Hydrophone detects cracking sounds: Non-intrusive monitoring of bivalve movement

Abstract

Bivalve mollusks are of major ecological and economical importance in coastal ecosystems. They are natural archives of environmental information extractable from its shell. The formation and size of growth increments delimited by striae are affected by environmental stressors. The mechanisms linking shell growth and striae deposition in relation to environmental variations are poorly understood but are likely associated with the animal's valve-movement behavior. Here, we present a first attempt to record scallop valve movement using passive acoustics. This method has the advantage of being totally non-intrusive and deployable continuously, over the long term (months) and on a large number of individuals. By comparing simultaneous acoustic recordings with data from animal-attached movement sensors, we show that bivalve (Pecten maximus) adduction movements (here ‘coughs’) produce a specific sound. To evaluate the use of passive acoustic monitoring of these sounds in natural environments, we estimated if scallop coughing sounds are detectable in typical scallop habitats with different ambient noise levels. We found that scallop coughing sounds can be detected from a few to several tens of meters in different ambient noise environments. Furthermore, their acoustic characteristics are distinctive from those of other known benthic organisms. These results indicate that scallop valve movements can be monitored using passive acoustics in situ. We emphasize that acoustic recording is likely to become a powerful, non-intrusive method for the long-term monitoring of the behavior of a pectinid species and its responses to environmental changes affecting growth.