EVERY ONCE IN A WHILE, in the pursuit of underwater discoveries, you stumble across something unexpected – but deeply fascinating. Such were the sentiments of Dr Nicholas Higgs, postdoctoral research fellow at the University of Plymouth’s Marine Institute, upon viewing a recent video recorded by remotely operated vehicles surveying the seafloor around the Southern African nation of Angola for industrial exploration.
Amazingly, the footage shows the remains of a whale shark (Rhincodon typus) and three devil rays (Mobula sp.) sitting on the seabed, at an astonishing depth of 1,200 metres – well beyond the limit of tek divers. Fed on voraciously by a range of fish, each carcass represents an island of food down below. The scavengers did not even have to travel very far for their next meal as all four carcasses were found within approximately one square kilometre of one another, over a period of two years. The video reveals a remarkable concentration of bodies, as previous estimates of nearest-neighbour distances for whale-falls (the incredible habitats created when a massive whale carcass sinks to the deep bottom) were about 16 kilometres in the ocean’s most whale-rich areas.
The discovery of so many ocean giants at this deep-sea graveyard is miraculous in itself. Finding a single large animal at such depths is a significantly rare event; only a handful has ever been discovered in the 50-odd years of deep-sea photography. While scientists have long suspected that the flesh of dead marine creatures might provide a food bonanza for specialist scavengers of the deep, corroborative evidence of such phenomena has been limited. We now know that whale-falls support specialist animals like Osedax worms, which consume the whale skeleton itself. However, despite intensive research on whale-falls, this is the first time ever that the carcasses of other large animals have been observed, let alone discovered together on one isolated portion of the ocean floor.