New insights on age estimation of the native oyster Ostrea puelchana: an approach by modern shell sclerochronology and chemistry techniques.

DOLDAN, MARÍA DEL S.; DE RAFELIS, MARC; MORSAN, ENRIQUE M.; PASCUAL, MARCELA

Puerto Madryn

Congreso; VIII Congreso Latinoamericano de Malacologia Aplicada (CLAMA).; 2011

Centro Nacional Patagonico

Some bivalves do not exhibit clear surface rings to estimate their age so alternatively methods have been sought in an attempt to overcome this difficulty.Modern shell chemistry techniques such as cathodoluminescence (CL), stable isotopes and the use of fluorochromes have been successfully tested for sclerochronology. CL provides an approach for identifying growth increments within biogenic carbonate shells that are not visible using conventional microscopy. Oxygen (δ18O) and carbon (δ13C) profiles allow determination of growth rates and seasonality from shells with accretionary growth. Calcein, a fluorescent compound,binds with calcium carbonate in biomineralised growing structures of organisms and has proven to be a suitable marker for bivalves? shells. We explored these techniques in parallel experiments to estimate individual age of the oyster Ostrea puelchana. Thick-sections of a set of oyster shells were photographed under an optical microscope with cathodoluminescence. Additionally, isotope samples were milled parallel to the growth axis, along a transect from the oldest (umbo) to the most recently formed shell portion in the hinge region of the shell. Samples per shell were yielded and analyzed on mass spectrometer for the determination of stable oxygen and carbon isotope ratios. A group of live oysters were stained with calcein and reared in lanterns suspended from a raft for one year to allow growth. To detect marks, shell sections were analyzed with blue light. CL-microscopy of the shell hinge sections of O. puelchana showed bright natural luminescence revealing growth increments. The variations in luminescence were attributable to seasonal variations during calcification. Photomicrographs of hinge sections and luminescence profiles were analyzed. Given the known date of death of the oyster shells and the age of one specimen, it was possible to interpret the δ C profiles and to provide an age model through the hinge region. Calcein provided a distinct conspicuous mark in ∼50% of the shells that allowed measuring the seasonal increment. Large inter-individual variability in growth rates was observed. Modern shell sclerochronology and chemistry techniques allow an approach in the detection of the patterns of seasonal growth in this species.