Sound production and associated behaviours of benthic invertebrates from a coastal habitat in the north-east Atlantic

Maerl beds are among the most endangered habitats in coastal temperate waters and a priority for conservation. Passive acoustics is a potential non-intrusive approach for surveying this fragile ecosystem with minor disturbances. Invertebrate sounds can be major contributors to natural coastal soundscapes but are not well studied. We conducted controlled tank-based experiments to identify sound-producing invertebrates inhabiting northeast Atlantic maerl beds and to characterise their sounds in terms of frequency features and source levels. We also determined which sound types are able to be detected above natural maerl ambient noise and suitable for in situ monitoring. Tank recording sessions of 20 abundant and potentially soniferous invertebrates from maerl beds revealed eight soniferous species and 15 different sound types. Two new sound-producing families were identified, Calyptraeidae and Majidae. Six sound types had properties consistent with detectability and identification for in situ acoustic studies: the feeding sound of sea urchins Echinus esculentus, Paracentrotus lividus and Psammechinus miliaris, snapping sound of the snapping shrimp Athanas nitescens, and feeding and other sounds of the spider crab Maja brachydactyla. Estimated detection distances ranged from a few metres for sea urchin feeding sounds up to about 40 m for A. nitescens snaps and spider crab feeding sounds. These invertebrates, particularly A. nitescens, probably make a substantial contribution to the maerl ambient noise. This invertebrate sound library sets a basis for in situ acoustic studies.