As record holders, the colorful Mantis Shrimps lead the way in the Caribbean. These unique predators have many adaptations unparalleled in the animal kingdom, and scientists are now looking to these animals to improve everything from satellite imagery to the early detection of cancer cells.
Despite their common name, Mantis Shrimps are not actually shrimps, but more closely related to lobsters and crabs. Usually shy and reclusive creatures, they can be found on most shallow reefs in the Caribbean, either hiding in sandy burrows or quickly venturing out to capture prey. They begin life in a planktonic larval stage and can commonly be seen feeding near the surface on night dives and blackwater dives. After three months or so they get too big to keep themselves up in the water column, and they settle onto reefs. Now they can begin hunting and feeding on fish and smaller invertebrates, using a remarkable set of adaptations:
Mantis Shrimps have the most complex vision on the planet, and it's fascinating to think how they must see the reef. We humans have three kinds of photoreceptors in our eyes, for seeing red, green and blue light. This is better than dogs, that have two photoreceptors for seeing greens and blues, but not as good as some birds, that can have four photoreceptors (green, blue, red and ultraviolet.) Mantis Shrimps put all other types of vison to shame, with 12 or even 16 different kinds of photoreceptors. They can even see polarized light.
When light hits certain surfaces (like the surface of the ocean on a sunny day) it scatters and creates glare. The best we can do is invest in a good pair of polarized sunglasses. Mantis Shrimps can actually see polarized light and make use of it. Males have areas on their bodies that reflect polarized light to other Mantis Shrimps, a secret form of communication that only they can see. They use it to attract females or to warn other males away from their territories. Medical researchers are very interested in this ability, as early cancer cells also react differently to polarized light. Endoscopic cameras that can detect polarized light can now catch cancer cells long before any other detection method.
It would be great to think that all these different photoreceptors means that the Mantis Shrimp sees the reef much better than other animals, but that doesn't seem to be the case. It just sees things differently. In fact their color vision isn't as refined as ours, and they can't make out very fine shades of color either. The processing power just isn't there for so many signals coming into a Mantis Shrimp's brain. Instead, it continuously scans the reef back and forth, ignoring much of the information until prey is detected, and then it can strike blazingly fast. This scanning activity from so many lenses has scientists looking at this system of vision as a model to improve satellite imagery from space.
Each eye can move independently on a moveable stalk, giving the Mantis Shrimp a 360 degree view of the reef around them. Different parts of each eye can look at the same subject from a slightly different angle, and this means they can have depth perception even when only one eye is being used, very useful when hunting.
A powerful punch:
There are two main types of Mantis Shrimps: "Spearers" and "Smashers"
"Spearer" species, such as the Scaly-Tailed Mantis (Lysiosquilla scabricauda) are ambush predators. They create L-shaped burrows in the sand, with a rounded hole on top. They can cover the top of this hole with sand so that only their eyes are poking out, scanning the reef for passing prey. The eyes are even camouflaged to look like sand. (Click here for video). They mostly target small fish. The name Mantis Shrimp comes from the set of sharp raptorial claws, similar to those of the Praying Mantis. When a fish gets close enough they strike out and spear or slice the fish, faster than the blink of a human eye. Click below to see the video:
"Smasher" species have club-like appendages they use to break into the shells of snails, hermit crabs or the hard carapace of crabs themselves. The powerful arms have a spring, shaped like a Pringle chip, and a rachet that locks the club in place. As the muscles flex, power is built up until the latch is released. This creates the fastest strike in the ocean, measured at 80 km/hr, and it has the same force as a 22-calibre bullet. Not bad considering the limbs are moving through water at the time.
This is only part of the force of the blow: the clubs move so quickly that they actually cause the water in front of them to boil, creating tiny bubbles. As these bubbles collapse, they release a tremendous amount of energy. These cavitation bubbles stun the prey, and even small flashes of light are produced. This one-two punch means that prey has little chance against a "Smasher". Click to see a video below:
A lot of the recent research on Mantis Shrimps has been done by Dr. Sheila Patek at Duke University. Geeks can visit her lab page for a more in-depth look into this behavior by clicking here, and see more videos of the research into Mantis Shrimps by clicking here.
Mantis Shrimps are often very tough to shoot underwater: The "Spearers" are so well hidden it can be tough to even find them. But when you do, you can visit them again and again, as they rarely seem to move. I've been visiting the same burrow of a Scaly-Tailed Mantis for years now. I don't like to get too close though, they have earned the nickname "Thumbsplitters!"
The "Smasher" species are very fast and don't often wait around for you to get your camera ready before they bolt back into shelter. They do tend to stick around more while they are feeding, but I'm always wary of getting my lens too close. There's a reason they are rarely kept in aquariums: they can break the glass. The thin glass in front of my housing would be no problem for them!
Mickey Charteris is an author/photographer living on Roatan. His book Caribbean Reef Life first came out in 2012 and is currrently into it's sixth printing as an expanded fourth edition.