Chemoautotrophic symbionts in the gills of the bivalve mollusc Lucinoma borealis and the sediment chemistry of its habitat.
ABSTRACT Lucinoma borealis has enlarged gills, which contain numerous prokaryotes in specialized cells (bacteriocytes) in the subfilamentar region. The gills also contain high concentrations of elemental sulphur and of a c-type cytochrome. Homogenates of gill tissue show ribulosebisphosphate carboxylase and phosphoribulokinase activity; they also show activity for adenylylsulphate reductase, an enzyme concerned in the oxidation of sulphur, and will phosphorylate ADP on the addition of sulphite or sulphide. Fixation of bicarbonate by gill tissue from starved animals is enhanced in the presence of 100 µM sulphide. The sediment in which the animals live contains 1-6 $\mu $g atoms per litre of dissolved iron and hence there is very little dissolved sulphide, 200 nM, or less (80 nmol dm-3 sediment). Thiosulphate concentrations are also low, 300 nM, or less (120 nmol dm-3 sediment). In contrast, there are acid-labile sulphide concentrations up to 14 mmol dm-3 and elemental sulphur concentrations up to 4 mg atom per cubic decimetre of sediment. The mean sulphate reduction rate in the sediment varied seasonally with temperature over the range 1640-4920 nmol sulphate reduced per hour per cubic decimetre. L. borealis was usually found below the region of maximum sulphate reduction. Hydrogen, methane and carbon monoxide concentrations were all 160 nmol dm-3, or less. Despite the low levels of dissolved sulphide the association between prokaryote and host appears to be able to exploit this habitat by the oxidation of reduced sulphur species; ways in which the bivalve may be able to extract these from the sediment are discussed. The bivalves may obtain half their carbon from the autotrophic prokaryotes.
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ABSTRACT: We conducted a species-level study of molluscs associated with a 5-m long carcass of a minke whale at a depth of 125 m in the Kosterfjord (North Sea, Sweden). The whale-fall community was quantitatively compared with the community commonly living in the surrounding soft-bottom sediments. Five years after the deployment of the dead whale at the sea floor, the sediments around the carcass were dominated by the bivalve Thyasira sarsi, which is known to contain endosymbiotic sulphur-oxidizing bacteria, while background sediments were dominated by another thyasirid, T. equalis, less dependent on chemosynthesis for its nutrition. The Kosterfjord samples were further compared at the species level with mollusc abundance data derived from the literature, including samples from different marine settings of the west coast of Sweden (active methane seep, fjords, coastal and open marine environments). The results show high similarity between the Kosterfjord whale-fall community and the community that developed in one of the Swedish fjords (Gullmar Fjord) during hypoxic conditions. This study indicates that at shallow-water whale-falls, the sulphophilic stage of the ecological succession is characterized by generalist chemosynthetic bivalves commonly living in organic-rich, sulphidic environments.Marine Biology Research 01/2014; 10(1):3-16. · 0.96 Impact Factor
- Experimental Approaches to Understanding Fossil Organisms: Lessons from the Living, Topics in Geobiology 41 edited by Hembree DI, Platt BF, Smith JJ, 01/2014: chapter 3: pages 49-72; Springer.
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ABSTRACT: The Azorean seabed is depauperate in terms of bivalve species richness, there being only between ~70 and 80 recorded to date, most being sub-tidal and generally lacking of specialists. Analysis of large numbers (>3200) of Azorean bivalve shells has revealed that, overall, each species is only ~50% the shell length size of Mediterranean conspecifics. Thus, although Azorean bivalve size may be a consequence of decreasing latitude (Bergmann's Rule), the islands are located at approximately the same latitude as the Mediterranean (and are influenced by those waters) where larger conspecifics occur. Hence, the main reason for bivalve dwarfism in the archipelago appears to result from low oceanic productivity (Foster's Rule). This, in turn, is associated with low diversity, possibly resulting from past extinctions and isolation, and low population sizes, except for Ervilia castanea, which here overwhelmingly occupies higher-energy inshore habitats and associated higher productivities. Nevertheless, this species too is dwarfed by mainland conspecifics. Similarly, the introduced Venerupis decussata, found solely within the lagoonal environment of Fajã de Santo Cristo on São Jorge, is somewhat smaller than its mainland conspecifics, although it is abundant enough to warrant artisanal exploitation. This study therefore, supports Foster's Rule and argues for the role of nutrient deficiency in regulating Azorean species richness and individual maximum size. In waters of locally higher productivities, however, population densities increase, but not size.Journal of the Marine Biological Association of the UK 05/2013; 94(03):567-578. · 1.13 Impact Factor