Oysters CAN Hear!     Nah….….They don’t have ears! 

Well, maybe not, but for you disbelievers there is new research that suggests that oysters not only can hear but are affected by the overall noise pollution of the seas.  Sounds such as cargo ships, underwater oil exploration and other noisy activities are causing interesting activities in molluscs as well as the fish and mammals.  There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, fish and ocean mammals, such as whales and dolphins but invertebrates? This week’s discussion at Hearing International will take on the issue of Oysters and their hearing.

Can Oysters Hear?

Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species the valves (or shells) are highly calcified, and many are somewhat irregular in shape. The  bivalve class is characterized by a hinged shell with right and left halves which covers its visceral mass. In bivalves the foot extends out between the shells and is used for locomotion. The bivalves lack a radula. Familiar bivalves include mussels, clams, and oysters and are part of the phylum of Mollusca, which biologically classifies a number species from snails to octopus as well as oysters. More than 15,000 species of clams, oysters, mussels, scallops, and other members of the phylum Mollusca characterized as bivalves by this shell that is divided from front to back into left and right valves. The valves are connected to one another at a hinge.  Primitive bivalves ingest sediment; however, in most species the respiratory gills have become modified into organs of filtration called ctenidia. In keeping with a largely sedentary and deposit-feeding or suspension-feeding lifestyle, bivalves have lost the head and the radular rasping organ typical of most mollusks.  While some Mollusca have rather well developed eyes, they are known for not having a traditional auditory mechanism. 

Most invertebrate sound detection studies have been conducted on crustaceans but little is known about sound detection and sensitivity in bivalve mollusca despite their importance to the marine ecosystem. The question then remains, What, if any, sounds do these Mollusca perceive?    This was a question investigated recently by Charifi (2017) and a team of scientists at the University of Bordeaux.  They investigated Magallana gigas (Crassostrea gigas) sometimes called pacific oysters using pure tone exposures, an 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 analyzed: 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. The greatest response fell within the frequency range 10–200 Hz, with 60–95% of animals responding during each test. 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. This was a complex study involving not only acoustic measurements but also the movement of the valves to the stimulus.  So, the deduction from the study conducted by the University of Bordeaux was that underwater noise pollution can affect oysters as they close their shells when exposed to low frequencies of sounds in experimental conditions. Oysters rely on hearing waves and currents to regulate their circadian rhythms, and perception of weather events—such as rain—may induce spawningCargo shipspile drivers, and explosions conducted underwater produce low frequencies that may be detected by oysters causing disruption of these activities. 

So….Yes Virginia, Oysters can Hear!

 

References:

Charifi, M. Sow, M., Ciret, P., Benomar, S. &  Masabuau (2017). The sense of hearing in the Pacific oyster, Magallana gigas.  Plos One.  Retrieved November 6, 2017. 

Unknown (2017).  Discovery of sound in the sea.  University of Rhode Island.  Retrieved November 6, 2017.

 

Last week at Hearing International we left this story with the “the jury is still out” as to whether the attack is real or a myth.   It was pointed out by one of our readers, a physicist, that this “sonic attack” could possibly have been the result of an Infrasound.  His suggestion was that studies from medical and audiological professionals as well as independent acoustical experts have concluded that some individuals near industrial wind projects will experience adverse health effects due to the noise generated. 

Recall that in Cuba these strange medical symptoms emerged in the fall of 2016, when several employees at the US Embassy in Havana began complaining of physical symptoms. Many of the individuals were new to the embassy and some had to return to the United States because of the severity of their symptoms — the details of which have yet to be disclosed but have been suggested to be hearing loss, nausea, and tinnitus among others.  An investigation by the US government concluded that the symptoms could be attributed to a device that operated outside the audible hearing range and was used somewhere, possibly in their houses. Right now, there’s no word on whether these sonic devices were deliberately used or it was simply a noise such as an infrasound within the environment.  While the mysterious Cuban story has a lot of holes, Charles Liberman, a hearing loss researcher at Harvard Medical School and Massachusetts Eye and Ear in Boston seems to agree with our reader that one possibility is that the workers were exposed to infrasound, or low-frequency sound waves that are below the audible hearing range.  

