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  • 1995-1999  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Cell-specific density of symbiotic dinoflagellates in tropical anthozoans (1998)
    Springer
    Coral reefs 17 (1998), S. 329-337 
    Details
    ISSN: 1432-0975
    Keywords: Key words Coral ; Sea anemone ; Dinoflagellates ; Symbiosis ; Eutrophication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  Symbiotic dinoflagellates are abundant in the endoderm cells of tropical marine anthozoans, but the cell-specific density (CSD) of symbionts has not yet been investigated. In this study we used mechanical and enzymatic methods of maceration, and staining with substrate-specific fluorochromes, to observe a large number of individual host cells from 33 species of tropical anthozoans collected in Florida, Hawaii and Jamaica or cultured in Monaco. In the majority of species, most of the host cells contained a single algal cell (singlet). Host cells with two or more (up to six) algae were much less abundant. The average CSD for the 33 species was 1.54±0.30 (range 1.11 to 2.19). Singlets arranged in a monolayer can account for the areal density of algae observed in many anthozoans. The dinoflagellates occupy most of the interior of macerated host cells, leaving the host cytoplasm and cell membrane as a thin outer layer, often unresolvable by light microscopy. This spatial arrangement may favor diffusion and transport of CO2, bicarbonate ions, and nutrients from the environment to the algae. The effect of nutrient enrichment on CSD was determined by exposing eleven species to chronically elevated levels of ammonium-N. After four weeks all species exhibited a dramatic increase in algal mitotic index and CSD. The potential consequences of environmentally induced increases in CSD in tropical anthozoans are discussed in terms of the decreased cell-specific photosynthesis (CO2 limitation) and decreased rates of calcification observed in other studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003380050133
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  • 2
    Electronic Resource
    Electronic Resource
    Morphology of coral desmocytes, cells that anchor the calicoblastic epithelium to the skeleton (1997)
    Springer
    Coral reefs 16 (1997), S. 205-213 
    Details
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract.  We used light, scanning, and electron microscopy to investigate the ultrastructure of desmocytes in the scleractinian Stylophora pistillata from the Red Sea. Desmocytes are abundant on the calicoblastic epithelium, numbering up to 150 per mm2 in the coenosarc. The surface of the skeleton bears shallow pits which may represent desmocyte attachment scars. Previously described as cell remnants or extracellular products, coral desmocytes appear to be bona fide cells as they manifest plasma membranes, organelles, and nuclei. Desmocytes attach to the mesoglea in mortise and tenon fashion. A field of 40 or more tenons protrude fingerlike from the proximal surface of the desmocyte and interdigitate with the mesoglea. Each tenon is coated extracellularly with short fibers which are joined to fibers of the mesoglea. The arrangement resembles previously described “fascial” hemidesmosomes. The short fibers pass through the plasma membrane and connect with relatively long intracellular fibers which occupy the center of each tenon. The long fibers extend distally and attach to structures resembling vertebrate hemidesmosomes. These, in turn, attach to the skeleton. The fiber arrangement and orientation seems designed to resist tensile forces. The dynamic adhesion potentially provided by the distal hemidesmosomes may enable desmocytes to detach and reattach to the skeleton during episodes of mineral accretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003380050075
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  • 3
    Electronic Resource
    Electronic Resource
    Permeability of the oral epithelial layers in cnidarians (1996)
    Springer
    Marine biology 126 (1996), S. 43-53 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to characterize the permeability of the oral epithelial layers in cnidarians, we investigated the kinetics of transport of labelled ions (45Ca,22Na,36Cl) and organic molecules (14C-inulin-carboxyl,14C-ala) through the oral tissue of two cnidarian species,Anemonia viridis (Forsskål, 1775) andHeliofungia actiniformis (Quoy and Gaimard, 1833) using the Ussing chamber method. In both species, unidirectional Ca, Na and Cl fluxes were the same in both directions (ectoderm towards endoderm and vice versa), the net flux being equal to zero. The insensitivity of these unidirectional transepithelial fluxes to metabolic inhibitor (1 mM sodium cyanide) and calcium channel inhibitor (100 μM verapamil) and their linear dependence on calcium concentration suggest that these fluxes are simple driven by diffusion via a paracellular pathway. The epithelial layers were not permeable to inulin. Low-molecular weight amino acids such as alanine did not cross the epithelia but were absorbed by the ectoderm. The permeability coefficients indicate that the oral epithelial layers are leaky. It is suggested that the coelenteric cavity represents a compartment in which the ionic pool can be entirely renewed by simple diffusion. This process seems efficient enough to meet all calcium requirements in scleractinian corals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00571376
