Assessing the lifespans of coldwater octopods (Cephalopoda: Octopodiformes)
This thesis dissertation investigates longevity of deep-sea and Antarctic octopodiform species using life history traits and the quantification of growth increments in the octopods’ beaks (chitinous jaws). The first chapter investigates how life history traits including embryonic development, hatchling size, size- and age-at-maturity are correlated with habitat characteristics (water temperature and depth of occurrence), using published data of 26 octopodiform species. The second chapter tests the hypothesis that the incirrate benthic octopods living in the vicinity of the Antarctic Peninsula (-2 to 2°C) have longer lifespans than their temperate and tropical relatives. Age was investigated in specimens of the family Megaleledonidae (Pareledone spp., Adelieledone spp. and Megaleledone setebos) and in Muusoctopus rigbyae, using the quantification of growth increments deposited in their beaks. Age estimates are discussed and were compared to those in other octopod species in which the periodicity of beak growth increments has been validated to be daily. The third chapter also uses the quantification of growth increments in beaks to assess if the deep-sea pelagic octopodiforms Japetella diaphana and the vampire squid Vampyroteuthis infernalis have longer lifespans compared to benthic relatives. Their remarkable low metabolic rates and reproductive biology rather suggest that growth increments in the beaks may require more than one day to be formed.