The behaviour of sacrificing body parts as a defense strategy is not uncommon in the marine habitat. An encounter with Stichopus horrens during a survey at Pulau Semakau gave me a personal experience of the unique defense responses displayed by the Holothurian (sea cucumber).
Holothurians have seven main types of anti-predatory mechanisms to defend themselves from potential predators, which include (Bingham & Braithwaite, 1986; Francour, 1997): (1) having thickened body wall, (2) toxic and noxious skin and organs, (3) body welling or stiffening, (4) swimming, (5) nocturnal activity, (6) cryptic or burrowing, and (7) autotomy or evisceration.
While evisceration and ejection is more common, where Holothurians discharge their guts or Cuvierian Tubules to ensnare and distract their enemies (National Geographic Society), the S. horrens protects itself from predation in a more unusual manner. When I removed it from the water to take photographs, the S. horrens surprised me by detaching a piece of its body wall within a few seconds, after arching into a “U” shape.
After placing it back into the water immediately, the usually slow S. horrens moved much faster away from the spot where I left it. These observations were consistent with a study done, where S. horrens were observed to contract the body into a “U” shape, followed by shedding of a piece of body wall and down current bounding locomotion when attacked, which was proven to be rather successful for escape (Kropp, 1982). It is also said that members of this genus if removed from the water too long, can “melt”, become limp and even disintegrate all together (Hauter & Hauter). Thankfully, if they are not too badly “melted”, they can reverse this process and recover.
Handle sea cucumbers with care the next time you see one. After all, we are their potential predators.
Bingham, B. L., & Braithwaite, L. F. (1986). Defense adaptations of the dendrochirote holothurian Psolus chitonoides Clark. Journal of Experimental Marine Biology and Ecology , 98 (3), 311-322.
Francour, P. (1997). Predation on holothurians: a literature review. Invertebrate Biology , 116 (1), 52-60 .
Hauter, D., & Hauter, S. (n.d.). Sea Cucumber Family Profile. Retrieved April 15, 2010, from About.com.: Saltwater Aquariums: http://saltaquarium.about.com/blcucumberfam_stichopodiae.htm
Kropp, R. K. (1982). Responses of five holothurian species to attacks by a predatory gastropod, Tonna perdix. Pacific Science , 36 (4), 445-452.
National Geographic Society. (n.d.). Sea Cucumber Holothuroidea. Retrieved April 15, 2010, from National Geographic: http://animals.nationalgeographic.com/animals/invertebrates/sea-cucumber
“Pink sea cucumber,” by Ria Tan. Wildsingapore, June 2009. URL: http://www.wildsingapore.com/wildfacts/echinodermata/holothuroidea/pinkspot.htm (accessed on 16 April 2010)