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  • 4
    Electronic Resource
    Electronic Resource
    Transient Na+ stress in symbiotic dinoflagellates after isolation from coral-host cells and subsequent immersion in seawater (1997)
    Springer
    Marine biology 129 (1997), S. 581-589 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Dinoflagellates which live in intracellular symbiosis with corals (zooxanthellae), probably share the ionic conditions of their host cells, i.e. are subjected to lower sodium and calcium concentrations than ambient seawater. Although free-living zooxanthellae are not generally found in waters of reef ecosystems, they can be released in either a controlled diurnal regulation or an uncontrolled (coral bleaching) reaction by their animal hosts. Upon release, zooxanthellae experience new external ionic conditions. The aims of this study were to (1) examine the ionic conditions experienced by zooxanthellae in hospite, (2) determine changes in the intracellular Na+ concentration of dinoflagellates (Symbiodinium sp.) following isolation from the scleractinian coral Galaxea fascicularis (Linnaeus, 1767), and (3) characterize the mechanism of Na+ regulation and control. On the basis of equilibrium studies, it has been suggested that zooxanthellae in coral-host cells experience a Na+ concentration of ≃60 mM. The intracellular concentration of Na+ in zooxanthellae, as determined by flame photometry, was found to be ≃0.300 μequiv mg−1 protein, or 30 to 35 mM when the water content of cells was taken into account. Half the cell Na+ seems to be compartmentalized (i.e. non-exchangeable) in freshly isolated zooxanthellae (FIZ), while in cultured zooxanthellae (CZ) all the Na+ was exchangeable. Isolation of zooxanthellae into seawater from their intracellular environment caused a transient two-fold increase in Na+ concentration within the first 30 min. This increase was directly proportional to extracellular Na+ concentration, suggesting passive influx. After 30 min the Na+ concentration decreased, reaching its initial level within 1 to 3 h. Following isolation for up to 3 h, the Na+ influx rate measured during short incubations (5 min) was constant, suggesting that some Na+-regulation mechanism, probably a Na+ efflux system, was created or stimulated within the first 30 min. Since this mechanism is independent of DNA transcription (as proved by its insensitivity to 100 μM actinomycin D) and protein synthesis (insensitivity to 100 μM cycloheximide or emetin), we conclude that activation of an efflux system already present in the zooxanthella membrane occurred during the first 30 min after isolation in seawater. This mechanism was cyanide (CN)- and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU)-sensitive and dependent on extracellular K+. However, while we found an ouabain-sensitive ATPase activity in zooxanthella homogenates, suggesting the involvement of a Na+/K+ ATPase, no correlation was found between Na+ efflux and K+ influx [measured using 86Rb (rubidium chloride) as a tracer]. The results presented show that isolation of symbiotic dinoflagellates into seawater causes major ionic stress, resulting in a two-fold increase in intracellular Na+ concentration. Within 30 min, a Na+-efflux mechanism (putatively involving Na+-ATPase), in the membrane of zooxanthellae in hospite is stimulated. The Na+ concentration of the cell consequently returns to its initial level 3 h after isolation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050199
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  • 5
    Electronic Resource
    Electronic Resource
    Photosynthesis, respiration and calcification of a zooxanthellate scleractinian coral under submerged and exposed conditions (1997)
    Springer
    Marine biology 129 (1997), S. 175-182 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An experimental set-up was designed to investigate photosynthesis, respiration and calcification of zooxanthellate scleractinian corals under submerged and exposed conditions. The results of experiments to determine the effect of exposure to air on the metabolism of Stylophora pistillata (Esper, 1797) revealed that: (1) maximum gross photosynthesis ( p g max) is 3.6 times higher in water than in air; (2) an indicator of photoadaptation (I k ) does not reveal any difference between water and air; (3) the difference between submerged and aerial respiration is not statistically significant; (4) aerial photosynthesis–irradiance (P–I) curves display lower initial slopes (α) than aquatic P–I curves; (5) there is no calcification in air.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050158
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  • 6
    Electronic Resource
    Electronic Resource
