FAUNAL COMMUNITY STRUCTURE OF A CHEMOAUTOTROPHIC ASSEMBLAGE ON WHALE BONES IN THE DEEP NORTHEAST PACIFIC-OCEAN

Modern and fossil chemoautotrophic communities supported by organic-rich whale skeletons have been reported from the bathyal-abyssal seafloor in the eastern and western North Pacific. Based on studies with the research submersible ALVIN, we describe here general habitat characteristics, and macro- and megafaunal community structure of one such community, estimated to be >4 yr old, associated with an 18 m balednopterid skeleton at 1240 m in the Santa Catalina Basin (SCB) off California, USA. The visible remains of the whale in 1988-91 consisted of partially buried skeletal material (primarily vertebrae and the head complex) with a plan area Of approximately 7.9 m2. White and yellow mats of sulfur-oxidizing bacteria covered many of the bone surfaces, yielding an estimated mat area of at least 4.0 m2. Bone collections indicated a total attached macrofaunal community of at least 12490 individuals distributed among greater-than-or-equal-to 43 species, with 6 species with population sizes of >1000 individuals. Megafauna associated with the skeleton consisted primarily of the vesicomyid clam Vesicomya cf. gigas, with an estimated population size of 400 to 800 individuals. The whale-skeleton faunal community was taxonomically distinct from that of the surrounding SCB, with >97% of its individuals belonging to species very rare or absent in background sediments. The whale-skeleton assemblage exhibited strong taxonomic and functional affinities to other deep-sea reducing habitats (e.g. hydrothermal vents and cold seeps), marked by a prominence of vesicomyid clams and mytilid mussels with sulfide-oxidizing, chemoautotrophic bacterial endosymbionts. In addition, 5 of the whale-fall species (Pyropelta corymba, P. musaica, Bathykurila guaymasensis, Idasola washingtonia and Cocculina craigsmithi) also appear to occur at Juan de Fuca and/or Guaymas Basin hydrothermal vents, despite geographic separation of approximately 1800 km. We conclude that whale falls may nurture substantial, sulfide-dependent communities at the deep-sea floor, and that some species may be dispersing to hydrothermal vents from whale-fall habitat islands.