CHUNKS of methane ice at the bottom of the Gulf of Mexico are teeming with
life鈥攊n the shape of plump pink-and-white worms. The worms are the first
animals found living on ice mounds.
The worms were discovered last month during a dive to a depth of 700 metres
in a small submersible, about 240 kilometres south of New Orleans. Deep-sea
biologist Charles Fisher of Pennsylvania State University and the sub鈥檚 pilot
Phil Santos were astonished to see a huge number of worms thriving on a mound of
methane ice that had recently erupted through the sediment.
鈥淭he surface of the ice was etched with dimples,鈥� Fisher told New
快猫短视频. 鈥淚t looked like the outside of a beehive, with a worm in each
dimple.鈥� The worms are polychaetes, or bristle worms, and appear to be a new
species belonging to a group called the hesionids, Fisher says. Two further
dives last week revealed more about the worms and their unlikely living
quarters.
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Methane ice is a gas hydrate, a dense crystalline structure made of water,
methane and other hydrocarbons. It forms a solid only at high pressure and low
temperature. The Gulf of Mexico is one of the few places where such gas hydrates
sometimes burst through the sediment to form mushroom-like ice mounds.
The worms, which are between 2 and 5 centimetres long, look like typical
polychaetes, with a row of bristly 鈥渇eet鈥� along each side. A haemoglobin-type
molecule in their blood gives their bodies a pinkish colour, and their bristles
are white.
The worms almost certainly live off the energy stored in the ice鈥攂ut
cannot feed on it directly. Like other animals that live in the peculiar
environments around hot vents and hydrocarbon seeps, they probably acquire the
energy they need through a bacterial intermediary. 鈥淭here is no doubt in my mind
that bacteria help them to live off the hydrates,鈥� says Fisher. 鈥淏ut we don鈥檛
know whether they live inside the worm鈥檚 body or on the outside鈥攐r simply
grow in mats on the surface of the ice.鈥�
During last week鈥檚 dives, oceanographer Ian MacDonald of Texas A&M
University and his colleagues brought some solid chunks of hydrate to the
surface in a pressure chamber. MacDonald found worms right through the ice. 鈥淭he
burrow system appears to be quite extensive,鈥� he says.
One question that remains is whether the worms are opportunists that colonise
the ice when it emerges through the sediment, or whether they live on hydrates
beneath the surface. The first worms were found on ice that had only just
emerged from the mud and they were adults, which suggests they were well
established before the ice erupted, says Fisher.
Biologists are not the only researchers interested in the worms. Gas hydrates
are potentially a vast source of natural gas, and future hydrate prospectors
will want to know how much the worms erode the ice. They seem to carve burrows
into the mounds with ease, but whether they have 鈥渕ined鈥� away the potential fuel
source from the inside is anyone鈥檚 guess at this stage, says the team.
鈥淲e already had evidence that bacteria live on the hydrate but we were
astounded by the discovery of the worms,鈥� says MacDonald. 鈥淚t鈥檚 amazing how we
keep being surprised by these new undersea habitats.鈥