Contrasting reproductive biology of two hydrothermal gastropods from the Mid-Atlantic Ridge: implications for resilience of vent communities

The recovery of populations and their ability to recolonise a disturbed habitat is mainly dependent on their reproductive biology (e.g., fecundity, frequency of reproduction, and time to maturity) and recruitment success. To assess recolonisation processes and connectivity of vent communities, and infer their resilience to natural and anthropogenic disturbances, we studied the life-history traits of two dominant species of vent gastropods from the northern Mid-Atlantic Ridge: Protolira valvatoides and Pseudorimula midatlantica. Gonad morphology, gametogenesis, and reproductive outputs related to shell length were described using histological analyses, and population structure was assessed from individuals' size-frequency distributions. Samples were collected at different locations of the Montsegur and Eiffel Tower edifices (Lucky Strike vent field) in April 2015, July 2017, and August 2018 to inform on spatial and temporal variations of their reproductive outputs and demography. All stages of oocyte development were found in the gonads of both species, suggesting a continuous gametogenesis and asynchronous reproduction. However, the two species showed contrasting reproductive strategies. Indeed, while P. midatlantica is gonochoric with a fecundity of up to 327 mature oocytes, P. valvatoides is hermaphrodite with an extremely low fecundity including a maximum of eight vitellogenic oocytes. Maximum oocyte size was 176 mu m for P. midatlantica and 272 mu m for P. valvatoides. We infer from previous knowledge and our results that both species exhibit a lecithotrophic development of larvae. There was no evidence of temporal variability of reproductive traits, but environmental conditions seem to affect gametogenetic maturity and oocyte size of P. midatlantica limpets. Variations in population structure at the edifice scale suggest habitat selection of individuals related to biotic and abiotic factors.