Fish trophic divergence along a lake productivity gradient revealed by historic patterns of invasion and eutrophication

相似文献   

The seasonal biomass and productivity of the submerged macrophytes in a polluted Wisconsin stream

SUMMARY 1. We measured biomass and light/dark bottle productivity of macrophytes in a Wisconsin stream throughout one growing season. Except for a brief period in early spring when a Cladophora glomerata -filamentous algal community was dominant, Potamogeton pectinatus was the dominant macrophyte species in Badfish Creek.
2. Maximum community biomass was 710 g DW m⁻², with a maximum above ground biomass of 620 g DW m⁻² and a maximum below ground biomass of 120 g DW m⁻². Annual productivity was estimated at 1435 g DW m⁻² year⁻¹, with a calculated P/B of 2.01.
3. In situ net production averaged 2.83g C g AFDW⁻¹ h⁻¹ Net positive carbon gain by the P. pectinatus community occurred when water temperatures were above 15°C, and daylength at least 12h. This is correlated to the onset of tuber germination in spring, and the point of maximal biomass decline in autumn.     

The osprey-like reversible outer toe: a conspicuous trait in the overlooked morphology of the Grey-headed and Lesser Fish Eagles

The ability to rotate the fourth toe to accompany the first toe in opposition of the second and third toes is well known for the Osprey Pandion haliaetus, as an adaptation to have a stronger grip in catching and carry fish. The presence of a similar ability in the Grey-headed Fish Eagle Haliaeetus ichthyaetus and Lesser Fish Eagle Haliaeetus humilis, not shared with other piscivorous eagles, has largely been overlooked. Based on the growing number of photographs of these birds on the internet, the still scarce literature on their ecology and phylogeny, and personal field observation, I draw attention to this and other traits of their morphology, speculating on their origin and adaptive value.     

Habitat preference, breeding success and the effect of primary productivity on Tawny Eagles Aquila rapax in the tropics

Breeding success of 176 Tawny Eagle pairs nesting on basalt (4724 km²– 92 pairs) and kalahari sand (9876 km²– 84 pairs) was monitored from 1973 to 1984 in Hwange National Park, Zimbabwe. Flat-topped trees were preferred for nesting but kalahari sand pairs used round-crowned trees more often, probably due to tree availability. Mean inter-nest distances on both biomes were significantly different (3–5 km on basalt, 59 km on kalahari sand). Clutch size and frequency of one-egg clutches in both biomes were similar and many more one-egg clutches were laid in the drier period of the study (1979–1984). There was no correlation between laying date and breeding success. More basalt pairs laid synchronously, probably due to the smaller inter-nest distances. Breeding success in both biomes was similar and significantly more chicks were reared during 1973–1978 than during 1979–1984 (wet and dry periods, respectively). Some districts produced more chicks than others, suggesting good and marginal areas within both biomes. The greater inter-nest distances and ability to breed successfully in round-crowned trees by kalahari sand Tawny Eagles resulted in a similar number of chicks reared per breeding attempt as basalt pairs, in spite of the lower primary production of the sand area.     

High incidence of selenite-resistant bacteria from a site polluted with selenium

The level of selenium-resistant bacteria in water, algal mats, and sediment from Kesterson reservoir, Calif., a site with known selenium pollution, was compared with that in nearby Volta reservoir, a site with low selenium levels. A high percentage (greater than 50%) of all isolates from the Kesterson samples were resistant to 10 mM selenite. In contrast, only a small percentage of the Volta isolates were resistant to this level of selenite. The identity of some selenite-resistant isolates and MICs of selenite, selenate, arsenate, tellurite, and tellurate were determined.     

High productivity and photosynthetic flexibility in a CAM plant

Summary In the annual succulent Mesembryanthemum crystallinum growing in situ, the balance between C₃ and CAM carbon fixation shifted rapidly in response to changes in water availability. When water was plentiful, M. crystallinum fixed carbon dioxide by the C₃ pathway and grew at rates comparable to other C₃ species. Under drought conditions, M. crystallinum fixed carbon by the CAM pathway at an average rate which exceeded 1 nanomole of carbon dioxide per square centimeter of leaf surface per second, a very high rate for a CAM plant.     

