The Goby and Pistol shrimp… Nature’s guide dog

The sea floor can be an unforgiving place when you’re a small crustacean barely larger than the size of a human finger. The Pistol shrimp has formed a mutualistic relationship with the goby fish as it is almost completely blind. The goby acts as a "guide dog", so to speak, alerting the shrimp of any danger nearby by keeping a point of constant contact with its antenna. More than one species of goby share relationships with shrimps, so in this post I will focus on the Yellow Watchman Goby (Cryptocentrus cinctus) and the Tiger Pistol Shrimp (Alpheus bellulus).

Figure 1. Yellow Watchman Goby (Cryptocentrus cinctus) standing guard while the Tiger Pistol Shrimp (Alpheus bellulus) excavates the burrow. Note the iridescent blue spots on the goby. Photographer: Anonymous 

The pistol shrimp spends a large portion of its time constructing and maintaining small channels and tubes beneath the sandy rubble sea floor. The pistol shrimp is almost blind due to a permanent sheath that covers its eyes and relies largely on its goby partner to do the seeing. The goby simply stands guard using its modified pectoral fins to sit on the sea floor and keep watch for danger. The shrimp generally keeps a point of contact with the goby via antennae whilst shifting rubble to the exterior of the pair’s hideout. The shrimp rarely ventures outside of the retreat and if it does so the goby attends to its side allowing the constant contact. The shrimp has little reason to leave the burrows except short trips to a collect algae which grows in close proximity to the burrows entrance. The goby will rarely leave the shrimps side except when in search of food; the goby’s main food source are small animals which are found by sifting through the sandy rubble (Polunin and Lubbock, 1977).

The pistol shrimp is equipped with a large modified claw that can generate powerful blows that stun prey items within short range; so powerful in fact it is often described as ripping the water apart. The claw can shut at speeds of one hundred kilometres per hour creating a cavitation bubble. In certain parts of the bubble temperatures exceed 5000 degrees kelvin, which are comparable to temperatures on the sun’s surface; light is also generated by the implosion of water caused by the negative pressure of the bubble. The claw is only effective at short range as the shrimp has extremely limited eye sight due to a protective sheath that is believed to evolve to protect the shrimps eyes from the powerful blows (Torres et al., 2007).

Figure 2. Diagram of Pistol shrimp's claw.
 Photographer: Knowlton and Moulton, (1963). 

Marine environments are filled with predators of all shapes and sizes and if organisms are to survive they must do so by any means possible, just as the goby and shrimp have struck up their mutualistic relationship. The below videos shows how the goby and shrimp stay in with each other and also how the pistol shrimp can generate such powerful blasts from its modified claw.

Video with thanks to FantasticAnimal. https://www.youtube.com/watch?v=aSTk2pui5X4

Video with thanks to Earth Unplugged. https://www.youtube.com/watch?v=QXK2G2AzMTU

References:

POLUNIN, N. V. & LUBBOCK, R. 1977. Prawn‐associated gobies (Teleostei: Gobiidae) from the Seychelles, Western Indian Ocean: systematics and ecology. Journal of Zoology, 183, 63-101.

TORRES, J., WASHINGTON, K., WONG, S., ZARZECKI, M., CHENG, Y. & DIEZ, F. Velocity Measurements of a Pistol Shrimp's Micro Water Jet Using High Speed PIV.  APS Division of Fluid Dynamics Meeting Abstracts, 2007.

Figure 1. Anonymous (n.d) Yellow Watchman Goby (Cryptocentrus cinctus) and Tiger Pistol Shrimp (Alpheus bellulus). https://www.tumblr.com/search/Yellow+watchman+goby. Retrieved on 26/03/2015.

Figure 2. Knowlton and Moulton. 1963. Biol. Bull. 125:311-331. Diagram of Pistol Shrimp's claw. http://www.dosits.org/audio/marineinvertebrates/snappingshrimp/. Retrieved on 26/03/2015.