Reproductive aspects of two bythograeid crab species from hydrothermal vents in the Pacific-Antarctic Ridge

Abstract

Bythograea laubieri, B. vrijenhoeki and alvinellid polychaetes dominate the vent faunaof the Pacific-Antarctic Ridge. We studied gonadal development in females of both crabs. They haveovary microstructures characteristic of brachyuran decapods. The ovaries are paired organs overlyingthe hepatopancreas beneath the carapace. Oogonia proliferate from the germinal epithelium anddevelop into previtellogenic oocytes that grow to 60 Mm before undergoing vitellogenesis. Theobserved maximum sizes of mature oocytes were 209 Mm in B. laubieri and 138 Mm in B. vrijenhoeki.No ovigerous females were found in the samples, which agrees with the segregation behaviour ofovigerous females away from the direct influence of the active chimney in some related species. Incontrast to other species of bythograeid crabs, the oocyte size-frequency data suggest that B. laubieriand B. vrijenhoeki lack synchrony in reproduction of the population as a whole. Synchrony and seasonalityin reproduction of B. thermydron have been linked to the formation of phytoplankton bloomsin surface waters. We suggest that the biogeography of bythograeid crabs is determined by contrastingoceanographic regimes that influence the reproductive patterns observed in different species