Class on November 8 2018

Lucie kicked off module three, Food Webs in Extreme Environments, with a review of what we had learned to care about when considering best practices for creating a food web model. She then introduced Dr. Roxanne Beinart who provided an hour-long lecture and discussion entitled Hydrothermal Vent Food Webs.

Such vent communities tend to thrive at 1000 to 2500 meters below sea surface (although they exist in shallower and deeper waters as well). Since photosynthesis is only possible in the top 200 meters of the water column (sunlight no longer permeates the water column at 1000 meters depth), life needs contribution from the photosynthetic process (falling down to depth) or needs to find a different source of energy to survive.

In 1977, a symbiotic tube worm community was found on the ocean bottom around Galapagos Islands. A symbiotic relationship with chemosynthetic bacteria allows the tube worms to farm necessary energy from the bacteria, through their surface and/or through bacteria living within the worms. Since 1977, many hydrothermal vent communities have been discovered and analyzed, although a surprising number of active questions regarding them are far from being answered scientifically. Adapted mussels, snails, crabs, shrimp, and 'dinner plate' sized clams seem to thrive at depth upon living off the vents.

Only bacteria and archaea life forms are capable of synthesizing methane, sulfide, iron, and hydrogen into food in chemosynthetic process (each chemical providing different energy amounts). Thus the food web needs to build upon that source of energy as other food webs build upon terrestrial and shallow water photosynthesis. Our course is ideal for students to wear the hat of emergent (even theoretical) food web modelers considering potential food web processes as in this image here:

The tectonic processes at the boundaries of tectonic plates make vents possible. They magma contributing astehnosphere pushes up into the lithosphere to create cracks and the heat attempts to rise — warming water and releasing chemicals that are involved in microbial processes into the resultant fluid flow.

The vent communities vary in life elements (animals, bacteria, microbes, etc.) in regional differences that likely evolved separately or adapted to different tectonic attributes (chimney v. diffuse, active tectonics v. stable, asthenosphere processes, etc.). As a result, models can have different parameters and equations similar to how our NPZ study in module two suggested differences for photosynthetic based food webs in the ocean).

Interesting questions discussed during Dr. Beinart's visit included:

  1. What are the differences in organism life span and metabolism for vent communities v. terrestrial (some tube worms are estimated to be over 800 years old)?
  2. Is there a Redfield ratio for organisms living at depth (unsure but certainly a useful thing to consider)?
  3. Why isn't there more predation of the symbiotic animals living at vents (perhaps they are too toxic with the chemicals they live in and have introduced to their bodies)?
  4. What are the limiting nutriets/chemicals for the vent communities (plenty of iron & metals, nitrite abundant by vents, depleted in phosphorous in place but unsure as of now)?
  5. Is there a significant microbial loop among the primary and secondary trophic levels that cycles carbon effectively (seems likely in the absence of other carbon cycling processes)?
Students were encouraged to continue their teamwork in order to pursue the November 20th assignment. Jeremy provided mentoring for the last ten minutes of class. Brian provided a useful Python tutorial site for students to learn from for coding their NPZ models. site