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  • 1
    Electronic Resource
    Electronic Resource
    Relationships between dissolved free amino acids, chemical composition and growth of the marine diatom Chaetoceros debile (1983)
    Springer
    Marine biology 77 (1983), S. 93-100 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The release of dissolved free amino acids in axenic batch cultures of the diatom Chaetoceros debile during different growth phases was studied during the late summer of 1982. Variations due to ASP, HIS, ALA, SER, THR, PHE+NH4, LEU and ORN were observed. The proportions of each amino acid differed according to growth phase. Maximum release and accumulation in the medium, corresponding to a rise ranging from 10-8 to 10-6 M, occurred at the transition between the exponential and stationary phases, and coincided with a shift in the intracellular protein and carbohydrate concentrations, and in the chlorophyll: phaeophytin ratio. It is suggested that zooplankton grazers can benefit from the accumulation of phytoplankton standing stock and nutritious compounds at times when the concentration of extracellular amino acids is high enough to trigger chemosensory detection of algal food; i.e., at the end of the exponential growth phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393214
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  • 2
    Electronic Resource
    Electronic Resource
    Variation in Vitamin C content of sprat larvae (Sprattus sprattus) in the Irish Sea (1991)
    Springer
    Marine biology 108 (1991), S. 39-48 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sprat (Sprattus sprattus) eggs and larvae were sampled from plankton and the Irish Sea in 1988 and 1989 and analysed forl-ascorbic acid (Vitamin C) content, which is considered an index of the nutritional well being and thus indicative of the status of the population in relation to environmental (physical and biological) structures. In one month, the Vitamin C content of larvae in different developmental stages decreased from 800 to 300µg g−1 in the youngest larvae (4 to 14 mm) and to 250µg g−1 in the oldest larvae (14 to 28 mm). No significant differences in the Vitamin C content per unit weight were found between larvae collected at four sites located in western stratified waters, central stratified, central mixed and eastern mixed waters. The mean Vitamin C content per larva, as well as mean length and wet weight of larvae were lowest in central mixed and eastern mixed waters in May–June. The estimated increases in Vitamin C, length and weight of individuals in the population of larvae varied significantly from April to June and between western stratified and eastern mixed areas. Highest rates coincided with stratified water conditions and with suitable quantity and quality of food, which seemed to constitute the most favourable environmental conditions for abundance and growth of sprat larvae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313469
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  • 3
    Electronic Resource
    Electronic Resource
    Co-occurrence of copepods and dissolved free amino acids in shelf sea waters (1991)
    Springer
    Marine biology 108 (1991), S. 373-385 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The vertical distribution of chlorophylla, copepods, dissolved free amino acid concentration and the fixation of14C by phytoplankton were monitored in the springs of 1983, 1987 and 1988 in the Ushant front region, shelf edge of the Celtic Sea and central Irish Sea, respectively. In each area, two stations characterized by mixed and stratified water conditions were compared. Vertical distributions of amino acids coincided with the distribution of copepods. A positive and significant correlation was found between the abudance of copepods and the concentration of amino acids dissolved in seawater. A negative and significant correlation was found between chlorophylla and the concentration of amino acids. Enrichment of amino acids (≥ 20 to 500 nM l−1 at specific depths) due to aspartic and glutamic acids, glutamine and ornithine, was assumed to reflect copepod feeding activity and faecal production. At these depths, the natural concentration and diversity of amino acids, including aspartic acid, glutamic acid, asparagine, serine, histidine, glutamine, arginine, threonine, glycine, alanine, tyrosine, valine, phenylalanine, ornithine and lysine, were high enough and in the correct proportions for triggering feeding and swimming and swarming behavior of copepods, as well as their remote detection of food at the micro- and meso-scales (1 to 10 m). This accumulation of amino acids also constitutes a potential additional source of organic nitrogen for bacteria and phytoplankton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313646
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  • 4
    Electronic Resource
    Electronic Resource
    A comparative study of the inhibitory effect of diatoms on the reproductive biology of the copepod Temora stylifera (1995)
    Springer
    Marine biology 121 (1995), S. 533-539 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Egg production and viability in the copepod Temora stylifera (collected in the Bay of Naples, Italy in 1992) were strongly dependent on food type. A flagellate (Isochrysis galbana) diet induced the production of good quality eggs that developed to hatching. By contrast, two diatoms (Chaetoceros curvisetum, Phaeodactylum tricornutum) resulted in poor egg quality, with hatching success as low as 20% of total egg production. With the third diatom tested, Skeletonema costatum, females produced eggs for only 3 to 4 d, after which time they either became sterile or died. These results are discussed in relation to previous findings regarding the impact of the dinoflagellate Prorocentrum minimum and the diatom Thalassiosira rotula on the hatching success of T. stylifera eggs. Low egg viability was possibly not due to an absence of remating or a deficiency of some specific essential nutrient required for egg development but to the presence of inhibitory compounds blocking cell division during early copepod embryogenesis. This questions the traditional view that diatoms are an important food item regulating copepod secondary production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349463
