clams preserved so well in spite of the relatively low 

 population levels in many portions of the clam beds?" One 

 possibility is that, when active seepage stops, dissolution 

 rates also drop, so that shells still remaining can be 

 indefinitely preserved. We have developed a method to date 

 time-since-death for molluscs based on the rate of protein 

 decomposition in the shell and will apply that method to 

 dating the age of seep sites and to look at the relative 

 ages of shells in active and inactive areas of seepage 

 within the sites. This is, in effect, a variant of time 

 averaging, since patch migration on the sea floor results in 

 a much wider distribution of shell material of many 

 different ages than would be expected from the current 

 distribution of the living fauna. The shells are, however, 

 stratigraphically equivalent. 



SUMMARY 



Chemosynthetic ecosystems composed of tube worms, 

 mussels and/or clams are widely distributed on the Gulf of 

 Mexico continental slope. The distribution of these 

 ecosystems are controlled by the seepage of oil and gas 

 which provides the driving energy. The chemosynthetic 

 mussels which can utilize methane as a result of symbiotic 

 bacteria in their gills (Childress et al . , 1986) are in most 

 cases associated closely with bubbling gas seepage. The 

 tubeworms and clams are associated more closely with the 

 presence of high sediment concentrations of oil. The 

 chemosynthetic communities represent extremely high biomass 

 densities for the deep-sea benthos and isotope evidence 

 indicates that chemosynthetically produced carbon is being 

 transferred into the background deep-sea fauna (e.g., crabs, 

 crustaceans) at the seep sites. The ecology, physiology, 

 chemistry, and geology of these ecosystems and sites are 

 very complex requiring coordinated multidisciplinary 

 studies. 



LITERATURE CITED 



Brooks, J. M., M. C. Kennicutt II, R. R. Fay, T. J. McDonald, 

 and R. A. Sessen. 1984. Thermogenic gas hydrates in the 

 Gulf of Mexico. Science , Vol. 225, pp. 409-411. 



Brooks, J. M. , M. C. Kennicutt II, R. R. Bidigare and R. R. 

 Fay. 1985. Hydrates, oil seepage and chemosynthetic 

 ecosystems on the Gulf of Mexico slope. EOS , Vol. 66, 

 No. 10, p. 105. 



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