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  • 1990-1994  (3)
Document type
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Larval development in the Antarctic nemertean Parborlasia corrugatus (Heteronemertea: Lineidae) (1993)
    Springer
    Marine biology 116 (1993), S. 301-310 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Embryonic and larval development were followed from fertilisation to settlement in the Antarctic heteronemertean Parborlasia corrugatus (McIntosh, 1876). The first cleavage occurred 10 to 15 h after fertilisation, and the second at ≃17 h. Larvae hatched at the gastrula stage, between 170 and 200 h post-fertilisation, and were ≃150 μm in diameter. Early larval stages aggregated in dense groups near the surface of incubation vessels and were positively phototactic. Early pilidium larvae were recognisable 435 h post-fertilisation. They were 155×152 μm in size, and possessed a complete apical tuft of cilia and a full marginal band of locomotory cilia. At this stage, the gust was visible through the body wall, and the mouth was open and was ≃40 μm in diameter. Late pilidia, 222×193 μm in size, were helmet-shaped. They had an apical tuft over 100 μm long, and possessed a lobed marginal band of locomotory cilia. Pilidia were observed aggregating close to the bottom of incubation vessels 1200 to 1350 h (50 to 56 d) after fertilisation, and this was interpreted as settlement behaviour. At this stage, the apical tuft had been lost and they were highly contractile, being capable of compressing their bodies. However, neither developing juveniles within the larval envelope nor hatched juveniles were observed. Pilidia consumed the microalgae Tetraselmis suecica, Thalassiosira pseudonana and Isochrysis galbana. They also fed on particulate organic material 〈 1 μm in size, as shown by the presence of material in the guts of larvae offered filtered extracts of algal cultures. There was some indication that larvae could use dissolved organic material, since pilidia held in seawater with organic material removed did not survive as long as those in filtered seawater or in filtered water with added amino acids. However, the only larvae to exhibit settlement behaviour in the feeding experiments were those offered Tetraselmis succica and Thalassiosira pseudonana, and these required a longer development time to reach this stage than pilidia in the standard cultures, where a mixed algal diet was offered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350020
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Pelagic larval development in the brooding Antarctic brachiopod Liothyrella uva (1994)
    Springer
    Marine biology 120 (1994), S. 279-286 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Larvae of the Antarctic brachiopod Liothyrella uva (Broderip, 1833) were released by brooding females between 10 and 15 January 1992. They were collected and cultured for the ensuing 45 d. At release they were at the gastrula stage, and were recognisable as the usual brachiopod three-lobed larva from around 18 d after release. At ≃22 d post-release, larvae began to congregate under shell fragments placed in culture vessels as potential settlement substrata. However, the larvae showed no signs of settlement which, combined with the absence of many of the attributes of mature larvae seen in previous studies, was taken as evidence that these larvae had not reached fully competent stages. Previous work had shown that L. uva spawns in October, indicating that the developmental period lasts for a minimum of between 115 and 160 d. The release and subsequent development of larvae also shows that what was previously thought to be a brooding species combines a long brooding period with a free-swimming phase. If this is true of other brachiopod species, then there may need to be a recategorization of some species from brooding to combined brooding and free-swimming developmental types. Even though the development period in L. uva was likely to have been underestimated because a fully competent stage was not reached, a comparison with development rates for temperate species indicated a slowing of between 8 and 70 times. This dramatic slowing of development rate in brachiopods now joins similar data previously reported for echinoderms and nemerteans, suggesting that this is a very widespred, perhaps universal, attribute of Antarctic marine invertebrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349689
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Growth and population structure in the infaunal bivalve Yoldia eightsi in relation to iceberg activity at Signy Island, Antarctica (1993)
    Springer
    Marine biology 117 (1993), S. 235-241 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth rates in the infaunal nuculanid bivalve mollusc Yoldia eightsi (Couthouy) were assessed for field populations in Factory Cove, Signy Island, Antarctica, between. February and April 1992. Daily increments in length (maximum shell dimension) ranged from 2.3 μm d-1 for a 30 mm individual to 5.1 μm d-1 for a 10 mm specimen. These growth rates were converted to annual increments, based on a growing season for the Signy population of around 5 mo, and ages for the largest individuals in the population (35 mm in length), were calculated to be ≃65 yr. Specimens of 43 mm in length have been found near this site and, if their growth rates are similar to this population, their ages would be in the order of 120 yr. Size distributions from two sites in the same Y. eightsi bed 300 m apart showed significant differences. At the more exposed site the distribution was dominated by small juveniles, with 86% of the population 10 mm in length, while 13% were 〉20 mm in length. At the less exposed site the values were 27% 〈10 mm and 56% 〉20 mm. Icebergs have often been seen grounded on the Y. eightsi bed in this study, especially on the exposed outer portion. This factor, in association with inhibition of larval settlement by high densities of large individuals, is proposed as an explanation of the observed population distributions and the absence of very large specimens in the Factory Cove population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00345668
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    Paper (German National Licenses)
    Fulltext
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