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: Six Cretaceous methane-seep deposits are reported from the Raukumara Peninsula, eastern North Island, New Zealand. Dinoflagellate dating indicates a Late Albian to mid-Cenomanian age for three deposits from Port Awanui, and a mid-Campanian age for two deposits from Waipiro Bay and for one from Owhena Stream. The dominant petrographic fabric of the carbonates is detrital micrite, and the numerous fenestrae and vugs are filled with various cements including two types of non-detrital micrite, and botryoidal and banded fibrous calcites. These petrographic features, in combination with negative δ 13 C values of early diagenetic micrites (as low as −29.2‰ vs. V-PDB) and 13 C-depleted molecular fossils such as the archaeal biomarkers pentamethylicosane (−97‰ vs. V-PDB) and biphytane (−99‰), and the bacterial biomarker anteiso-C 15 fatty acid (−47‰), reveal that sulfate-dependent anaerobic oxidation of methane (AOM) induced the formation of these deposits. The carbonates preserve a typical mollusk dominated, Late Mesozoic, deep-water seep fauna including the large modiomorphid bivalve Caspiconcha, the lucinid bivalve Ezolucina, and limpets, hokkaidoconchids and a large abyssochrysoid among the gastropods, with close biogeographic relationships to North Pacific seep faunas of Cretaceous age. In contrast to the general marine mollusk fauna of New Zealand, which shows a high degree of endemism in both the Cenozoic and Recent, New Zealand's Cretaceous to present-day seep faunas consist largely of taxa known from coeval seeps around the world. Thus while deep-water seeps in New Zealand were repeatedly or continuously colonized by members of the global seep fauna, the general mollusk fauna of the New Zealand region developed a considerable degree of endemism during this time.Palaeogeography Palaeoclimatology Palaeoecology 01/2013; · 2.75 Impact Factor
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ABSTRACT: Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis, a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve-sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters and offer new prospects for seagrass ecosystem conservation.Science 06/2012; 336(6087):1432-4. · 31.20 Impact Factor
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ABSTRACT: Deep-sea bivalves found at hydrothermal vents, cold seeps and organic falls are sustained by chemosynthetic bacteria which ensure part or all of their carbon nutrition. These symbioses are of prime importance for the functioning of the ecosystems. Similar symbioses occur in other bivalve species living in shallow and coastal reduced habitats worldwide. In recent years, several deep-sea species have been investigated from continental margins around Europe, West Africa, East America, the Gulf of Mexico, and from hydrothermal vents on the Mid-Atlantic Ridge. In parallel, numerous more easily accessible shallow marine species were studied. We here provide a summary of the current knowledge available on chemosymbiotic bivalves in the area ranging west-to-east from the Gulf of Mexico to Marmara Sea, and north-to-south from the Arctic to the Gulf of Guinea. Characteristics of symbioses in 51 species from the area are summarized for each of the five bivalve families documented to harbor chemosynthetic symbionts (Mytilidae, Vesicomyidae, Solemyidae, Thyasiridae and Lucinidae), and compared among families with special emphasis on ecology, life cycle, and connectivity. Chemosynthetic symbioses are a major adaptation to ecosystems and habitats exposed to reducing conditions, yet relatively little is known regarding their diversity and functioning apart from a few "model species" on which effort has focused over the last 30 yr. In the context of increasing concern about biodiversity and ecosystems, and increasing anthropogenic pressure on Oceans, we advocate for a better assessment of bivalve symbioses diversity in order to evaluate the capacities of these remarkable ecological and evolutionary units to withstand environmental changeBiogeosciences 06/2013; 10:3241-3267. · 3.75 Impact Factor