Hierarchical non-linear mixed-effects models for estimating growth parameters of western Mediterranean solitary coral populations. Ecological Modelling

Marine biologists usually assess coral growth through the von Bertalanffy growth function (VBGF), a func-tion of several biological parameters linked to age by a non-linear relationship. Coral growth parametersare then evaluated via ordinary least squares after a linear transformation of the VBGF. Current litera-ture focuses on linearization techniques, but these methods are often used without considering a carefuldata examination and the presence of variability in coral of the same age or in coral of the same colony.For these reasons, a more thorough approach based on a hierarchical non-linear mixed-effects model isproposed. This model takes into account the influence of sites’ characteristics to model heterogeneitybetween sites. Moreover, the contribution of environmental factors and all the reliable information thatmay influence coral growth can be suitably modelled. Two model specifications based on the standardand new VBGF parameterizations are introduced to analyse the growth of a solitary coral species Bal-anophyllia europaea. Results from the proposed modelling approach show the importance of includingenvironmental conditions for species coral growth and support; furthermore, the results show the impor-tance of the possibility of accounting for variability from different sources in terms of estimated growthcurves.