Conservation implications of low contemporary connectivity along the Mid-Atlantic Ridge in hydrothermal vent gastropods.

Polymetallic sulfide deposits produced at hydrothermal vent fields are targets for mining exploitation along the Mid-Atlantic Ridge, threatening the functioning and resilience of vent ecosystems that provide multiple ecosystem services. Knowledge about connectivity between vents will inform conservation practices. The present-day genetic structure and demographic history of the two vent-dwelling gastropod species, Lepetodrilus atlanticus and Peltospira smaragdina, were investigated using more than 15,000 single-nucleotide polymorphisms and mtCox1 sequences. Each species comprised three genetic groups. Genetic breaks were stronger for L. atlanticus, separating three distinct operational taxonomic units (5°S, Broken Spur at 29°N, and the Azorean vent fields near 37°N). Peltospira smaragdina was also geographically separated into three groups: Broken Spur, TAG, and Snake Pit (23-29°N); Lucky Strike (37°N); and Moytirra (45°N). A semipermeable zone was detected south of Rainbow (35°N), similar to that of vent mussels in this area, suggesting the presence of a multispecies hybrid zone. Demographic inferences supported secondary contact between most pairs of metapopulations for both species, but the time since contact was insufficient for allele frequencies to rehomogenize. Gene flow between vent fields may be sporadic and rare or restricted by genetic barriers. The fragmentation of species into isolated metapopulations may reduce their resilience to disturbance and create the need for specific conservation measures. Isolated populations (e.g., Moytirra for P. smaragdina, 5°S and Broken Spur for L. atlanticus), source populations (e.g., Lucky Strike for P. smaragdina), admixture areas, and sites that may act as stepping stones within a metapopulation must be protected from deep-sea mining. An average distance of <100 km between favorable habitats in regional environmental management plans could help maintain the species' genetic diversity and connectivity along the ridge.