Oily whale bones fuel unique ecosystems
1 September 2010 by Tom Marshall
The skeletons of fallen whales on the ocean floor attract specialised animals that live on the oil in their bones.
But some bones have more oil than others, and this affects how quickly they decay and which creatures they attract, a new study suggests.
Scientists have long known that whale carcasses form islands of food on the largely barren plains of the deep-sea floor. But the realisation that the all-you-can-eat banquet carries on even after the whale's flesh is all stripped away has come more recently.
The researchers believe these 'whale falls' could even form stepping-stones that explain how various organisms reached and colonised other deep-sea environments like hydrothermal vents, where hot fluids jet into the water from beneath the seabed.
The team examined old records from the whaling industry in the Natural History Museum's library archives to find out more about how much oil is found in different bones from different kinds of whale.
"Whale-falls act as oases of food in the hostile deep-sea environment and support rich communities, fuelled by the tonnes of oil in the whale skeletons. But scientists have never been sure just how much oil is in the whale bones." says Nicholas Higgs, a PhD student in zoology at the Natural History Museum in London and University of Leeds, and lead author of the paper, which appears in Proceedings of the Royal Society B.
"Now we can see that the oil is concentrated in certain bones. This answers several outstanding puzzles, such as why some bones have different animals living on them or why some bones appear to degrade faster than others," he adds. "Knowing how these islands of life function and evolve is important for understanding the surprising diversity of life that we find in the deep-sea."
Whalers had a strong incentive to get as much oil as possible out of a carcass, so they did research into how much different body parts yielded. In the 1930s, a method was developed for extracting oil from whales' meat and bones as well as from their blubber; this breakthrough led to independent studies in Russia, Norway and Japan on how much oil there is in different bones and species.
Higgs and his co-authors examined their results, and found strong agreement between the three studies despite their widespread geographical origin. The bones in whales' heads, for example, tended to contain lots of oil, as did the vertebrae towards the rear of their spines. Ribs and vertebrae from the middle of whales' backs have much less oil in them. These results suggest several new and potentially important ideas. One is that the bones with more oil provide more food for certain communities of bacteria, tube worms, mussels and other organisms than less oily parts of the same skeletons.
"When I looked at the data I realised that I had seen this pattern before: all of the oiliest bones seemed to be the ones that lasted the longest on the seabed and appeared most abundant in the fossil record; this suggested that the oil protects the bones from the micro-organisms that destroy them," explains Higgs. "Some of these skeletons can last on the seabed for decades and we expect that as the oil runs out the animals will be restricted to the oiliest bones, but these new theories need to be tested."
Like the organisms found around hydrothermal vents, these microbes depend on hydrogen sulfide (familiar to some as swamp gas) for energy, and this gas is produced as whale oil breaks down. So Higgs thinks these will be found more on the oiliest bones.
Other kinds of microbe found on whale carcasses eat the hard structure of the bones themselves rather than the oil they contain but can't tolerate sulfide-rich conditions. So Higgs thinks the bone-eating microbes may eat the less oily bones, causing them to break down more quickly, while their oil-loving relatives form thick bacterial mats on oily bones but don't break down their structure. This means the oily bones last longest on the seabed.
Also found in whale skeletons are Osedax worms, which burrow into bone for food. So far there hasn't been much research on which bits of skeletons Osedax worms are found in most, but Higgs says in his studies he's noticed a pattern of some worms staying in bony areas while others burrow into the centre of bones where there's more oil, and thinks these may be different subgroups adapted to different niches.
He is now awaiting the results of experiments done by dropping parcels of whale bone onto the seabed around the UK and monitoring how they decompose. This work will help confirm or disprove the ideas suggested by studying the archives - is it true, for example, that oilier bones break down less quickly, but attract far more sulfide-loving bacteria? Returning to examine other researchers' pictures of other whale skeletons will also help test the theory's predictions.
It's possible that whale falls could have helped specialised organisms spread between isolated deep-sea environments like hydrothermal vents, though establishing this will need much more research. "Having these huge food islands on the seabed increases the number of environmental niches, so the habitat can support a greater diversity of life," Higgs says.
The work may also have implications for the archaeological study of whale-hunting ancient peoples. Archaeologists have started to investigate the idea that some north American tribes used whale bones for burning as well as hunting whales for meat; they have backed these claims up with simple analyses of the kinds of bones found with the remains of the camps these people lived in.
This work tended to be based on anecdotal observations such as that the head bones contain more oil, though. Higgs thinks his more detailed breakdown of the oil content of different whale bones could help these researchers analyse which bones people brought back from the hunt in more detail, and so provide more insight into how they used these bones.
'Bones as biofuel: a review of whale bone composition with implications for deep-sea biology and palaeoanthropology' - Nicholas D Higgs, Crispin TS Little, Adrian G Glover. Published online before print 11 August 2010, doi: 10.1098/rspb.2010.1267