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| A Pacific Humpback Whale calf. |
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| A baleen whale carcass, at a depth of 9800 ft, on the floor of Monterey Canyon. |
The deep ocean floor (greater 9800 ft deep) is an
inhospitable place of cold (36F), great pressure (4400 pounds/in2),
and permanent, absolute, unrelenting darkness. The earth’s surface, including the sea floor, is composed of
a series of large, mobile plates. It wasn’t until 1977 that marine geologists
discovered hydrothermal vents, sites where plates are moving apart on the ocean
floor and water heated by magma, surges out of the crust at temperatures as
high as 870oF and as
acidic as vinegar. The heated water comes spewing out as black or white
smokers.
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| At a vent resort vestimentiferan worms enjoy the good life as two black smokers eject 800F water. |
In contrast to most of the deep sea floor, vent systems have
diverse and abundant life. This
diversity of vent life is even more amazing because it occurs in darkness. Most
ecosystems depend on sunlight, converted to biomass through photosynthesis, as
the source of energy that drives the system.
But light only penetrates a few hundred feet in the ocean. So without light, and therefore without
photosynthesis, how do the vent communities survive, much less prosper?
My molecular biologist / bio-chemist son has drummed into me that
almost everything starts with and ultimately depends on microbes. The hydrothermal vents are no exceptions. The super heated water is rich in sulphur and
other dissolved minerals. Archaean bacteria specialize in metabolizing those
minerals and converting them to energy, a chemical analog of phontosynthesis
known as chemoauthotrophy That abundance of those microcorganisms forms the
basis for the food web and animal communities that live in the vent ecosystems.
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| Thousands of white vent crabs exemplify the abundance of life found around vents, these in the Antarctic Ocean. |
How rich is life at the vent systems? In spite of the difficulty of visiting these
sites and the problem of trying to sample life forms at such great depths, a
new species of vent life has been named in the scientific literature every two
weeks since the first paper in 1979.
However, the volcanic activity on the sea floor is not
consistent long term and can turn off in some areas and appear in others
further away. So the animals living at
the vents must be able to get around, maybe great distances. Many vent organism are sessile and cannot
move and many others cannot mover great distances. Besides, leaving the area of the vent means
traveling from a warm area into the frigid cold. For many animals it’s the larvae, rather than
adults, that are carried far away by currents and hopefully land in a favorable
spot of the deep sea floor.
During a deep sea dive in 1987, researchers accidentally
came across the skeleton of a blue or fin whale in the Santa
Catalina Deep. This was the first whale
carcass to be observed on the deep sea floor. What was remarkable was the large
number of organism living on the carcass, many of which were not seen elsewhere
on that sea floor, although a number of them were known from vent communities
elsewhere. Mats of chemoautotrohphic bacteria covered the
seafloor and bones and other species present host such bacteria internally and
live off the energy released by the bacteria. What had been discovered was a
chemoautotrophic community like those of the vent communities, living on a dead
whale.
Although there were no hydrothermal vents at the whale site,
the bacteria were performing their miracle by metabolizing the fats in the
whale bones! Since that time other
natural deep sea whale fall occurrences have been found, but those discoveries
are dependent upon luck. To better
understand decomposition of whales and their utilization a number of whale
carcasses have been sunk to the sea floor and their exact location recorded so
they can become subjects for long term studies.
This is now a rich field of study and has revealed much about the
ecology of the deep sea floor.
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| Snacking at the Cafe Cetacea. Multi-colored bacterial mats metabolize bone fats (top left), hagfish consume soft tissue (top right), bone-eating worms feast on the skeleton (bottom left) and vent crabs do general clean up (bottom right). |
Some food falls to the deep sea floor from higher in the
water column, but at a very slow rate, and has been names “marine snow”. Much
of it is small to microscopic. A 40 ton whale carcass sinking to that sea floor
provides the equivalent of 200 years worth of food from marine snow. And whale arrives as single, all be it very
large, package --- and the largest cetacean, the blue whale, reaches a greater
weight of 200 tons! Although several
stages of decomposition of the carcass
can be identified, the longest lived stage is that of the vent community organisms
that colonize and consume the bone
lipids. This community includes certain bacteria, as well as specific groups of
crabs and other crustaceans, clams, snails, worms, and others. Some species
occur in the tens of thousands of individuals.
Given that the bones of large whales can be 60% lipid by weight and the
cold temperature in deep water, large whale skeletons may last more than 50
years on the sea floor.
