. Fouling by these species at the densities used here reduced mussel growth and flesh weight, likely resulting in economic losses for the industry, and requires consideration when developing biofouling mitigation strategies.     

Oxidative stress in Perna perna and other bivalves as indicators of environmental stress in the Brazilian marine environment: Antioxidants, lipid peroxidation and DNA damage

Oxidative stress can take place in marine bivalves under a series of environmental adverse conditions. The study of different systems related to oxidative stress in these organisms can give important information about their physiological status and also about environmental health. Bivalves have been proposed as good sentinel organisms in pollution monitoring studies through the analysis of biochemical biomarkers, and most of the biomarkers analyzed are those related to oxidative stress. However, it is very important to know how other environmental factors not associated to the presence of pollutants might affect these parameters. We have studied a series of mechanisms related to oxidative stress in mussels which inhabit the Brazilian coast, especially in Perna perna species, subjected to different stress conditions, such as the exposure to different contaminants in the laboratory and in the field, the exposure of mussels to air and re-submersion, simulating the tidal oscillations, and in mussels collected at different seasons. Both oxidative damage levels and antioxidant defense systems were strongly affected by the different environmental stress. This review summarizes the data obtained in some studies carried out in bivalves from the Brazilian coast.     

The intracellular pH of the thermophilic bacterium Thermoanaerobacter wiegelii during growth and production of fermentation acids

The thermophilic glycolytic anaerobe Thermoanaerobacter wiegelii grows over the pH range 5.1–7.7, and no growth is observed below pH 5.0 or above 7.7. When T. wiegelii was grown in pH-uncontrolled batch culture, glucose was fermented to ethanol, acetate, and lactate. Small amounts of lactic acid were produced once the external pH reached 6.0, and a fructose-1,6-diphosphate (FDP) activated lactate dehydrogenase (LDH) was detected in cell-free crude extracts. Maximal activation of LDH by FDP was observed at pH 6.2. As the pH of the medium declined from 6.7 to 5.1 due to the production of acetate and lactate, the total protonmotive force (Δp) remained between −110 and −130 mV, and the membrane potential (ΔΨ) decreased from −104 to −65 mV. This decrease in ΔΨ was paralleled by an increase in the chemical gradient of protons (ZΔpH) from −31 to −62 mV at pH 5.1. Based on these results, T. wiegelii maintained a small ΔpH (0.3–0.9 units, inside alkaline) as the medium pH declined and interconverted ΔΨ to ZΔpH to maintain the total Δp relatively constant. Intracellular potassium decreased from 150 mM at pH 6.70 to 50 mM at pH 5.1, and this represented a 33-mV decline in the transmembrane chemical potential of potassium. The ability to synthesize ATP remained constant as the external pH declined, and therefore metabolic energy per se was not a critical aspect of pH sensitivity. Received: March 16, 2000 / Accepted: May 8, 2000     

Heterogeneity and tissue specificity of tropomyosin isoforms from four species of bivalves

Heterogeneity and tissue specificity of tropomyosin isoforms obtained from four species of bivalves (Scapharca broughtonii (ark shell), Mytilus galloprovincialis (mussel), Atrina pectinata (surf clam) and Crassostrea gigas (Pacific oyster)), were examined. Tropomyosins were extracted from translucent and opaque portions of posterior adductor muscle, respectively, and cardiac muscle of each bivalve. There were two tropomyosin isoforms in the ark shell, the surf clam and the Pacific oyster. They were designated as TMa and TMb. In the ark shell, TMa was the common isoform and TMb was specific for the opaque portion of the adductor muscle. In the surf clam, TMb was the common isoform present in all tissues. TMa was found only in the translucent portion of muscle. In the Pacific oyster, TMb was the major component in both portions of adductor muscle and TMa was the major component in cardiac muscle, although both tropomyosins were included in all tissues. The mussel had only one tropomyosin.     

