The music of the shipworm …
J. Coston-Guarini & F. Charles
25 Jan 2021 [v. 26012021]
For decades marine bioacoustic studies in ecology have concentrated on the sounds produced by marine mammals and a small number of crustacean and fish species. Besides sound sequences emitted intentionally, like whale songs, there are many more sounds produced as a consequence of a living organisms’ usual day-to-day activities (i.e. moving, hunting prey, grazing, …).
Lurking under these studies is a more fundamental question, that is are these sounds ‘heard’? Is it communication or a signal? Are there changes in behaviours in consequence? This question is also important to questions of environmental impact. If an anthropogenically produced sound is to be treated as a negative factor, evidence of the negative biological effect should be demonstrable.
Studies of the acoustic reactions of bivalves (one of the largest groups of marine animals), have rarely demonstrated consistent patterns. The reasons for this are probably due to many things, including: the challenges of controlled experimental systems for bioacoustics, the difficulty to predict complex dynamics because of non-linear processes and unknown factors, or perhaps the absence of a precise biological hypothesis for an impact (or effect) in existing literature.
Enter the shipworm. The shipworm, or “Taret” in French, which is the common name given to a group of bivalves that pierce and live in wood. The most famous representative of this family is Teredo navalis, or the ship ‘piercer’. This group (the Teredinidae) appear in some of the oldest scientific literature and the damage they cause to ships, seawalls, pilings and other wood structures has earned them many sensational nicknames throughout history.
There are quite literally thousands of documents written on the topic, spread over hundreds of years. Historical writings relate, for the most part, the sometimes spectacular and deadly, secondary effects caused by the work of the “taret”, such as ship sinkings or catastrophic collapse of port infrastructures. One of the most important technological challenges of the late modern and early modern maritime activities has been to find ways to prevent shipworm (and other borer) damage.
In 1892, based on a popular saying, Henri de Lacaze-Duthiers (1821-1901), founder of the Laboratoire Arago (Banyuls-sur-Mer, France), wondered if the “music” of the shipworm could be perceived by the human ear. He wrote a short account that he was unable to verify the anecdote:
“Ces bois proviennent d’un vivier créé à Banyuls, et qui ont été immergés, il n’y a pas un an. […] Il y a au bord de la mer un dicton ainsi conçu : “ces petits animaux font leur musique. “ J’ai essayé d’entendre le bruit qu’ils font en attaquant les bois, je n’ai pu y parvenir.”
— de Lacaze-Duthiers, F. J. H. 1892. Le Taret. Bulletin des Séances de la Société Nationaled’Agriculture de France CR Mensuel, 52: 555-557.
One hundred and thirty years later, we are getting close to demonstrating the kernel of truth in this saying. We have recorded the sounds produced by living shipworms as they tunnel into pine test boards. The faint rasping sounds are in the frequency range of human hearing, but they would not be audible without amplification. Our recordings indicate boring is done with intermittent, short bursts of activity. The sharp sounds are produced by the valves’ exterior surfaces contacting and then pulling across the wood surface.
Today, teredinids continue to be of concern for the conservation of marine and underwater archaeological heritage, but they have also become a widely used biological model for testing ecological concepts and understanding the transformation of cellulose into energy. Longstanding questions can now be studied about the rhythms of their biological activity, or whether the vibrations produced constitute a signal of the presence of a another individual. Sound is, perhaps, the key to understanding why the galleries bored by shipworms remain separate, only rarely intersecting.
Additional links
A French version of this text is here.
Source
Charles, F. and Coston-Guarini, J. 2021 [workshop paper] Hey, do you hear me? : The elusive song of the shipworm. Presented during “The Naval Shipworm Teredo navalis. A global player and its entangled histories.” German Maritime Museum/ Leibniz-Institute for Maritime History, 21-22 Jan 2021. Co-organisers: M. Vennen and R. Schilling. 27pp