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At least 127 records · Page 7Linked to original sources
PubMed2001

On the extinction of radiation by a homogeneous but spatially correlated random medium.

Exponential extinction of incoherent radiation intensity in a random medium (sometimes referred to as the Beer-Lambert law) arises early in the development of several branches of science and underlies much of radiative transfer theory and propagation in turbid media with applications in astronomy, atmospheric science, and oceanography. We adopt a stochastic approach to exponential extinction and connect it to the underlying Poisson statistics of extinction events. We then show that when a dilute random medium is statistically homogeneous but spatially correlated, the attenuation of incoherent radiation with depth is often slower than exponential. This occurs because spatial correlations among obstacles of the medium spread out the probability distribution of photon extinction events. Therefore the probability of transmission (no extinction) is increased.

Journal Article↗
PubMed2003

Girdles as the main infection site for Paradeontacylix kampachi (Sanguinicolidae) in the greater amberjack Seriola dumerili.

In this study, we provide new information about the habitats selected by the blood fluke Paradeontacylix kampachi in the greater amberjack Seriola dumerili based on an exhaustive anatomical examination. From May to October 1998, 21 fish of the 0+ age class were collected from tanks of the Spanish Institute of Oceanography in Puerto de Mazarrón, Spain, for parasitological analysis. Individuals of P. kampachi were found in 17 of the 21 fish analysed (mean intensity +/- SD: 13.6 +/- 16.6; median: 6). Worms occurred in the girdles, cephalic kidney, sinus venosus, kidney and branchial arteries. A Friedman test with a post-hoc contrast revealed a significantly higher number of worms in the girdles when compared with the other sites, suggesting this may be the main habitat for P. kampachi. This location had never been reported as a habitat for any species of Paradeontacylix, probably because it had not been examined before. Girdles should be routinely examined to estimate the actual intensity of infection and to maximize the likelihood of finding this species of digenean.

Animals↗
PubMed2000

Cytometric quantification of nitrate reductase by immunolabeling in the marine diatom Skeletonema costatum.

BACKGROUND: The uptake of nitrate by phytoplankton is a central issue in biological oceanography due to its importance to primary production and vertical flux of biogenic carbon. Nitrate reductase catalyzes the first step of nitrate assimilation, the reduction of NO(3) to NO(2). A cytometric protocol to detect and quantify relative changes in nitrate reductase (NR) protein content of the marine centric diatom Skeletonema costatum is presented. METHODS: Immunolabeling of NR protein was achieved with polyclonal antibodies raised against S.costatum NR. Antisera specific to a NR protein subunit and to a NR polypeptide sequence were compared, and cytometric results of NR protein abundance were related to Western analyses. Changes in cellular NR abundance and activity were followed during an upwelling simulation experiment in which S. costatum was exposed to a shift from ammonia to nitrate as major nitrogen source. RESULTS: NR protein could be detected in NO(3)-grown cells and at extremely low levels hardly discernible by Western Blot densiometry in NH(4)-grown cells. The protocol allowed observation of early stages of NR induction during an upwelling simulation. NR abundance increased after the nutrient shift to reach a new physiological "steady-state" 96 hrs later. NR activity exhibited diel variation with maxima at mid-day. NR abundance as estimated by both flow cytometry and Western analysis exhibited a hyperbolic relationship to NR activity. This pattern suggests post-translational activation of NR protein. CONCLUSIONS: The presented protocol allows the differentiation of NH(4)- versus NO(3)-grown algae as well as the monitoring of early stages in the induction of nitrate assimilatory capacities.

Diatoms↗
PubMed2002

Concepts and approaches for marine ecosystem research with reference to the tropics.

