Size- and sex-based habitat partitioning by Lepetodrilus fucensis near hydrothermal vents on the Juan de Fuca Ridge, Northeast Pacific

This study examines habitat partitioning by a hydrothermal vent limpet, Lepetodrilus fucensis, along environmental gradients and among vents with differing levels of flux. To test for spatial patterns in size structure, two distances from isolated vent flows were sampled (0–25 cm and 51–75 cm). Lepetodrilus fucensis displays a size gradient: juveniles are rare in flow (relative abundance < 5%, density = 56 ± 46 individuals·dm–2) and abundant peripherally (>95%, 2616 ± 2002 individuals·dm–2). Next, sex-based habitat partitioning was examined. High flux locations are female-biased (proportion male = 0.34 ± 0.07), whereas males are overrepresented peripherally and at waning vents (0.64 ± 0.08). The spatial mismatch between the sexes within a vent is driven by differential habitat occupation at decimetre scales. One hypothesis to explain this pattern is that females suffer a higher cost of reproduction and outcompete males for habitats with high food availability. Indeed, relatively higher percentages of females in waning vents had empty gonads in comparison with males (32%–78% vs. 0%–16%, respectively). Furthermore, females transplanted to the vent periphery for one year displayed much lower survivorship than males (2% vs. 27%). This finding suggests that differential survivorship between the sexes when food is limited can yield male-biased populations at waning vents.