Population structure of two deep-sea hydrothermal vent gastropods from the Juan de Fuca Ridge, NE Pacific

The gastropods Lepetodrilus fucensis and Depressigyra globulus are abundant faunal components of animal communities at deep-sea hydrothermal vents along the Juan de Fuca Ridge in the NE Pacific. The population structure and recruitment pattern of both species were studied using modal decomposition of length–frequency distributions. Gastropod populations were collected from Axial Volcano and Endeavour Segment in 2002 and 2003. Polymodal size–frequency distributions, particularly at Axial Volcano vent sites, suggest a discontinuous recruitment pattern for D. globulus. In contrast, there were no distinct peaks visible in the distributions of L. fucensis, suggesting a continuous recruitment pattern for this species. For both species, distributions were positively skewed towards the smaller length–classes, implying post-settlement mortality is high. However, variations in growth, due to short- and long-term variability in environmental conditions in the hydrothermal vent habitat, as well as biological interactions, may also be influencing the distribution and abundance of subsequent life-history stages. Using maximum shell lengths from populations of known ages, the growth rate of L. fucensis was estimated as 9.6 μm day−1, indicating adulthood would be reached in ∼1 year. Our results suggest that, despite occupying the same habitat, abundance and population structure are regulated by different biotic and abiotic processes in L. fucensis and D. globulus.