Seasonal variability of free amino acids in two marine bivalves, Macoma balthica and Mytilus spp., in relation to environmental and physiological factors

The seasonal variability of the intracellular free amino acid (FAA) concentration was studied in 5 Macoma balthica populations and 7 Mytilus spp. populations along their European distribution. Because of the well known physiological role of FAA as organic osmolytes for salinity induced cell volume regulation in marine osmoconformers, FAA variations were compared in bivalve populations that were exposed to high vs. low intraannual salinity fluctuations. In general, seasonal FAA variations were more pronounced in M. balthica than in Mytilus spp. In both bivalve taxa from different locations in the Baltic Sea, highest FAA concentrations were found in autumn and winter and low FAA concentrations were measured in summer. Seasonal patterns were less pronounced in both taxa at locations with constant salinity conditions. In contrast to Baltic Sea populations, Atlantic and Mediterranean bivalves showed high FAA concentrations in summer and low values in winter, regardless of seasonal salinity fluctuations. Significant seasonal FAA variations at locations with constant salinity conditions showed that salinity appeared not to be the main factor in determining FAA concentrations. The seasonal patterns of the main FAA pool components, i.e. alanine, glycine and taurine, are discussed in the context of seasonal variations in environmental factors (salinity, temperature) and physiological state (glycogen content, reproductive stage).     

Invasion of the southern Gulf of St. Lawrence by the clubbed tunicate (Styela clava Herdman): Potential mechanisms for invasions of Prince Edward Island estuaries

All but one of the nine non-native marine species that established populations in the southern Gulf of St. Lawrence (sGSL) in the past decade initially invaded the sGSL via coastal and estuarine waters of Prince Edward Island (PEI). Almost half of these species are tunicates, and all but one still occur only in PEI. Recent introductions include Styela clava Herdman in 1997, Botryllus schlosseri (Pallas) in 2001, Botrylloides violaceus Oka in 2002, and Ciona intestinalis (Linnaeus) in 2004. The goal of this paper was to investigate which characteristics of PEI estuaries may have resulted in their being more susceptible to tunicate invasions than estuaries elsewhere in the sGSL. At least one genus that recently established viable populations in PEI was previously introduced to the Gulf of St. Lawrence, apparently without establishing permanent populations. This implies that either propagule pressure has increased or environmental factors are more conducive to establishment now than they were previously. The fluctuating resource availability model predicts increased invasibility of environments that experience pulses of resources such as space or nutrients. Intense development of both agriculture and aquaculture in PEI, and high population density compared to other areas of the sGSL, are associated with high and fluctuating estuarine nutrient levels and a large surface area of artificial substrates (mussel socks) that is kept relatively free of competitors, and is replaced regularly. Changes in nutrient loading and the development of aquaculture have also occurred within the past two to three decades. The provision of artificial structure is likely a critical factor in the successful establishment of tunicates in PEI, because natural hard substrates are scarce. Facilitation by green crabs (Carcinus maenas L.) may be a contributing factor in the spread of Styela. Only one estuary lacking green crabs has an established population of Styela, and at least two known inoculations of Styela into estuaries without green crabs have failed. A likely mechanism for facilitation is the consumption by green crab of the snail Astyris lunata, a known Styela predator.     

New genotypes and factors associated with Cryptosporidium detection in mussels (Mytilus spp.) along the California coast

A 3 year study was conducted to evaluate mussels as bioindicators of faecal contamination in coastal ecosystems of California. Haemolymph samples from 4680 mussels (Mytilus spp.) were tested for Cryptosporidium genotypes using PCR amplification and DNA sequence analysis. Our hypotheses were that mussels collected from sites near livestock runoff or human sewage outflow would be more likely to contain the faecal pathogen Cryptosporidium than mussels collected distant to these sites, and that the prevalence would be greatest during the wet season when runoff into the nearshore marine environment was highest. To test these hypotheses, 156 batches of sentinel mussels were collected quarterly at nearshore marine sites considered at higher risk for exposure to livestock runoff, higher risk for exposure to human sewage, or lower risk for exposure to both faecal sources. Cryptosporidium genotypes detected in Haemolymph samples from individual mussels included Cryptosporidium parvum, Cryptosporidium felis, Cryptosporidium andersoni, and two novel Cryptosporidium spp. Factors significantly associated with detection of Cryptosporidium spp. in mussel batches were exposure to freshwater outflow and mussel collection within a week following a precipitation event. Detection of Cryptosporidium spp. was not associated with higher or lower risk status for exposure to livestock faeces or human sewage sources. This study showed that mussels can be used to monitor water quality in California and suggests that humans and animals ingesting faecal-contaminated water and shellfish may be exposed to both host-specific and anthropozoonotic Cryptosporidium genotypes of public health significance.     

