Zombie Worms

 

This article was written by Jessie

Whales are huge (approximately

10 to 20 metres long and 100-200

tonnes in weight) while Zombie

worms are only about the length

of your finger - 5 centimetres. Surely

it must be that whales are eating

the Zombie worms? No, it is indeed

the other way around.

Zombie worm larvae live and drift as

they search for a special habitat

at the bottom of the ocean called a

whale fall. When an adult whale dies

its body sinks from the surface of the

ocean - where it used to live - to

the bottom of the ocean.

In the deep ocean there

is little for animals to eat so

a whale fall is an important

supply of food - thousands

and thousands of kilograms

to be used as food by

hungry creatures.

After the whale’s body

has landed on the ocean floor

hundreds of animals get to work

eating it. First, the large swimming

scavengers like sharks, rattails and

hagfishes move in to rip and tear at

the whale’s flesh to expose the oily

blubber. Once the flesh is torn apart,

small scavengers swarm in and soon

the whale body is stripped almost

to the bone. But that doesn’t mean

that the food is all gone.

Now is the opportunity for huge

numbers of polychaete

worms, crabs, sea

cucumbers, brittle stars

and snails to move in.

They nibble tissue and fat

off the bones and crawl

over the sea bed that the

whale is lying on, picking

up the bits that fell off as

the big scavengers filled

their bellies.

Once most of the meat and blubber has been

consumed, the Zombie worms arrive! They are

bone specialists and it is their job to RECYCLE

the bones! When they are done, there will be

nothing left of the whale: not even the skeleton.

How can Zombie worms ‘eat’ the whale bones

– especially since they have NO mouth parts?

Well, they get another species to help them.

What happens? Each individual Zombie worm

lives inside a transparent, jelly-like tube. This tube

is topped with feathery palps through which the

worm gets oxygen dissolved in the water. Inside

this tube is a heart, blood vessels, long muscles and

glands. The muscles let the worm pull in the palps if

something disturbs it. At the bottom end of the trunk is a

large sac where the female produces lots of eggs. This

egg sac is covered with a green tissue that extends into

root-like structures.

 But wait! The Zombie worm is an animal, not a plant! Surely worms don’t

have roots?! Normally they don’t – Zombie worms are the ONLY ones to have

these root-like growths which dissolve their way into the whale bones by

secreting an acid.

The reason Zombie worms can now settle into the bones is the fact that

inside the green ‘root’ tissue there is a special kind of bacteria called

Oceanospirillales. These bacteria digest the fats and oils inside the

hard bone structure and pass on some of this nutrition to their hosts, the

Zombie worms. Who needs mouth parts if you are getting fed by these

helpers living inside you!

Because the bacteria are getting help by the acids digesting the whale

bone, the root-like structure of the worms can grow deep inside the bones

leaving only the trunk and crown of the worms poking out and getting oxygen

dissolved in the water.

 This partnership of the Zombie worms and the bacteria within them is called symbiosis

 as each partner helps the other. (Symbiosis: sym = together; biosis = living).