Finding a large animal carcass on the deep seafloor is a pretty rare event. Only a handful have ever been discovered in the 50+ years of deep-sea photography. So when I was presented with video footage of four large carcasses from one small part of the seafloor, I knew that this was an important find.
Scientists have long suspected that the carcasses of dead animals might provide a food bonanza to specialist scavengers in the deep sea, but direct evidence of these events has been limited. The most well known examples are whale-falls; the amazing habitats created when a massive whale carcasss falls to the deep seafloor. Their carcasses support specialist animals, like the Osedax worms that eat the whale skeleton itself!
Despite lots of research on whale-falls, this is the first time that the carcasses of other large animals have been observed.
There is no sure way to tell. Accidental strikes from vessels and entanglement are possible causes of death. It should also be noted that this footage comes from surveys carried out by the oil industry (namely BP). So... are oil & gas operations to blame? I don't think so and here's why:
It seems that the waters above this part of the seafloor are a hotspot of ocean productivity that attracts high numbers of large plankton-feeding animals like whale sharks, manta rays and whales. So it is only natural that you will get a higher concentration of their carcasses in this area.
These carcasses represent 4% of the total food (carbon) arriving at the deep sea floor. This is about 10 times the previous estimate of food supply provided by dead whale carcasses to deep-sea scavengers. It is more in line with the 11% previously estimated to be the amount of food supplied by all animal carcasses. So remarkable: yes, but not unlikely. This is just the first time that such a productive are has been surveyed in such detail.
It turns out that in area such as this, where you have a lot of very big animals eating more of the plankton they actually increase the efficiency of the ocean ecosystem in removing carbon from the upper ocean. When these huge beasts die, the quickly sink into the deep sea where the carbon locked up in their bodies is effectively sequestered away from the surface ocean/atmosphere system. For example, a previous study showed that by rebuilding depleted whale populations, their sinking carcasses would remove 160,000 tonnes of carbon per year! That is equivalent to planting 110,000 hectares of forest!
The evidence here shows that in highly productive areas, ocean giants can and do export a significant amount of carbon to the deep ocean. This is not only important for the scavengers that depend on this source of food but also for scientists trying to understanding or ocean ecosystems.
Please credit all images and video to the Serpent Project and add a link to the original PLOS ONE article