The present article gives an overview on the leading concepts and modelling approaches for marine ecosystems' research including (1) The trophodynamic theory of pelagic ecosystems, (2) Compartment/network models, (3) Mesocosm experiments and (4) Individual based modelling approaches and virtual ecosystems (VE). The main research questions addressed, as well as the potential and limits of each approach, are summarized and discussed and it is shown how the concept of ecosystem has changed over time. Aquatic biomass spectra (derived from the theory of pelagic ecosystems) can give insight into the trophic structure of different systems, and can show how organism sizes are distributed within the system and how different size groups participate in the system's metabolism and production. Compartment/network models allow for a more detailed description of the trophic structure of ecosystems and of the energy/biomass fluxes through the explicit modelling of P/B- and food consumption rates and biomasses for each system compartment. Moreover, system indices for a characterization and comparison with other systems can be obtained such as average trophic efficiency, energy throughput, and degree of connectivity, degree of maturity, and others. Recent dynamic extensions of trophic network models allow for exploring past and future impacts of fishing and environmental disturbances as well as to explore policies such as marine protected areas. Mesocosm experiments address a multitude of questions related to aquatic processes (i.e. primary production, grazing, predation, energy transfer between trophic levels etc.) and the behaviour of organisms (i.e. growth, migration, response to contaminants etc.) under semi-natural conditions. As processes within mesocosms often differ in rate and magnitude from those occurring in nature, mesocosms should be viewed as large in vitro experiments designed to test selected components of the ecosystem and not as an attempt to enclose a multitude of interacting processes. Models that use individual organisms as units can provide insight into the causes of natural variability within populations (growth, phenotype, behaviour) and into the role of intraspecific variation for interspecific processes, succession, and feedback mechanisms. In biological oceanography, interdisciplinary research is increasingly using "Virtual Ecosystem" to simulate non-linear interactions between the dynamics of fluctuating ocean circulation, the physics of air-sea interaction, turbulence and optics, biogeochemistry, and the physiology and behaviour of plankton, which can be compared with real observations. The different approaches available for the analysis of aquatic ecosystems should be seen as complementary ways for the description and understanding of ecosystems. The modern view of marine ecosystems, as has emerged from ecosystem analysis over the last decades, is that of a composite of loosely coupled subsystems of desynchrone dynamics which through their combined action maintain the fundamental structure and function of the whole.

Animals↗
PubMedDate not supplied

[The discovery of anaphylaxis, a brief but triumphant encounter of two physiologists (1902)].

In 1901, during one of his oceanography cruises, Prince Albert the First of Monaco asks Paul Portier and Charles Richet to study the toxicity of small jellyfish fishing filaments (Coelentera). In the course of their work on the effects of a hypnotoxin extracted from various coelentera, they observe mortal accidents that are not a function of the dosage of the injections. Dogs that respond this way have all received a preparative injection, yet some dogs have no reaction to a second injection. In contrast the injection are activating when they occur more than 10 to 12 days after the first. This phenomenon is independent of the administered dosage, which may well be inferior to a toxic quantity. They call this phenomenon anaphylaxis, the contrary of protection, and analyze its primary characteristics. Paul Portier eventually returns to the Faculty of Sciences where he is Dastre's assistant. Charles Richer pursues research on anaphylaxis on his own in his laboratory at the Medical Faculty. By showing that an immune response could be pathogen as well as healing, these two scientists - who did not know each other before, working together for a few short months - made a discovery that opened up new venues in the growing field of medical immunology.

Anaphylaxis↗
PubMed1984

[Relation between the structure of the skate brain and its ecology].

The original and the literature data on the brain structure in 20 species of skates have been examined in connection with their systemic position and ecology. Certain morpho-ecological brain peculiarities have been defined which are also specific for other groups of Chondrostei, such as: sharks and Holocephala. Allunion Institute of Marine Fishery and Oceanography, Moscow.

Adaptation, Biological↗
PubMed1995

Nuclear genes from the copepod Calanus finmarchicus.

For biological oceanography it is important to understand the coupling between physical and biological processes in pelagic systems. The calanoid copepod Calanus finmarchicus dominates the zoo-plankton biomass and is an important link between primary producers and higher trophic levels in the northern Atlantic. Thus understanding how the physical environment affects gene expression or population genetics in this species is important. However, very few nuclear genes have been characterized from this species, making it difficult to perform these types of studies. Four cDNAs encoding actin, hexokinase, phosphoglucose isomerase, and phosphofructokinase, as well as a hexokinase genomic DNA, have been isolated and characterized. These sequences constitute important molecular tools for biological oceanographers.

