Diving on ‘Bush Hill’
(Originally Published in People, Land & Water, Dec., 2000)
Gregory S. Boland, Minerals Management Service
Though I joined the Minerals Management Service only two years ago, I have worked on
many MMS-funded projects in the last two decades, beginning as a graduate student
researcher at Texas A&M University.
As a biological oceanographer, one of the most significant and
exciting periods of my research was in the mid-1980s when I was involved in the first
discoveries of chemosynthetic communities in the Gulf of Mexico. This work was part of the
Northern Gulf of Mexico Continental Slope Study, funded by MMS from 1983 to 1988.
I was a principal investigator for the study, working for LGL Ecological Research
Associates. As the scientist in charge, I was responsible for operating a deep-sea camera
system that was lowered 9,800 feet to the bottom of the gulf. I also analyzed the results
of these surveys. Our study culminated with the first submersible dives on true
hydrocarbon seep chemosynthetic communities in the gulf.
There are various kinds of chemosynthetic animals, including tube worms, clams, and
mussels. But they all harbor in their tissues a symbiotic bacteria that can use simple
chemicals such as sulfide and methane gas as a source of energy. Chemosynthetic animals
are remarkable because this energy source is independent of photo-synthesis and the
sun-dependent photosynthetic food chain that supports most life on earth.
Large chemosynthetic animals were unknown to science
until 1977, when they were first discovered at hydrothermal vents in the Pacific Ocean.
Two groups of researchers made the first discoveries of these creatures in the central
Gulf of Mexico in November 1984.
Photographic images of tube worms and clam communities were obtained at two different
sites using the LGL camera system.
The tube worm photo was particularly amazing in that it showed a still unexplained
relationship between tube worms and a clam (genus Acesta). The clams were
attached only to the ends of the tube worms with the plumes of the worms living inside the
clams. The British journal Nature published this photo. Later in November of that
year, researchers from Texas A&M University unexpectedly brought up live clams and
tube worms in a trawl taken through an area known to have gas hydrates and oil-laden
sediments.
The next year MMS awarded additional funds to LGL and its subcontractor, Texas A&M
University, to conduct a special cruise and use the submersible Johnson Sea Link to dive
on locations where chemosynthetic animals had been found the previous year. I had the
privilege of being the scientific observer in the acrylic sphere with pilot Don
Liberatore, of the Harbor Branch Foundation.
Though I had been an observer in Texas A&M University’s small submersible Diaphus,
this was my first dive in the Johnson Sea Link. Sitting in the completely transparent
sphere of the Sea Link is strikingly different and truly spectacular. You can see in
almost every direction, even under your feet. It often gives the sensation of being in a
fishbowl, while the marine life outside study you.
I was filled with anxious anticipation on the long ride to the bottom at 1,800 feet.
The only light not coming from the sub at those depths was from deepsea bioluminessing
animals. We finally reached the bottom, and with instructions from the surface, Don
maneuvered the sub toward a large elevated mound in the distance.
As we slowly cruised up the slope of the hill (where we knew oil had been found in core
samples), we suddenly came across an area of tube worm clusters. My first words were,
“Wow, look at all the bushes of tube worms, there are bushes everywhere!”
The researchers back on the ship heard this on the radio and decided that “Bush
Hill” would be a good name for the first chemosynthetic site in the central gulf. We
saw dense clusters of tube worm “bushes” and mussel beds throughout an area that
covered many acres. Mussels were seen for the first time living directly on active gas
vents. It was a memorable experience and the beginning of many studies of chemosynthetic
communities in the gulf, much of it funded by MMS. And Bush Hill has become one of the
most thoroughly studied chemosynthetic sites in the world.
Greg Boland is with the Environmental Studies Section of the MMS Gulf of Mexico
Region.
For more information, contact Keith Good.
