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BACKGROUND INFORMATION |
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Since the discovery of the first hydrothermal vent
in 1977 (Corliss et
al., 1979), one of the most important findings in Ocean Sciences
of the XXth century, vent research has been mainly of descriptive nature.
Quantitative approach was hindered by the specific technical, financial,
infrastructural and human resource constraints associated with deep-sea
research. However, now that the importance of hydrothermal vent circulation
within the global oceans is being increasingly realized, an international
co-operation is growing to overcome technological and scientific challenges
for exploring, observing and monitoring these extreme deep-sea ecosystems.
The newly discovered hydrothermal vents, in the vicinity of the Azores
islands have brought the Portuguese archipelago and its reputable marine
research institutes in the confluence of these international scientific
goals.
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Although hydrothermal vents are hostile (Sarradin et
al., 1999), they are crowded with life (Fowler and Tunnicliffe, 1997)
the main features of the ecosystem being strong biological endemisms and
high productivity. Additionally, while anatomy and physiology of vent species
is extensively investigated the mechanisms that are responsible for surviving
under complete darkness, closed to the hot vent discharge, in the presence
of heavy metals and other toxic compounds, and the remarkable water pressure
are not yet elucidated.
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Mussels (Bathymodiolus azoricus) from the
MAR dominate the vent community due to their flexible feeding strategy
(Fisher et al., 1989): they are filter feeders that simultaneously rely
on a dual symbiosis (Kadar et al., 2005; Fiala-Medioni et
al., 1986). The
constant discharge of toxic metals at hydrothermal vents (over 4000 ppm
Fe, 500 ppm Cu and Zn, 12 ppm Hg, etc) (Kadar et al., 2005a) provides a
useful analogue of contaminated marine environments, with the notable difference
that the time scale of contamination here is geological, thus having deep-seated
evolutionary implications of the detoxification mechanisms.
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Shell formation of hydrothermal bivalves per
se, and
its involvement in detoxification lacked attention of vent scientists.
Shell morphology and ultra-structure reflects many aspects of growth related
processes such as potential seasonal effects, the rate of shell dissolution
vs growth etc, all unresolved processes in vent mussels. As the basic mechanism
of skeleton crystallization is common among living organisms, using bivalves
as a model, is a very practical way to widen our general knowledge of crystallization
laws relative to the influencing phisico-chemical factors. Application
of the theoretical concepts resulting from this research would contribute
to our understanding biomineralisation of calcareous deposits with prospective
medical applications (osteoporosis research).
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Deposition of heavy metals into the shell has been
previously reported as a detoxification mechanism in shore bivalves from
anthropogenically-polluted areas (Schein et al., 1991) and thus it is important
that this process be investigated in vent species that are naturally exposed
to various toxic metals.
Because bacteria, the primary producers of these ecosystems derive energy by
mediating thermodynamically favorable chemical reactions, it is axiomatic that
the chemical and physical environment will have a direct impact on the type of
organisms that can exist there. Investigation of the organism habitat interaction
is therefore the key to understand these geologically and biologically unique
features on Earth, and may light the way to the development of new drugs, industrial
processes, and other products useful to us all.
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Bibliography
- 1. Corliss, J.B., et al. (1979) Submarine thermal spings
on the Galapagos Rift.
Science, 203:1073-1083
- 2. Fialamedioni, A., et al. (1986). Ultrastructure of the
Gill of the Hydrothermal-Vent Mytilid Bathymodiolus Sp. Marine Biology 92,
65-72.
- 3. Fisher, C. R., et al. (1989). Microhabitat Requirements
of the Hydrothermal Vent Mussel, Bathymodiolus-Thermophilus. American
Zoologist 29, A81-A81.
- 4. Fowler, C. M. R. and Tunnicliffe, V., 1997. Hydrothermal vent
communities and plate tectonics. Endeavour 214: 164-168.
- 5. Gustafson, R. G., et al. (1998). A new genus and five new species
of mussels (Bivalvia, Mytilidae) from deep-sea sulphide/hydrocarbon
seeps in the Gulf of Mexico. Malacologia 40, 63-112.
- 6. Kádár E, Bettencourt R, Costa V, Santos Rs, Lobo-Da-Cunha
A, Dando P, (2005b) Experimentally induced endosymbiont loss and re-acquirement
in the hydrothermal vent bivalve Bathymodiolus azoricus Journal
of Experimental Marine Biology and Ecology 318: 99-110.
- 7. Kádár E, Costa V, Martins I, Santos RS, Powell JJ (2005a)
Enrichment in trace metals of macro-invertebrate habitats at hydrothermal vents
along the Mid Atlantic Ridge. Hydrobiologia 548: 191-205.
- 8. Sarradin, P. M., et al. 1999. Chemical environment of
the hydrothermal mussel communities in the Lucky Strike and Menez Gwen
vent fields, Mid Atlantic ridge. Cahiers De Biologie Marine 40
(1): 93-104.
- 9. Schein E, et al. (1991)Ecological parameters recorded
by bivalve shell - pluridisciplinary approach. Bulletin De
La Societe Geologique De France 162
(4): 687-698.
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