These whale skeletons thus serve as a way station of sorts,
where deep sea communities can grow and ultimately send their larvae on
to colonize other shale carcasses or real hydrothermal vents on the sea
floor. Some estimates place whale
carcasses, at least along whale migration routes, as close together as 6 miles. So
the death of these air breathing giants provide crucial food and colonization
sites for some of the most specialized deep sea organism in the ocean.
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Whenever I read about an interesting biological phenomenon, like our tale of the whale, I often wonder how far back in time the phenomenon originated. Fortunately, the fossil record can often provide some insight and constraints.
The earliest whales evolve from terrestrial ungulate mammals
by the Eocene, some 40 million years ago.
These are predatory, primitive whales achieve lengths of 50 feet or
more. However, the bone structure of
these whales shows that they had not yet evolved the high oil content in their
bones. So it is not too surprising that
no vent community type fossils are known from those fossil skeletons. It is not until the Miocene, about 11-15
million years ago, that whale fossils with associated invertebrate fossil
characteristics of vent communities first appear, when the bone oil content reaches critical mass.
What of the fossil record of vent communities? Hydrothermal vents on the sea floor
occur far back in time, billions of years, even before life first evolved. More than 50 fossil hydrothermal vents with an
associated fossilized communities are known, extending as far back as the
Cambrian in China, some 522 million years ago.
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I can’t manage to drag dinosaurs into this post. Although dinosaurs were the dominant large
land dwelling vertebrates of the Mesozoic, and took their phenomenal success to
the air when small maniraptoran theropods evolved into birds, they never
evolved into aquatic or marine forms.
That’s not to say that dinosaurs aren’t found in marine rocks. Hadrosaurs, ankylosaurs, and therzinosauroids
have all been recovered from marine environments and some even laid on the sea
floor long enough to have oysters begin to grow on their bones. However, all these occurrences are of
terrestrial dinosaurs whose carcasses floated out to sea, either from the
shoreline or carried out by a river. While
they came to rest on the sea floor, they did not live in the ocean. Having normal bones with low fat content, it
is no surprise that vent community organisms have never been found on one of
those skeletons.
Although dinosaurs never invaded the fresh and salt water
realms, other groups of Mesozoic reptiles did, and some achieved large size.
Ichthyosaurs, reptiles resembling
dolphins and porpoises, grew
quite large (up to 70 feet in length) and some were deep diving predators. Mosasaurs are ocean-going predatory marine
lizards, related to the Komodo dragon, the largest of which achieved a length
of 57 feet (17.5m). The plesiosaurs are
the final large group of predatory Mesozoic marine reptiles and reached 20 m (?
Ft) in length. Certainly the largest
members of each of these groups would be a tremendous food packet when a
carcasses fell to the sea floor, just like a whale, and several paleontologists
have speculated on the ecological effects of such events.
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| The largest known Mesozoic marine reptiles compared to a sperm whale and a scuba diver. |
In 2008 a paper appeared providing the first documentation
of a Mesozoic marine reptile with fossil remains of a chemoautotrophic
community preserved in intimate association with a skeleton --- in fact two such
skeletons of plesiosaurs. Although one
cannot directly measure the oil content of these ancient bones, the abundance of
iron sulfide inside the plesiosaur bones is evidence of bacterial sulfate
reduction of bone lipids. Numerous snails and clams among the bones of the
skeletons belong to groups that occur at modern day and fossil hydrothermal
vents.
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| Part of a Cretaceous plesiosaur reptile skeleton from Japan, with vent community snails (yellow circles) and clams (blue circles) organisms preserved between the bones. |
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| A collection of fossil snails from the plesiosaur skeleton. |
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Sometimes putting together a Land of the Dead post is pretty
straightforward, at other times less so. I have been following research on
hydrothermal vent communities pretty much since their discovery. Not that I read every scientific paper on the
subject, far from it, but I do have enough of a fascination with them that I’ve
put visiting a deep-sea hydrothermal vent community on my “bucket list”. And I remember when the discovery of
hydrothermal vent communities on whales fall was first announced.
A number of weeks ago I watched Into The Deep, an episode of the PBS series American Experience, about the history of sperm whale
hunting out of Nantucket Island and the sinking of the whaling ship Essex in
1820 after being “stove by a whale” in the middle of the Pacific Ocean. I knew
very little about that part of American History, so it was eye opening. Following
that I listened to Philbrick’s In The
Heart Of The Sea, a magnificent book about the Essex disaster, and one I
highly recommend as a most remarkable, and long forgotten, story of extreme survival
at sea. That led to Dolin’s Leviathan, a history of North American
whaling from 17th through 19th centuries. Leviathan
begat my current reading project, Whitehead’s
Sperm Whales: Social Evolution in
the Ocean, a remarkable overview of the biology of a most remarkable
animal.
