Abstract
Abstract. Deep-sea bivalves found at hydrothermal vents, cold seeps and organic falls are sustained by chemosynthetic bacteria that 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, eastern Americas, the Gulf of Mexico, and from hydrothermal vents on the Mid-Atlantic Ridge. In parallel, numerous, more easily accessible shallow marine species have been studied. Herein we provide a summary of the current knowledge available on chemosymbiotic bivalves in the area ranging west-to-east from the Gulf of Mexico to the Sea of Marmara, and north-to-south from the Arctic to the Gulf of Guinea. Characteristics of symbioses in 53 species from the area are summarized for each of the five bivalve families documented to harbor chemosynthetic symbionts (Mytilidae, Vesicomyidae, Solemyidae, Thyasiridae and Lucinidae). Comparisons are made between the families, with special emphasis on ecology, life cycle, and connectivity. Chemosynthetic symbioses are a major adaptation to ecosystems and habitats exposed to reducing conditions. However, 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 a better assessment of the diversity of bivalve symbioses in order to evaluate the capacities of these remarkable ecological and evolutionary units to withstand environmental change.
Highlights
Bivalve mollusks occur in a variety of marine and freshwater ecosystems, at aOll cdeepathns aSndcliaetitnudcees
Tamu fisheri, which inhabits the base of Lamellibrachia luymesi (Annelida: Siboglinidae) aggregations and beds of B. childressi, and Idas simpsoni from the North Sea both harbor extracellular sulfur-oxidizing bacteria associated with their gill epithelial cells
L. nassula, occurs in seagrass beds near Florida and has a very similar symbiont sequence (Durand and Gros, 1996) symbiosis was characterized based on gill tissue ultrastructure or molecular evidence in a variety of other coastal reduced sediment or seagrass bed species including Myrtea spinifera, L. floridana, L. borealis, and Loripes lucinalis, with estimates that the latter could be responsible for up to 16 % of the primary production observed in seagrass bed habitats in a lagoon in upper Corsica (Dando et al, 1994, 1985, 1986; Distel et al, 1988; Johnson and Fernandez, 2001; Johnson et al, 2002)
Summary
Bivalve mollusks occur in a variety of marine and freshwater ecosystems, at aOll cdeepathns aSndcliaetitnudcees. Symbiotic nutrition through gill-associated bacteria is the most recently discovered nutrition mode It was demonstrated in large clams and mussels found around deep-sea hydrothermal vents, first discovered in when they d1i9sc7o7ve(LreodTnlsahdragelee,fCa1u9rn7ya7o,)i.snScplcuihdenientigrsetbsivwaelvreespaunzdzlgeidant tube worms around chimneys emitting high-temperature, toxic fluids. A survey of the literature indicates that approximately 200 bivalve species, in these areas, belong to families or subfamilies reported to be associated with chemosynthetic bacteria This number certainly underestimates the true diversity, as new species are often discovered upon exploration of new sites. Efforts are currently being made to connect “old” names (such as Idas modiolaeformis Sturany 1896) with recent molecular data, but a reassessment of bivalve taxonomy combining morpho-anatomical and molecular characteristics is needed (Lorion and Samadi, 2010) This must be kept in mind when dealing with the names of species and genera (Table 1).
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