Differential regulation by trophic conditions of phosphorylating and non-phosphorylating NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenases in Chlorella fusca.

The two NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenases present in the green alga Chlorella fusca, namely, the phosphorylating (chloroplastic) enzyme and the non-phosphorylating (cytosolic) enzyme, are differently affected by the trophic conditions prevailing in the cell cultures. The addition of metabolizable sugars to cell cultures growing in the light promotes a marked decrease of the phosphorylating enzyme activity down to a barely detectable cellular level. In contrast, the cellular level of the non-phosphorylating enzyme is even enhanced in the presence of such sugars. These effects are not observed, however, with a number of non-assimilable sugar analogs. After sugar removal, a recovery of the phosphorylating activity--in a process which is inhibited by cycloheximide but not by lincomycin--is observed in illuminated cells but not in darkness, thus indicating a light-dependent nuclear synthesis of the chloroplastic enzyme. It seems therefore that the two dehydrogenases are adaptative enzymes subject to differential regulation by nutritional conditions.     

Modeling the role of wind and warming on Microcystis aeruginosa blooms in shallow lakes with different trophic status

This study focuses on the role of wind exposure and storm events, in interaction with trophic status and temperature, on the competition between two species: Microcystis aeruginosa and a typical green alga. It is based on a water column model containing ecological and fluid mechanic features including mixing and shear stress at the bottom. This model addresses for the first time the impact of storm events (inducing sediment and nutrient resuspension) on algal dynamics. Simulations with realistic environmental forcings were performed with different sets of wind, temperature, and trophic conditions. With normal temperatures, conditions for dominance and bloom formation of M. aeruginosa in summer are restricted to hypertrophic waters with low wind exposure. Higher wind exposure (above 2 m s^?1) impairs the formation blooms even in favorable trophic conditions and enhances the dominance of green algae. Hotter temperatures allow the dominance of M. aeruginosa for lower phosphorus conditions and higher wind exposure and lead to the exclusion of green algae for high phosphorus content and low wind exposure. Nevertheless, high wind exposure (above 3 m s^?1) still prevents dense bloom formation and allows the coexistence of both species. Storm events bring two counterbalancing features: sediment and nutrient resuspension. The first leads to a decrease of phytoplankton density in response to high turbidity, and the second leads to an increase and better maintenance of M. aeruginosa blooms due to high phosphorus concentration released in the water. This result depends on the timing of the event and on general wind exposure as phosphorus release only benefits M. aeruginosa if exposure to wind is low.     

Carotenoid pigments and trophic behaviour of deep-sea shrimps (Crustacea, decapoda, alvinocarididae) from a hydrothermal area of the mid-atlantic ridge

Pigments and trophic behaviour of three species of Alvinocarididae from a Mid-Atlantic hydrothermal site were analysed. Carotenoid pigments are responsible for the more or less marked colouration of these animals. The carotenoid content of whole animals and different tissues were evaluated. Rimicaris exoculata exhibits an increased carotenoid level at the juvenile stage, while Chorocaris chacei and Alvinocaris markensis contain only few traces of pigment. Free and esterified astaxanthin, reported for most pelagic crustaceans, are present in these deep-sea shrimps. The origin of carotenoids of crustaceans living in the aphotic zone is discussed.     

Digestion in relation to feeding strategies exhibited by crustacean larvae

Decapod crustaceans have adopted a full range of reproductive strategies from the release of large numbers of small eggs (Penaeoidea) to the release of relatively low numbers of large advanced larvae (Nephropidae). As larval size determines trophic position in planktonic food webs, all food sources from phyto- to zooplankton are exploited, with many species changing trophic level during ontogenetic development. Comparative studies on digestive enzymes, levels of activity and changes during ontogeny, together with measurements of gastroevacuation rates and food energy values appear to reveal a general pattern. While herbivorous decapod larvae adapt to low food energy values with high enzyme activity levels, rapid food turnover and low assimilation efficiency, carnivorous larvae exhibit low levels of enzyme activity but compensate by extending retention time of high-energy food to maximise assimilation efficiency. New studies on digestive enzyme levels during development in the penaeid Litopenaeus vannamei, the caridean Lysmata debelius and the cirriped Elminius modestus, appear to agree with previous observations.     

