Shell morphometry, pre-mortal taphonomy and ontogeny-related growth characteristics of freshwater pearl mussel in northern Finland

Museum collection of endangered freshwater pearl mussel (Margaritifera margaritifera) shells was studied. The ontogenetic ages of the mussels were estimated to be between 12 and 178 years. Information from shell increments, morphometry and taphonomy was combined into age-dependent life-trait reconstructions that were modelled using linear and non-linear growth functions. Nearly all the life-trait records were best explained by non-linear models and only the shell weight was best modelled by the linear growth function. In accordance with the previously set theory about the plasticity of the species life-traits and their dependence on climate and hydrogeochemistry, the shells with northern origin reached relatively large sizes with slow growth rate. The ontogenetic age could be statistically predicted using the composite dataset of life-trait information. Based on the morphometrics, we theorized that the over 60-year-old mussels are better hedged against the potential hydrological changes resulting from climat change than younger individuals.