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Another really interesting animal that lives in this environment is a mussel. This is a mytilid mussel as well. You can't see very clearly here, but they live around a brine pool. This brine pool is really spectacular. What has happened is that over geological time, salt has been trapped in the Gulf, in the Gulf of Mexico. It's percolating up, its pushing through the surface of the earth, but what happens when it gets to the top is that the salt deposits mix with the sea water. They create these hypersaline pools of brine but they are so dense that they stay stationary, they don't dissolve up into the water column. They are dense enough that they can actually land the submarine and sit the submarine on the surface of this water. It's quite spectacular.

In terms of the biology, the brine pools are encircled by these colonies of mussels. And, interestingly, in this environment, these mussels which are chemosynthetic in there metabolism, that is they have bacteria that live within their gill tissue, but rather than utilize the sulfide in this case, they are utilizing methane. So they are in fact methanotropic mussels. So this is another. aspect of every animal has its own spin on the story. They have somehow evolved the ability to use methane as their energy source, to power their chemosynthetic bacteria and do quite well in this environment. So they seek out that interface. They try to get as close to the brine as possible because the methane is percolating out of it, but if they get too close and fall in, that's it, they die.

The tubeworms again have been a principle interest of my research group in this environment. You can see it is a much more delicate animal. Actually, they can get to be quite long. I'll show you a picture of us in the laboratory with them. They can be three meters in length, but they are only about a half a centimeter in diameter, and they are more delicate and not as robust. You can see the respiratory structures sticking out of the chitinous tube here, I believe. Yes, this is an image of one of the worms taken from our recent trip. This is taken off the dive table, therefore the data all over it, but you can see the individual worm with its plume sticking out of the chitinous tube.

The reason that we are particularly interested in the seep vestimentiferan tubeworms has to do with their ecophysiology, that is how they are managing to make a living in the seep environment compared to the tubeworms that are living in the vent environment. The key differences in the environment being that there is no hydrogen sulfide present in the ambient water. Hydrogen sulfide is present only in the soft sediment.. Therefore, we are hypothesizing, and we are gaining more and more evidence, that they are taking up the hydrogen sulfide across the root, we like to call it a root, of the tubeworm. The tube extends way down into the sediment and actually seems to sort of seek out or appear to be associated with sulfide deposits so that is interesting in and of itself in terms of the microhabitat and the environmental niche that they are occupying. But in terms of the physiology for us, it is quite interesting, because rather than taking up hydrogen sulfide across the plume surface along with oxygen, like the vent tubeworm, they are actually bringing hydrogen sulfide across the body wall, which is a very aerobic tissue, and potentially really subject to sulfide damage - sulfide poisoning. So, we've done a number of studies looking at tissue level hydrogen sulfide detoxification, and it turns out, as you might imagine, that these animals are well adapted to the presence of hydrogen sulfide and can detoxify it and maintain their aerobic metabolism in this environment.

On our recent trip you can see, this was actually on the 14th (July 14, 1997), my post doctoral associate, David Julian, and I just returned from an expedition in the Gulf of Mexico just ten days ago. The expedition is on-going right at this moment, the second leg of it continues and as Sam mentioned, there has been quite a bit of attention paid to this, because while we were out this time, we discovered what we think is a new organism in association with a new habitat. I don't have a lot of slides of this, again, this was just taken off the dive table and is not in the best of shape, but what it's showing here is the side of a structure that occurs in the seep environment, down at 600 meters (1757 feet). This structure is actually, interestingly, a mound of frozen methane. So what happens is that the methane percolates out of the sediment as I was mentioning before, but at this particular temperature and pressure, importantly...8° Celcius and at the pressure at this depth, it freezes. There is actually a hard structure. These mushroom shaped mounds of frozen methane are approximately three by two meters in size. The geologists that we work with have known that they have been there for quite some time, and that is not really a new finding, but to the biologist, the really interesting thing is that they are extensively coloni. zed by small worms I wasn't in the submarine, but Charles Fisher, the Chief Scientist, from Penn State and David Julian, my associate, were in the submarine and they noticed some movement on the hydrate, so they went up to it and it turns out that there are individual burrows all over the under surface of the hydrate. Within each individual burrow, there is an little polychaete worm. And they all sit there very orderly and occupy individual microhabitats.

So for us, this was wow, a worm in a microhabitat, that's really exciting, but for the rest of the world, I think that everybody is interested in what they are doing on the frozen methane, and how they are making a living. This again, the resolution is terrible, but if you use your imagination, you can sort of see the individual worms. Each one of these is an individual worm. They are about an inch and a half in length and they made the front page of the Chronicle this morning. Here is one under a dissection scope. You can see it a little bit better. It is a pretty standard looking polychaete. It has all the classic, beautiful polychaete parapodia and setae and everything. It has quite a lovely (and of course I was quite thrilled about this) dorsal vessel here filled with hemoglobin, bright red hemoglobin. Interestingly, it doesn't have much of a feeding structure. It does have a complete digestive tract so we don't believe that it is chemosynthetic. It is probably feeding on methanotropic bacteria that are living on the hydrate. It is possible that they might have bacteria colonizing their appendages as well. And, so they are sort of carrying around their vegetable garden on their own back is the analogy. and eating the bacteria off their appendages. A neat discovery, and one that we will pursue here in our laboratory in Tiburon is particularly addressing metabolism and blood transport capabilities.