Somewhere in all of this I got the idea for a post about
whale falls past and present which led me to the work of marine biologists
Smith, Baco, Kiel, Higgs, and others. Researching the paleontological record of whale falls,
ancient marine reptiles, and associated fossil vent communities led to the work
of Hogler, Kiam, Martill, and others. Those who know me will recognize the behavior exhibited here. “Dan’s got
a new favorite” is how it was once described.
When I finish Whitehead’s book it will be time to move on to
some other topic. However, the circuitous path for the whale fall post is a
manifestation of what the Nobel Prize winning theoretical physicist Richard
Feynman described as “the joy of finding things out.” Coming across a small fact can lead you to
learn about a fascinating area about which you knew little about ----
if you are willing to follow your nose. Nose
following is probably preferable to chasing one’s tail, although I will need to
check with Nut and Buster, my two resident experts on such matters, to get a
professional opinion.
And no, I haven’t read Moby Dick!!
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PHOTOS
Humpback Whale calf:
Whale carcass: http://www.mbari.org/news/news_releases/2004/whalefall.html
Vestimentiferans and smokers:
Antarctic vent crabs:
Cafe Cetacea:
Plesiosaur skeleton and vent fossils: From Kaim et al. 2008 (below)
SOURCES
Dolin, E.J. 2008. Leviathan: The History of Whaling in
America. W.W. Norton and Co.: 512 pp.
Goedert, J.L, Squires, R.L., and Barnes, L.G. 1995. Paleoecology
of whale-fall habitats from deepwater Oligocene rocks, Olympic Peninsula,
Washington State. Paleogeography, Palaeoclimatology, Palaeoecology 118:
151-158.
Goffredi, S.K., Paull, C.K., Fulton-Bennett, K., Hurtado,
and Vrijenhoek, R.C. 2004. Unusual benthic fauna associated with a whale fall
in Monterey Canyon, California. Deep-Sea
Research 51: 1295-1306.
Higgs, N.D., Little, C.T.S., and Grover, A.G. 2011. Bones as biofuels: a review of whale bone
composition and implications for deep-sea biology and palaeoanthropology. Proceedings of the Royal Society B 278: 9-17.
Hogler, J.A. 1994. Speculations on the role of marine
reptile deadfalls in Mesozoic deep-sea paleoecology. Palaios 9: 42-47.
Kaim, A., Kobayashi, Y., Echizenya, H., Jenkins, R.G., and
Tanabe, K. 2008. Chemosynthetic-based associations on Cretaceous plesiosaurid
carcasses. Acta Palaeontologica Polonica 53(1): 97-104.
Kiel, S. and Goedert, J.L. 2006. Deep-sea bonanzas: early
Cenozoic whale-fall communities resemble wood-fall rather than seep
communities. Proceedings of the Royal
Society B 273: 2625-2632..
Martill, D.M., Cruickshank, A.R.I., and Taylor, M.A. 1991.
Dispersal via whale bones. Nature 351: 193.
Philbrick, N. 2001. In the Heart of the Sea: The Tragedy of
the Whaleship Essex. Penguin: 302 pp.
Pyenson, N.D. and Haasl, D.M. 2007. Miocene whale-fall from
California demonstrates that cetacean size did not determine the evolution of
modern whale-fall communities. Biology Letters, Royal Society London 3:
709-711.
Smith, C.R. and Baco, A.R. 2003. Ecology of whale falls at
the deep-sea floor. Oceanography and
Marine Biology: an Annual Review 41: 311-354.
Smith, C.R., Kukert, H., Wheatcroft, R.A., Jumars, P.A., and
Deming, J.W. 1989. Vent fauna on whale remains.
Nature 341: 27-28.
Wang, X.Q., Shi, X.Y., Jiang, G.Q., and Zhang, W. 2012. New
U-Pb age from the basal Niutitand Formation in South China: implications for
diachronous development and condensation of stratigraphic units across the
Yangtze platform at the Ediacaran-Cambrian transition. Journal of Asian earth Sciences
48: 1-8.
Whitehead, H. 2003.
Sperm Whales: Social Evolution in the Ocean. University of Chicago Press: 464
pp.
