Teacher Logbook:
Monday, July 10, 2000 1600 hrs.

Previous NeMO cruises witnessed white microbial floc streaming (mpg video) out of the ocean floor as a snow-blower near a vent field named Magnesia. Upon our return this year the scientists in the control room were surprised at the changes that had taken place. The snowblower was dead. Somewhere the subterranean piping that fed this area changed. In just one year Magnesia went from an oasis of life to a biological desert. Obviously the habitat here is very unstable, always subject to change without further notice. Vent conduits may clog as sulfides are deposited. "Barbecue pits" have been observed with vent creatures encapsulated in fresh lava. Chemosynthesis may cease due to vent fluid chemistry changes. A dynamic system indeed.

With no habitat insurance, how do vent organisms pass on their genes and keep their population, possibly even their species, from dying out completely? Creatures must simply migrate over time and colonize new vent habitats. Since many of the animals at the vents are sessile (unable to move), current based larval dispersal becomes the only method of migration. These young must venture out to find new real estate. This is not an easy task given the volume of the oceans and the fact that hydrothermal vents are a discontinuous string following oceanic spreading centers.

Two models have surfaced regarding larval dispersal from hydrothermal vents. First is the stepping stone model that predicts that organisms jump from one vent to the next and eventually colonize all 40,000 km's of rift zone. This would explain why vent community animals at Axial Volcano are more related to vent community animals on the other side of the planet than to deep-sea animals located just a few hundred meters from them. On the other hand, the island pool model predicts that if the vent animals put enough larvae into the water column, by shear chance some larvae will land close enough to a vent to colonize. This is similar to wind pollination in terrestrial plants. Talking to larval dispersal expert Anna Metaxas I found out that both models are probably true, depending on the particular organism. Anna shared that there is very little larval dispersal information at this time because it's an extremely tough topic to tackle. She mentioned that by researching larvae she was really just opening up a new can of worms.

Jeff

Chains of limpets extending down into a vent crack at Cloud Vent.