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So Transparent!

Category: General Article

Back to Creep into the DEEPEND

Thursday, August 27, 2015

Summary: How do you hide from predators in a place where there’s no place to hide? For some deep-sea animals, this means becoming invisible by being transparent! Dr. Tamara Frank explains.

Hello Virtual Science Team,

What would you do if you lived in a place full of predators, and there was no place to hide? Many animals face that problem in the middle of the ocean. We call it the “deep pelagic zone.” The deep pelagic zone is far from shore, deep in the sea somewhere between the surface and the seafloor.

In the dark deep pelagic zone, there’s nothing to hide behind. No trees, no bushes, flowers, or rocks.

If you lived in the deep pelagic zone, and you could choose a camouflage, how would you hide? What kind of camouflage would work in the middle of the sea?

Many deep-sea animals solve this problem by being invisible or transparent. Really! Being transparent means the animal is as see-through as glass!

It is a lot harder for other animals to see a transparent animal, especially in the dimly lit deep sea. Jellies, fish, squid, crustaceans, many animals in the deep are transparent.

Many larvae use this type of camouflage. Larvae are often very small, so invisibility is a great camouflage. Especially since a predator’s rule in the wild is “if you’ll fit in my mouth, I will eat you!” As larvae mature, most change into the adult form when they find the right place to settle down. Sometimes, if they can’t find the right place to settle down, they get bigger and bigger. This is true for both the lobster larvae and the eel larvae (see photos of these animals and others in the slideshow on the right-hand sidebar).

One problem with being transparent is that you cannot have a lot of muscles, because muscles aren’t transparent. That means a transparent animal cannot swim very fast. However, being invisible means you wouldn’t need to outrace predators.

Some jellyfish and crustaceans remain transparent their entire lives. Some of the most amazing animals that I have ever seen are crustaceans in a group called “hyperiid amphipods.” One kind is the Cystisoma. It gets huge. What I like most about Cystisoma is that its whole head is an eye!

Cystisoma is cool, but nothing can beat Phronima for the cool factor because it looks like a space alien! A female Phronima has a challenge. She likes to care for and protect (brood) her eggs. But how does a crustacean in the middle of the ocean care for her eggs and newly hatched babies? Find a floating home or at least make one. She uses another animal to make a barrel for her eggs and herself. Not just any animal, of course, she uses either a salp or a pyrosome.

The female Phronima chews off a piece of the salp (or pyrosome) then smooths down the inside and outside to make a nice smooth barrel in which to lay her eggs. (See photo) You can see Phronima in her barrel with the eggs placed around the edges. She broods her eggs until they hatch.

Smaller Phronima have small barrels. When they get too big for the barrel, they dump it, find another salp, and smooth out another bigger barrel. Oddly enough, we sometimes find male Phronima in barrels, too, although they don’t lay eggs. We hypothesize that when the females dump barrels that are too small, a male floating along finds the empty barrel and decides that it will make a nice safe home.

Of course, for every remarkable adaptation one animal uses to hide or avoid predators, a predator has an equally amazing adaptation to find prey. Many animals find and eat transparent creatures. Sadly, marine animals often mistake human-made debris like plastic bags with transparent or semi-transparent animals they normally feed upon. Needless to say, eating a plastic object usually causes the animal to die.

What we do on land, whether it’s carelessly disposing of trash or forgetting the importance of reducing, reusing, and recycling, affects ocean animals – even in the deep sea. You can learn more about marine debris and how you can prevent it by watching the videos to the right.

Dr. Tamara Frank, Team Crustacean and Deep-sea Explorer

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Marine Debris Hunters, Part 1

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Marine Debris Hunters, Part 2

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