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  • 1995-1999  (2)
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  • 1
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In situ growth rates were determined, using two, 1-yr mark/recapture experiments, conducted between September 1991 and July 1993, for an undescribed mytilid, Seep Mytilid Ia, at three hydrocarbon seep sites in the Gulf of Mexico. The sites are located at depths of 540 to 730m, approximately 27°45′N; 91°30′W, and are separated by distances of 6 to 18 miles. These seep mytilids harbor methanotrophic endosymbionts and use methane as both a carbon and energy source. The mussel habitats were chemically characterized by analysis of water samples taken from precisely located microenvironments over, among and below the mussels, using small-volume, interstitial water samplers and the “Johnson Sea Link” submersible. Substantial differences were found in habital conditions, growth rates, and population structure for the mussels at the three sites examined. The growth rate of these seep mytilids reflects the methane concentration in their immediate habitat. Mussels at sites with abundant methane had growth rates that were comparable to shallow water mytilids at similar temperatures (5 to 8°C) with increases in shell length up to 17 mm yr−1 documented for smaller mussels (〈40 mm shell length). In conjunction with measurements of growth rates, three condition indices (glycogen content, tissue water content, and the ratio of ash-free dry weight to shell volume) were used to determine the relationship between the condition of the mussels, their growth rates, and their habitat chemistry. The three condition indices were correlated with growth rate and were often significantly different between mussels in different samples.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hydrothermal vent vestimentiferans Riftia pachyptila Jones, 1981 and Ridgeia piscesae Jones, 1985 live in habitats with different abundances of external CO2. R. pachyptila is found in areas with a high input of hydrothermal fluid, and therefore with a high [CO2]. R. piscesae is found in a range of habitats with low to high levels of hydrothermal fluid input, with a correspondingly broad range of CO2 concentrations. We examined the strategies for dissolved inorganic carbon (DIC) use by the symbionts from these two species. R. pachyptila were collected from the East Pacific Rise (9°50′N; 104°20′W) in March 1996, and R. piscesae were collected from the Juan de Fuca Ridge (47°57′N; 129°07′W) during September of 1996 and 1997. The differences in the hosts' habitats were reflected by the internal pools of DIC in these organisms. The concentrations of DIC in coelomic fluid from R. piscesae were 3.1 to 10.5 mM, lower than those previously reported for R. pachyptila, which often exceed 30 mM. When symbionts from both hosts were incubated at in situ pressures, their carbon fixation rates increased with the extracellular concentration of CO2, and not HCO3 −, and symbionts from R. piscesae had a higher affinity for CO2 than those from R. pachyptila (K 1/2 of 7.6 μM versus 49 μM). Transmission electron micrographs showed that symbionts from R. piscesae lack carboxysomes, irrespective of the coelomic fluid [DIC] of their host. This suggests that the higher affinity for CO2 of R. piscesae symbionts may be their sole means of compensating for lower DIC concentrations. The δ13C values of tissues from R. piscesae with higher [DIC] in the coelomic fluid were more positive, opposite to the trend previously described for other autotrophs. Factors which may contribute to this trend are discussed.
    Type of Medium: Electronic Resource
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