Mutualism of the month: Anemones and their shrimp protectors

Every month we showcase a relationship between two or more species which are considered a mutualism: a relationship where both members benefit. This month’s mutualism is between the pistol shrimp Alpheus armatus and the corkscrew anemone Bartholomea annulata.

The corkscrew anemone Bartholomea annulata. Photo source. Click for a bigger image.

The ocean is a rough place to live. Competition for space on the bottom is high and everyone’s out to eat you – so why not bring a friend to weather the storm? Protection mutualisms are a great way to reduce predation; one organism (called a host) provides a protective habitat and, in return, receives protection from another organism against its predator. There are a lot of examples of this in nature. For some really neat examples see these other Mutualisms of the Month: ants and acacias, sponges and scallops, and mouth bacteria and humans (there are plenty more here).

Anemones and corals embrace these relationships whole-heartedly (so to speak since they don’t have hearts). This group of animals (also known as Anthozoans) makes an excellent protective host with it stinging cells.  However, due to their immobility they have a hard time protecting themselves from predators. To compensate for this, they pair up with some amazing partners including anemonefish (including clownfish), crabs, and shrimps. Recently, a new relationship has been described by a couple scientists at the University of the Virgin Islands and Florida Atlantic University between a pistol shrimp and an anemone.

The red pistol shrimp Alpheus armatus. The right claw is the characteristic pistol claw. Photo source. Click for a bigger image.

Pistol shrimp are an interesting group with a characteristic claw capable of producing a loud snapping sound. This snapping sound is two parts of the claw quickly shutting together, creating a cavitation bubble. Essentially it snaps so quickly, it creates enough pressure to turn water to vapor underwater! The vapor almost immediately returns back to liquid, but in the process releases enough energy to create a miniature shockwave and a small bit of light (called sonoluminescence). As the bubble collapses, temperatures within the bubble can reach 8500 °F (nearly as hot as the surface of the sun). They use this shockwave to hunt their prey, communicate with one another, and for protection.

The anemone in question, the corkscrew anemone B. annulata, is one of the largest and most common species in Caribbean corals reefs. It hosts a variety of different shrimps and crabs including cleaner shrimp like the purple Pederson shrimp and the spotted cleaner shrimp as well as the red pistol shrimp A. armatus. The shrimps and anemone are known to trade several resources including nitrogen, which is a limited resource in reefs; food resources such as anemone mucus (yum); and protection by the anemone through toxic stinging cells.

The question is, is the role of protector reciprocal?

The bearded fireworm Hermodice carunculata. Photo source. Click for a bigger image!

The corkscrew anemone, as well as many solitary Caribbean anemones, are consumed by a large worm called the bearded fireworm (Hermodice carunculata). The bearded fireworm is a voracious predator and, given the chance, will completely consume an anemone. The fireworms are aptly named. They carry thousands of hollow hairs filled with toxins, which, when in contact with skin, are painful and inflammatory (trust me). Most of the corkscrew anemone’s symbiont associates are small; can they protect them from this worm monstrosity?

Turns out, pistol shrimp are champions. While the other shrimps were content with cleaning the worm or doing nothing, pistol shrimp aggressively attacked fireworms. They rushed the intruder, pinching and snapping them back using their modified claw. In about 1/3 of the trials worms showed external damage with a few dying from the damage. The shrimp seemed unphased by the toxic hairs of the worms.

The epic defense of the anemone. In frame (a) the shrimp stands between the worm and the anemone. In (b) it starts its attack, snapping and pinching followed by (c) the worm recoiling and (d) crawling away. Photo courtesy of Amber McCammon.

To read the original scientific article from the journal Symbiosis click here. The article may be behind a pay-wall so if you really want to read it, send me an email and I’ll grab you it.

Video of the shrimp protection by Amber McCammon.

Don’t forget to check out more mutualisms of the month and all the other great articles on FTDM! Stay hungry!

More Mutualisms of the Month!