1. Department of Biology, Faculty of Science, University of Ottawa, 30 Marie Curie Street, P.O. Box 450, Station A, Ottawa, Ontario, K1N 6N5 Canada, Department of Oceanography, Texas A&M University, 5007 Avenue U, Galveston, Texas 77551, and Department of Geosciences, Guyot Hall, Princeton Unversity, Princeton, New Jersey 08544