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Alligators in the Abyss: Part 2

Connecting the oceans to land are numerous carbon highways.  These conduits bring food from land to the ocean, supporting an abundance of life.  Our group explores these carbon chains and explores some potential methods of carbon delivery to the deep.  Thus, alligators on the abyss.

At
first it may seem fanciful that an alligator carcass might find its way to the
deep.  However, dozens of species of
alligators and crocodiles are found across the globe, in high numbers, and
often in coastal areas.  Through either
their normal migrating or foraging activities, or during flooding events,
individuals may be found offshore in the ocean. 
If one of those individuals meets an unfortunate end, it may fall to the
seafloor.

A crocodile swimming in the open sea. Crocodilian species have been utilizing marine habitats more in recent years.

In
prehistoric times, the impact to the deep oceans could have been even larger,
as large reptiles such as ichthyosaurs and plesiosaurs dominated the sea.
Deploying a reptile in the deep sea today may reveal the animals that
specialized on the carcasses of long-extinct ancient emperors of the sea.

Ancient marine reptiles such as this one dominated prehistoric oceans. Studying alligator falls today may give us insight into what happened when these large predators of the past died and sunk to the seafloor.

Earlier
this year, our research group placed three alligator carcasses 1.5 miles deep
on the seafloor of the Gulf of Mexico in the first-ever alligator fall
experiment.  Each of the three alligators
met a different fate.

The first alligator had been on the bottom of the ocean for less than 24 hours. Despite the tough hide of the alligator, scavengers quickly got through and began to gorge themselves on the flesh of the alligator. Football-sized animals called giant isopods, relatives of rolly pollys or pillbugs, penetrated the hide in this short time-frame.  This demonstrates the speed and precision with which deep-sea scavengers can utilize any carbon source, even food from land and freshwater systems.

Giant isopods made it through the tough hide of the alligator in less than 24 hours. These scavengers opportunistically gorge themselves and then can go years without eating another meal!

A
little over 60 miles to the east of the first alligator, the second alligator
had been sitting on the seafloor for a little over a month and a half.  All the soft tissue of the alligator had been
removed by scavengers.  A small animal
called an amphipod was still darting around looking for scraps, but the only
thing that remained was a skeleton.  All of the soft tissue had been
consumed. The spine curved just as it had been left.  A depression in the sediments indicated where
the full body once laid.  The skull was turned over, likely by scavengers
while picking at the flesh on the skull.

The second alligator had been reduced to a skeleton in only a month and a half.

A
fuzzy carpet covering the bones of the second alligator represented a brand-new species, previously unknown to
science.  These zombie worms, or Osedax,
colonize the bones of many types of vertebrates and consume the lipids
within.  This was the first time zombie worms had ever been observed in
the Gulf of Mexico or from an alligator fall. 
They also demonstrate yet another pathway in which carbon from land
makes its way into deep-sea food webs.

The fuzzy carpet covering the skull is a brand-new species of zombie worms, or Osedax, previously unknown to science!

Another
60 miles east lay the third alligator.  It had only been eight days since
it was laid on the seafloor.  As the
camera panned to the marking device, a floating bucket lid attached to a rope
like an underwater flag, it became clear that the alligator was missing
All that remained where it had been dropped was an alligator-shaped
depression in the sediments.  Drag marks
in the sediment paved a path to what remained of the alligator fall.  An
animal dragged this alligator 30 feet and left only the 45-pound weight and rope.  The rope had been bitten completely through.
To consume an alligator, and create this disturbance, the animal must have been
of great size.  We hypothesize that most
likely a large shark, like a Greenland shark or sixgill shark, consumed this
alligator whole.

The third alligator was missing after eight days! The depression shown here was where the carcass had once laid.

Three
alligator falls in the abyss met three very different ends, from being consumed
by football-sized cousins of rolly polys, to zombie worms eating their bones,
to a large shark dragging it away and consuming it whole.  This research has given us a glimpse into
what impact large reptiles had in past oceans, as well as the role they play
today.  It is clear that deep-ocean
scavengers have no qualms about successfully and quickly consuming food that
originated on land or freshwater.

Read more about this research in our group’s recent publication in PLOS One: “Alligators in the abyss: The first experimental reptilian food fall in the deep ocean.”

River Dixon (4 Posts)

River Dixon is a Ph.D. fellow in the lab of Dr. Craig R. McClain at the University of Lousiana Lafayette and the Louisiana Universities Marine Consortium. Dixon studies the energetics of trophic structure in the deep sea.

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