Specific features of feeding and trophic status of mass species of the family Macrouridae in the northwestern part of the Pacific Ocean

Based on materials of expeditions of TINRO-Center into the northwestern part of the Pacific Ocean, we analyze data on feeding of mass species of Macrouridae. Grenadiers Albatrossia pectoralis and Caryphaenoides longifilis are consumers (in order of importance) of cephalopods, fish, and crustaceans and C. acrolepis and C. cinereus are consumers of crustaceans, cephalopods, and fish. All grenadiers demonstrate age-related variability of food composition from polychaetes and small crustaceans to fish, squids, and large crustaceans. The change in dominant prey of A. pectoralis occurs upon its reaching a length of 50?C60 cm, and that in C. cinereus occurs upon its reaching a length of approximately 50 cm. Changes in the feeding spectra from prey of in- and epifauna to macroplanktonic and nektonic organisms indicate the widening of trophic niches of grenadiers in ontogenesis. The spatial position of each species of grenadiers correlates with its size: the smaller the species, the less it is separated from the ground trophically. According to the type of feeding, C. cinereus is a bentho-planktonic feeder, A. pectoralis is a nekto-benthonic feeder, and C. acrolepis occupies an intermediate position between them. According to the calculated values of trophic levels, the studied species are (in order of decrease) A. pectoralis, C. acrolepis, and C. cinereus; the trophic level of C. longfilis can be preliminarily assessed as close to that of A. pectoralis.     

The effects of ultraviolet irradiation on a coccoid blue-green alga: survival, photosynthesis, and photoreactivation

The effects of UV irradiation (254 mμ) on a coccoid blue-green alga Agmenellum quadruplicatum, Strain PR-6, have been examined in terms of the survival curve and measurement of short time photosynthetic rates. From study of survival evidence has been found for a strong photoreactivation centered near 430 mμ. Measurements of photosynthetic rate suggest that there is a correlation between decay of photosynthesis and survival after UV exposure. The UV induced decay in photosynthetic activity is reversed by the identical photoreactivation conditions that increase the survival level. The photosynthetic data are interpreted as demonstrating a photoreactivation of photosynthesis in blue-green algae.     

Stress-induced changes in the nitric oxide system of shore crabs living under different ecological conditions

The NO synthesis system in the brain and hemolymph of shore crabs Hemigrapsus sanguineus (Decapoda: Varunidae) living under different ecological conditions was examined under normal conditions and under acute stress. Intact crabs sampled from an area with a high anthropogenic load had a higher initial level of NO compared to crabs from a relatively clean location. After acute damaging exposure, the dynamics of the NO system activity in crabs from different stations differed markedly. The number of NO-positive elements in the brain and the level of NO metabolites in the hemolymph dramatically increased immediately after injuries in all groups of crabs. One hour after acute exposure, the expression of inducible NO-synthase in the protocerebral neurons was observed in crabs inhabiting the chronically polluted area. These results demonstrate for the first time the influence of pollution on the activity of NO-ergic processes and the involvement of nitric oxide in the formation of behavioral defense response in crustaceans under acute stress.     

The barbs (Barbus spp.) of Lake Tana: a forgotten species flock?

Synopsis All living species occupy an ecological niche, and are positioned within a trophic hierarchy. Extinct organisms presumably held similar behavioral and coevolutionary characteristics in the past, and were susceptible to the same kinds of natural ecological pressures operating today. Paleoecological investigations are limited by the incompleteness of the fossil record, and particularly by a lack of behavioral data that are so fundamental to ecological studies of living communities and habitats. Opportunities to examine the coevolutionary structure of ancient communities from empirical data are extremely rare. One such opportunity is provided by the Lower Cretaceous Santana Formation of north-eastern Brazil, a series of richly fossiliferous strata approximately 110 million years old. Many fossil fishes from the Santana Formation contain identifiable prey, including decapod crustaceans and fishes. A trophic hierarchy of these organisms is reconstructed here, and their ecological relationships are discussed. Comparison is made with a similar fish fauna from the Upper Jurassic Solnhofen Limestone of Germany. Low-level, intermediate and high-level predators are identified in each fauna. Predator-prey relationships in the Santana fauna are strongly hierarchical, and are more focussed at the intermediate predator level than in Solnhofen. Comparison with a model of predator-prey relationships between fishes and benthic fauna of the Baltic Sea (which like the Araripe Basin represents a semi-enclosed environment) suggests that heavy predation on teleosts such asRhacolepis, occupying an intermediate trophic level, may have permitted benthic decapods to proliferate and exclude other benthic organisms. Less intense predation on fishes at the intermediate trophic level would allow their numbers to increase, thereby increasing the intensity of predation on the benthos at the base of the trophic hierarchy.     

