Statoliths of Rapana venosa (Valenciennes, 1846): Microstructure, application for age determination and growth modelling

Rapana venosa (Valenciennes, 1846) is an invasive species that has spread widely around the world, which has commercial importance. For scientifically sound fishery management, accurate age determination is necessary, while the methods currently used have disadvantages. To fulfill the need for a more accurate technique, the microstructure of R. venosa statoliths collected in the northern part of the Black Sea (near the Bolshoy Utrish cape) was studied. Statoliths have well-marked concentric increments, which allows counting with sufficient accuracy. The annual periodicity of R. venosa statolith increments was cross validated using spawning marks on the shells. The growth of veined whelks was the best described by Von Bertalanffy function, with the following coefficients: L∞ = 96.19; k = 0.125; t0 = 0.043. The model accounted for 83% of variance. Moreover, the possibility to reconstruct the age of molluscs based on statolith diameter was tested. It was revealed that the number of increments versus statolith diameter relationship is exponential, the developed model described 99% of variance. Based on these data the growth of R. venosa was modelled again, resulting model accounted for 88% of variance. Coefficients of the model were: L∞ = 106.42; k = 0.102; t0 = 0.136. Potential benefits and limitations of the applied methods are discussed.