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  • 5
    Electronic Resource
    Electronic Resource
    The diatom Thalassiosira rotula affects reproductive success in the copepod Acartia clausi (1996)
    Springer
    Marine biology 125 (1996), S. 279-286 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fecundity, egg viability and fecal pellet production are reported for Acartia clausi females collected in the Bay of Naples, Italy, from April to October 1992 and fed either with a diatom (Thalassiosira rotula) or dinoflagellate (Prorocentrum minimum) diet, at food saturated conditions. The diatom diet significantly reduced both egg and fecal pellet production as well as hatching success. Blockage of egg development occurred with both axenic and non-axenic cultures of T. rotula, suggesting that inhibitors were provided by the diatoms and not by the bacteria associated with diatom cultures. Low hatching success was also artificially induced by exposing newly spawned A. clausi eggs to high concentrations of diatom extracts, indicating the presence of deleterious, inhibitory compounds blocking copepod embryogenesis. Fecundity and hatching success diminished significantly with female age. In contrast, female longevity was not significantly modified by food type. The presence of males did not significantly alter fecundity or egg viability. Females continued to produce viable eggs throughout the period of incubation, with and without males, in both food conditions, indicating that remating is infrequent and not necessary to sustain viable egg production in this species. The succession in low and high population densities may therefore be the outcome of variations in survival rates of eggs, rather than reproductive protential perse; such variations may strongly depend on the adult copepod diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346308
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  • 6
    Electronic Resource
    Electronic Resource
    Feeding rates and diel vertical migration of copepods near South Georgia: comparison of shelf and oceanic sites (1992)
    Springer
    Marine biology 114 (1992), S. 49-56 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seventeen Longhurst Hardy Plankton Recorder profiles were taken over a diel cycle in January 1990 to study the feeding of four major copepods over the South Georgia shelf. Ontogenetic changes in vertical migration were followed and feeding cycles determined by gut fluorometry for Calanoides acutus Stage CV, Calanus sinillimus CV and CVI♀, C. propinquus CV and Rhincalanus gigas CV and CVI♀. In common with a neighbouring oceanic site visited two weeks later and reported elsewhere, all four species had a diel cycle of feeding and migration. The vertical distributions of C. simillimus (all stages), R. gigas (nauplii) and Euphausia frigida (postlarvae) were similar at both sites, the night being spent within the chlorophyll maximum at 15 to 30 m. However, the biomass dominants, C. acutus and R. gigas, dwelt below the chlorophyll maximum, about 30 m deeper than their oceanic counterparts. Unlike the oceanic site, feeding at the shelf site was not restricted to darkness, but increased 6 to 10 h before nightfall and finished at dawn; the intervening period coincided with sinking and digestion. Daylight feeding may have been induced by the shorter night, lower light levels or greater food requirements at the shelf site, despite planktonic predators being over three times more abundant. Daily ration estimates for R. gigas at both sites were only ∼2% body carbon per day. These low values contrast with its smaller competirors, whose rations were in the range 5.6 to 27%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350855
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of diet on levels of amino acids during embryonic and naupliar development of the copepod Calanus helgolandicus (1999)
    Springer
    Marine biology 134 (1999), S. 89-98 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The contents of free amino acid (FAA) and total amino acid (TAA) pools were determined in the eggs, embryos and N1 and N2 nauplii generated by Calanus helgolandicus females fed either the diatom Phaeodactylum tricornutum or the dinoflagellate Prorocentrum minimum for 3 and 10 d. With both diets, egg production rates increased by a factor of 5 to 10, and free amino acid (FAA) and total amino acid (TAA) contents were double those measured in eggs spawned by wild females. Higher levels were measured for almost all amino acids, except methionine, taurine, glutamine, glutamic acid, aspartic acid and ornithine. When embryos developed to live nauplii, 50 to 72% of the initial concentration of the FAA content was used. There was no preferential utilisation of essential over non-essential amino acids. The TAA pool also varied with development. The mean FAA:TAA ratio remained between 11 and 19. With the Prorocentrum minimum diet, hatching success remained constantly 〉85%, whereas it declined to 0% at the end of the 10 d incubation period with Phaeodactylum tricornutum. After 10 d of feeding on this alga, the FAA content of developing embryos increased significantly, indicating liberation of amino acids due to proteolysis. None of these embryos developed to hatching. Inhibition of hatching success related to the ingestion of P. tricornutum was not due to a lack of any amino acid. The results indicate that the chemical composition of freshly spawned copepod eggs is sensitive to the maternal diet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050527