Tidal movements of the macrofauna on an exposed sandy beach in South Africa

All epifaunal and shallow-burrowing, intertidal macrofauna on an exposed sandy beach appear to undergo tidal migrations which vary in extent but are all upshore on the incoming tide and downshore on the outgoing tide during day and night. In the crustaceans this is probably endogenous rhythmic behaviour and they show increased activity at night. In the molluscs this movement is not synchronised by an intrinsic mechanism but results from behavioural responses to changing physical conditions. The large wedge clam, Donax serra, shows no tidal migrations but does show a semilunar rhythm of movement from just above mean tide level (MTL) during springs to the low tide level during neap tides.     

Quantifying the impact of above‐ and belowground higher trophic levels on plant and herbivore performance by modeling1

Growing empirical evidence suggests that aboveground and belowground multitrophic communities interact. However, investigations that comprehensively explore the impacts of above‐ and belowground third and higher trophic level organisms on plant and herbivore performance are thus far lacking. We tested the hypotheses that above‐ and belowground higher trophic level organisms as well as decomposers affect plant and herbivore performance and that these effects cross the soil–surface boundary. We used a well‐validated simulation model that is individual‐based for aboveground trophic levels such as shoot herbivores, parasitoids, and hyperparasitoids while considering belowground herbivores and their antagonists at the population level. We simulated greenhouse experiments by removing trophic levels and decomposers from the simulations in a factorial design. Decomposers and above‐ and belowground third trophic levels affected plant and herbivore mortality, root biomass, and to a lesser extent shoot biomass. We also tested the effect of gradual modifications of the interactions between different trophic level organisms with a sensitivity analysis. Shoot and root biomass were highly sensitive to the impact of the fourth trophic level. We found effects that cross the soil surface, such as aboveground herbivores and parasitoids affecting root biomass and belowground herbivores influencing aboveground herbivore mortality. We conclude that higher trophic level organisms and decomposers can strongly influence plant and herbivore performance. We propose that our modelling framework can be used in future applications to quantitatively explore the possible outcomes of complex above‐ and belowground multitrophic interactions under a range of environmental conditions and species compositions.     

A review of gastric processing in decapod crustaceans

This article reviews the mechanical processes associated with digestion in decapod crustaceans. The decapod crustacean gut is essentially an internal tube that is divided into three functional areas, the foregut, midgut, and hindgut. The foregut houses the gastric mill apparatus which functions in mastication (cutting and grinding) of the ingested food. The processed food passes into the pyloric region of the foregut which controls movement of digesta into the midgut region and hepatopancreas where intracellular digestion takes place. The movements of the foregut muscles and gastric mill are controlled via nerves from the stomatogastric ganglion. Contraction rates of the gastric mill and foregut muscles can be influenced by environmental factors such as salinity, temperature, and oxygen levels. Gut contraction rates depend on the magnitude of the environmental perturbation and the physiological ability of each species. The subsequent transit of the digesta from the foregut into the midgut and through the hindgut has been followed in a wide variety of crustaceans. Transit rates are commonly used as a measure of food processing rates and are keys in understanding strategies of adaptation to trophic conditions. Transit times vary from as little as 30 min in small copepods to over 150 h in larger lobsters. Transit times can be influenced by the size and the type of the meal, the size and activity level of an animal and changes in environmental temperature, salinity and oxygen tension. Ultimately, changes in transit times influence digestive efficiency (the amount of nutrients absorbed across the gut wall). Digestive efficiencies tend to be high for carnivorous crustaceans, but somewhat lower for those that consume plant material. A slowing of the transit rate allows more time for nutrient absorption but this may be confounded by changes in the environment, which may reduce the energy available for active transport processes. Given the large number of articles already published on the stomatogastric ganglion and its control mechanisms, this area will continue to be of interest to scientists. There is also a push towards studying animals in a more natural environment or even in the field and investigation of the energetic costs of the components of digestion under varying biotic and environmental conditions will undoubtedly be an area that expands in the future.     

