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  • 1
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    Colloquium on diatomcopepod interactions (2005)
    In:  EPIC3Marine ecology-progress series, 286, pp. 293-305
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
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    The Relevance of Marine Chemical Ecology to Plankton and Ecosystem Function: An Emerging Field (2011)
    In:  EPIC3Marine Drugs, 9, pp. 1625-1648
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
    Electronic Resource
    Electronic Resource
    Reproductive energetics, endocrinology and population dynamics of Nephtys caeca and N. hombergi (1985)
    Springer
    Marine biology 88 (1985), S. 235-246 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An investigation of gametogenetic cycles and spawning success in populations of Nephtys caeca and N. hombergi from the River Tyne estuary, North Shields, England, in relation to production of gonadotrophic (GH) and spawning hormones (SH) has been made, based on data collected from 1978–1984. The data show that a consistent pattern of gametogenesis and efficient spawning occurs in populations of N. caeca in north-east England, but that the reproductive cycle of N. hombergi is erratic. Premature oosorption and gametogenic failure in this latter species is associated with a low level of GH production. Following high levels of GH production, gravid females sometimes fail to spawn owing to the non-release of SH. The reproductive energetics and reproductive success of N. caeca and N. hombergi are described in relation to the observed patterns of endocrine activity and the consequent changes in population structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392586
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  • 4
    Electronic Resource
    Electronic Resource
    Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina (2000)
    Springer
    Marine biology 136 (2000), S. 1003-1017 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes, well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270000283
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  • 5
    Electronic Resource
    Electronic Resource
    Reproductive success, relative abundance and population structure of two species of Nephtys in an estuarine beach (1981)
    Springer
    Marine biology 63 (1981), S. 189-196 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During 1978 and 1979 specimens of Nephtys hombergii in the River Tyne estuary (North East England) became gravid during the winter but did not spawn in the spring breeding season; instead their gametes were resorbed. The drastic effects of these spawning failures were apparent in the population structure in 1980, when the 1978 and 1979 year-classes were shown to be virtually absent, by the size of the individuals in the population and the numbers of growth lines in their jaws. The population structure in 1975, by contrast, indicated that recruitment during the preceding 4 to 5 yr had been good. Spawning was also effective in 1980, and an 0 group was detected in August 1980. Comparable data has been obtained for N. caeca, which occurs in the same beach. It shows that recruitment of this species during 1976–1980 was consistently good, whereas analysis of the age-class frequencies suggests that recruitment of N. caeca was poor in 1973 and 1975. The dominance relationship of the two species in the beach has been reversed during the period 1975–1980. It is suggested that the sympatric distribution of the two species is maintained in part by periodic reproductive failure. The causes of this are not yet known; possible reasons, including the extremely cold conditions experienced in 1978–1979 are discussed. The difference in frequency of the 1978, 1979 and 1980 year classes will now permit a rigorous evaluation of the relationship between the number of growth lines in the jaws and age in N. hombergii.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00406827
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  • 6
    Electronic Resource
    Electronic Resource
    An ultrastructural study of oogenesis in the polychaeteNephtys hombergi Savigny (1989)
    Springer
    Helgoland marine research 43 (1989), S. 157-169 
    Details
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The polychaeteNephtys hombergi has an annual cycle of reproduction. Ovaries were fixed for electron microscopy during the gametogenic phase from September to March, and during the breeding and post-breeding periol. Oogenesis takes place entirely within the ovary, the integrity of which is maintained by a network of simple follicle cells. Previtellogenic oocytes have close contacts with the peri-vasal cells which surround the genital blood capillaries. These contacts are lost as the oocytes enter vitellogenesis. The vitellogenic oocytes have a cytology typical of oocytes which are thought to undergo autosynthetic production of protein yolk. Biochemical studies would be required to establish whether heterosynthesis of yolk also occurs. As the oocytes proceed through vitellogenesis, cortical material is laid down near the periphery of the oocyte and a microvillous surface is developed. When the microvillous surface is complete the oocytes, by then hormone independent, are ovulated from the ovary and are ready to be spawned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02367896
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  • 7
    Electronic Resource
    Electronic Resource
    An ultrastructural study of spermatogenesis and sperm morula breakdown inArenicola marina (L.) (Annelida: Polychaeta) (1992)
    Springer
    Helgoland marine research 46 (1992), S. 185-199 
    Details
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Spermatogenesis in the lugwormArenicola marina, in common with other members of Arenicolidae, occurs in the coelomic fluid and results in the formation of discs of mature spermatozoa known as a morulae. Within a morula, individual spermatozoa are connected by a common mass of cytoplasm called the cytophore and therefore make up a syncitium. Immediately prior to spawning, and in response to an endocrine substance known as “Sperm Maturation Factor” (SMF), the structure of the sperm morulae breaks down and free spermatozoa are liberated. These are subsequently spawned from the body cavity. The investigation described here uses transmission electron microscopy to investigate the ultrastructural changes, which accompany spermatogenesis and the breakdown of sperm morulae in response to SMF in vitro. The study demonstrates that the cytophore appears to have a key role both during spermatogenesis and during sperm morula breakdown. The ultrastructure of sperm morulae and of mature spermatozoa is described. The structure of spermatozoa is shown to be primitive with a single flagellum which appears to be coiled at its distal end. The phagocytosis of free spermatozoa by coelomocytes is also described and it is suggested that these may play a role in the resorption of unspawned gametes in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02366054
