On the role of bone-eating worms in the degradation of marine vertebrate remains.

While the study of terrestrial vertebrate taphonomy is well advanced, our knowledge of the fate of large vertebrates in the marine environment is extremely poor, owing to the deep and distant locations of most recently deceased marine organisms. These include the largest animals ever to have existed, the great whales. In recent years, a series of both serendipitous discoveries and planned experimental manipulations have provided some of the first data on the fate of whale remains in the deep sea (Smith 2006). One of the more remarkable discoveries has been a specialized ‘whale-fall’ fauna, including organisms such as Osedax, a sessile polychaete worm that is capable of burrowing into whalebones to extract energy through microbial symbioses (Rouse et al. 2004; Glover et al. 2005). The recent paper in this journal by Jones et al. (2008) puts forward the hypothesis that Osedax is not specialist on whalebones, based on the observation of Osedax growing on cow bones suspended above the seafloor of the Monterey Canyon. In this comment, we show that a range of other observations on the fate of small marine vertebrates do not, as yet, lend any support to this hypothesis. The enigmatic polychaete genus Osedax is now thought to consist of at least 11 known species recorded from the depths of 30–2900 m in both the Atlantic and Pacific oceans (Dahlgren et al. 2006; Braby et al. 2007; Jones et al. 2008; Rouse et al. 2008). Osedax presents a biogeographic paradox. If whale falls are rare and ephemeral habitats in the marine environment, a restricted distribution might be expected, similar to that recorded for the closely related hydrothermal vent vestimentiferans, which are endemic to the deep Pacific. However, the broad biogeographic range of Osedax is similar to that for cold-seep vestimentiferans and shows even greater bathymetric range. Furthermore, the molecular studies of mtCO1 diversity suggest both large global population sizes (Rouse et al. 2004), and a high level of haplotype diversity at single sites (Glover et al. 2005; Dahlgren et al. 2006). The latter point suggests that at any one single location in the ocean, Osedax larvae from more than one population may be available to colonize a whale carcass, should it so appear. Three hypotheses can be erected to explain the biogeographic pattern of Osedax: (i) whale falls (in the form of whalebones lying on the seabed) are very common on regional scales, as suggested by Smith & Baco (2003), (ii) Osedax reproductive output, larval longevity and life-history strategies show specific adaptations for exploiting isolated yet food-rich ephemeral habitats (Rouse et al. 2004), and (iii) Osedax are able to colonize a wider range of vertebrate remains, such as