Age validation in Octopus vulgaris beaks acrossthe full ontogenetic range: beaks as recorders of life events in octopuses

Abstract

This study demonstrates the daily deposition of increments in Octopus vulgaris beaks for both lateral wall surfaces (LWS) and rostrum sagittal sections (RSS). Forty-nine marked wild animals kept in aquaria (weight range, 158–3,521 g) and 24 captive-reared known-age individuals (paralarvae, 0–98 days old; adults, 200–734 days old) were studied, encompassing for the first time the full age range of the species, including known-age individuals older than 1 mo. The daily deposition of beak increments was validated in the LWS by injection of Calcofluor, and in the RSS by environmental marking (thermal, confinement, capture, and stress of the chemical marking process). A total of 111 successful validations (when beak increments corresponded precisely to days elapsed) were achieved, and the maximum validated periods were 57 days (LWS) and 112 days (RSS). In the pelagic stage and transition to the settlement stage, a new pattern of microincrements that record age was demonstrated in the lateral hood surfaces of upper jaws, where stress checks were observed. In the benthic stage, tip erosion in beak RSS results in some underestimation of age; however, the demonstration that RSS can record environmental stress renders it a potentially useful tool for documenting life events.