MEPS 317:143-156 (2006)  -  doi:10.3354/meps317143

Experimental and natural cathodoluminescence in the shell of Crassostrea gigas from Thau lagoon (France): ecological and environmental implications

D. Langlet1,4*, M. Alunno-Bruscia2,5, M. Rafélis1, M. Renard1, M. Roux3, E. Schein3, D. Buestel2,6

1JE Biominéralisations & Paléoenvironnements, FRE CNRS 2400 Case 116, Université Pierre & Marie Curie, 4 Place Jussieu, 75252 Paris Cedex 05, France
2IFREMER-LCM (Laboratoire Conchylicole de Méditerranée), BP 171, 34200 Sète Cedex, France
3Laboratoire des Sciences de la Terre, Université de Reims, Centre de Recherches sur l’Environnement et l’Agronomie, UMR CNRS 5561, Biogéosciences, 2 Esplanade Roland Garros, 51100 Reims, France
4Present address: Section de Pétrographie-Minéralogie-Géochimie, Musée Royal de l’Afrique Centrale, Leuvensesteenweg 13, 3080 Tervuren, Belgium
5Present address: CRELA (Centre de Recherche sur les Ecosystèmes Littoraux Anthropisés ), UMR 6217 CNRS, IFREMER & Université de La Rochelle, Place du Séminaire, BP 5, 17137 L’Houmeau, France
6Present address: IFREMER-COP (Centre Océanologique du Pacifique), BP 7004, 98719 Taravao, Tahiti, French Polynesia

ABSTRACT: We present a cathodoluminescence (CL) study of growth layer deposition in the shell of the oyster Crassostrea gigas. CL is based on the physical properties of lattice-bound manganese (Mn2+), which is the main activator in calcium carbonate. Our study involved chemical marking by immersing individuals in seawater to which manganese chloride had been added, and subsequent reading of the shell with CL microscopy coupled with numeric treatment of microphotographs; CL emission was analyzed using a scanning electron microscope coupled to a spectrometer. Since the marking did not harm the oysters, repeated markings were possible, allowing validation of the inferences made from analysis of the shell rings. Oysters reared in a French Mediterranean lagoon (Thau lagoon) were marked in June and October 1999, i.e. at the beginning and end of the main shell growth period, respectively. In a few specimens sacrificed 24 h immediately after marking, we observed a bright marking line, suggesting rapid coprecipitation of Mn2+. In oysters collected from March to July 2000, we found 3 luminescent lines (with an emission peak at 620 nm peak) that corresponded to the 3 successive markings. The shells also exhibited weak background Mn2+-induced luminescence, which contrasted with the marking lines both in intensity and color. This background signal varied in intensity over time at 3 distinct scales, i.e. seasonal and daily scales plus an intermediate scale that might reflect tidal patterns. The luminescence intensity was clearly positively correlated with seawater temperature. We postulate that the temperature of the lagoon, combined with abiotic and biotic factors, may control both Mn2+ uptake by the bivalve through a stimulation of biomineralization processes, and Mn2+ bioavailability in water through biogeochemical processes. Our study confirmed the usefulness of Mn marking coupled with CL analysis to reveal (1) the complex functioning of the mantle epithelium with respect to carbonate deposition on a microscale, and (2) the relationship between the bivalve and its environment.

KEY WORDS: Oyster · Cathodoluminescence · Shell growth · Carbonate biomineralization · Manganese marking · Mediterranean lagoon

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