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Ashes to ashes, blubber to blubberIs there life after death?
Well, yes - and in the case of whales there is quite a lot of it. 'Whale fall', the phenomenon of whale carcasses sinking to the sea floor and decomposing, provides food and habitat for quite number of species. Many of those creatures couldn't even exist without it. Craig Smith is Professor of Oceanography at the University of Hawaii and a pioneer in the research of whale fall: "When all is said and done, whale fall is a massive injection of organic material in a normally food-poor ecosystem. After all, we're talking about the deepest regions of the deep sea, pitch dark and very, very cold." Since whales are so huge, they can also serve as living quarters and keep that function for quite some time. Highly specialised crabs and worms find shelter in the bare skeleton. "It creates a little micro-ecosystem at the bottom of the ocean," says Professor Smith. Attack of the Zombie worm 'Highly specialised' can mean 'very strange' when it comes to these creatures. One of them, living solely on dead whales, is the 'bone-eating zombie worm'. This worm has specially adapted to burrow into the bone: on their bodies they have a kind of 'root' that grows, then degrades the bone as the worm feasts on oils trapped in the whale's skeleton. Other worms and crab-like creatures are 'bacterial grazers': they scavenge the surface of the bone and eat microbes that live on them. A dead whale may be a micro-ecosystem, but the number of species that live exclusively on - and off - whale carcasses is quite large, as Professor Smith explains: "At least 32 species are whale fall specialists and we've only studied whale fall in a very limited part of the ocean, on a global scale there may be hundreds." Ballast Investigating whale fall is quite an undertaking, since the deep sea is vast and dark. Craig Smith and his colleagues can hardly rent a submarine and go look for them, so the solution is controlled experiments. Whales which are stranded or have died of natural causes are towed out to sea, ballast is fixed on the corpse, and then it's sunk to the deep sea floor. The ballast is needed because stranded whales are typically already decomposing and the trapped gasses in the corpse keep them afloat. Once the whale has found his final resting place, the researcher can go and visit the corpse and record what happens over a period of time, often lasting many years. Scavengers Professor Smith explains what communities develop in and around a whale carcass over time: "First, there are the mobile scavengers: sleeper sharks and hag fish consume the soft tissue remarkably quickly; a large whale can be reduced to a clean skeleton in a matter of months." "The second wave of colonisation involves 'enrichment opportunists': small animals that settle on the sediment around the whale or on the bones themselves.The sediments underneath the whale are very rich in organic material, and specialised worms and snails thrive in this setting, they can literally cover the skeleton completely." "The third stage is for sulphur-loving creatures. The decomposing whalebones release sulphide from anaerobic bacterial metabolism inside the bones. This sulphide serves as an energy source for clams and sulphur-consuming mussels. A broad range of crustaceans, molluscs and worms live exclusively on dead whales." Danger of extinction Of course, these whale-scavengers are not exactly the most endearing creatures on earth, but for the sake of biological diversity they need protection just like seals and the panda bear. Whaling has, in some parts of the ocean - and particularly in the North Atlantic - reduced the number of whales by 75 percent. Logically that means a 75 percent reduction in the habitat of these whale fall specialists. Professor Smith: "There is a potential for significant species extinction to have occurred in these whale fall communities from the removal of whales. The thing is, we'll never know: once they're gone, they're gone. The obvious thing to do now is to avoid over-exploiting whales, to not reduce their populations to levels that might cause extinction at the deep sea floor." Thijs Westerbeek 26-06-2006
See also Thriller, Killer, Invincible and Bad Origin of the Species - Chapters seven, eight and nine. |
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