Bathymetric and temporal variation among Osedax boneworms and associated megafauna on whale-falls in Monterey Bay, California

The discovery in 2002 of a natural whale-fall at 2893 m depth in Monterey Bay, California, led to the description of Osedax, a novel genus of bone-eating worms (Annelida: Siboglinidae). Osedax obtain their nutrition via ramifying roots that host symbiotic bacteria and consume whale bones. To assess the bathymetric range of these unusual worms and their role in whale-fall community succession, we sank beached whale carcasses at three additional depths (1820, 1018, and 385 m) in the Monterey Submarine Canyon. The four sunken carcasses experienced different temperature, oxygen, and disturbance regimes and hosted megafaunal communities that differed in both species diversity and composition. However, Osedax were found at all four sites, and molecular analyses allowed us to assign them to six distinct species, four of which are new to science. The previously known species, O. rubiplumus (1820–2893 m) and O. frankpressi (2893 m), were found below the oxygen minimum zone. One of the new species appears to be a late successional species that attacks sediment-covered bone fragments at the 2893-m whale-fall. The other new species occur at the shallower whale-falls, which are in oxygen-poor water. One is an early colonizer at the 1018-m whale-fall, and two occur at the 385-m whale-fall. Dense Osedax populations at the 1018-m whale-fall led to rapid degradation of whale bones, whereas sparse Osedax populations were associated with slow degradation at the 385-m whale-fall. Thus, we hypothesize that Osedax may be a foundation species in Monterey whale-fall communities, regulating the longevity of whale bones and thereby affecting the succession of associated megafauna.