May 9th, 2003; Leg 5, Day #19
Today’s dives were located along the
transform fault a few kilometers southeast of Pinkie’s Vent. Yesterday,
we bid farewell to our mascot, Pinkie. She will remain a marker of the
vent where much of our work has been located for the past three days.
Having a distinctive marker like Pinkie made relocating the vent site much
easier and gave us a point of reference for orienting the vehicle. Think
of what it would be like to survey a farm field from a helicopter on a
dark night with a flashlight. That’s much like how it is to navigate an
ROV on the seafloor, and you often don’t know what you’ll bump into.
Today we stumbled on some exciting chemosynethic communities. We encountered a broad expanse of a fluffy, white, bacterial mat and clusters of lamellibrachian tubeworms perched on carbonate rock outcrops on the seafloor. The pilots were successful in recovering chunks of these rock outcrops with tubeworms intact. What is most intriguing about these tubeworm
clusters is that on close examination in the lab, there are little baby tubeworms attached to the rocks we recovered. Little is known about the early life stages of lamellibrachian tubeworms and these samples will aid us in piecing together and expanding our understanding their life cycle.
You might wonder why chemosynthetic communities generate such interest and excitement for us. In thinking about how to put them into an ecological context, I am reminded of the analogy Marston Bates drew in his book, The Forest and the Sea, between the vertical structure of the oceans and tropical rainforests. Where sunlight penetrates the upper ocean and the top of the forest canopy, photosynthesis is the dominant process that fixes energy and creates a complex web of life. Dead and decaying organisms from the upper ocean rain down through the water column and are either consumed on the way down or land on the ocean floor. This is analogous to the accumulation of leaf litter on the forest floor. In both ecosystems, there are heterotrophs that graze on the accumulation of organic matter and bacteria and fungi that degrade complex organic material into more simple compounds. Holothurians, for example, are the street sweepers of the deep sea. Organisms that live on the seafloor in the deep sea need energy and raw materials (i.e., carbon- and nitrogen-containing molecules) to grow and to reproduce. In this model I have described, the energy and molecular building blocks come from the upper ocean, and deep-sea life, all the way down to the lowly Holothurian, is driven by photosynthesis.
About 25 years ago, chemosynthetic organisms were first discovered on this planet in the deep ocean. Chemosynethic organisms have the capacity to harvest chemical energy and to create biomolecules necessary for their life and reproduction and are not dependent on photosynthesis as a source of energy. Chemosynthetic organisms, such as Calyptogena clams and tubeworms have evolved symbiotic relationships with various types of bacteria that can harvest chemical energy from methane or hydrogen sulfide (the two most common types of reduced inorganic compounds). These endosymbionts live inside the host animal in a mutually beneficial relationship—they get shelter and help with maintaining their metabolism, and the host gets energy and raw materials. A pretty good deal all around. The real eye opener is this—there isn’t an analogous form of chemosynthetic life on land. Chemosynthetic organisms represent a fundamentally different life form of which we have little knowledge.
Tomorrow is another adventure exploring the trace of the transform fault and keeping an eye out for more chemosynthetic communities.
– Bill Ussler, reporting
Sunsets are spectacular along the Baja California Sur coast. It became a ritual every evening to stand along the rail and watch the sun set and hope for the green flash that often occurs just as the sun drops below the horizon. Some of us were delighted with their first ever sighting of a green flash.