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April 6th, 2003; Leg 4, Day #3

Today's update is provided by our Mexican collaborator, Luis A. Soto of UNAM, Institute of Marine Science and Limnology.

Area of Study: Guaymas Basin 

Site: Rebecca's Roost 

The target area for the second day of exploration in the Guaymas Basin was a site located in the Southern Trough at about 2,000 meters of depth. This site represents one of the most complex edifices recognized so far in the Guaymas Basin; it also harbors a variety of different sulfide deposits, which acquire pagoda-like shapes that may grow up to 15 meters in height. One can also distinguish other deposits similar to rounded mounds packed on their surface with thick clumps of vestimentiferan worms of the genus Riftia. Nearby there are tall chimney-like deposits, built up by the progressive deposition of sulfide materials; hydrothermal fluid can be seen flowing out of the top of such deposits. 

Apr6_JS holding riftia.jpg (71417 bytes)Undoubtedly, this site, commonly referred to by previous researchers as Rebecca's Roost, constitutes an exuberant vent system dominated by the luxurious development of dense colonies of Riftia pachyptila. At left is a photo of a Riftia individual in the lab. Joe Jones is holding the tube and Shana Goffredi is holding the animal from that tube. The external surface of the worm tubes provide an important substrate for the settlement of a complex fauna of epibionts, which graze the bacteria growing on the surface of the tube worms. This is the case of numerous scales worms (Polynoids), whose dark or pink coloration adds another attraction to the untrained observer. The so-called palm worms (Alvinellid worms) can also be seen attached to the external tube surface of Riftia, extending their bright brownish tentacles out of their own small tubes (see below). 

Apr6_riftia.jpg (82827 bytes)The video system mounted in the ROV provides an excellent close up look of the different morphology adopted by all these creatures; all of these developed to survive and thrive in an apparent hostile environment devoid of light, high hydrostatic pressure, the presence of toxic chemical compounds derived from the hydrothermal process itself, and extreme high temperatures. The high definition of display images of the organisms associated with deep hydrothermal vents, allows the experts, in most cases, to closely identify the organisms, which is required for specific research objectives.

Apr6_bacterial mat.jpg (79698 bytes)Indeed the notorious advance of unmanned remote controlled underwater vehicles has greatly facilitated our capacity to explore and study the hydrothermal phenomena. In the case of the Guaymas Basin, located in theCentral Gulf of California, there are a number of important features that make the area unique in comparison with some other known systems in the Pacific. The presence of gas and thermogenically produced oil and the precipitation of sulfide compounds, create a habitat heterogeneity clearly observed in the composition of the communities studied. During dive T-549 conducted today, we had the opportunity to sample the most contrasting habitats: from the solid deposits occupied by massive Riftia colonies, to the desolated plain bottoms whose only signs of life appear concentrated around white or yellowish mats of chemosynthetic bacteria (see above). 

There is evidently more biodiversity on the hard substrates than on the regular soft sediments. However, in both cases, the morpho-physiological adaptations exhibited by their inhabitants are equally fascinated. To test this idea, it is only necessary to obtain a temperature profile of the surrounding environment (water and sediment), to quickly realize the enormous stress that these organisms are exposed to. Inside bacterial patches, the temperature may reach up to 169º C, sufficient to break down the molecular structure of common marine individuals. 

Many question still remain unanswered in relation to the complex processes that make possible the existence of life in the deep hydrothermal vents. The unraveling of these mysterious forms of life represents a true challenge for modern science.  

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