Stauromedusan populations inhabiting deep-sea hydrothermal vents along the southern East Pacific Rise

Dense populations of "stalked jellyfish" (Stauromedusae) were encountered at two geographically-separated, deep-sea hydrothermal vent fields located at 7 degrees 26'S; and 20 degrees 02'S along the East Pacific Rise (EPR). DSV Alvin was utilized (on dives 3320 and 3334) at the sites to collect numerous stauromedusans, which were immediately frozen (at -70 degrees C) or preserved in 70% ethanol upon arrival on board the research support vessel (R/V Atlantis). High resolution images were collected of the organisms in situ. A 530-560-bp region of mitochondrial 16S was amplified, and edited 16S sequences were aligned, along with sequences from 7 other stauromedusans. Results suggest that the Stauromedusae encountered at 7 degrees 26'S, and 20 degrees 02'S are very closely related, if not conspecific. It remains unclear whether or not these Stauromedusae are distinct from Lucernaria janetae (collected from 8 degrees 37'N along the EPR), which was recently described by Collins and Daly (2005). To date, dense populations of stauromedusans have been encountered at four separate deep-sea hydrothermal vent fields along the EPR located at the following latitudes: 20 degrees 50'N, 8 degrees 37'N, 7 degrees 26'S and 20 degrees 02'S. Many fascinating questions remain concerning the biogeography and mechanisms of dispersal of these cnidarians between discrete deep-sea hydrothermal systems.