Reproductive biology of the original hydrothermal hairy snail, Alviniconcha hessleri, from the Mariana back-arc

Many life history traits of hydrothermal vent fauna are undescribed, yet this knowledge is crucial for the accurate assessment of the vulnerability of vent endemic species, which are endangered by anthropogenic impacts in the deep-sea. Here we advance the knowledge of life history traits in Hessler’s hairy snail, Alviniconcha hessleri , a dominant gastropod harbouring chemosynthetic endosymbionts endemic to hydrothermal vents along the Mariana back-arc. Snails were collected from sites at four hydrothermal vent fields to quantify reproductive periodicity using histology, larval developmental mode using oocyte and protoconch-I size, and differences in oocyte size across diverse venting environments. Results indicate that A. hessleri shares some of the same traits as other vent gastropods: continuous oogenesis and consistent provisioning to oocyte size, regardless of local vent fluid chemistry. A maximum oocyte size of 93 µm indicates planktotrophy for this species but could not be further supported using protoconch size due to excessive shell degradation. Our results suggest that this species maximizes reproductive output and oocyte quality, expected as a response to unpredictable environmental conditions to ensure the continued maintenance of existing populations and the establishment of new populations. Although the life history traits of A. hessleri may convey high reproductive and dispersal potential, the realized range of this species is limited to seven vent fields. Thus, this species may be vulnerable to habitat disruption due to its reliance on a restricted habitat, even though it has life history traits adapted to high environmental variability.