Subtle effects of biological invasions: cellular and physiological responses of fish eating the exotic pest Caulerpa racemosa

The green alga Caulerpa racemosa var. cylindracea has invaded Mediterranean seabed including marine reserves, modifying the structure of habitats and altering the distributional patterns of associated organisms. However, the understanding of how such invasion can potentially affect functional properties of Mediterranean subtidal systems is yet to be determined. In this study, we show that C. racemosa changes foraging habit of the native white seabream, Diplodus sargus. In invaded areas, we found a high frequency of occurrence of C. racemosa in the stomach contents of this omnivorous fish (72.7 and 85.7%), while the alga was not detected in fish from a control area. We also found a significant accumulation of caulerpin, one of the main secondary metabolites of C. racemosa, in fish tissues. The level of caulerpin in fish tissues was used here as an indicator of the trophic exposure to the invasive pest and related with observed cellular and physiological alterations. Such effects included activation of some enzymatic pathways (catalase, glutathione peroxidases, glutathione S-transferases, total glutathione and the total oxyradical scavenging capacity, 7-ethoxy resorufin O-deethylase), the inhibition of others (acetylcholinesterase and acylCoA oxidase), an increase of hepatosomatic index and decrease of gonadosomatic index. The observed alterations might lead to a detrimental health status and altered behaviours, potentially preventing the reproductive success of fish populations. Results of this study revealed that the entering of alien species in subtidal systems can alter trophic webs and can represent an important, indirect mechanism which might contribute to influence fluctuations of fish stocks and, also, the effectiveness of protection regimes.     

On the influence of fishes on the evolution of benthic crustaceans

Though the interweavement of trophic chains in marine ecosystems of the past cannot be reconstructed, as the abundance, nutrition, reproductive rates and other aspects of the biology of fossil species are not known, it is possible to correlate trends in the evolution of single groups of animals, in the presented case the Crustacea, with the influence of other evolving organisms. The evolution of carnivorous, buoyant, well swimming modern fishes probably induced profound changes in marine ecosystems and influenced the evolution of crustaceans. Indications for these interactions are a. the absence or rare occurrence of defenseless archaic crustaceans in habitats, which are populated by teleostean fishes and the survival of some of these forms in refuges like caves and subterranean waters, and b. the reduction of the pleon in the course of the mesozoic evolution of the Decapoda, which occurs parallel to the radiation of the Teleostei, namely in the period between the early Jurassic and the Tertiary. The shortening of the pleon is interreted as a consequence of the stepwise change from a hyperbenthic to a more benthic Iife-stJe and the abandonment of the caridoid escape reaction. Other adaptations are also construed as results from the selective pressure produced by predators. Extant crustaceans which are able to coexist with fishes, among the macrozoobenthos especially the Decapoda and Peracarida, have a variety of protective adaptations, which help to reduce predation.     

Biological patterns and ecological indicators for Mediterranean fish and crustaceans below 1,000 m: a review

The Mediterranean Sea is a relatively deep, closed sea with high rates of fisheries exploitation. In recent years fishing activity has tended to shift towards deeper depths. At the same time, the Mediterranean displays some rather special hydrographic and biogeographic conditions. The present paper reviews the present state of knowledge of the fisheries, biology, and ecology of the deep-sea fish and crustacean species in the Mediterranean dwelling below 1,000 m with potential economic interest, placing special emphasis on the western basin, for which more data are available, as a basis for future studies of the ecology, biodiversity, and effects of climate change and exploitation in this zone. This review reveals that mediterranean deep-sea fishes and crustaceans employ highly conservative ecological strategies, and hence the low fecundity and low metabolic rates in a stable environment like the deep-sea make these populations highly vulnerable. Moreover, ripe females of the main species mentioned here concentrate in the deepest portions of their distribution ranges. Deep-sea fish and crustaceans have high trophic levels and low to medium omnivory index values. The ecological indices discussed here, in combination with the limited knowledge of deep-sea ecosystems, clearly call for an approach based on the Precautionary Principle.     

