The sense of hearing in the Pacific oyster, Magallana gigas.

There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, but there is still insufficient data for most invertebrates. What do they perceive? We investigated this question in oysters Magallana gigas (Crassostrea gigas) using pure tone exposures, accelerometer fixed on the oyster shell and hydrophone in the water column. Groups of 16 oysters were exposed to quantifiable waterborne sinusoidal sounds in the range of 10 Hz to 20 kHz at various acoustic energies. The experiment was conducted in running seawater using an experimental flume equipped with suspended loudspeakers. The sensitivity of the oysters was measured by recording their valve movements by high-frequency noninvasive valvometry. The tests were 3 min tone exposures including a 70 sec fade-in period. Three endpoints were analysed: the ratio of responding individuals in the group, the resulting changes of valve opening amplitude and the response latency. At high enough acoustic energy, oysters transiently closed their valves in response to frequencies in the range of 10 to <1000 Hz, with maximum sensitivity from 10 to 200 Hz. The minimum acoustic energy required to elicit a response was 0.02 m∙s-2 at 122 dBrms re 1 μPa for frequencies ranging from 10 to 80 Hz. As a partial valve closure cannot be differentiated from a nociceptive response, it is very likely that oysters detect sounds at lower acoustic energy. The mechanism involved in sound detection and the ecological consequences are discussed

Noise pollution limits metal bioaccumulation and growth rate in a filter feeder, the Pacific oyster Magallana gigas

International audienc

Oysters responded to sound frequencies and exhibit two peaks of maximum sensitivity at 20 and 90–100 Hz.

<p>A, a logistic regression described the relationship between the percentage of responding oysters in a group and sound frequency. For each frequency, the distribution is described by quartiles (bold line, median). B1, the measured sound pressure level, SPL, for the studied frequencies expressed in rms. B2, the measured shell accelerations at various frequencies expressed in rms. C, the relationship between the percentage of valve opening amplitude and sound frequency. At each frequency, the data distribution is described by quartiles. N = 16 oysters. D1 and D2, Principal Component Analysis describing the correlation between the percentage of responding oysters (% Rep, D1) and valve opening-amplitude decrease (VOA, D2) combined with frequency (Hz), shell acceleration (Acc) and sound pressure level (SPL).</p

Typical oyster responses to 3 min of pure tone (100 Hz).

<p>A, relationship between shell acceleration and sound pressure level at various frequencies. B, from top to bottom, waveform and typical responses ranging from minimal to maximal responses as a function of time. Dashed lines, onset and offset of the stimulus; dotted line, end of the fade-in period; n = 4 individuals.</p

Identifying thresholds at various sound pressure levels for various frequencies.

<p>Four examples of logistic regression models describing the relationship between oyster group responses and sound pressure levels at 10, 40, 100 and 200 Hz. Sound pressure levels are expressed as dBrms.</p

The sense of hearing in the Pacific oyster, <i>Magallana gigas</i>

<div><p>There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, but there is still insufficient data for most invertebrates. What do they perceive? We investigated this question in oysters <i>Magallana gigas</i> (<i>Crassostrea gigas</i>) using pure tone exposures, accelerometer fixed on the oyster shell and hydrophone in the water column. Groups of 16 oysters were exposed to quantifiable waterborne sinusoidal sounds in the range of 10 Hz to 20 kHz at various acoustic energies. The experiment was conducted in running seawater using an experimental flume equipped with suspended loudspeakers. The sensitivity of the oysters was measured by recording their valve movements by high-frequency noninvasive valvometry. The tests were 3 min tone exposures including a 70 sec fade-in period. Three endpoints were analysed: the ratio of responding individuals in the group, the resulting changes of valve opening amplitude and the response latency. At high enough acoustic energy, oysters transiently closed their valves in response to frequencies in the range of 10 to <1000 Hz, with maximum sensitivity from 10 to 200 Hz. The minimum acoustic energy required to elicit a response was 0.02 m∙s^-2 at 122 dBrms re 1 μPa for frequencies ranging from 10 to 80 Hz. As a partial valve closure cannot be differentiated from a nociceptive response, it is very likely that oysters detect sounds at lower acoustic energy. The mechanism involved in sound detection and the ecological consequences are discussed.</p></div

Experimental set-up and quantification of oyster response.

<p>A, schematic view. Is, loudspeaker position; mpcg, multiplate current generator; o, oysters equipped with electrodes; tb, tennis ball; w, wooden board; sb, sandbox; tb, w and sb compose a vibration absorber. B1, commercial loudspeaker to produce tones at frequencies from 80–20000 Hz; B2, laboratory-made loudspeaker for frequencies from 10–80 Hz. D, typical valve closure response and measured values: y_max, daily maximum VOA (valve opening amplitude); y_min, daily minimum VOA; y₁, VOA prior to valve closing; y₂, minimal VOA during response; Δy, amplitude of the response expressed in %, see the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0185353#sec002" target="_blank">Materials and methods</a> section. C, set-up for shell acceleration measurement.</p

Response delay is function of sound frequency from 10–300 Hz.

<p>A, The response delay was systematically shorter from 10–80 Hz and the variability smaller from 10–80 Hz, with an exception at 60 Hz, illustrating a particular sensitivity to the lowest frequencies, N = 16 oysters. B1 and B2 represent the measured sound pressure levels, SPL, and shell accelerations for frequencies from 10–300 Hz.</p

Growth rate index in oysters <i>M</i>. <i>gigas</i> in the presence of cadmium with (Cd + N) or without (Cd) cargo ship noise.

<p>A, daily change of growth rate index. B, description by quartiles of the difference between growth index at day 14. The growth rate is smaller in presence of cargo ship noise. N = 13 oysters exposed to Cd and cargo ship noise and 12 oysters exposed to Cd alone.</p

Experimental setup and exposure characteristics.

<p>A, antivibration bench with 2 replicate tanks on it; B, complete scheme of a unit; C, inside view of an experimental tank. 1, sand; 2, frame angle structure; 3, chipboard panel; 4, air chambers; 5, concrete slab; 6, tennis ball; 7, pieces of thermal insulation; 8, oysters equipped for behavioral recordings; 9, oysters for tissue sampling; 10, electrode cables; 11, hemstitched support; 12, loudspeaker. D, 72 h of sound recording. Each vertical bar is the noise from one passing cargo ship. Black bands represent periodic absence of cargo ship noise. E: the change of cadmium concentration in the 4 tanks as a function of time. There were 2 antivibration benches and 2 replicate tanks per bench.</p