Aquamicrobium terrae sp. nov., isolated from the polluted soil near a chemical factory

A Gram-negative, aerobic, non-motile bacterial strain hun6^T isolated from the polluted soil near a chemical factory in northern Nanjing, China was investigated to clarify its taxonomic position. Growth of strain hun6^T occurred between 10 and 45 °C (optimum, 30 °C) and between pH 6.0 and 8.0 (optimum, pH 7.0). No growth occurred at NaCl concentrations greater than 5 % (w/v). The 16S rRNA gene sequence analysis indicated that strain hun6^T belongs to the genus Aquamicrobium. The sequence similarities of strain hun6^T to other type strains of Aquamicrobium genus were all below 98.5 %. The presence of ubiquinone-10, the predominant fatty acid summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c) and C_19:0 cyclo ω8c, a polar lipid pattern with phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol, phosphatidylethanolamine and phophatidylmonomethylethanoamine were in accord with the characteristics of the genus Aquamicrobium. The G+C content of the genomic DNA was determined to be 63.5 mol%. The results of DNA–DNA hybridization, physiological and biochemical tests and chemotaxonomic properties allowed genotypic and phenotypic differentiation of strain hun6^T from all known Aquamicrobium species. Therefore, strain hun6^T can be assigned to a new species of this genus for which the name Aquamicrobium terrae sp. nov. is proposed. The type strain is hun6^T (= CICC 10733^T = DSM 27865^T).     

High productivity ethanol fermentation on a mineral medium using a flocculent strain ofZymomonas mobilis

Summary A flocculent strain ofZymomonas mobilis (ZM4F JM1) was isolated in continuous culture. The parent strain, ZM4F, had lost its flocculating properties. The isolation was done in a conical fermentor at high dilution rate. Ethanol production by the new strain was then compared on a rich and mineral medium. The mineral medium showed high performance and could be used for industrial production of ethanol since it reduced one hundred fold the vitamin cost of the fermentation.     

High incidence of selenite-resistant bacteria from a site polluted with selenium.

The level of selenium-resistant bacteria in water, algal mats, and sediment from Kesterson reservoir, Calif., a site with known selenium pollution, was compared with that in nearby Volta reservoir, a site with low selenium levels. A high percentage (greater than 50%) of all isolates from the Kesterson samples were resistant to 10 mM selenite. In contrast, only a small percentage of the Volta isolates were resistant to this level of selenite. The identity of some selenite-resistant isolates and MICs of selenite, selenate, arsenate, tellurite, and tellurate were determined.     

Sakalava fishermen and Madagascar Fish Eagles: enhancing traditional conservation rules to control resource abuse that threatens a key breeding area for an endangered eagle

Watson, R.T. & Rabarisoa, R. 2000. Sakalava fishermen and Madagascar Fish Eagles: enhancing traditional conservation rules to control resource abuse that threatens a key breeding area for an endangered eagle. Ostrich 71 (1 & 2): 2–10.

Survival of the Madagascar Fish Eagle is threatened by human persecution and habitat loss. Of a global Madagascar Fish Eagle population estimated at 100 breeding pairs, the single most important concentration often pairs breeds on three adjacent lakes near the southern end of the species' range along the western seaboard of Madagascar. Fishing on the lakes is the main livelihood of local Sakalava tribespeople who have harmoniously shared these important wetlands with fish eagles for centuries. In the last five years Peregrine Fund researchers have documented a massive influx of up to 275 seasonal migrant fishermen who abuse local traditional resource extraction rules.

The economic incentive to endure the hardship of migration to the lakes and camping on the lakeshore for the season is strong. In 1995 per-capita income from fishing was about $1 500 for the six month season, 7.5 times the national annual average. Fish stocks were rapidly diminished through the fishing season as catches diminished to the point where fishermen gave up fishing before the end of the season. The resilience of introduced Tilapia sp. has so far ensured that stocks rebounded between fishing seasons. Fish stocks were at their lowest when Madagascar Fish Eagle nestlings fledged.