The effect of growth temperature on the bioenergetics of photosynthetic algal cultures

Two photosynthetic algal cultures, one Chlorella vulgaris, and the other a Chlorogonium sp., were cultured under light limitations in chemostats. The effects of growth temperature on their energy yield and maintenance energy requirement were studied. It was observed that a lowering in temperature resulted in a lower maximum growth yield from the light energy, Y(G). This was attributed to two reasons. First, at low temperatures there was a change in the algal cell composition with more energy being expended to synthesize a higher biomass protein content. Secondly, at low temperatures, a cyanide-resistant respiratory pathway became operative which led to a decrease in the number of ATP being generated. The maintenance energy coefficient was a function of temperature increasing with decreasing temperature. This might reflect energy wastage by the cell at low temperatures. The maximum specific growth rate dropped with decreasing temperature, and can be described by an Arrhenius type rate-temperature model up to the optimal temperature for growth; i.e., activation energy remained constant.     

Carbon isotope signatures reveal that diet is related to the relative sizes of the gills and palps in bivalves

In marine bivalves, the relative sizes of the gills and palps appear to be a useful functional trait that reflect feeding mode, i.e. suspension feeders have relatively larger gills than palps for pumping, whereas deposit feeders have relatively larger palps than gills for sorting. Also, within a species, the relative sizes of the gills and palps are related to changes in local food conditions. However, there is still no firm evidence showing that differences in the relative gill and palp sizes between species are related to diet selection. Based on the knowledge that carbon and nitrogen isotope signatures of an animals tissues reflect past diet, we compared the relative gill and palp sizes of bivalves from Roebuck Bay, northwestern Australia with their carbon and nitrogen isotope signatures. The carbon isotope signatures distinguished clear differences in diet between bivalves along a gradient from suspension to deposit feeding, and strikingly this pattern was closely followed by the relative sizes of the gills and palps of the bivalves. This study confirms that relative gill and palp sizes in bivalves are a functional trait that can be used to compare resource use between species. Furthermore, these data may suggest that morphospace occupation, as determined by relative gill and palp sizes of bivalves, could reflect a gradient of resource use between species.     

Development of a real-time PCR assay for detection of Mytilus species specific alleles: Application to a sampling survey in Scotland

Shellfish aquaculture is a growing industry in Scotland, dominated by the production of the mussel Mytilus edulis, the native species. Recently the discovery of Mytilus galloprovincialis and Mytilus trossulus together with M. edulis and all 3 hybrids in cultivation in some Scottish sea lochs led to questions regarding the distribution of mussel species in Scotland. The establishment of an extensive sampling survey, involving the collection of mussels at 34 intertidal sites and 10 marinas around Scotland, motivated the development of a high-throughput method for identification of Mytilus alleles from samples. Three Taqman®-MGB probes and one set of primers were designed, based on the previously described Me 15/16 primers targeting the adhesive protein gene sequence, and samples were screened for the presence of M. edulis, M. galloprovincialis and M. trossulus alleles using real-time PCR. Mytilus edulis alleles were identified in samples from all 44 sites. Mytilus galloprovincialis alleles were found together with M. edulis alleles extensively in northern parts of the west and east coasts. Mytilus trossulus alleles were identified in samples from 6 sites in the west and south-west of Scotland. Because M. trossulus is generally undesirable in cultivation and therefore preventing the geographical spread of this species across Scotland is considered beneficial by the shellfish aquaculture industry, these 6 samples were further analysed for genotype frequencies using conventional PCR. Although distribution of the non-native species M. galloprovincialis and M. trossulus have proven to be more widespread than previously thought, there is no evidence from our study of either M. trossulus or M. galloprovincialis acting as an invasive species in Scotland. The real-time PCR method developed in this study has proven to be a rapid and effective tool for the identification of M. edulis, M. galloprovincialis and M. trossulus alleles from samples and should prove useful in future surveys, ecological or aquaculture management related studies in both unispecific and mixed species areas of these species.