Actins↗
PubMed1989

Bioluminescence in oceanology.

For analytical purposes bioluminescence can be used in three main ways: 1. luminescence measurement of bioluminescent system components isolated in vitro; 2. determination of luminous organisms' reaction to the in vivo test-action; 3. measurement of bioluminescence in marine ecological systems. The majority of the reports of this Symposium are dealing with the first two topics. The aim of our presentation is to draw attention to the third one. The possibilities of bioluminescent analysis are wider than its traditional scheme of applications in the laboratory, when the emitting system is withdrawn from a native source and is placed in a cuvette of the light measuring device. The reverse scheme is also possible, i.e. the device can be introduced into light emitting system such as a marine biocenosis--the community of the sea inhabitants--where we obtain a highly sensitive and rapid means of gaining the information on the vital activity of marine ecosystems, i.e. their spatial structure, rhythms, man's influence upon them, etc. The present communication will consider the possibilities of this form of bioluminescent analysis.

Circadian Rhythm↗
PubMed1997

Entropy and charge in molecular evolution--the case of phosphate.

Biopoesis, the creation of life, implies molecular evolution from simple components, randomly distributed and in a dilute state, to form highly organized, concentrated systems capable of metabolism, replication and mutation. This chain of events must involve environmental processes that can locally lower entropy in several steps; by specific selection from an indiscriminate mixture, by concentration from dilute solution, and in the case of the mineral-induced processes, by particular effectiveness in ordering and selective reaction, directed toward formation of functional biomolecules. Numerous circumstances provide support for the notion that negatively charged molecules were functionally required and geochemically available for biopoesis. Sulfite ion may have been important in bisulfite complex formation with simple aldehydes, facilitating the initial concentration by sorption of aldehydes in positively charged surface active minerals. Borate ion may have played a similar, albeit less investigated role in forming charged sugar complexes. Among anionic species, oligophosphate ions and charged phosphate esters are likely to have been of even more wide ranging importance, reflected in the continued need for phosphate in a proposed RNA world, and extending its central role to evolved biochemistry. Phosphorylation is shown to result in selective concentration by surface sorption of compounds, otherwise too dilute to support condensation reactions. It provides protection against rapid hydrolysis of sugars and, by selective concentration, induces the oligomerization of aldehydes. As a manifestation of life arisen, phosphate already appears in an organic context in the oldest preserved sedimentary record.

Animals↗
PubMed2001

Control mechanisms of diel vertical migration: theoretical assumptions.

We explore control mechanisms underlying the vertical migration of zooplankton in the water column under the predator-avoidance hypothesis. Two groups of assumptions in which the organisms are assumed to migrate vertically in order to minimize realized or effective predation pressure (type-I) and to minimize changes in realized or effective predation pressure (type-II), respectively, are investigated. Realized predation pressure is defined as the product of light intensity and relative predation abundance and the part of realized predation pressure that really affects organisms is termed as effective predation pressure. Although both types of assumptions can lead to the migration of zooplankton to avoid the mortality from predators, only the mechanisms based on type-II assumptions permit zooplankton to undergo a normal diel vertical migration (morning descent and evening ascent). The assumption of minimizing changes in realized predation pressure is based on consideration of DVM induction only by light intensity and predators. The assumption of minimizing changes in effective predation pressure takes into account, apart from light and predators also the effects of food and temperature. The latter assumption results in the same expression of migration velocity as the former one when both food and temperature are constant over water depth. A significant characteristic of the two type-II assumptions is that the relative change in light intensity plays a primary role in determining the migration velocity. The photoresponse is modified by other environmental variables: predation pressure, food and temperature. Both light and predation pressure are necessary for organisms to undertake DVM. We analyse the effect of each single variable. The modification of the phototaxis of migratory organisms depends on the vertical distribution of these variables.

