Thiocystis spp., were also abundant over warm sediments. 

 Several different enrichments for sulfate reducing bacteria have 

 been obtained, and sulfate reducers were found in all three 

 sample types. 



Macrobenthos 



In addition to the prolific and colorful microbial 

 communities, dense populations of oligochaete worms were also 

 occasionally found congregated near fumaroles in warm sediments. 

 Worm densities in these small patches were an order of magnitude 

 higher than in the cool sandy sediments only a few cm away. 

 These "colonies" consisted of three tubificid species, 

 Limnodrilus hof f meisteri , L. udekemianus and L. profundicola , 

 and an occasional solitary, exceptionally large (for freshwater) 

 lumbriculid oligochaete of the genus Lumbriculus . The latter 

 represents either a new species or a particularly robust L. 

 variegatus , as it is twice the typical size reported for the 

 species (Brinkhurst and Jamieson 1971). Presumably the worms are 

 attracted by the healthy bacterial flora upon which they feed. 

 The fact that these worms live near their thermal limits in 

 sediments that reach 80° C at 3 to 4 cm depth is a unique 

 situation for these organisms. 



ACKNOWLEDGMENTS 



This work was supported by grants from the NOAA National 

 Undersea Research Program, the National Geographic Society, and 

 the Graduate School of the University of Wisconsin—Milwaukee. 

 This work could not have been carried out without the excellent 

 cooperation and assistance of R. Jones and R. Gresswell of the 

 U.S. Fish and Wildlife Service. The authors would also like to 

 thank W. Hamilton and the National Park Service for their 

 cooperation and interest, P. Anderson, F. Binkowski, M. 

 Kapinski, J. Krezoski, J. Maki and R. Paddock for their help 

 and collaboration in the field and laboratory, and Dave and 

 Rebecca Lovalvo of Eastern Oceanics Inc. for their very capable 

 operation of the ROV. This is the Center for Great Lakes 

 Studies Contribution Number 309. 



LITERATURE CITED 



American Public Health Association, American Water Works 



Association, and Water Pollution Control Federation. 1985. 

 Automated method for molybdate-reactive silica. In: 

 Standard Methods for the Examination of Water and 

 Wastewater , 16th Ed., APHA, Washington, D.C., pp. 461-463. 



Brinkhurst, R. 0. and B. G. M. Jamieson. 1971. Aquatic 



Oligochaetes of the World . Toronto, Univ. of Toronto Press. 

 860 pp. 



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