Seasonal periodicity of growth and composition in valves of Diplodon chilensis patagonicus (d'Orbigny, 1835)

Freshwater mussels of the genus Diplodon (Unionida) are common inhabitants of lakes and rivers in South America, and have slow growth and long life spans. We established the annual periodicity of incremental shell growth in Diplodon chilensis patagonicus (d'Orbigny, 1835) and calculated growth rates at different ages, using internal ring counting supported by dyeing methods and δ 18 O isotope analyses, in two Patagonian populations (Lago Steffen and its effluent Rio Manso Inferior, Argentina). Longevities of ca. 90 years (Lago Steffen) significantly extend the life spans reported in the past. Growth rates for old individuals (>30 years) from both lake and river populations average 0.16 mm p…