ABSTRACT: We collected megalopa larvae and early juveniles of the crab Bythograea thermydron from a depth of 2500 to 2600 m at a hydrothermal vent field along the East Pacific Rise (ca 9° to 10° N, 104° W). Taxonomic identification of the megalopa larvae was accomplished through the use of morphological characteristics corroborated by molecular genetic analysis of an amplified portion of DNA from the mitochondrial 16s rRNA gene. We successfully reared megalopa larvae through metamorphosis and through subsequent juvenile molts at atmospheric pressure in the laboratory. This is the first time that this has been reported for any vent species. Laboratory data were combined with measurements of field-caught juveniles to allow estimation of carapace width, dry weight, and stage duration of the first 5 juvenile stages. Results of behavioral experiments indicated that B. thermydron megalopae swim actively over the range of temperature expected near the vents (2 to 25°C). Swimming speed varied with temperature (4 to 10 cm s^-1), but generally exceeded the speed of bottom currents at the vent fields. Moreover, the propensity to swim was inversely related to temperature. These results suggest that swimming behavior may be an important component of locating warm vent settlement sites in the otherwise cold waters surrounding a vent field.

KEY WORDS: Hydrothermal vents · Crab · Megalopa · Juvenile · Behavior · Development

Published in MEPS Vol. 185 (1999) on August 20
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999