Life history traits of the deep-sea pelagic cephalopods Japetella diaphana and Vampyroteuthis infernalis

The pelagic cephalopods Japetella diaphana and Vampyroteuthis infernalis are charismatic and widely distributed members of deep pelagic ecosystems. Their habitat temperatures, metabolic rates, feeding and reproductive strategies all together suggest that the pace of life in these species is reduced when compared to neritic octopod species, but information on longevity, growth rates and age estimations are absent to date. To estimate the pace of life in pelagic octopods, this study investigated size at maturity, reproductive strategy, and the number of growth-increments in the upper beak lateral walls (LWS) of J. diaphana (an octopod) and V. infernalis (a vampyromorph). Daily deposition of growth increments in hard body structures (e.g., beaks and stylets) has been validated experimentally in some temperate and tropical octopods, but remains unquantified and not yet validated for most deep-sea and high-latitude cephalopods. We used a diverse assemblage of specimens ranging from early juveniles to adults for both species. Mature J. diaphana had a mantle length (ML) of 53-144 mm and a body mass (BM) of 18-235 g. A brooding female of J. diaphana captured at 1352 m in the Gulf of California was carrying 1419 eggs in pre-organogenetic stage that measured similar to 2.5 mm in diameter. The size range of mature V. infernalis was ML 66-122 mm and BM 34-286 g. The number of growth increments in the beaks ranged from 21 to 207 in J. diaphana and from 89 to 375 in V. infernalis. If the growth increments are formed daily, like in tropical octopod species, age estimates are incongruent with the low metabolic rates and reproductive strategies of the two species. These observations suggest that growth increments may require more than one day to be formed. To better understand the life histories of invertebrates in the largest but least studied habitat on the planet, age and growth validation studies are critical.