Freshman year, in Dr. “Kip” Herreid’s Evolutionary Biology class, I was given the assignment of reading and summarizing a scientific paper. These days, I review a dozen or more a week, but at that time I had never read an actual peer-reviewed research paper. The one I chose was on the subject of hydrothermal vent communities. (Sorry – I can’t recall the exact title). Since then, I have been fascinated with these strange deep-sea sites and the organisms that live at them.
Hydrothermal vents are fairly recent discoveries. Although there was evidence of their existence as early as 1949, it wasn’t until 1979 that scientists using the submersible Alvin, at a depth of 2500 meters on the mid-ocean ridge in the East Pacific, were able to see these communities with their own eyes. And what they saw wasn’t like anything else on Earth.
Hydrothermal vents are also known as “black smokers” because they resemble chimneys thrust up from the ocean floor. It wasn’t so surprising to find geysers of hot water, in areas where the floor was actively spreading. What was astonishing was the abundance of strange and new forms of life living off these super-heated plumes. Like travelers huddled around a campfire on a very cold winter night, the organisms at these vents live in close proximity to the hot plumes of mineral-rich water that pour out of the seafloor at 270 – 380 degrees C (515 – 716 degrees F).
Giant tube worms, Riftia pachyptila, are the most conspicuous members of Pacific vent communities. One end is attached to the ocean floor while the other sports a bright red fringe of tissue flush with hemoglobin that captures the hydrogen sulfide to feed to the symbionts living within. Rapidly growing to 1.5 meters (4.9 feet) at a rate of up to 84 cm (33 inches) a year, these tube worms are believed to be the fastest-growing marine invertebrates. (And anyone who has owned a boat knows how fast marine inverts can grow on a clean surface).
As impressive as the worms are, the true stars of this deepwater production are the billions of chemosynthetic bacteria; the entire foodchain rests on the “shoulders” of these bacteria due to their ability to oxidize hydrogen sulfide. These bacteria live symbiotically with other organisms, including the worms, crabs, mussels and numerous other vent creatures.
One of the things that fascinates me about these communities, is that hydrothermal vents (and their cold seep* cousins) are the only ecosystems known on earth that are completely independent of the sun. That is, they do not rely on the sun’s energy AT ALL. In contrast, every action, thought, process, event or activity in your day started out as sunlight. The cereal you had for breakfast started out as plants that directly captured sunlight to build the plant tissue that ended up in your bowl. If you had chicken for dinner or beef or some other land creature, it ate plants that “ate” sunlight. In the ocean, the chain may be longer but it stills starts the same way. The tuna you had for lunch got its energy from smaller fish, which likely ate even smaller fish that may have snacked on zooplankton or directly on phytoplankton. The phytoplankton, of course, caught some rays and made some more phytoplankton material before becoming someone else’s meal.
Not only food, both most other forms of energy** start out as sunlight: heat from the sun warms the air and oceans, generating the wind that turns turbines. Even the gas you pump into your tank or the coal burned for heat started out as plants (and animals) many millions of years ago.
Since they are completely isolated from the surface, hydrothermal and cold seep communities may be the only ones on Earth immune to climate change. On the other hand, if climate change dramatically alters ocean chemistry or circulation in the deepest parts of the sea, these communities may also be affected. Something to wonder about. (And if anyone has thoughts or theories about this, please let me know).
For more information on these amazing communities, check out these websites:
NOAA’s Vents program conducts research on the impacts and consequences of submarine volcanoes and hydrothermal venting on the global ocean. Their site is detailed, interesting and fun to explore.
Woods Hole Oceanographic Institution (WHOI) hosts a site aimed at the non-technical visitor and includes explanations as well as fabulous photos and videos taken from Alvin of hydrothermal vents around the world.
Tell them I sent you!
* Cold seeps are areas where hydrogen sulfide, methane and other energy-rich fluids seep out of the ocean floor, supporting bacteria that can utilize these materials for energy (“chemoautotrophs”) and other organisms that live off of these bacteria, mostly as symbionts. For more info, check out: http://people.whitman.edu/~yancey/califseeps.html.
**Most but not all – geothermal power comes from the energy stored in the Earth.