    An improved 45Ca protocol for investigating physiological mechanisms in coral calcification (1995)
    Springer
    Marine biology 122 (1995), S. 453-459 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A sensitive experimental protocol using cloned corals (hereafter “microcolonies”) of the branching scleractinian coral Stylophora pistillata and 45Ca has been developed to enable reproducible measurements of physiological and biochemical mechanisms involved in calcium transport and compartmentalization during coral calcification. Cloned S. pistillata microcolonies were propagated in the laboratory from small fragments of parent colonies collected in 1990 in the Gulf of Aqaba, Jordan. Cloned microcolonies have several intrinsic properties that help to reduce unwanted biological variability: (1) same genotype; (2) similar sizes and shapes; and (3) absence of macroscopic boring organisms. Errors specifically associated with long-standing problems to do with isotopic exchange were further reduced by producing microcolonies with no skeletal surfaces exposed to the radioisotope-labelled incubation medium. The value of the technique resides principally in its superior ability to elucidate transportation pathways and processes and not in its ability to quantitatively estimate calcium deposition by corals in nature. We describe here a rapidly exchangeable calcium pool in which up to 90% of the radioactive label taken up during incubations is located. This pool (72.9±1.4 nmol Ca mg-1 protein) is presumably located within the coelenteric cavity as suggested by the following: (1) it has 4-min half-time saturation kinetics; (2) the accumulation of calcium is linearly correlated with the calcium concentration of sea-water; and (3) its insensitivity to metabolic and ion transport inhibitors indicate that membranes do not isolate this compartment. Washout of this large extracellular pool greatly improved estimates of calcium deposition as evidenced by 10 to 40% reduction in coefficients of variation when compared with previous 45Ca2+ methods described in the literature. Comparisons of calcification measurements simultaneously carried out using the alkalinity anomaly technique and the 45Ca protocol described here show that the correlation coefficient of both techniques is close to 1. Unlike previous reports, our 45Ca2+-derived measurements are slightly lower than those computed from the alkalinity depletion technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350879
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  • 7
    Electronic Resource
    Electronic Resource
    Fatty acids of the scleractinian coral Galaxea fascicularis: effect of light and feeding (1995)
    Springer
    Journal of comparative physiology 165 (1995), S. 183-192 
    Details
    ISSN: 1432-136X
    Keywords: Zooxanthellae ; Fatty acids ; Light ; Feeding ; Coral, Galaxea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In order to investigate nutritional interactions in the symbiotic scleractinian coral-zooxanthella association, fatty acids of the coral Galaxea fascicularis were analysed in two groups of cultured microcolonies. The first group was fed with Artemia sp., while the second group was starved. After an initial 1-month period during which both groups were subjected to the same “normal” light conditions (constant irradiance of 125 μE·cm-2·s-1 and 14:10 h light:dark), a light cap was used to cover the aquarium and keep all the microcolonies in permanent darkness for 20 days. During the light phase of the experiment it was shown that the nutritional status lead to large variations in the percentage of saturated, mono-unsaturated and polyunsaturated fatty acids. Palmitic acid (C16:0) was the most abundant fatty acid in both groups. Important differences between fed and starved microcolonies occurred during the dark phase of the experiment. In the fed group the dark phase was characterized by a significant increase in polyunsaturated fatty acids. Particularly arachidonic acid (C20:4 n-6) became the most important fatty acid followed by docosatrienoic acid (C22:3 n-3). A slight increase in these two fatty acids was also found in the starved group but the bulk of polyunsaturated fatty acids was significantly decreased. In this group, palmitic acid remained the most important fatty acid while an increased concentration of cis-vaccenic acid (C18:1 n-7) was found at the end of the experiment. The increased concentration of cis-vaccenic acid might indicate that bacteria serve as a source of energy. While the number of zooxanthellae per milligram of protein and the chlorophyll a to protein ratio strongly decreased in the starved microcolonies immediately after the beginning of the dark period, the decrease in fed microcolonies was delayed for about 10 days. Furthermore, after 20 days of dark incubation the chlorophyll a to protein ratio was the same as measured at the beginning of the dark period. This suggests that in the dark the metabolic requirements of the zooxanthellae are in part met from the animal host through a heterotrophic mode of nutrition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00260809
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