We're back in this central location after
the glitch gremlin re-appeared and cut short our northern excursion.
Nothing serious, just a loose connection inside a camera housing that led
us to believe there were bigger problems on the vehicle than there
Yesterday we measured the abundance and
diversity of animal life in the plume of a hydrothermal vent. No one has
ever done this before with an ROV (at least not that we are aware of), so
we had to "invent" some methodology on the spot. In the past,
researchers addressed this problem by sampling along horizontal paths that
ran over the vents and then compared these with runs made at a distance
from the vents. Their results were always equivocal, with no apparent
We decided to come at the problem from a
different angle—literally. We figured that because the vents are point
sources, horizontal sampling runs might not be best because they are only
in the plume for a brief period. So our approach was to come down on the
vent from above, in a vertical profile, and compare this with profiles
made away from the vent. Well, it worked. In our first comparison, we ran
right down the middle of the smoky plume and saw many more animals and
more kinds of animals than in the profile we ran later about a kilometer
We repeated the process several times on
the following day and learned that currents will bend the plume, and thus,
the picture isn't always as straightforward as it appeared to us
initially. Nevertheless we have a great data set of quantitative video
profiles that should answer the question, at least for this vent. Our
experience also illustrates that the best expeditionary science is often
done on the fly. In the middle of these operations, the pilots asked us,
“What do we do next?" We could only reply with "Give us a
minute, we're making this up as we go along!"
Can you remember the first time you saw a giant redwood tree? Well, something like that happened to us today. We were descending through 1300 meters when a dark visual target appeared, out at some distance from ROV Tiburon. We stopped our descent and flew toward it. Looming up out of the dark distance appeared a fantastic creature. It was the biggest medusa that any of us had ever seen.
gigantea lives in cold, deep water and is only very rarely seen.
Swimming across its dark brown bell and through its voluminous oral arms
was a commensal fish that we did not recognize. Everyone gathered in the
control room to watch.
Using our lasers for a scale reference we
estimated the diameter of the bell to be at least a meter and the length
of the oral arms at two to three meters. That's a big jellyfish Jack! With
skillful flying we examined the surface and structure of the thing from
every angle. We found that the entire outer surface was dusted with
batteries of nematocysts (stinging cells). The fish is apparently immune
to them because it snuggles right in.
Later, when the fish moved off a little, Buzz
Scott used Tiburon like a cutting horse to isolate it and
maneuver it into our suction sampler. Got it. Now we can measure the fish
and use it as a reference for determining the size of the jelly. Back in
the lab, after the dive, Jeff
Drazen identified the fish as Thalassobathia.
Tomorrow we'll work again in the Farallon
Basin, testing Tiburon's low-light SIT camera and surveying the
water column for how vertical distribution patterns are influenced by low
oxygen levels. We'll let you know how it goes...