Luminescent responses to predation in the scale worm Harmothoe imbricata
Trevor J. Rivers
Bioluminescence is a phenomenon that has evolved many different times in many different organisms, especially in marine systems. For all that is known about how many of these species luminesce (physiologically and chemically), often much less is known about why they exhibit this behavior. Harmothoe imbricata is a luminescent scale worm found in abundance in the intertidal and subtidal habitats of coastal Maine, whose luminescence has been well studied in laboratory settings for well over 50 years. Luminescence occurs in the elytra (scales), which can emit light while still attached to the worm as well as when shed from the body. In addition, worms can autotomize, with the posterior segments luminescing while the anterior segments remain dark, eventually regenerating. Although these displays have been hypothesized to have evolved as a defense against predation, there have been no specific tests using actual predators to confirm these hypotheses. Using low-light CCD cameras with infra-red (IR) illumination, a night vision device with an IR barrier filter, and a photomultiplier, we recorded the behavior of dark-adapted H. imbricata when attacked in complete darkness by three different species of crab (Carcinus maenus, Cancer irroratus, and Hemigrapsus sanguineus) and by the American lobster, Homerus americanus). All but H. sanguineus consistently attacked the worms. We have definitive evidence that luminescence does often function as a successful decoy to predators, either by the worms dropping scales or by whole-segment autotomization. In addition to decoy luminescence, we observed instances of worms exhibiting warning flashing before their potential predator even attacked, indicating that H. imbricata uses its luminescence in a multitude of ways to avoid predation.
Rivers, Trevor J. and Perreault, Tamara R., "Luminescent responses to predation in the scale worm Harmothoe imbricata" (2012). Marine Lab Student Papers and Projects. Paper 9.