The most serious impact of fishermen may be on the lake-side forest, which was used as a source of dugout canoes and wood to fuel fish-drying fires. Up to 275 trees were cut for canoes in 1995 and up to 90 wood fires burned for a total of about 111 500 hours to dry a catch of almost 6.9 million fish. To conserve this important breeding site we aim to prevent loss of fish eagle nesting habitat, increased nest site disturbance, and reduced prey availability by working with community members and local leaders to enforce traditional resource use rules and find alternatives to unsustainable forms of resource extraction.

Watson, R.T. & Rabarisoa, R. 2000. Pêcheurs Sakalava et Aigles pêcheurs de Madagascar: relancer les règles traditionelles pour contrôler l'abus de ressources menaçant la zone clé de reproduction d'un aigle en danger. Ostrich 71 (1 & 2): 2–10.

La survie de la Pygargue de Madagascar est menacée par la persecution humaine et la perte de l'habitat. A l'intérieur d'une population globale estimée à 100 couples reproductifs, la seule concentration importante rassemble 10 couples se reproduisant au niveau de trois lacs adjacents situés près de l'extrémité sud de l'aire de distribution de l'espèce, qui longe la zone côtière ouest de Madagascar. La pêche sur les lacs est la principale source de subsistance de la tribu Sakalava qui a su vivre en harmonie avec les aigles en partageant ces milieux humides d'importance considérable au fil des siècles. Au cours de ces cinq dernières années, l'équipe du Peregrine Fund a enregistré une migration massive de plus de 275 pêcheurs saisonniers violant les règies traditionnelles d'exploitation.

Les lacs exercent un tel attrait économique que les difficultés de la migration et les conditions de campement au bord du lac sont endurées. En 1995, le revenu foumi par la pêche était de $1 500 pendant les six mois de la saison, soit 7.5 fois la moyenne annuelle de revenue. La régénération de l'espèce introduite Tilapia sp. assurait la récrudescence du stock de poisson entre les saisons. Ce stock de poisson a connu une décroissance rapide durant la saison, la diminution du produit a poussé les pêcheurs à abandonner la pêche avant la fin de la saison. Le stock était au plus bas au moment oú les jeunes aigles commençaient à voler.

L'impact de l'existence de pécheurs apparaît plus sérieusement au niveau des forêts autour du lac, qui sont sollicitées comme source de pirogues et de combustible pour le séchage du poisson àfumer. En 1995, plus de 275 arbres ont été abattus et plus de 90 feux de bois ont brûlé pendant une période totale de 111 500 heures pour faire sécher 6.9 millions de poissons. Assurer la conservation de cet important site de reproduction requiert la prévention contre la perte ou la perturbation du lieu de nidification de l'Aigle pêcheur, et contre la diminution de la disponibilité du poisson. Nous collaborons dans ce sens avec les membres de la communauté et les responsables locaux afin de renforcer les règles d'utilisation des ressources et trouver des alternatives concernant leur exploitation informelle.     

High productivity of human recombinant beta-interferon from a low-temperature perfusion culture

Recombinant human interferon-beta (β-IFN), used in the therapeutic treatment of multiple sclerosis (MS), can be produced on a large-scale from genetically engineered Chinese hamster ovary (CHO) cells. However, its hydrophobicity causes non-reversible, molecular aggregation in culture. The parameters affecting aggregation were determined to be concentration, culture residence time, temperature and glycosylation. Although the protein can be produced in Escherichia coli in a non-glycosylated form, the addition of glycans confers a reduced rate of aggregation as well as a 10-fold higher bioactivity. We report on the application of a low temperature perfusion culture designed to control the parameters that cause aggregation. In this three-phase culture system there is a transition to a low temperature (32°C) in a batch mode prior to implementing perfusion at 1 volume/day using an acoustic cell separator. Perfusion at the low temperature resulted in a 3.5-fold increase in specific productivity and a 7-fold increase in volumetric productivity compared to the batch culture at 37°C. The percentage aggregation of β-IFN was reduced from a maximum of 43% in batch culture to a minimum of 5% toward the end of the perfusion phase. The glycosylation profile of all samples showed predominantly sialylated biantennary fucosylated structures. The extent of sialylation, which is important for bioactivity, was enhanced significantly in the perfusion culture, compared to the batch culture.     