Comparison of size-structured and species-level trophic networks reveals antagonistic effects of temperature on vertical trophic diversity at the population and species level

It is predicted that warmer conditions should lead to a loss of trophic levels, as larger bodied consumers, which occupy higher trophic levels, experience higher metabolic costs at high temperature. Yet, it is unclear whether this prediction is consistent with the effect of warming on the trophic structure of natural systems. Furthermore, effects of temperature at the species level, which arise through a change in species composition, may differ from those at the population level, which arise through a change in population structure. We investigate this by building species-level trophic networks, and size-structured trophic networks, as a proxy for population structure, for 18 648 stream fish communities, from 4 145 234 individual fish samples, across 7024 stream locations in France from 1980 to 2008. We estimated effects of temperature on total trophic diversity (total number of nodes), vertical trophic diversity (mean and maximum trophic level) and distribution of biomass across trophic level (correlation between trophic level and biomass) in these networks. We found a positive effect of temperature on total trophic diversity in both species- and size-structured trophic networks. We found that maximum trophic level and biomass distribution decreased in species-level and size-structured trophic networks, but the mean trophic level decreased only in size-structured trophic networks. These results show that warmer temperatures associate with a lower vertical trophic diversity in size-structured networks, and a higher one in species-level networks. This suggests that vertical trophic diversity is shaped by antagonistic effects of temperature on population structure and on species composition. Our results hence demonstrate that effects of temperature do not only differ across trophic levels, but also across levels of biological organisation, from population to species level, implying complex changes in network structure and functioning with warming.     

Photochemical Performance of the Acidophilic Red Alga Cyanidium sp. in a pH Gradient

The acidophilic red alga Cyanidium sp. is one of the dominant mat-forming species in the highly acidic waters of Río Tinto, Spain. The culture of Cyanidium sp., isolated from a microbial mat sample collected at Río Tinto, was exposed to 9 different pH conditions in a gradient from 0.5 to 5 for 24?h and its physiological status evaluated by variable chlorophyll a fluorescence kinetics measurements. Maximum quantum yield was determined after 30?min, 1?h, 2?h, 4?h, 6?h and 24?h of exposure after 15?min dark adaptation. The effect of pH on photochemical activity of Cyanidium sp. was observable as early as 30?min after exposure and the pattern remained stable or with only minor modifications for 24?h. The optimum pH ranged from 1.5 to 2.5. A steep decrease of the photochemical activity was observed at pH below 1 even after 30?min of exposure. Although the alga had tolerated the exposure to pH?=?1 for at least 6?h, longer (24?h) exposure resulted in reduction of the photochemical activity. At pH above 2.5, the decline was more moderate and its negative effect on photochemistry was less severe. According to the fluorescence measurements, the red alga Cyanidium sp. is well-adapted to prevailing pH at its original locality at Río Tinto, i.e. pH of 1 to 3. The short-term survival in pH?相似文献   

Feeding ecology and trophic position of a Mediterranean endemic ray: consistency between sexes, maturity stages and seasons

The study of trophic ecology of marine predators is crucial to better understand the ecological factors that condition their role within marine ecosystems. Here we investigated the trophic habits and position of a Mediterranean endemic predator, the starry ray, Raja asterias. Specifically, we quantified the diet composition of this endemic ray in a highly exploited area of the NW Mediterranean, and we evaluated the effects of sex, maturity-stage and season on its feeding habits. Our results revealed that the starry ray is a predator of crustaceans (crabs and shrimps), and to a lower extent on teleosts, molluscs and polychaetes. This species has a high trophic position within its food web and feeds mainly on crabs (mainly Liocarcinus depurator and Goneplax rhomboides), independent of their sex, maturity-stage or season. The great importance of crabs in the diet of starry ray may be due to the fact that crabs are the dominant crustaceans in terms of biomass and abundance in the area where starry rays were collected, thus allowing them to exploit the most abundant food resource. Since the starry ray has shown a progressive decline on the catch, further research is needed to analyse the main drivers of starry ray dynamics in the Western Mediterranean Sea. Our results present important new data that will allow us to further explore the population dynamics of starry rays and the role of crustacean availability and fishing activity.     

