Wednesday, July 31, 2013

Whale fall

Large cetacean carcasses at the deep-sea floor, known as ‘whale falls’, provide a resource for generalist-scavenging species, chemosynthetic fauna related to those from hydrothermal vents and cold seeps, and remarkable bone-specialist species such as Osedax worms. Here we report the serendipitous discovery of a late-stage natural whale fall at a depth of 1444 m in the South Sandwich Arc. This discovery represents the first natural whale fall to be encountered in the Southern Ocean, where cetaceans are abundant. The skeleton was situated within a seafloor caldera, in close proximity (<250 m) to active hydrothermal vents. We used a DNA Barcoding approach to identify the skeleton as that of an Antarctic minke whale (Balaenoptera bonaerensis). The carcass was in an advanced state of decomposition, and its exposed bones were occupied by a diverse assemblage of fauna including nine undescribed species. These bone fauna included an undescribed species of Lepetodrilus limpet that was also present at the nearby hydrothermal vents, suggesting the use of whale-fall habitats as stepping stones between chemosynthetic ecosystems. Using Remotely Operated Vehicle (ROV) videography, we have quantified the composition and abundance of fauna on the whale bones, and tested a hypothesis that varying concentrations of lipids in the bones of whales may influence the microdistribution of sulfophilic whale-fall fauna.

This text is from the abstract of a new paper now published in Deep Sea Research Part II. Well, first of all they did not do DNA Barcoding. The complete cytochrome b gene and a part of a tRNA coding region are good DNA identification markers for this particular study but that's not what we call DNA Barcoding.

Enough of the caviling as the study is actually pretty cool. I remember some great footage presented in the BBC series "Blue Planet" which ran 11 years ago. The crew filmed a grey whale carcass in deep water and showed how it was consumed by hagfish, sleeper sharks, and a variety of invertebrates such as crabs. The filming crew did not come across this carcass by chance but instead they used one of a stranded whale and sank it at a different location they revisited for a number of times to film all scavengers that come to feed on it. A year and a half later the carcass was stripped to the bone. This new study could be viewed as the scientific sequel to that initial footage as the researchers look at the skeleton of a minke whale (Balaenoptera bonaerensis) and the organisms that inhabit the bones. The whale species identity was confirmed using DNA and the inhabiting organisms were identified based on ROV video material (see image). 

This was the first natural whale fall to be observed in the Southern Ocean, despite this area harbouring an abundance of large cetaceans. The presence of large amounts of lipids in the bones showed that the carcass was still able to support life on the seafloor even after a considerable time, and the diverse faunal assemblage found on this skeleton included several undescribed species.

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