Modelling microalgal productivity in a High Rate Algal Pond based on wavelength dependent optical properties

A model is presented to predict algal biomass concentration and productivity in a High Rate Algal Pond (HRAP) at all possible combinations of incident photon flux density (PFD), pond depth and hydraulic retention time (HRT). The total extinction coefficientk _t and the absorption coefficient k_a of algal biomass were measured at 1 nm intervals. Thek _t values were used to calculate the underwater light climate, which included the spectral narrowing of the photon flux density with increasing depth. The number of quanta absorbed (QA) from the photosynthetic available radiation (PAR) was calculated using thek _a /k _t ratio and incident PFD at 1 nm intervals. Algal oxygen production is related to QA by the quantum requirement (QR), which was determined fromk _a ,and the slope of the photosynthesis versus irradiance curve (α). Based on this calculation we propose a new concept: the compensating absorption rate (CAR), which represents the rate of photon absorption necessary to balance oxygen consuming processes. The model calculated productivities using literature data on HRT, pond depth and incident PFD, that compared well with the actual measured productivities. To achieve optimal HRAP productivities under fluctuating climatological conditions, we propose a pond management strategy based on model simulations.     

Denitrification by the sessile microbial community of a polluted river

Denitrification by the sessile microbial community of the River Tamagawa was studied in laboratory experiments. Inorganic nitrogen loss was observed when river water was incubated with sessile microbial community of the river in a continuously circulating system. It was confirmed by the ¹⁵N tracer technique that both sessile microbial communities of unpolluted and polluted areas had denitrifying activity, even though they were incubated in oxygenated river water. The denitrification rate of the sessile microbial community taken from a polluted area, measured by the ¹⁵N tracer technique, was 8–16 mg N/m²/day in October and December, 1977, and it was enhanced 10-fold by raising the water temperature from 14 to 30° C. Denitrification in the river was also suggested by determining the N₂: Ar ratio of gases evolved from the river bed.     

Biodegradation of alkylpyridines by bacteria isolated from a polluted subsurface

Ten bacterial strains were isolated fromalkylpyridine polluted sediments 7.6 m below thesurface. These strains were able to degrade 11different alkylpyridine isomers. Degradation ratesdepended on number and position of the alkyl group. Isomers with an alkyl group at position 3 were moreresistant to microbial attack. Of the 10 strains, 6isolates were selected for detailed study. Theseisolates mineralized the isomers to CO₂,NH₄ ⁺, and biomass. All strains weregram-negative rods with a strict aerobic metabolism. Characterization of physiological and biochemicalproperties revealed similarity between strains. Eeachstrain however, had a limited substrate range whichenabled it to degrade no more than 2 to 3 compounds ofthe 14 alkylpyridine isomers tested. Examination ofthe genetic variability among cultures with therandomly amplified polymorphic DNA technique revealedhigh levels of genomic DNA polymorphism. The highestsimilarity between 2 strains (0.653) was observedbetween 2-picoline and 3-picoline degrading cultures. The molecular basis of the differences in substratespecificity is under investigation.     

Biodegradation of alkylpyridines by bacteria isolated from a polluted subsurface

Ten bacterial strains were isolated from alkylpyridine polluted sediments 7.6 m below the surface. These strains were able to degrade 11 different alkylpyridine isomers. Degradation rates depended on number and position of the alkyl group. Isomers with an alkyl group at position 3 were more resistant to microbial attack. Of the 10 strains, 6 isolates were selected for detailed study. These isolates mineralized the isomers to CO2, NH4+, and biomass. All strains were gram-negative rods with a strict aerobic metabolism. Characterization of physiological and biochemical properties revealed similarity between strains. Eeach strain however, had a limited substrate range which enabled it to degrade no more than 2 to 3 compounds of the 14 alkylpyridine isomers tested. Examination of the genetic variability among cultures with the randomly amplified polymorphic DNA technique revealed high levels of genomic DNA polymorphism. The highest similarity between 2 strains (0.653) was observed between 2-picoline and 3-picoline degrading cultures. The molecular basis of the differences in substrate specificity is under investigation.     

