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Spying on scallops with underwater microphones

Scallops are noisy mollusks; when closing, their valves emit a characteristic sound the study of which can provide useful informations on the behavior of the animals and their reaction to changing environmental conditions.



As most bivalve molluscs, scallops record environmental variations in their shells, thereby providing valuable information on past climates. Understanding the effects of the environment on their physiology is therefore an essential step to interpret the natural archives contained in their shells. The underlying physiological and biochemical processes are highly complex, and their study could be complemented by that of their behaviour, which is a visible manifestation of the way scallops react to the fluctuations of their environment.

The recent advances in passive underwater acoustics (i.e. recording of sounds by immerged hydrophones) opened original perspectives in this field, as scallops are one of the natural sound sources in the marine environment. It is known to have a whole range of behaviours; the most usual and one of the noisiest of them is "coughing", a rapid closing of the valves associated with the expulsion of water, faeces and other substances from the mantle cavity. This activity is related to environmental changes involving temperature, light, suspended matter, food, toxins, etc.

Listen to the "scallop's song"

This study explores the potential interest of acoustic recordings of sounds produced by the movements of scallop valves. Three complementary experiments were conducted:
- to confirm the link between sound production and shell movement, a scallop was placed in a laboratory tank and fitted with a device measuring and recording the opening and closing movements of its valves; a hydrophone was immerged in the tank during the whole experiment
- to identify key features in the scallop valve sounds in order to be able to distinguish them from the other ambient noises, sixteen scallops were kept in a tank under semi-natural conditions (natural substrate, continuous fresh seawater input, density of individuals); their sound production was recorded by a hydrophone located at the centre of the tank
- to test whether these sounds are detectable at ambient noise levels typical for scallop habitats, the ambient noise was recorded in the field, in the Bay of Brest (where scallop density is high and shipping traffic noisy) and in the Natural Marine Park of Iroise (where scallop density and anthropogenic noise level are lower).


The design of the second experiment


During the one-hour recording of the first experiment, twenty "coughing" behaviours were observed; the perfect correspondence between movement and sound production confirms their cause-to effect relation.

Sounds produced by scallops are broadband signals (3 to 48 kHz) of short duration (0.35 s in average), with a rapid onset followed by a relatively slow decay. They begin with a ‘crack’, likely attributed to the friction between the two valves. The subsequent more continuous part of the sound is probably created by the turbulence of the water flow when the scallop quickly closes its valves. These sounds are perceived by the human ear as short cracks; only a part of them (up to 20 kHz) is audible, the rest being ultrasounds.

Intensity of a scallop sound

Frequencie emitted by the same noise as above
(higher intensities are shown by the darker areas)

Is scallop sound audible in the natural sound ambiance of its submarine environment? According to its location (laboratory, Bay of Brest, Iroise Sea) the distribution of ambient noise level is quite different, but in most cases scallops are noisier than their environment. Comparing these levels allows the estimation of the maximum distance at which scallop sounds can be detected: this range is close to 20 m in lab conditions but only around 1 to 2 m in the field. It is thus possible to estimate the size of the patch that could be monitored with passive acoustics in different ambient noise environments. In the conditions of field experiments, this area is in the range 3-25 m².


Distribution of ambiant noise according to its intensity in various environments

This study is the first one to use passive acoustic techniques to explore the behaviour of scallops. As opposed to traditional methods, they have the potential to be a powerful, non-intrusive way of long-term monitoring of a pectinid species with high ecological and economical value. This approach could help establishing the link between the records on the shell and the variations of the environment. Furthermore, the detection of changes in the natural variability of such behaviours may serve as an early warning system of human health hazards in the environment, such as the presence of toxic algae, involving important economical implications for e.g. scallop fisheries.


The paper

L. Di Iorio, C. Gervaise, V. Jaud, A. A. Robson, L. Chauvaud, 2012. Hydrophone detects cracking sounds: Non-intrusive monitoring of bivalve movement. Journal of Experimental Marine Biology and Ecology 432–433 : 9–16.
See the first page

The authors

This work is the result of the collaboration of scientists from Lemar laboratory of IUEM, ENSTA-Bretagne (Brest), the laboratory Grenoble Images Parole Signal Automatique (GIPSA) and Ardtoe Marine Laboratory (Great Britain)

The journal

Journal of Experimental Marine Biology and Ecology is an Elsevier journal which publishes papers on biochemistry, physiology, behaviour, and genetics of marine plants and animals in relation to their ecology; all levels of biological organization are considered, including studies of ecosystems and ecological modelling.



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