Abstract
Summary Few species of reptant decapod crustaceans thrive in the cold‐stenothermal waters of the Southern Ocean. However, abundant populations of a new species of anomuran crab, Kiwa tyleri, occur at hydrothermal vent fields on the East Scotia Ridge.As a result of local thermal conditions at the vents, these crabs are not restricted by the physiological limits that otherwise exclude reptant decapods south of the polar front.We reveal the adult life history of this species by piecing together variation in microdistribution, body size frequency, sex ratio, and ovarian and embryonic development, which indicates a pattern in the distribution of female Kiwaidae in relation to their reproductive development.High‐density ‘Kiwa’ assemblages observed in close proximity to sources of vent fluids are constrained by the thermal limit of elevated temperatures and the availability of resources for chemosynthetic nutrition. Although adult Kiwaidae depend on epibiotic chemosynthetic bacteria for nutrition, females move offsite after extrusion of their eggs to protect brooding embryos from the chemically harsh, thermally fluctuating vent environment. Consequently, brooding females in the periphery of the vent field are in turn restricted by low‐temperature physiological boundaries of the deep‐water Southern Ocean environment. Females have a high reproductive investment in few, large, yolky eggs, facilitating full lecithotrophy, with the release of larvae prolonged, and asynchronous. After embryos are released, larvae are reliant on locating isolated active areas of hydrothermal flow in order to settle and survive as chemosynthetic adults. Where the cold water restricts the ability of all adult stages to migrate over long distances, these low temperatures may facilitate the larvae in the location of vent sites by extending the larval development period through hypometabolism.These differential life‐history adaptations to contrasting thermal environments lead to a disjunct life history among males and females of K. tyleri, which is key to their success in the Southern Ocean vent environment.We highlight the complexity in understanding the importance of life‐history biology, in combination with environmental, ecological and physiological factors contributing to the overall global distribution of vent‐endemic species.
Highlights
The abundant assemblages of fauna at deep-sea hydrothermal vents are largely sustained by microbial primary2012; Rogers et al 2012)
As a result of local thermal conditions at the vents, these crabs are not restricted by the physiological limits that otherwise exclude reptant decapods south of the polar front
High-density ‘Kiwa’ assemblages observed in close proximity to sources of vent fluids are constrained by the thermal limit of elevated temperatures and the availability of resources for chemosynthetic nutrition
Summary
The abundant assemblages of fauna at deep-sea hydrothermal vents are largely sustained by microbial primary2012; Rogers et al 2012). The abundant assemblages of fauna at deep-sea hydrothermal vents are largely sustained by microbial primary. The same constraints are thought to account for high endemism and in situ evolution of the Antarctic benthos (Brandt et al 2007), among which invertebrates exhibiting high reproductive investment in fewer, larger eggs, with lecithotrophic development, prevail (Thorson 1950; Thatje 2012). Both vent sites on the ESR are visually dominated by a new species of anomuran, Kiwa tyleri The more southern E9 vent field is influenced by lower Weddell Sea Deep Water with ambient water temperature typically at À1Á3 °C and colder than its northern counterpart at E2 (c. 0Á00 °C; Rogers et al 2012)
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