engleski

Biomineralization in bivalve molluscs and calcareous algae in the Adriatic Sea. An overwiev

Biomineralization is a complex combination of biochemical and physiological processes, which depend on the endogeneous events in the organism and the environmental influence. These processes take place in protective or skeletal structures of about 55 distinct phyla, resulting in about 60 diverse biominerals, one half of these are calcium minerals. In the present work an XRD study of the mineral composition of some marine organisms is described, as a part of a wide scope investigation of biomineralization in land, freshwater and marine beings during the last decade. The shell calcification of the oyster Ostrea edulis, sampled in the Limski Kanal, was followed by XRD from the embryonic through the settlement-attachment-metamorphosis stages up to the juvenile stage. In the gastrula stage only an amorphous tissue was present. The shell formation in early trochophores manifested in the appearance of calcite (up to 7% of the total volume) and then aragonite (up to 1%). In the veliger larva stage the amorphous and calcite fractions decreased, while the fraction of aragonite increased. In the prodissoconch and pelagic periods aragonite was dominant, accompanied by a small amorphous fraction and traces of calcite. During metamorphosis the fraction of calcite rapidly increased and the fraction of aragonite decreased. The valves of juvenile and adult oysters contained mainly calcite, except for the resilium and myostracum which remained aragonitic. A series of calcareous algae, Corallinaceae, Rhodophyta, collected in the Rovinj and Kornati regions, contained magnesium calcite, which was dominant in all but in two cases. Diffraction lines were broadened indicating crystallite size of about 40 nm. The content of Mg in magnesium calcite was about 18%. Aragonite was dominant (up to 80%) in two samples of Pseudolithophilum expansum (Kornati) which also contained magnesium calcite and calcite. In other samples aragonite was detected in small fractions. The fact that under certain microclimatic and marine conditions the same organism forms different minerals confirms that the environmental effects are imprinted in its skeleton composition.

biomineralization. Ostrea edulis. XRD

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