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imageOne of the most dramatic and most well known of the animals from the hydrothermal vent environment is the giant tubeworm. This is Riftia pachyptila. Riftia, named after rift. Colonies of Riftia group together around effluent points in the hydrothermal vent. In other words, they are growing right in the water that is percolating out from the sea floor. An individual animal lives inside one of these chitinous tubes. This red structure out the end is the respiratory plume. The animal can retract that plume back into the tube if it's disturbed. And I will talk more about the physiology and anatomy of this worm later.

imageThere are a number of taxa, new animals that were identified from hydrothermal vents. This was another real boon to science in that most of the animals discovered at the hydrothermal vents were in fact, new to science. And this data on the slides is a few years old. Just by way of example if you look at the number of species that had been described from the vent environment at this point in time, there were about 300 and 284 of the 300 or so species that were found on the vent environment were new, had been previously undescribed.

Again we have a lot of new biology in the sense of new genera families and even several new phyla that have been described from the hydothermal vent biota. The large vestimentiferan tubeworm, Riftia that I just showed you, the discovery of that tubeworm elevated the group, (there were others that were known from the deep sea) to phylum status based on the unusual morphology of this particular worm. So this is quite an exciting aspect of hydrothermal biology as well.

image video button sound button  Probably the most important aspect of the hydrothermal vent animals and what was going on in this remote habitat had to do with the basis of the food chain, the source of the energy to power, basically, the biology at this remote location. Typically, or prior to the discovery of the hydrothermal vents, most biologists believed that all life depended upon the energy of sunlight. That is, the basis of the food chain was photic energy which powered photosynthesis, obviously in green plants that went down the chain with animals eating plants, and animals eating animals. When the hydrothermal vents were discovered, it was clear very rapidly that they were a very enriched biological environment, very, very remote from the surface sunlight. It was difficult to imagine that energy could basically drift down in high enough quantities to nurture this environment, if you will. Other interesting data that came to mind, or that came to be known, were that most of the animals here, the large invertebrates, basically had no digestive system. The large tubeworm, Riftia, has no mouth, no gut, no anus. However, it is a huge animal - they're about a 1.5 M in length and up to 2 cm in diameter and there are many, many of them in these hydrothermal vent sites. So the question was, how are they managing to make a living down there?

Well, it became clear fairly rapidly based on the morphology of the animal and various other characteristics, enzymatic characteristics, etc. that what was happening here was that the major invertebrates were harboring bacteria within their body cavities. Now bacteria, free living bacteria, in this environment and in our own backyard, have been known for years to be able to use chemical energy as a basis of their metabolism. So in the case of the free living bacteria, there are many sulfide oxidizing bacteria which can use chemical sulfide to basically run their metabolic pathways - to produce organic compounds, small nutrient compounds, that form the basis of their nutrition. video button sound button  What is happening in some of the hydrothermal vent animals is that they are harboring these chemical utilizing bacteria, within their body tissues. So for instance the large tubeworm, Riftia, and the clam, Caliptogena, harbored dense aggregations of bacteria, either in what was the residual gut of the tubeworm or in the gill area for the clam. These bacteria then are able to utilize the inorganic chemicals in the environment. They utilize hydrogen sulfide. What they do with the hydrogen sulfide is analogous to what plants do with photic energy. So it is called chemosynthesis rather than photosynthesis.

What is happening is that hydrogen sulfide is oxidized, so oxygen is necessary for this process, and the energy released from this oxidation of this hydrogen sulfide molecule is used to power, the fixation of carbon dioxide into small organic compounds. So this cycle here, the Calvin - Benson cycle, is the same metabolic pathway that is utilized by plants in photosynthesis. And basically it takes inorganic carbon dioxide and fixes it into organic compounds that are then food. But, the difference here, the critical difference, is that rather than using sunlight, these animals and bacteria are completely independent of sunlight. They utilize chemical energy to power that reaction. So the net result is that free living bacteria in the environment and also symbiotic bacteria living within the animal's tissues are able to live independent of sunlight, the energy from the sun, utilize the chemicals from the environment , create small organic compounds that are either utilized by the bacteria themselves or leaked to the host animal and the basis of the nutrition for these giant tube worms is basically the bacterial metabolism that goes on within their interior organs. So this was a fairly fundamental discovery, because this was the first very well defined ecosystem, and very elaborate ecosystem, that was completely independent of sunlight at any level of the food chain.

imageSo let me talk about Riftia a little bit and introduce you to some of the animals in a little bit more detail. I'll focus again on the hydrothermal vent tubeworm Riftia. This a photograph that was taken with a stereo camera off the front of the submarine which it is difficult to take photographs at depth as you'll appreciate by the time we get through this seminar. So this is Riftia. Here is the temperature probe video button of the front of the submarine itself, and this is a mytilid mussel very similar to our own mussel that grows here locally in the Bay. This genus Bathimodiolus mytilid mussel also harbors chemoautotrophic, chemosynthetic bacteria in its gill tissues as well as Riftia. Here is one of the free living Brachyuran crabs, genus Bythograea themydron. These are typical brachyuran crabs wandering through the environment scavenging. They're looking for any kind of dead or dying material that they can eat. So, they are basically opportunistic in this environment rather than having some kind of specialized metabolism.

We collect these animals in the original explorations and the continuing explorations have occurred through the use of the deep sea submersible Alvin. Alvin is a three person submarine that is operated by the Woods Hole Oceanographic Institution in Massachusetts. It is an interesting submarine. It can dive very deep because it is basically a titanium sphere. So what you see here is a lot of fiberglass outer structure to basically keep the submarine afloat and maneuver it, but at the core of the submarine there is a large, it is not huge, titanium sphere. It has three Plexiglas windows associated with it.image You can see one here. This is the pilot's viewport. On the interior of the submarine three people can sit--one pilot, two observers. It is rather crunched and cramped, and you sort of focus out this little window. Diving to the bottom , it's about an eight hour dive all told to get to the bottom and back up again. It's a little awkward working at depth. Obviously you can't lookout and swim around in your scuba or anything because of the immense pressure down there so we are limited to the use of the manipulator arms video button. There are two manipulator arms on the submarine. There is one here, and I believe the other is over here. They are used for a variety of purposes. They can be used to collect animals from depth which is mostly what physiologists like myself are interested in. Also deploy certain sampling devices into the environment, water sampling is the big issue with us looking at the environmental characteristics, holding cameras, traps etc.

video button Video of sub from sub camera

video button Video of cucumber from sub camera

video button Video of trap being set by manipulator arm

imageWe bring the animals up to the surface in temperature insulated buckets, not pressure insulated. Interestingly, it appears that temperature is the biggest problem in terms of keeping the animals healthy and alive for further study. To try to capture them and keep them at pressure is very problematic. It takes a lot of technology.

This is Riftia. This gives you a feeling for the size of the animal and again this is Calyptogena that large clam that co-occurs with it in the environment.

So basically we collect them at depth, put them in temperature insulated boxes housed in the front of the submarine, bring them up to the ship and on the ship board laboratory we try to do as much work as we can rather than bringing them back home because of the onerous problems of keeping the animals alive and healthy.


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