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  • 8
    Electronic Resource
    Electronic Resource
    Sperm ultrastructure in two species of the polychaete genusHarmothoe (Polynoidae) (1992)
    Springer
    Helgoland marine research 46 (1992), S. 171-183 
    Details
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The structure of spermatozoa is described for two species of polynoid polychaete,Harmothoe imbricata andHarmothoe impar, from material fixed and examined by both scanning and transmission electron microscopy. The two species undergo spermiogenesis within discrete testes. The testis ofH. imbricata is shown to have a layer of epithelial cells which possess an outer cuticular layer and a microvillous inner surface. Spermatocytes of both species are spherical but there are marked differences in the shape and size of the spermatozoa of the two species.H. impar has a classical primitive spermatozoon with a rounded head (2 μm long) and a button-shaped acrosome. Fully differentiated spermatozoa ofH. imbricata are modified from the primitive form by having a long head (10 μm length) with a pointed acrosome about 6 μm in length. Spermatozoa ofH. imbricata have a ring of up to fourteen mitochondria around a centrally inserted flagellum at the posterior whereasH. impar has a ring of four or five spherical mitochondria. Spermiogenesis is well synchronised inH. imbricata but all developmental stages can be found simultaneously in the testis ofH. impar. The differences in sperm structure of the two species may be related to differences in breeding biology which are hitherto unknown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02366053
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  • 9
    Electronic Resource
    Electronic Resource
    Sexual Satellites, Moonlight and the Nuptial Dances of Worms: the Influence of the Moon on the Reproduction of Marine Animals (1999)
    Springer
    Earth, moon and planets 85-86 (1999), S. 67-84 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The evidence that the moon has a profound effect on the timing of reproductive activities of marine animals is compelling. Some moon phase related spawning events are revealed by the constant phase relationship between the timing of “once per year” spawning events and the lunar phase as in the highly synchronised breeding of the palolo worm Palola viridis and the Japanese crinoid Comanthus japonicus In other cases there is a repeated lunar cycle of reproductive activity and again the marine worms provide many good examples. The breeding of the palolo worm involves the highly synchronised release of what are in effect detached sexual satellites and the timing of this has annual (solar year), lunar, daily and tidal rhythm components. In a similar way, the onset of sexual maturation and participation in the nuptial dance of Platynereis dumerilli has strong lunar components. Sexual reproduction is the culmination of a process of sexual maturation that takes many months for completion and the mechanisms by which moon phase relationships are imposed on this process must have been selected for by mechanisms relating to reproductive success. The polychaetes provide excellent models for investigation of both the selective advantage and the physiological processes involved in reproductive synchrony. We have recently shown that the spawning of the lugworm Arenicola marina has lunar components and we conclude that an interaction between solar and lunar signals is widespread in the timing of reproduction in marine animals. Carl Hauenschild was the first to demonstrate the existence of a free-running circa-lunar rhythm in marine animals using captive populations of Platynereis dumerilli His experiments also provided clear evidence for the influence of moonlight (light at night) as the zeitgeber for this rhythm. This implies a high level of sensitivity to light, and the operation of appropriate endogenous biological rhythms. Using Nereis virens we have demonstrated a high level of sensitivity to low intensity solar light signals in relation to rhythmic processes with the properties similar to the circadian and photoperiodic mechanisms of terrestrial organisms. The spawning of N. virens is also believed to have lunar components reflecting the complex influences of the sun and the moon in the marine domain, where influences of the moon and sun are more equal. We suggest that evolution of biological rhythmicity that can be entrained to either lunar or solar systems arose in the marine domain. Recent advances in understanding the molecular components of the circadian clock system suggest that a search for a common molecular mechanism for both lunar and solar related biological rhythms in marine organisms might be very fruitful.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017039110161
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  • 10
    Electronic Resource
    Electronic Resource
    Intermittent swimming in the spermatozoa of the lugworm Arenicola marina (L.) (Annelida: Polychaeta) (1994)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 29 (1994), S. 186-194 
    Details
    ISSN: 0886-1544
    Keywords: sperm motility ; intermittent swimming ; Arenicola marina ; annelida ; polychaeta ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Motile spermatozoa of the polychaete Arenicola marina were observed to swim intermittently. On the basis of the behaviour of the flagellum, the quiescent periods can be classified into two main types. The first are those in which, although the generation of the flagellar wave appears to be initiated, its passage down the axoneme appears blocked. This results in the formation of an acute bend (of approximately 2.65 rad) in the proximal region of the flagellum with the remainder of the axoneme remaining straight. These have been termed Type I quiescent periods and are very similar to the “cane-shaped” configuration which has been described in the spermatozoa of some sea urchins. Sperm may also enter a Type II quiescent period, in which both the propagation and the generation of flagellar waves appears blocked. The flagellum of such sperm appears straight or slightly curved and they can remain in this configuration for several minutes. With increased intensity and duration of irradiation, the length of time spent in Type II quiescent period was increased significantly. Both types of quiescent period were (1) reduced in duration and frequency by deletion of calcium from artificial sea water (ASW); (2) either abolished or reduced in duration by the addition of 1 mM cadmium chloride to ASW. In addition, flagellar waveforms very similar to those displayed by spermatozoa in Type I quiescent periods could be induced (if only for a short time) by the addition of the divalent cation ionophore A23187 to ASW. It is suggested that this type of behaviour may be induced following an influx of calcium into the intraflagellar compartment of spermatozoa and that this may be mediated by certain intensities and wavelengths of light. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970290210
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