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  • 8
    Electronic Resource
    Electronic Resource
    Water-soluble extracts of the diatom Thalassiosira rotula induce aberrations in embryonic tubulin organisation of the sea urchin Paracentrotus lividus (1999)
    Springer
    Marine biology 134 (1999), S. 147-154 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Eggs and embryos of the sea urchin Paracentrotus lividus were used as a model to study the effect at the cellular level of potential anti-mitotic compounds extracted from the diatom Thalassiosira rotula. Eggs and embryos incubated in a water-soluble diatom extract, corresponding to 5 × 106 and 107 cells ml−1, were totally blocked (i.e. cell division was blocked) at the one-cell stage. At lower concentrations (2.5 and 1.25 × 106 cells ml−1), the first mitotic division was inhibited in 32 ± 26% and 25 ± 3.5% of the zygotes, respectively, demonstrating the dose-dependent effect of diatom extracts on sea urchin development. Immunofluorescence dyes, specific for DNA and α-tubulin subunits, were used to stain nuclei and microtubules in sea urchin embryos during various phases of development. Images with the confocal laser scanning microscope showed that tubulin was not organised in filaments at the sperm aster and cortex levels, and that the pronuclei were not fused in embryos incubated soon after fertilisation with water-soluble diatom extracts corresponding to 107 cells ml−1. At lower diatom-extract concentrations (4 × 106 cells ml −1), fusion of the pronuclei occurred but the mitotic spindle was not formed. Microtubules were clearly de-polymerised and the chromatin appeared globular and compacted at the centre of the cell. A similar structure was observed for sea urchin embryos incubated with 0.1 mM colchicine, a potent anti-mitotic compound. When sea urchin embryos were incubated in water-soluble diatom extracts at different times prior to the first mitotic division, microtubules appeared de-polymerised at each step, from pronuclear fusion to telophase, and cell division was blocked. At the histological level, embryos incubated with 4 × 106 cells ml−1 diatom extract showed nuclear fragmentation without cytokinesis. The possible use of sea urchin embryos as a bioassay to test for other unknown compounds with cytotoxic activity in phytoplankton species is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050533
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  • 9
    Electronic Resource
    Electronic Resource
    Feeding of Pseudocalanus minutus on living and non-living particles (1976)
    Springer
    Marine biology 34 (1976), S. 117-125 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A seasonal study of carbon content of living and of carbon and nitrogen content of non-living particulate material in seawater is presented. Grazing by Pseudocalanus minutus on living and non-living particles has been investigated over 1 year. Seasonal variations in the food uptake were associated with seasonal variations of each chemical component of the particles in the water. The amount of non-living carbon constituted the major part of the food ingested, irrespective of season. The ingested living carbon always accounted for a small fraction of the total copepod body carbon. The proportion of living carbon ingested could be equivalent to or even higher than non-living carbon at times during the late spring, summer and fall. The concentration of both living and non-living material within each particle peak of the spectra in the water seemed to affect the balance between non-living and living particle uptake. Non-living particles cannot be considered only as a supplementary food source for small copepods; they are a basic food for P. minutus at all times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390753
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  • 10
    Electronic Resource
    Electronic Resource
    Diel vertical migration and feeding of copepods at an oceanic site near South Georgia (1992)
    Springer
    Marine biology 113 (1992), S. 583-593 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Twelve Longhurst Hardy Plankton Recorder (LHPR) profiles were taken over a 16 h period in January 1990, in order to study feeding of four copepod species at an Antarctic oceanic site near South Georgia. Vertical distributions of their life stages, as well as those of dominant competitors and predators, are described in relation to the feeding cycles of Calanoides acutus CV, Calanus simillimus CV, Calanus propinquus CV and Rhincalanus gigas CIII, CV and CVI♀. Comparisons with vertical ring-net catches, which were used for concomitant gutevacuation experiments, demonstrated the suitability of the LHPR for these fine-scale studies. Planktonic predators, with the exception of the diel migrant Themisto gaudichaudii, resided deeper than the herbivores. During the day and around midnight, when feeding rates were low, species and stages reached their maximum vertical separation. At these times, new generation copepodites of the four species lived progressively deeper and the overwintered generation (i.e., R. gigas Stages CIV, CV, CVI) were progressively shallower. During the afternoon or evening (depending on species), all stages older than CII, as well as Euphausia frigida and T. gaudichaudii, migrated upwards, to amass in the surface mixed layer. Feeding was restricted to darkness, although R. gigas commenced several hours before dusk. In detail their migration and feeding differed widely, with combinations of unimodal and apparent bimodal cycles. As a whole, the results suggest that (1) feeding could occur during sinking as well as during upward migrations, (2) upward migrations were not always associated with feeding increases, and (3) individuals appeared to descend after filling their guts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349702
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