Shell growth, microstructure and composition over the development cycle of the European abalone Haliotis tuberculata

The shell of the European abalone Haliotis tuberculata is a model for studying mechanisms of mollusc shell formation, but the early steps of shell formation and calcification remain poorly documented. The microstructure and the mineralogical and geochemical composition of larval and juvenile shells were investigated by scanning electron microscopy, infrared spectroscopy and ion microprobe analyses (NanoSIMS). Analyses were performed on shells obtained from controlled fertilisations at the hatchery France-Haliotis (Plouguerneau, France) in July 2009 and 2010 using abalone from Roscoff. Shell cross sections revealed the microstructural arrangement of the developing shell, showing progressive biomineral organisation into two differentiated layers, i.e. the outer granular and the internal nacreous layer. Infrared analysis confirmed that the European abalone shell, at every stage of development, was mostly composed of CaCO3 in the form of aragonite. Variations in trace element composition, i.e. Sr/Ca, were measured in the different stages and correlated with micro-structural changes in the shells. Experimental manganese labelling of live abalones produced cathodoluminescence marks in the growing shell sections. The increase in shell thickness can be used to determine the growth rate of an early adult abalone shell.