Biology of the Vent Crab Bythograea thermydron: A Brief Review

Abstract

This paper provides a review of relevant literature concerning the vent crab Bythograea thermydron. This body of work describes a crab species that shares fundamental biological characteristics with typical shallow-water brachyuran crabs, yet possesses a suite of highly evolved traits specific for life at hydrothermal vents. Bythograea thermydron is one of only six known species of Bythograea and is very abundant at vent sites along the East Pacific Rise. Because of the large amount of scientific work at this location, almost everything known about bythograeid vent crabs is based on studies of this single species. This review specifically deals with biogeography, systematics, and evolution; morphology, physiology and special adaptations; ovarian development; mating, brooding, and hatching; and larval biology and dispersal. The various sections emphasize comparisons with shallow-water crabs and highlight characteristics such as: (1) the unique eye structure in the adult stage, which is adapted for sensing the exceptionally dim light that is generated by the vents themselves; (2) the extreme tolerance of adults and juveniles to conditions of low oxygen and high sulfides; (3) the exceptional eurythermal character of juvenile and adult physiology; and (4) the seasonality of ovarian development and subsequent reproductive activity. Discussion of larval biology presents various scenarios of larval dispersal and recruitment back to the vent sites.