Intrinsic and extrinsic influences on cardiac rhythms in crustaceans

Several factors cause predictable changes in heart rate of crustaceans thus affecting basic heart rhythms. In decapod crustaceans these consist of: many internal factors including influences from neural and neurohormonal systems and chemosensory influences; many external factors including startling stimuli and other disturbance; ventilatory (scaphognathite) reversals; tail flips and other postural movements including locomotor activity; and variations in environmental factors such as oxygen level, temperature and air-exposure. In many cases the initial response involves temporary bradycardia or cardiac arrest. These responses may quickly facilitate to sustained low level stimuli although maintained strong stimulation will eventually be associated with cardio-acceleration and escape responses. Measurement of change in heart rate alone is rarely a sensible monitor of cardiac performance in crustaceans since simultaneous changes in cardiac stroke volume occur which may confound diagnosis. Hypoxia for instance causes decrease in heart rate of adult crustaceans but the apparent decrease in cardiac output is offset or reversed by increase in stroke volume. Concomitant changes occur in cardiac output and in the proportion of cardiac output which is delivered to particular tissues. In fact change in heart rhythm is only one factor in a complex suite of responses involving several physiological systems which compensate uniquely for changes in environmental or other stimuli. Both neural and neuro-hormonal factors are known to play a role in control of these complex responses.     

The control of dark repair mechanisms in meiotic cells

Summary The responses to UV irradiation of pre-meiotic and meiotic cells of the unicellular green alga Chlamydomonas reinhardi have been examined in a wild type and a UV-sensitive mutant (UVS1) strain. During late interphase and early prophase the cells become highly sensitive to UV under dark conditions, but show much less change in sensitivity following photoreactivation (PR). At these times the effect of PR is not dose-modifying, but very large PR factors are obtained — at the 50% survival level in some stages values up to 23 being obtained. The enhancement of dark sensitivity is attributed to a diminution in dark repair activity, and it is suggested that this is associated with the process of genetic recombination that occurs in these meiotic cells. In addition at those times when the dark repair capacity is at a low level, a phenomenon akin to UV reactivation occurs, in that within a certain dose range, survival increases with increasing dose. The possible basis of this phenomenon is discussed.     

Predator–prey mass ratio drives microbial activity under dry conditions in Sphagnum peatlands

Mid‐ to high‐latitude peatlands are a major terrestrial carbon stock but become carbon sources during droughts, which are increasingly frequent as a result of climate warming. A critical question within this context is the sensitivity to drought of peatland microbial food webs. Microbiota drive key ecological and biogeochemical processes, but their response to drought is likely to impact these processes. Peatland food webs have, however, been little studied, especially the response of microbial predators. We studied the response of microbial predators (testate amoebae, ciliates, rotifers, and nematodes) living in Sphagnum moss carpet to droughts, and their influence on lower trophic levels and on related microbial enzyme activity. We assessed the impact of reduced water availability on microbial predators in two peatlands using experimental (Linje mire, Poland) and natural (Forbonnet mire, France) water level gradients, reflecting a sudden change in moisture regime (Linje), and a typically drier environment (Forbonnet). The sensitivity of different microbial groups to drought was size dependent; large sized microbiota such as testate amoebae declined most under dry conditions (?41% in Forbonnet and ?80% in Linje). These shifts caused a decrease in the predator–prey mass ratio (PPMR). We related microbial enzymatic activity to PPMR; we found that a decrease in PPMR can have divergent effects on microbial enzymatic activity. In a community adapted to drier conditions, decreasing PPMR stimulated microbial enzyme activity, while in extreme drought experiment, it reduced microbial activity. These results suggest that microbial enzymatic activity resulting from food web structure is optimal only within a certain range of PPMR, and that different trophic mechanisms are involved in the response of peatlands to droughts. Our findings confirm the importance of large microbial consumers living at the surface of peatlands on the functioning of peatlands, and illustrate their value as early warning indicators of change.