The deep-sea neogastropod Buccinum scalariforme: Reproduction, development and growth

- This study monitored the complete life cycle of a deep-sea gastropod in mesocosm settings.
- Egg masses were laid in the spring and fall, during peaks in deposition of particulate matter.
- Intracapsular development lasted ~4-5 months and relied on oophagy and adelphophagy.
- Based on the first 2.5 years, growth to maximum adult size could require 20-50 years.
- B. scalariforme has lower fecundity and slower growth than shallow-water neogastropods.

Specimens of the neogastropod Buccinum scalariforme (60-70 mm shell height) collected between 700 and 1450 m depth along the continental slope of eastern Canada were kept for 4 years in mesocosm settings. Their mating, spawning and development were assessed, thereby generating the first complete life cycle account of a deep-sea gastropod. Egg laying occurred in March and September, with a total of 9 egg masses laid in 2013 and 2015, coinciding with periods of maximum deposition of particulate organic matter (phytodetritus). Oviposition lasted 2-3 days and the female protected the egg mass for ~3 more days until it had hardened. Typically, egg masses contained 50-75 egg capsules, each measuring 5-8 mm in diameter. A capsule contained between 100 and 150 spherical eggs (300-500 µm) of which ≤50 developed into embryos. Potential fecundity calculated from the entire egg mass at spawning was between 1500 and 2250 propagules; it drastically decreased over ~4-5 months of development to an effective fecundity of 30-50 juveniles emerging from the mass (0-2 juveniles per capsule). Development went through early embryonic stages in ~15 days and reached the trocophore in 15-21 days, followed by intracapsular veliger larva (480 µm) and intracapsular pediveliger (~1000 µm) after ~90 days. Completion of development relied on oophagy and adelphophagy. The juveniles hatched at a shell height of 1-2 mm and consumed the capsule membrane. Over 2.5 years, they reached a maximum size of ~8-10 mm shell height at an average of 9.8 µm day−1. Estimations indicate that B. scalariforme could require between 20 and 50 years to reach maximum adult size. Large gastropods like B. scalariforme are among the most abundant motile benthic invertebrates of the bathyal zone of eastern Canada. Knowledge of their reproductive biology constitutes a first step in assessing their vulnerability and resilience to ever growing anthropogenic pressures, including fisheries, and oil/gas exploration and exploitation.