Living on the edge: population parameters of the wedge clam Donax hanleyanus in the southernmost limit of its distribution range, southwestern Atlantic, Argentina

Abstract

The wedge clam Donax hanleyanus Philippi, 1845 is a conspicuous member of the sandy beach macrofauna along hundreds of kilometres in the northern coasts of Argentina. Age, growth, mortality, and productivity of this species were assessed in the southernmost limit of its distribution range (Mar del Plata, Buenos Aires province, Argentina). The parameters of the von Bertalanffy growth function were SL∞ = 23.23 mm, K = 1.62 year−1, and t0 = 0.08 years. The maximum individual production was 7.9 × 10−7 g shell-free wet mass (SFWM)·year−1 at a shell length of 14–16 mm. Individuals between 10 and 12 mm contributed the most to the secondary production (P) of 0.01 g SFWM·m−2·year−1. The mean annual biomass (B) was 0.002 g SFWM·m−2·year−1. Annual P/B ratio and mortality coefficient (Z) were 4.48 year−1 and 4.78 year−1, respectively. Low production and high mortality could be caused by a sharp decrease in habitat quality, given the suboptimal temperatures at the southernmost edge of the species distribution. These results strongly limit its potential for future commercial exploitation.