When huge marine species die, they either get washed ashore or fall into the depths of the world's oceans. When death leads them down the shadows of the ocean floor, it could mean survival for the bottom-dwellers of the ocean.
Not much is known about the life in the oceans especially in the deepest parts, but a chance discovery of a "graveyard" may now enable scientists to better understand the process behind ocean's ecosystems and possibly unlock solutions to increasing carbon content in the world's oceans.
Footages of a whale shark's and three rays' carcasses gave scientists from the University of Plymouth and the National Oceanography Center in United Kingdom a one-of-a-kind and a first-hand observation in the of the ocean's bottom-dwellers wild feasting on a massive food fare that fell from above.
Deep-sea dwellers big and small such as crabs, giant isopods, sea cucumbers, lobsters, sharks, and bone-feeding Osedax worms flock on the remains of the whale sharks and rays to feed, while others such as the eel pouts lurked near the area to prey on unsuspecting crustacean or amphipod.
The carcasses, one found in 2008 and in 2009 and two in 2010 at the average depths of 1,200 meters, were filmed by the oil and gas industry while surveying the ocean's floor off the coast of Angola using a remotely-operated vehicle Subsea 7 Hercules.
According to Nicholas Higgs, a postdoctoral research fellow at the Marine Institute of the University of Plymouth and lead author of the study, spotting a large carcass on the ocean floor is already a rare event, but discovering four bodies in "such close proximity is unprecedented."
"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," wrote Higgs in his blog.
He also noted in his research paper [pdf] published recently in the journal Plos One that only nine vertebrate carcasses have ever been documented.
Perhaps, food-falls or whale-falls are frequent in the region since the coast near Angola is a hotspot of ocean productivity, explained Higgs, attracting planktivores such as whale sharks, mantas, and whales in the area. The cause of their deaths is still unclear, though scientists surmised it could either be because of ship strikes and accidental entanglements or because of natural causes such as attacks from other sharks and killer whales.
While the study found no signs of rich seabed environment, except for the two carcasses, Higgs figured that these carcasses could, in fact, help the ocean ecosystem by reducing the carbon present in the upper oceans, in the same way bodies buried in the ground could be used as fertilizers.
Mammoth marine species that feast on plankton could take in large amounts of carbons in their body and in their death could sink down into the ocean's void together with the carbon locked up in their bodies, effectively "sequestering" away carbons from the surface ocean, and possibly, the atmosphere as well. The carbon is also food to deep-sea scavengers, and Higgs estimated the carcasses they found had four percent carbon in them.
This claim is supported by another study he also conducted, which found out that whales could hack a fairly large amount of carbon in the air and water only, and only if, their population swell.
"Their sinking carcasses would remove 160,000 tons of carbon per year. That is equivalent to planting 110,000 hectares of forest!" he said in his blog.
