In Ecology, the von Bertalanffy growth function (VBGF) is the standard model used to investigate the body growth of marine species. The parameters of this function are usually estimated by a classical method that might induce bias in the results: this method does not allow to distinguish the variability at individual or population level nor to take into account the contribution of environmental factors. A Bayesian hierarchical non-linear model for estimating the VBGF parameters is proposed in order to overcome the limitations of the traditional method. The proposal improves both the statistical accuracy and the quantification of uncertainties affecting marine species growth. The proposal is assessed through a case study concerning two Mediterranean corals, Balanophyllia europaea and Leptopsammia pruvoti.