submersible support ship R/V Lulu to make a number of dives in the submersible
Alvin to the crest of the Galapagos Ridge, close to the equator in the eastern Pacific.
Possible venting sites had been identified by towed thermistors and cameras prior to
the dives. Corliss was first down. He promptly found the vents and saw that they were
surrounded by a remarkable community of attached and motile benthic animals
(Corliss et al. 1979; Plate 15.1). The history of this initial discovery of the vents is
told by Cone (1991). Ridges, vents, and vent biology are reviewed in books by
Humphris et al. (1995), Van Dover (2000) and Desbruyères et al. (2006).
(^) The expedition was well prepared. Their cameras, rock-collecting equipment
(grasping arms and holding baskets), thermometry, and chemical sampling gear
allowed an amazingly complete first characterization of the vent systems, including
collections of the animals. It was soon evident that the system was very unusual, since
large concentrations of organisms whose near relatives are aerobic were living in
water supersaturated in sulfide, which is a poison for cytochromes, the electron
transfer enzymes fundamental to oxidative metabolism. The source of food, however,
was immediately obvious. The vent walls and water were covered with bacterial mats
that were assumed to be a food source. The presence of sulfide suggested that these
would be chemosynthetic bacteria utilizing sulfide as a source of reducing capacity, a
group of bacteria already well known from their presence in sulfide-rich sediments.
Biologists who heard the story and saw the movies figured that out long before it was
proved. Some (e.g. Enright et al. 1981), anxious that this be proved before it was
accepted, suggested that enhanced flow along the bottom, driven by warm water
rising from the vents, might concentrate particulate food for filter-feeders. There are
filtering animals near vents, especially patches of serpulid polychaetes with
tentaculate crowns. However, extended observation has shown that their principal
food is particles emerging from the vent, not particles approaching from the
surrounding seafloor.
(^) Corliss turned the animals over to the invertebrate curators at the Smithsonian
Institution, who distributed them to experts on the various groups represented. It took
those experts a long while to come out with descriptions and names, but they did an
admirable and complete job. What we have learned since is that most of the sessile
fauna around the vents, for example, from the first-visited sites, the tube worms
(pogonophorans now known as vestimentiferans, Riftia pachyptila), the clams
(Calyptogena magnifica) and the mussels (Bathymodiolus thermophilus) have evolved
symbiotic relationships with sulfide-oxidizing chemosynthetic bacteria which provide
their nutrition. The mussels also can filter-feed. Other members of the community, the
crabs (Bythograea thermydron and several galatheid crabs) and fish in particular, are
wandering about taking nips off the sessile forms. Others, including zooplankton that
swarm in the vent plumes, filter-feed on the bacteria flooding from the vent. The first
vents discovered were relatively quiet, without abundant mineral particulates in the