What Exactly is an Infrasound?

Infrasound, sometimes referred to as “low-frequency sound”, is sound that is lower in frequency than 20 Hz or cycles per second, the “normal” limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure (or loudness) must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body.  The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.1 Hz and rarely to 0.001 Hz.  Scientists use this frequency range for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in ballistocardiography and seismocardiography to study the mechanics of the heart.  Infrasound is also characterized by an ability to cover long distances and get around obstacles with little dissipation. 

What About Wind Farms

One industry with well documented health issues is wind farms.  Cuba is in many ways an isolated island that has difficulty producing its own electricity and importing enough energy sources.  A few years ago, the government made a significant commitment to expanding wind farms on the island.  In 2015, the Ministry of Energy and Mines announced plans for 13 wind farm projects to increase the island’s capacity to more than 2,000 MegaWatts (MW). A wind farm is a group of wind turbines in the same location used to produce electricity. A large wind farm may consist of a few or several hundred individual wind turbines and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other purposes. There are, however, numerous reports of infrasound causing health issues in areas where are a lot of these wind farms [click here for a video].

Just in case this seems a bit far fetched, check out You Tube there are all kinds of videos from around the world on issues just like those being reported at the Cuban Embassy.  Weichenberger et al (2017) demonstrated that infrasound [signals below 20 Hz.] near the hearing threshold may induce changes of neural activity across several brain regions, some of which are known to be involved in auditory processing, while others are regarded as key players in emotional and autonomic control. While they felt that more study was needed, their findings allow for speculation on how continuous exposure to infrasound could exert a pathogenic influence on an organism. Some long term investigators into the effects of wind farms such as Punch & James (2016) reviewed evidence as to the adverse effects of infrasounds emitted by wind turbines on humans.  Their research overwhelmingly supports the notion that acoustic emissions from industrial wind turbines are a leading cause of adverse health effects in a substantial segment of the population.  The closest wind farm to Havana is in Matanzas about 52 miles away from the Embassy (see the figure to the left).  It depicts the proximity of the closest wind farm to Havana.  While that is a large distance, infrasounds have long wave lengths and these waveforms are capable of traveling distances.  

A few months ago Hearing International did a story on “The Hum” a noise that plagues a number of areas around the world. While the Cuban “sonic attacks” could very well be from infrasounds, possibly created by wind farms or other sources they may also be related “The Hum”.  As with the Cuban sounds,  The Hum is also only heard indoors and is louder at night than during the day.  Modern manifestations of the contemporary Hum have been widely reported by national media in the United Kingdom, the United States and Australia since the early 1970s.  In 2006, Moir and Alam pinpointed the low-level drone at a frequency of 56Hz, which is very close to the 50Hz frequency produced by the 240 volt AC main electricity supply delivered to homes in New Zealand (and Australia). Although 56Hz is within the standard range of human hearing (20-20,000 Hz.), it is too low for many people to pick up. While all this makes great discussion and presents the affects of infrasound, if the wind farms or the Hum were the causes, there would be Cuban citizens just as affected as the embassy employees.

Of course, these attacks could just be that – attacks that harnessed the infrasound and directed it toward the embassy employees.

References:

Ghose, T. (2017). Weaponizing Sound: How a ‘Silent’ Sonic Weapon Might Work.  Seeker, Live Science.  Retrieved October 30, 2017.

Hutcheon, S. (2006). Mystery humming sound captured.  Sydney Morning Herald:  Tech.  Retrieved October 31, 2017.

Weichenberger, M., Bauer, M., Kuhler, R., Hensel, J., Forlim, C., Ihlenfeld, A., Itterman, B., Gallinat, J., Koch, C., & Kuhn, S. (2017).  Altered cortical and subcortical connectivity due to infrasound administered near the hearing threshold – Evidence from fMRI.  Retrieved October 30, 2017.

Videos:

Wilde, J. (2016) Can Low Frequency Sound Waves Make You Sick.  SCI.  Retrieved October 30, 2017.