Animals↗
PubMed1992

Molecular phylogeny of some polychaete annelids: an initial approach to the Atlantic-Mediterranean speciation problem.

The polychaete Eupolymnia nebulosa (family Terebellidae) displays two alternative modes of reproduction. In the Mediterranean, larvae are brooded in a mucous mass while in the Atlantic and English Channel, larvae follow a plank-tonic development. This paper attempts to discern whether this difference is expressed at the population, infraspecies, or species level. Specimens of E. nebulosa and representatives of a number of control species were sampled from Atlantic/English Channel and Mediterranean locations. Genetic sequencing of the Large-subunit ribosomal RNA 5' end of six representative species allowed one to infer the relative position of E. nebulosa within the Terebellidae and the position of the latter within the animal kingdom. The relative genetic distances calculated between the different species were also used to approach the speciation problem raised by the differences between the Mediterranean and Atlantic/English Channel population of E. nebulosa. The genetic distance between Mediterranean and Atlantic populations of both E. nebulosa and Lanice conchilega are of the same order, suggesting that differences between the populations of E. nebulosa are infraspecific.

Animals↗
PubMed1987

Prey localization by surface wave ray-tracing: fish track bugs like oceanographers track storms.

Surface-feeding fish accurately determine direction and distance to the center of a concentric wave stimulus, even if only a single, short lasting wave train is presented. It has been suggested that one cue used by these fish to localize the wave center is the distance dependent frequency modulation of the initial part of a wave stimulus. Here we show how the distance information contained in the fractional frequency change of a capillary wave group can be decoded. We suggest that wave source localization in surface-feeding fish in part is based on a principal similar to that used by oceanographers to track storms by the frequency change of forerunners of swell.

Animals↗
PubMed2006

Assessment of mangrove response to projected relative sea-level rise and recent historical reconstruction of shoreline position.

We predict the decadal change in position of three American Samoa mangroves from analysis of a time series of remotely sensed imagery, a geographic information system, tide gauge data, and projections for change in sea-level relative to the mangrove surface. Accurate predictions of changes to coastal ecosystem boundaries, including in response to projected relative sea-level rise, enable advanced planning to minimize and offset anticipated losses and minimize social disruption and cost of reducing threats to coastal development and human safety. The observed mean landward migration of three mangroves' seaward margins over four decades was 25, 64, and 72 mma(-1), 12 to 37 times the observed relative sea-level rise rate. Two of the sites had clear trends in reductions in mangrove area, where there was a highly significant correlation between the change in position of the seaward mangrove margin and change in relative sea-level. Here it can be inferred that the force of sea-level rise relative to the mangrove surface is causing landward migration. Shoreline movement was variable at a third site and not significantly correlated with changing sea-level, where it is likely that forces other than change in relative sea-level are predominant. Currently, 16.5%, 23.4%, and 68.0% of the three mangroves' landward margins are obstructed by coastal development from natural landward migration. The three mangroves could experience as high as a 50.0% reduction in area by the year 2100. A 12% reduction in mangrove area by the year 2100 is possible in the Pacific islands region.

American Samoa↗
PubMed1992

What determines the volume of the oceans?

The volume of Earth's oceans may be determined by a dynamic mechanism involving exchange of water between the crust and the mantle. Fast-spreading mid-ocean ridges are currently submerged to a depth at which the pressure is close to the critical pressure for seawater. This ensures optimal convective heat transport and, hence, maximal penetration of hydrothermal circulation along the ridge axes. The oceanic crust is hydrated to a depth of a kilometer or more and can therefore carry a substantial flux of water to the upper mantle when it is subducted. The current ingassing rate of water by this process is probably at least sufficient to balance the outgassing rate. If the oceans were shallower, as they may have been in the distant past, convective heat transport would be reduced and the depth of hydrothermal penetration and crustal hydration would decrease. Outgassing would exceed ingassing and ocean volume would increase. The system is self-stabilizing as long as the depth of the oceans does not exceed its present value. This mechanism could explain why continental freeboard has remained approximately constant since the Archean despite probable increases in continental area.

Climate↗