We thank Drs. Wuchang Wei and James Pospichal for their critical review and helpful suggestions, which greatly improved this paper. We are grateful to Mitch Covington of BugWare for providing the counting software used in collecting the data. Samples were provided by the U.S. National Science Foundation (NSF) through the Ocean Drilling Program (ODP). This research used samples and/or data provided by ODP. ODP is sponsored by NSF and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. A. Di Stefano was funded by MRST Cofin 1999 (9904152971) grants to Professor I. Premoli Silva. Laboratory facilities for K. McGonigal were provided by NSF grant No. DPP 94-22893.