18 April 2020 | New Scientist | 43have come to rely entirely on dead trees
and branches.
The LUMCON team left logs on the sea
floor for between 12 and 18 months and is
analysing which animals made them their
home. The results haven’t been published
yet, but there seem to have been as many as
60 species per log. As in previous wood falls
McClain has carried out off the Californian
coast, the Gulf of Mexico logs are riddled with
clams called Xylophaga (in Latin, this means
wood-eaters) that dig their way in with the
sharp edges of their shells, creating boreholes
that other species could then inhabit, including
sea cucumbers, squat lobsters and sea stars.
For the latest wood-fall study, McClain
collaborated with Clifton Nunnally, a specialist
at LUMCON on the Gulf ’s deep ecosystems,
to test a concept called the theory of island
biogeography – but in the deep. This ecological
“law” was proposed in the 1960s to explain the
diversity of animals on islands. The smaller
and more isolated an island is, the fewer
species live on it. McClain and Nunnally want
to know if the same goes for isolated oases of
wood in the abyss. As well as understanding
how these ecosystems assemble, the study
could help predict how changes on land –
deforestation or increased hurricanes because
of climate change, for example – may be felt in
the remote reaches of the deep.
The alligator and wood drop studies do show
a strong link between the land and the sea
floor, with a host of organisms waiting in theThe first scientific
reptile drop: When
the carcass of an
alligator was placed
on the sea floor it
quickly attracted a
horde of giant pink
isopodsHelen Scales is a writer
based in Cambridge, UK,
and Finistère, France, and
author of Eye of the Shoaldeep for food parcels from the shore. “There’s
this highway that connects the land to the
oceans,” says McClain.
But not all the items dropped to the deep
meet a slow fate as they are eaten by a variety
of organisms. Another of the alligators sunk by
the LUMCON team met a very different demise.
Eight days after it was dropped, the alligator
had disappeared. All the team could find was
the weight that had once been holding the
carcass in place. The rope fixed to it had been
bitten clean through. “You could see where the
weight had been drug through the sediment,”
says McClain.
It is probable that the alligator was snatched
away by a shark. Six-gill and Greenland sharks,
which can reach 7 metres long, are known in
these depths in the Gulf of Mexico. “They have
the bite strength and the sharpness to be able
to chew through a half-inch polypropylene
line,” says McClain.
Nobody was there to witness the event,
but the missing alligator is another piece of
evidence showing the multiple pathways that
land-based carbon can take when it enters the
deep-sea food web. And it goes to show that
there is more than one way to eat an alligator
in the abyss. ❚from a plesiosaur that swam in the oceans
100 million years ago and put it into a CT
scanner. The bone was perforated with
characteristic worm holes, supporting the
idea that Osedax evolved long before whales.
It is possible that the skeleton of the alligator
dropped by McClain and his colleagues could
have been devoured by zombie worms
descended from those that consumed the
bones of these ancient reptilian sea monsters.
Reptiles aren’t the only unlikely food
source sustaining life in the deep ocean. As
well as dropping an alligator, the LUMON team
sank chunks of wood in the Gulf of Mexico.
Remarkably, there are animals living on
the deep sea floor that seem to specialise
in eating trees.
Perhaps this shouldn’t be surprising, given
rivers carry lots of uprooted trees and woody
debris to the sea, where they become sodden
and sink. Previous studies have shown that
most species colonising rotting logs on the
sea floor live nowhere else in the deep and
“ Reptiles aren’t
the only unlikely
food source
sustaining life in
the deep ocean”