Abstract
© 2015 Inter-Research. Many anthropogenic activities in the oceans involve direct contact with the seabed (for example pile driving), creating radiating particle motion waves. However, the consequences of these waveforms to marine organisms are largely unknown and there is little information on the ability of invertebrates to detect vibration, or indeed the acoustic component of the signal. We quantified sensitivity of the marine bivalve Mytilus edulis to substrate-borne vibration by exposure to vibration under controlled conditions. Sinusoidal excitation by tonal signals at frequencies within the range 5 to 410 Hz was applied during the tests, using the 'staircase' method of threshold determination. Thresholds were related to mussel size and to seabed vibration data produced by anthropogenic activities. Clear behavioural changes were observed in response to the vibration stimulus. Thresholds ranged from 0.06 to 0.55 m s -2 (acceleration, root mean squared), with valve closure used as the behavioural indicator of reception and response. Thresholds were shown to be within the range of vibrations measured in the vicinity of anthropogenic operations such as pile driving and blasting. The responses show that vibration is likely to impact the overall fitness of both individuals and mussel beds of M. edulis due to disruption of natural valve periodicity, which may have ecosystem and commercial implications. The observed data provide a valuable first step to understanding the impacts of such vibration upon a key coastal and estuarine invertebrate which lives near industrial and construction activity, and illustrate that the role of seabed vibration should not be underestimated when assessing the impacts of noise pollution.
Highlights
Sound energy travels as a longitudinal wave, alternately compressing and rarefying the particles across the medium, and causes an oscillation of molecules parallel to the direction of travel (Van der Graaf et al 2012)
Clear valve gape changes were observed in all mussels in response to the vibration stimulus, which were distinct from the valve movements during natural rhythms of feeding
As with all vibrational and acoustical studies, the results here should be taken within the experimental context, involving a particular exposure duration, frequency range, substrate, vibration stimulus, and species
Summary
Sound energy travels as a longitudinal (compressional) wave, alternately compressing and rarefying the particles across the medium (pressure), and causes an oscillation of molecules parallel to the direction of travel (particle motion) (Van der Graaf et al 2012). For an underwater sound source encountering a solid, the particle motion may disperse via the water column, and by the substrate (Hazelwood 2012, Hazelwood & Macey 2015) causing ‘water-borne’ and ‘substrateborne’ particle motion. Energy in the substrate may re-enter the water column at high levels, at large distances from the original source (Popper & Hastings 2009). Anthropogenic activities, especially those directly in contact with the seabed such pile driving and drilling, may produce such substrateborne vibrations. Underwater noise has been identified as a major stressor in marine systems and is subject to recent governance initiatives, for example the European Marine Strategy Framework
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