Food sources for the early life history stages of the hydrothermal vent crab Bythograea thermydron: a stable isotope approach

Abstract

We used stable isotope analysis to examine food sources for early life-history stages of the vent crab Bythograea thermydron. During two cruises to a hydrothermal vent site along the East Pacific Rise, we collected a variety of endemic organisms, including approximately 300 specimens of B. thermydron. The crab collection consisted mainly of megalopae and early juveniles, but also included adults and a single zoea. As expected, the carbon-isotope composition of newly released zoeae (−12.2%) was similar to the female (−11.1%) and clearly different from megalopae (21.7%). Because we were unsuccessful in culturing the zoea larvae, we were not able to conduct experiments to determine the effect of diet on isotopic composition. The tissue of megalopae was depleted in 13C (−21.7%) when compared to indigenous prey species, but was similar to that expected for carnivorous zooplankton dependent on surface primary production. The nitrogen-isotope composition of megalopae was enriched in 15N (10%) relative to potential prey species, again suggesting a photosynthetic source of primary production. The mean carbon-isotope composition of newly metamorphosed juvenile crabs (−19.9%) resembled megalopae, while tissue from subsequent juvenile stages was enriched in 13C (−10.9%) with values similar to those measured in co-occurring prey species. These results imply that megalopae are dependent on a source of primary production exogenous to the vents, but switch to a vent-based food web soon after metamorphosis to the juvenile stage.