High productivity continuous ethanol fermentation with a flocculating mutant strain of Zymomonas mobilis

High fermenter (volumetric) ethanol productivities (80 g/lh^–1) were attained in a simple single-stage continuous-stirred-tank-reactor (CSTR) employing a flocculent mutant of Zymomonas mobilis with a feed containing 100g/l glucose. Under these conditions a final ethanol concentration of 47.6 g/l was obtained, representing a maximum conversion efficiency of 97% of theoretical.Nomenclature SR = Medium glucose concentration (g/l)X Biomass concentration (g/l) - P Ethanol concentration (g/l) - VP Volumetric productivity (g ethanol/l/h) - Yp/s Product yield coefficient (g ethanol/g glucose consumed) - Qp Specific rate of ethanol formation (g ethanol/g cells/h) - D Dilution rate (h^–1) - Dmax Maximum dilution rate: ie., highest dilution rate at which the effluent glucose concentration 4g/l (h^–1)     

Primary productivity by symbiont-bearing planktonic sarcodines (Acantharia, Radiolaria, Foraminifera) in surface waters near Bermuda

Rates of primary productivity by the symbiotic algae of a varietyof planktonic sarcodines (Acantharia, Radiolaria, Foraminifera)were measured at two times of the year in 1991 from surfacewaters of the Sargasso Sea near Bermuda Rates of symbiont production(expressed on a ‘per host’ basis) were not significantlydifferent for the two seasons, but measurements for individualsarcodine species varied by more than four orders of magnitudeand were roughly correlated with sarcodine size (and therebywith the biomass of the protozoan host). Overall, Acanthariahad the lowest production rates per host, while solitary andcolonial Radiolaria displayed the highest rates. Symbiont-bearingplanktonic sarcodines were always microenvironments of highlyconcentrated primary production in this oligotrophic oceanicenvironment. Rates of primary production within the volumesdefined by the extension of the cytoplasmic networks of thesarcodines generally exceeded rates of primary production inequivalent volumes of the seawater surrounding these associationsby more than four orders of magnitude and showed no clear differencesamong the sarcodine groups Total symbiont production, however,contributed a small fraction (generally <1%) of the totalprimary production in surface waters because of relatively lowsarcodine abundances (compared to other primary producers) andbecause of high total primary production in surface waters.Combining the production rates measured in this study with seasonalabundances of Acantharia and Foraminifera, however, indicatesthat these assemblages may have contributed an average of     

High ethanol productivity from lactose by immobilized cells of Kluyveromyces fragilis and Zymomonas mobilis

Ethanol production from 200 g lactose/l by Kluyveromyces fragilis immobilized in calcium alginate was 63 g/l whereas with co-immobilized K. fragilis and Zymomonas mobilis 72 g ethanol/l was attained. With free cells of K. fragilis, only 52 g ethanol/l was obtained. The beads were relatively stable without significant reduction in activity for about six batches of fermentation.The authors are with the Department of Microbiology and Microbial Technology, School of Biological Sciences, Madurai Kamaraj University, Madurai 625 021, India.This paper is dedicated to Professor M. Lakshmanan, Vice-Chancellor, Madurai Kamaraj University, in commemoration of his 60th birthday.     

Fragmentation of a Neotropical migratory fish population by a century-old dam

Loss of connectivity in impounded rivers is among the impacts imposed by dams, and mitigation measures such as fish passages might not accomplish their purpose of reestablishing an efficient bi-directional gene flow in the fish populations affected. As a consequence, fish populations remain fragmented, and a new interpopulational structure may develop, with increased risk of reduced genetic diversity and stochastic extinction. In order to evaluate the effects of the Gavião Peixoto Dam, which was constructed almost a century ago on the Jacaré-Guaçu River in the Upper Paraná River basin, Brazil, a comparative morphometric study was undertaken on the populations of the Neotropical migratory characid fish Salminus hilarii living up- and downstream of this dam. Population dynamics, spatial segregation, and habitat use by different age classes were monitored for 2 years. We found that segregation caused by the dam and long periods with no efficient connection by fish passages have led to fragmentation and interpopulational structuring of S. hilarii, as revealed by canonical variable analysis of morphometric features. The fish populations occupying the up- and downstream sections have succeeded in performing short-distance reproductive migrations in the main river and tributaries, have found suitable habitats for completing their life cycle, and have been able to maintain distinct small-sized populations so far.