Détermination de l'âge d'araignées de mer Maia squinado par mesure des radioisotopes 228 Th et 228 Ra de la carapace

228 Th and 228 Ra activities were measured in the carapaces of adult spider crabs. The 228 Th/228 Ra ratio provides a physical chronometer, good up to ten years, and thus allows the calculation of the time elapsed since the last molt.  The spider erab is a speeies wi th a terminal mol t which is also the molt of puberty, thus the radiometrie measurements give the time elapsed since the terminal molt, that is an "adult age". We first tested the radiometric ages on individuals that molted in captivity, therefore of known age, and then we applied the method to a sample from the spider crab population of the English Channel