Cuvierian tubules in tropical holothurians: Usefulness and efficiency as adefence mechanism

The tropical holothurians, Holothuria leucospilota, Bohadschia argus and B. marmorata responded to tactile stimulation by expelling Cuvierian tubules in proportion to the intensity of the stimulation. They were able to target the stimulated area with variable success depending on the location of the stimulus, Field surveys showed that 2.3-6.1% of H. leucospilota presented signs of having recently used their Cuvierian tubules and laboratory experi ments revealed that they released tubules in response to several natural pr edators. The tubules did not adhere nor cause any distress to fish, but pro ved effective in discouraging attacks. Crabs, molluscs and echinoderms were entangled and also efficiently repelled. H. leucospilota without tubules w ere wounded and even killed by predators that were usually discouraged by t ubule discharge. Conversely, after having induced the release of tubules on ce, 96% of the predators placed in the presence of H. leucospilota three da ys later remained at a distance. Released tubules that did not adhere to an y surface were quickly retracted, while regeneration of a complete set of t ubules took 15-18 days. The release of Cuvierian tubules by tropical holoth urians therefore appears to be a sensitive defence mechanism. Data on H. le ucospilota further suggest that they are readily used against predators in the field.